MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - The abandoned project continues

The '73 B seems to run OK but I did the 500 mile valve adjust today. Afterwards, a copression test showed # 1-210, #2-190, #3-170 AND #4-120. The head gasket is new, there is no smoke or coolant loss. Should I be concerned? Thanks, Tom---going for a cruise.
Tom

Tom,

From 120 to 210 is a mighty big split. The rule of thumb in an ideal world is 10% diff. Is this a fresh engine or one that sat idle for years?

I think I would do the compression test again. Are you hitting each cylinder the same number of times during the test?

Charley
C R Huff

Hey Charley, the engine sat for a few years but I have put about 500 miles on it. About 200 miles ago it blew a head gasket, I was unaware of the need to re-torque the head after initial warm up. COuld the head gasket again leak? Regards, Tom
Tom

Tom,

Yes, the head gasket could leak again, but probably not as a result of failing to re-torque after warm up. Opinions differ, but I generally retorque after about 500 miles. Some say the Payen head gasket does not require re-torquing at all.

I would want good verification that your numbers are right before pulling the head again, and I would double check the valve adjustment. I would try another gauge too.

Are you able to watch the gauge while you do it? If you are running between the engine and the key, maybe your gauge is bleeding off before you see it, or leaking at the plug threads.

I would do it both dry and wet.

If the results are still all over the board, I would consider doing a cylinder leak down check.

If you do pull the head again, check to see if the pistons have the same dish, see if they all go to the same maximum height, see if the bore is the same in each cylinder, and measure the combustion chambers in the head to see if they are the same.

I think normal compression on a stock high compression engine would be 155 psi.

Charley
C R Huff

Tom

I agree with Charlie and check the compression with another compression tester.
A leak down tester will tell you quite a bit as well, if the intake valves are not sealing you will hear air leaking out through the carb. If the exhaust valves are leaking you will hear air out through the exhaust pipe, if the head gasket is leaking you should have air bubbling into the rad. great tool for cases like this.

Did you replace the head bolts. They can become stretched? I once re-did a head only to have it leak again. Replaced the head bolts and all was fine.

Good luck


Bruce Mills

Thanks for the leak down test information. I had to "google" it to find out what it is. Off to the parts store for a tester. The haed studs are new and "uprated". Tom
Tom

Tom,

Certainly nothing wrong with owning a leak down tester, but the suggestions I made above were intended to be chronological. Nothing cast in stone about that, but it's probably the order I would pick.

Charley
C R Huff

OK folks, I rigged up a leakdown tester and found that when #4 is TDC, any air applied comes out #3. Not good. The adventure continues.....Tom
Tom

Keep us informed
Bruce Mills

Tom,

Is that #4 TDC on the firing stroke? What happens when you pressurize #3? Have you rechecked your valve adjustment yet?

Charley
C R Huff

Thans for the thoughts. Yes, it appears that the head gasket is gone between 3 & 4. I am out of town this week but will pull the head the first chance I have. My current thinking is (1) head gasket or (2) the head is cracked. I know that the previous owner had the head "shaved". I am thinking that if # 1 & 2 show around 200 pounds of compression, the head gasket is doomed to failure between 3 & 4. Perhaps a thicker, copper gasket to reduce overall pressure? Thanks folks, Tom
Tom

Tom-
This is typical of failure to retorque properly, all other opinions notwithstanding.

"Yes, the head gasket could leak again, but probably not as a result of failing to re-torque after warm up. Opinions differ, but I generally retorque after about 500 miles. Some say the Payen head gasket does not require re-torquing at all."

Especially in view of the fact that you seem to have quite high compression, which will make it all much more critical.
Send me an email and I will send you the real fix.
FRM
FR Millmore

Cant say that I have ever seen that high a compression on anything but a significant race engine. How much did the PO shave off that head?
Bruce-C

FR Millmore,

I have read a number of your posts in the past, and so have no doubt that you are technologically savvy.

That said, those compression numbers don't look too typical of anything to me. My first thought was that it was a typo, and my second thought was that the test needed to be repeated.

However, I am always willing to learn.

Not that my compression was that high, but I built my engine here in Kentucky, put 100 miles on it locally, and then drove it to California. My first extended stop for sleep was in New Mexico, and I planned to retorque the head there since it was the first time it sat long enough to cool down to ambient temps. But, the wind was so vicious when I woke up that it would have torn the aluminum hood off of the car. I had to hold on to the hood while I checked the oil. So, I drove it on to northern California before I retorqued. No problem so far in about 15,000 miles.

Charley
C R Huff

Charley-
I was referring to the gasket failure, not the compression readings. The comp numbers are quite odd actually. Nowadays it is not safe to assume anything about these cars, since so many have been altered.
It could have a late small chamber head, which we think has been cut. The block may have been cut as well, and who knows what pistons, cam, valve timing? Were the throttles open, or if not, carbs balanced when tested?

I've seen unexpectedly high readings on some apparently stock & unmolested cars - c180-185 with really good batteries and cables.

The odd part is the spread, assuming the given numbers are true. # 1-210, #2-190, #3-170 AND #4-120. -20 difference from 1 to 2 is a bit much on a rebuilt engine or head, or is it rebuilt? -20 more to #3 is weird, and -50 to #4 is clearly a problem. I'd be more likely to believe numbers in pairs, given that Tom seems to have identified a compression leak between 3 & 4 - like 200-200-120-120 or close. Variation in excess of 5psi is usually a result of valve seat deterioration, which shouldn't be the case if the head was just done. It could be that there is actually some leakage from #2 as well. But when I see this kind of scatter, I look for something else.

One possibility is a bad battery that has just been on charge. The voltage can be higher than normal but drop quickly under load, giving sequentially lower readings. Or a starter motor or connections that drop off as they get hot, etc. In these cases I always redo the comp test in reverse order.

But, assuming Tom has done the leakdown test correctly - cylinder under test at TDC firing - then he has a HG problem, whatever else is going on.

I would certainly try to find or figure out what sort of cam and pistons it has, what the deck clearance is, what head, and what's been taken off the head. Also, since the head is off, examine the tappets and cam - worn or mistimed cams can give high comp readings at cranking speed. If the parts are such that the comp really is c200psi, then Tom ought to put a hairy cam in the thing!

I have just updated my Boltbabble.doc, preparatory to sending it to Tom, and will send you a copy too.

You will see that various factors other than plain retorque interval affect gasket failure, and the time before it happens. One that is not included is how hard the car is driven with a shaky gasket situation like not retorqued when it should be. If the throttles are not fully open under load, the cylinder pressures are far below max, and a loose gasket can survive. I have blown a couple of customer gaskets while road testing after involved fixes of the work of multiple mechanics trying to straighten out a problem. After fixing the carbs, timing, distributor, fuel feed, I went up the hill under full throttle and the gaskets blew. Examination showed that the HG had been leaking for a long time, and was probably the original trouble everyone was attempting to fix. These episodes were responsible for my current practice of checking head bolt torque on engines before I take them apart - it helps a lot in diagnosis to know that the nuts were at 20lbft (or scattered between 10 & 70!)when you find a blown gasket.

You'd be surprised at how many MGB used to drive around with the throttles opening only half way - I had quite a few first time customers come back immediately after picking up their car from a tune-up "what in the hell did you do to my car, I've had it two years and it never ran like this." Apparently the same dealers who left heads loose did not know how to set throttle linkages.

In your case, you likely drove your new engine a bit gingerly for the first little while, and from your posts you qualify as a decent mechanic, so I'm not really surprised that you got away with the "no retorque til Cafilornia" deal. If you used a Payen gasket, they are pretty good for extended but not infinite intervals before retorque, assuming correct initial fitting.
And, iron heads get torqued hot, but it's not critical.

And I know about the desert wind too.
Cheers,
FRM
FR Millmore

FRM,

Ah, I see. I thought you were relating the compression readings to the head gasket problem, and I could not see the logic.

Yes, you are right that I was driving my fresh engine with a light foot. Also, because it was a cross-country trip in January, I kept it moving with very few long stops. So, it saw very few temp cycles for the miles covered.

Good point about the aged battery on a fresh charge. I hadn't considered that one.

I'm glad I caught your note here about the Boltbabble.doc you sent. When I checked my e-mail this morning, Boltbabble looked like a nonsense word and I didn't recognize your address. So, I had hit delete, but, when I saw your mention of it here, I retrieved and downloaded it. I'll give it a read this evening.

Thanks,
Charley
C R Huff

OK folks, I pulled the head tonight and saw that the head gasket was indeed kaput. The haed is a # 12H2923 AFIH that is 3.08" thick. Moss says it was originally 3.177 to 3.192 thick. It appears that it is at least 10 thousants under. The bore is 3.16". The cam is the Moss # 222-270, "fast street cam". Does anyone know how to do the math for compression ratio and anticapated compression? I'm in over my head. Tom
Tom

Tom,
Well we can try to guesstimate, but need more info.
First tell us what you think or have been told was done to this engine.
12H2923 would be the OE for 72-74 small chamber head (39cc), and if your 3.08 (3.080) is correct,then .097 to .112 has been cut = a lot. Say 100 thou.
That's most of why the compression is so high, but maybe not all of it.
Is the 3.16 (OE) for bore size an actual measurement, or are you reading that from a book?
Are there any markings on the piston tops? OE pistons usually just have a part number, OE replacements may say "STD", oversize usually have "010, .020, .030" etc., with or without a + sign.
Are the pistons dished and how deep is the dish?
You NEED to measure piston to deck height with piston at TDC. OE will be something around .040 below deck; if it has been decked it may be anything up to flush or even negative = piston above deck.
(I stamp deck cuts on top of the block, but I've never seen an engine besides mine so marked; same with heads)
Is there any sign that grinding has been done in the combustion chambers = grinding marks or high polish?


You must use at minimum 1/8" thick washers. With that much off the head, you must check that the threads on the head studs extend down to the head face before you put the washers on, or you will bottom the threads before the head is tight enough to clamp the gasket correctly. Otherwise you need additional washer thickness.

With that much off the head, I would check that there is sufficient clearance between the exhaust valves when full open and the reliefs in the block .060 is about minimum.

At that compression, you need to be meticulous about the head installation and retorques - cut no corners.

You will also need to be careful with timing and should have the distributor set up correctly.

You don't dare run lean.

But with the cam you have, it should go like a scared cat!

For more education/confusion, go to:
http://www.mgbmga.com/tech/index.html
and start reading the wonderful archived tech articles.

I will resend Boltbabble.doc
FRM

FR Millmore

The adventure continues, I cleaned the crud from the top of one piston and found it to be an AE#18802 +.020. It is dished.

It appears that the fellow who did the motor wanted to race? I am thinking of finding another, thicker head. Would this give the rest of the componants a longer life?

Thanks and regards, Tom
Tom

Tom-

18802/020. Piston set, approx. 6.2cc piston dish.

That's the OE high comp piston, so things are getting pretty squishy. The +.020 overbore also increases the comp ratio and pressure. This will give compression around the high limit with the small chamber head, even WITHOUT the excessive cutting of the head.

Recheck your head measurements and if the current numbers hold, look for a new head.
With those pistons and bore, an earlier (large chamber) head would be better.
See Info on heads in earlier referenced website.
But you should still determine if the block has been decked, so you know what to expect and how to set it up.

FRM
FR Millmore

Tom,

Once you have checked the deck height/depth as FRM suggests, you are only missing one important piece of the data with which to calculate the static compression ratio.

You need to use a burette to check the volume of the combustion chambers in the head. Then you can compare the displacement volume (swept volume) to the total clearance volume to find the static compression ratio (CR). You should check all four to see if they are matched.

The total clearance volume is the sum of the combustion chamber, piston dish, volume between piston crown and deck top, and volume created by head gasket thickness. Technically you should add in the volume around the piston crown above the top ring, but that is not a significant volume in my opinion. If your piston is coming above the deck, you will have to subtract that from the head gasket volume.

Add the total clearance volume to the swept volume, and then divide that sum by the total clearance volume and you have your static CR.

Then you can decide if the CR is too high. Being too high or not depends in part on your cam specs, but it is likely that getting over 10:1 is pushing it.

If it is too high, you can then decide if it is more practical to get another head or to cut some iron out of the combustion chambers of your existing head to lower the CR.

If you don’t already have the Peter Burgess book on MGB engines, maybe now is the time to get it. The title is (approximately anyway) How to Power Tune the MGB.

Charley
C R Huff

Holy Cow! Turns out the block has been "decked" and the pistons come even with the top. Also, small "eyebrows" are cut into the block, I guess to allow valve clearance. The head is in the machine shop to check for warpage and valve seal.

Question, my scotch brite cleanup has left small scrathes in the block surface. Will this preclude the use of a "normal" head gasket?

Can a "normal" headgasket work? Thanks, Tom
Tom

Scotchbrite scratches are the least of your problems, and are not a problem anyhow.
Not gonna work.
Read what I said in my last post.
Calculate the CR according to info Charley gave you and from mgbmga site.
Or pay me to do it!
It will be way high, and IF you can keep a gasket in it long enough, you WILL destroy the engine by detonation, unless you run straight alcohol.
Calculate, get an early uncut head or a replacement alloy one, calculate - much cheaper than melted pistons and an infinite pile of blown gaskets!
FRM
FR Millmore

Tom,

You can't hurt the block surface with Scotch-Brite. Well, at least you can't unless you have about 2 weeks to spend at the job.

Sorry if I am belaboring the point, but when you say that the pistons come up to the top of the deck, do you mean that in an absolute sense, or do you mean that it looks kind of like that is happening? Have you dropped a straight edge across the block top and tried to slide feeler gauges between the straight edge and the piston tops? I don't know the standard clearance for the B, but for the A-series I think it was about 0.015 inch. If yours is not truly zero, you need to know how many thousands of an inch it is so you can calculate the volume. Don't be terribly surprised if they are not all the same.

If you don't have the expertise and a burette to measure the combustion chambers in the head, and if your machine shop is good, they should be able to do it for you cheap. It's not that hard.

Until you have the numbers, you can't make an intelligent decision.

You also need to know the volume of the valve clearance cuts in the block since that is also un-swept volume and should be added into the equation.

Charley
C R Huff

Hey Folks, thanks for all of the information. I will recheck the piston height at my first opportunity. (Today is fathers day and I have some family obligations). I am coresponding with a fellow who has a 74 head for sale, with the rocker assembly. It measures 3.138. Will this work on a 73 block? Is that enough rise to reduce the compression enough?

I don't know what a burette is but I will "Google" it when I'm done here. My machine shop is very good but..kind of far away. The adventure continues....
Tom

Tom,

A burette is a long thin glass tube with graduation marks on it indicating the volume. They come in various sizes and are used in chemistry for precise measuring of liquids. The kind I have used trap the liquid by holding your thumb on the top like you would with a soda straw. Come to think of it, I guess that might be called a pipette instead of a burette, which I think uses a valve.

For measuring the combustion chamber volume, you level the head upside down, fill the burette (usually with kerosene but you can use water) and then fill the combustion chamber from the burette. By seeing how much it took to fill the combustion chamber, you know the volume. For head work, you would normally use a burette calibrated in cubic centimeters (cc) with a mark for each 1/10 cc.

Most instructions say to use a Plexiglas plate greased to the head with a fill hole drilled in it. I found the Plexiglas frustrating, so I eyeball when the chamber is full. Eyeballing it makes kerosene a better choice than water because it has less surface tension so that it has less tendency to "hump up" above the head surface.

If you shop is far away, just call them and see if they can do it.

Generally heads are physically interchangeable, but I don't know the details on the one you are considering.

Again, you need the numbers. I suspect you could enlarge the chambers in your existing head if the numbers indicate it is needed, and thicker head gaskets may be available. Using 2 head gaskets is not unheard of, though reports of success vary. I never had the need so I never tried it myself.

Charley
C R Huff

Thanks again to FRM & Charley. Wow, am I in over my head. To Summerize, I have a 73 B with an 1800 engine. The head is a 112H2923 AFIH that has been shaved to 3.08". (The original was between 3.177 and 3.192). It was originally a 39cc, small cumbustian chamber head.

The cam is a Moss 222-270 "mild street cam."

The pistons are AE 18802, +.020. They are dished. The raise to between .022 and .025 from flush with the deck.

I have gone through 2 head gaskets in 500 miles.

My head is spinning but, if thepistons are +.20 would that not offset some of the volume decrease from a shaved head and deck?

Should I just go to a copper head gasket?

Thanks, Tom
Tom

Tom,

You say, "The raise to between .022 and .025 from flush with the deck."

If that means that the top of the pistons are 0.022 to 0.025 inches below the top of the block, then it is likely that the block has NOT been decked. Like I said earlier, I don't really know what it was out of the factory, but 0.025 inches sounds like it is in the ballpark of standard.

You ask, "My head is spinning but, if the pistons are +.20 would that not offset some of the volume decrease from a shaved head and deck?"

Nope, other way around. Boring increases both the swept volume and the total clearance volume, but the swept volume increases a lot and the clearance volume only increases a little. So, all things being equal, boring 0.020 over increases the compression ratio. Swept volume is the volume the piston passes through as it sweeps from the bottom of its stroke to the top of its stroke.

If you gather the raw data (the numbers we have been speaking of) then either FRM, myself, or any number of people on this board can run them through a calculator and tell you your static compression ratio in about 30 seconds.

Assuming I understood what you meant about piston to deck clearance, I think the two missing pieces now are the volumes in the combustion chambers of the head, and the volumes of the valve cut outs in the block. Get those figures, and we can calculate the static compression ratio.

If you are not grasping the concept, you can e-mail me direct and I can send you my phone number. I can probably tell it to you a lot faster than I can write it.

Charley
C R Huff

"Thanks again to FRM & Charley. Wow, am I in over my head. "
We knew that!

To Summerize, I have a 73 B with an 1800 engine. The head is a 112H2923 AFIH that has been shaved to 3.08". (The original was between 3.177 and 3.192). It was originally a 39cc, small cumbustian chamber head.

The cam is a Moss 222-270 "mild street cam."

The pistons are AE 18802, +.020. They are dished. The raise to between .022 and .025 from flush with the deck.
From below:
Oversize Bore Size Capacity
020" 3.180" 1822cc = 455.5 cc/cyl

From info I supplied above, 6.2cc dish in piston

I have gone through 2 head gaskets in 500 miles.
Let's not do it anymore!

My head is spinning
Yah...

but, if thepistons are +.20 would that not offset some of the volume decrease from a shaved head and deck?
No, it makes it worse.

Should I just go to a copper head gasket?
NO, NO, NO! It will work at first, then start seeping, as detailed in Boltbabble.

From Charley: "Eyeballing it makes kerosene a better choice than water because it has less surface tension so that it has less tendency to "hump up" above the head surface"
Yes, add a few drops dishwashing detergent to water to eliminate the surface tension problem.

Burettes etc: Get a big syringe from a farm supply place - up to 50cc, cheap. Fill syringe to 50cc, fill chamber, see what's left.

From aforementioned MGBMGA site,MGB10:
OEM PISTON CHOICE
We seldom see the use of +010" oversize pistons so we shall
concentrate on the following oversizes:
Oversize Bore Size Capacity
020" 3.180" 1822cc
030" 3.190" 1834cc
040" 3.200" 1846cc
060" 3.220" 1868cc

8.7:1 compression ratio (CR) pistons 1963-71 were designed with a
piston dish cc (cubic centimeters) capacity of approximately 6cc,
and were designed to be used with cyl/heads having a combustion
chamber volume of 42.5cc-43.5cc. These cyl/heads are identified as
follows:
Part # Engine # Casting # Year
48G318 18G/GA/GB 12H906 1963-67
48G538 18GF/GH/GK 12H2389 1968-71

8:1 CR pistons (18V 1972->) on were designed with a piston dish cc
capacity of approximately 16cc and were designed to be used with cyl/heads
having a combustion chamber volume of 39cc. These cyl/heads are
identified as follows:
Part# Engine # Casting # Year
48G644 18V584/5 672/3 12H2923 1972-74 1/2
BHM1062 18V797/8 801/2 CAM1106 1975 on
18V883/4

NOTE: The above is applicable to the USA market. UK and over markets may
have similar cylinder heads with different indentification markings.

The use of 8.7:1 CR pistons, with cyl/heads designed for use with
8:1 CR pistons, will result in abnormally HIGH CR's unsuitable for
street usage with today's low octane fuel unless octane boost is
added; otherwise, detonation and engine damage will occur.

Conversely, the use 8:1 CR pistons with cyl/heads designed for use
with 8.7:1 CR pistons, will result in abnormally LOW CR's. Although
you will not suffer from detonation problems, the vehicle will
certainly lack performance quality.

Information on CR's can also be found within the website.

From aforementioned MGBMGA site,MGB11, with known data plugged in:
Swept volume (SV) (1822cc divided by 4) 455.5 cc
*****
Add together following for clearance volume:

piston dish 6.2cc

Cyl/head cc (spark plugs fitted) (must be determined) **H**

Cyl/head gasket cc compressed 3.21cc (factory info) 3.21

Cyl/bore exhaust valve notch. (see information) .30

Piston below deck cc (see information) 3.06cc
From your nos, (about .020 has been cut from deck) avg. piston/deck clearance is .0235, so:
3.142" x 1.59sq x .0235" x 16.39 = 3.06cc.

Total of the above _12.77 +**H**_____ cc
*****
The formula for CR:
CR = SW vol + Clr vol divided by Clr vol
or, CR = 455.5 +12.77 +H Divby 12.77+H
IF I did it right!,
then for 9:1CR H = 39.26cc, for 10:1 H = 37.84cc

An unmolested late head is nominally 39cc
From MGB25, "Usually the rule of thumb is by removing .010" we have a 1cc loss in clearance volume. "
Your present head is somewhere around .100 under. or -10cc, for a total of 29.
From the formula, Clr vol is 12.77+29=41.7, CR is 11.9
For the head you are dealing on, which seems to be -.045 or -4.5cc = 34.5cc,
Clr vol is 34.5+12.77= 47.27
CR = 10.6, aka too much! 9.5 is usually taken as the high limit for pump gas today.
An early 43cc head with -.040 would give you the requisite 39cc, and that's the solution I suggested way up there.
You could grind a bit out of the head you've already found, but it needs to be done correctly, and measured accurately. IF the valves/seats have been cut a lot, you may be part way there; again, only measuring will tell.

I take no responsibility for the calculations, and you should still measure and calculate it all yourself.

FRM
FR Millmore

What about going with a thicker head gasket? Know there are some companies out there that make solid copper gaskets in various thicknesses.

One that will custom make them is

http://www.cometic.com/custom.aspx
Bruce-C

Charley posted whilst I was figuring all that out.
MGBMGA indicates that OE deck clearance was -.040 -.045, which is about right.

FRM
FR Millmore

Hey FRM, are you a math teacher? Holy Cow! I have asked a seller on E-bay to measure the thickness of an early head he has for sale. If it is thick enough, I'll buy it. It comes with the rocker assembly also. Short of that, would a thicker head gasket work? I am a bit intimadated by all of this.

Secondly, if either of you get to the Hudson Valley, I owe you an "Old Speckled Hen." Thanks again, I'll keep you all posted. Tom
Tom

Fletcher.........is Pretty SHARP(smart)
rich osterhout

Tom-
Not a math teacher, just afflicted with a lifelong need to know what's really going on.

Thicker head gasket not the best idea. Most are solid copper, with the aforementioned faults. Double gaskets likewise.

I will take you up on the OSH in the fall - daughter going to school in Mass, so I'll be commuting right past you.
In the worst case. I could consult on site if you are not up & running.
And, I might give you a couple shekels for your chopped up head - I may have an LC engine that could use it. Gotta study my numbers!!

Good luck on the ebay head, keep us informed.

FRM
FR Millmore

Hey FRM, you are on for the OSH. Just give us a little notice as we have a wedding in August, our nephew, and a GOF in September.(Glens Falls)

I recieve a call from the machine shop today. Ed says that the head is warped .002 and #3 & #4 have valves that no longer seal. He expects to find warped seats. I told him to hold up until this ebay thing is decieded. He expects that the head got too hot. I gave him FRM's numbers and he punched them into a computer program. Guess what, FRM and the computer agree!

Hoping that this experiance helps another soul, I will keep you posted. Tom
Tom

Well yes Tom, of course FRM's numbers and the computer program agreed. It's arithmetic, and there is only one right answer. That is why we have been trying to get you to go get the numbers. Then we can do the arithmetic.

Charley
C R Huff

Hey folks, Ed, the machinest guru, (Yoda?), says that he has remedied the problem of too much material removed, in the past, with "head savers." They are either a stainless or cooper sheet of various thickness'. They go on top of the block, between the head gasket and the block. He claims good success with high powered V-8s. Any feedback? Thanks, Tom
Tom

Tom,

Sounds reasonable to me. I have heard of similar things for dropping CR to use turbo/super chargers.

Is he going to make it, buy it off the shelf, or have it custom made? How much $s ?

You might see if it is cheaper to have him do some cutting, such as unshrouding the valves, to see if that will drop the CR enough. The Peter Burgess book is a good guide to cutting heads.

Do you run the plate with a gasket on each side?

Still, I would ask your machinist to measure the combustion chambers of your head and then run the numbers. I would assume that the "head savers" come in a choice of thickness, so you are going to have to pick one.

Charley
C R Huff

Hey folks, I purchased a "special" SS, vitron coated head gasket for the "B". It is .092 and cost $114.00 with shipping. I'll start installing it tonight, hopig to finish tomorrow using FRM's method. Wish me luck! Tom
Tom

Tom,

Did your machine shop do any work on the head? I think you reported that they said something about valves that leaked as well as a bit of warpage.

Are you bolting this head back on without ever checking the combustion chamber volume?

Charley
C R Huff

Hey Charley, thanks for asking. Yes, I had the head to the machine shop and he re-did the valves and shaved .oo2 to make it flat. He measured the combustion chambers and I have a printout in the garage. I don't remember the number.

More to follow............Tom
Tom

Good news, Tom. Sounds like you are about to have it sorted out.

Charley
C R Huff

Hey Charley & FRM, FYI, the combustion chamber is , (are) 33.5 CC. The head gasket is .098 inches. The head is on the block, I'm going for a ride in the TC. Too nice a day to spend entirley in the garage. More to follow, Thanks to all, I'll try and do the math later. Tom
Tom

Tom,

Gathering the data discussed throughout this thread, I think that should give you about a 9.3 compression ratio, which sounds pretty good to me. You reported the gasket at 0.092 in your earlier post and 0.098 in your later post. The 9.3 is based on 0.092. It would be about 9.2 if is 0.098.

I used your 0.020 overbore size and the 6.2 cc piston dish that FRM cited. I ignored the volume from the piston crown down to the top ring (I have no data for that) but I also pretended that the head gasket would not compress. So, those two should be about a wash.

Anyhow, it looks like you are in the ballpark of what will work.

Charley
C R Huff

The adventure continues............I finally found the time to start the re-assembly of the engine last evening. Tourqed every thing to 20 pounds than let it sit overnight. Early this morning, I started tourqung to 40 pounds in 5 pound steps. Sh*t, the last stud, #11, snapped off. Yes, they were lubricated.

I have ordered a new , upgraded, set. Question, can I re-use the head gasket which has nver been heated?

Thanks again, Tom frustrated in NY.
Tom

Tom-
Yes, head gasket ok.
I am astonished at the number of people who have busted studs. In probably 10,000 MGA/B/Spridget/Mini stud tightenings I've never broken one, not even visually somewhat shaky ones that I would rather replace.
Can you post a good closeup of the busted stud?

And the new numbers sound promising.

FRM
FR Millmore

Tom, have you calibrated the torque wrench?
Art Pearse

Hey FRM & Art, I can take a picture or two of the broken stud but I'm not sure I can upload it. I'll do it in the morning. If I fail at the upload, I'll send the bolt to you, it's of no use now.

The Torque wrench that I have is about 4 years old from Sears. I have used it on two XPAG heads and keep it in its original box. It is the kind that "clicks" at the desired torque. How does one calibrate a torque wrench? I am interested in having it accurate. It would seem that starting at 10 pounds, in five pound increments, I could "feel" the difference. Perhaps compare it to another wrench?

More to follow. Tom
Tom

Tom-
To calibrate the wrench, you need to apply a known load at a known distance from the center of the drive. So, you could clamp the drive in a vise, or clamp a big bolt and use the appropriate socket. With the wrench horizontal, measure some distance like 18in from the drive center. Hang a bucket on it at that point and pour water in it, then weigh the bucket when the wrench clicks. distance in ft = 18" = 1.5ft x 40lbs of bucket and water = 60lbft. etc.(5gal H2O =40lbs + bucket weight)

Some automotive machine shops have calibration equipment, and know how to reset the wrench so the dial matches the real load.

Tool dealers like SnapOn send it away, take forever, and charge lots.

If you send the stud, send 'em all - I need some! Also I'd like to see if I can figure out why they break. I keep trying to get guys who think studs need to be replaced to send their OE ones. OE ones are center drilled or stamped "22" on the end, except early MGA ones. Unmarked OE ones are weaker.

FRM
FR Millmore

Hey FRM, thanks again. Send me your snail mail address and I'll send you the studs & nuts. Your advice and knowledge sharing have been a great help to me. (Know anything about growing hot peppers)? Regards, Tom
Tom

OK.
Hot peppers, like tomatoes, can be a PITA in our climate. Sometimes conditions are just not right. They hate nights below 55F; my wife the expert gardener said that one such night would set them back two weeks, and there ain't enuf two weekses in the year. Certainly not this year! (but I am loving this "Norwegian Summer"!) Try again next year.

FRM
FR Millmore

Hey FRM, Charley and others, I spent ALL of yesterday putting the "B" back together, totaly agrivating my bride. Throwing caution to the winds, I offered to take her out to dinner, kind of like a peace offereing. ( We are married 44 years).

We chanced the "B" and except for running a little hotter than I like, everything went fine. Thanks to all who have helped with advice and knowledge.

I followed FRM's advice on re-tourqing the head and re-adjusting the valves after the initial warmup. To my surprise, I got about a quarter of a turn from 2 head studs. It also runs quieter than before the mishap. The cylinders all now have compression between 150 and 160 pounds with the stainless, .098 head gasket. I hope this thread can help another wanabe MG mechanic some day or way.

Thanks again, Tom

(FRM, my tomatoes are fine but I won't try hot peppers again, I'm going for the garlic).
Tom

"We chanced the "B""

You really were pushing your luck!
Paul Hunt

This thread was discussed between 06/06/2009 and 19/07/2009

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now