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 - Rebuild of 5 main B

Hi. As some of you know, I made a trip of about 2000 miles across the US in my 67 MGB GT. The car rolled over 100,000 miles on the trip and I am pretty sure it is the first time (standard pistons in the car).

Unfortunately, about 300 miles from my destination, the car lost power and was only firing on 1 cylinder. Compression in #1,2,3 is below 90.

I am now in the process of pulling the engine and rebuilding it.

I have done two MGTD engines and a few american engines in my life, but never an MGB.

If you would not mind, I would appreciate input for a few questions.

I don't have my shop manual with me. Are there any electronic ones on line?

Does the slave cylinder for the Clutch have to be removed ? if no, does it need to be disconnected from the thowout bearing arm prior to pulling the engine?

Bruce Cunha

The slave cylinder doesn't have to be removed or disconnected in order to remove the engine.

I managed to download a pdf copy of the WSM a few years back, although I don't remember where from.
Dave O'Neill 2

Hi Bruce, this site will give you a factory workshop manual that you can download in PDF format.

http://www.geomatique-liege.be/MGJP/DocumentsPDF/MGB_Workshop_Manual.pdf

Hope it helps.

Andy


Andy Robinson

Thanks Andy

That saves me postage of having mine sent to me.
Bruce Cunha

Hey,
At least you were close to your destination. Where was your destination?
Steven Devine

Sad news indeed. The upside you were forunate enough to near help.

While you are at it, put a performance cam in it. It gave mine a "boost"

Keep us posted as to your progress.

Cheers

Gary
79 mgb
gary hansen

Gary

What cam did you go for?
Dave O'Neill 2

Engine bored .030 over, alloy head (original head cracked between 2 & 3 to the valve guide)
As the cam was already worn, it was replaced with a 'Crane 270' Got more power, still have respectable mileage (26 mpg, no O/D)and a smooth idle.

Cheers

Gary
79 mgb
gary hansen

I am leaning to go with the MGB rebuild kit that Hap Waldrup at Acme Speed Shop is selling. Hap's kit allows upgrading the cam and he has recommended this.

I have had e-mail contact with Hap. His response was very quick and he includes phone assistance with the rebuild as needed.

Have others used Hap's rebuild kits? http://www.acmespeedshop.com/

Bruce Cunha

I haven't used his kit as such but I had him get the parts together for the rebuild of my youbeaut supercharged engine.
He made sure all the bits were correct before delivery to Australia, and just as well because the alloy flywheel was incorrect and would have been a pain to send back to the states. Nice bloke to do business with. Denis
Denis4

Bruce, Hap has a great reputation for helping people of all levels of knowledge in putting together their engines. He sells you only the parts that he feels that you really need and he is there to guide you through the rebuild process. Having been in the business for such a long amount of time, he is very adept at spotting the parts, on the market today, that are to be avoided. You couldn't be in better hands. Now, when do I get your car? RAY
rjm RAY

Thanks Ray. While I have never met Hap in person. Just by the information he put in his e-mail gave me a comfortable feeling.


So I now have the engine out (very easy). Took off the head.

Here is the good news.

Payen head gasket that was put on about 14,000 miles ago when I had the head gone through and converted to unleaded is perfect.

While there is some carbon on the pistons, it is not all that bad.

Here is a picture of the block with head gasket on it.


The lifters also somewhat surprised me. Again, I don't know all the history of the car prior to my getting it but the lifters looked pretty good. a little pitting on one, but no dishing (see what a machinists square showes)

One item I do notice is that there is about 0.18 of clearance between the piston and the cylinder wall. Can't get a 0.2 between it but with a flashlight I can clearly see the rings. There is a ridge at the top. I think this will clearly mean a rebore.
Bruce Cunha

Thanks Ray. Just in reading the information that Hap send me (and the speed he answered my e-mail) gave me a good feeling about him.


Got the engine out. Really easy, about an hours work.

Have the head off and as we all know, there are always surprises when you get into an engine.

The good, is the payen head gasket. This was put on about 15,000 miles ago when I had the head converted to unleaded. It looks perfect.

Pistons have some carbon on them, but that was expected. I do note there is 0.18 inch clearance between the pistons and the cylinder walls. I can clearly see the rings when I shine a flashlight on the pistons. Think that is a pretty good indication that a rebore is needed.

Of note. Pistons say MOWOG 17078 and have a 4 inside a diamond and the word "front" on them. I am assuming these are stock pistons as I do not see any marking of oversized pistons.

Bruce Cunha

Now for the head. It clearly shows one of the issues. #1 intake valve has a chunk out of it. It is not burnt, so I am somewhat unsure what did that. No damage on the piston and no signs of a broken ring in the cylinder. Nothing setting on the piston. Know the engine had perfect compression no later than last summer.

Head was rebuild 15,000 miles ago and had new valves and hardened seats installed.

You can see that in #2 cylinder head, there is some accumulation of material. This was the cylinder that was fowling on the trip.
Bruce Cunha

Now for the head. It clearly shows one of the issues. #1 intake valve has a chunk out of it. It is not burnt, so I am somewhat unsure what did that. No damage on the piston and no signs of a broken ring in the cylinder. Nothing setting on the piston. Know the engine had perfect compression no later than last summer.

Head was rebuild 15,000 miles ago and had new valves and hardened seats installed.

You can see that in #2 cylinder head, there is some accumulation of material. This was the cylinder that was fowling on the trip.

Lifters looked surprisingly good. Most are without pitting or any obvious dishing. One has a little pitting. These will get replaced, but I also wondered if Delta Cams can resurface them and if it is wort having them resurfaced vs replacing them.

Bruce Cunha

Here is the block picture

Bruce Cunha

Here is my real surprise. I took off the water pump and this is exactly what it looked like. I have had the car since 2005 and have put on about 36,000 miles since I got it. Looks brand new, not a speck of rusk or corrosion.

I did clean the cooling system prior to the trip across the US and it has been changed about every 2 years using 50/50 antifreeze and waterwetter. (ran across the US with a 25% mixture)

Bruce Cunha

Bruce,

I suspect the missing piece of your valve did not break off, but rather that it burned off. I have had a valve (in a Volvo) burn instantly and it had a triangle missing from the edge that looked like it had been cut with a torch. I also suspect your trouble might have been brought about by the change in altitude. With SUs I generally lean them as I climb. When I went to Utah in my 77 B, it had a Weber so there was no adjustment. I think I may have cooked my cat as a result.

When you say you have 0.18 piston to bore clearance, I assume you mean 0.018 inches, or are you talking in millimeters, which would be about 0.007 inch if my math is right? I don't know what the clearance is supposed to be, but I suspect it is in the Haynes or similar. Remember that aluminum expands quite a bit when hot, so it may require more clearance than you would expect.

If you send your lifters to Delta, I think you should send them the cam as well. You didn't include the pic of the lifters, but you included the top of the block pic three times.

I don't understand why the head gasket looking good is such good news. Seems to me that it would be good news if it was blown and that was all that was wrong with the engine. You aren't thinking of using it again are you? That would perfectly acceptable as a roadside repair but not for an in-shop repair.

Sorry you didn't make it all the way, but at least you got within about 45 miles of the CA state line. Also, sorry you had to break down in Fernley. That always looked like a pretty dreary place to me, and just a bit farther would have been much nicer.

Charley
C R Huff

Bruce

With regards to your pistons, you need to measure the clearance at the bottom of the piston (skirt) rather than at the top. The diameter is considerably smaller at the top.
Dave O'Neill 2

Thanks CR. That is interesting on the valve and could be as I have not found another reason for the missing piece.

I was checking carbs and plugs while traveling and was adjusting for altitude but that is still a probability. I burned a valve in my MG TD going over the grapevine in California some years back.

As for the clearance on the piston to the cylinder. Yes, that should be 0.018 inch (feeler gauge). I think the cylinder wear is going to be up there as I have yet to see an engine where you can actually look between the piston and the cylinder and see the rings.

Good thing about breaking down in Fernley is that I have relations in that town. That made the wait for the tow vehicle from California a lot nicer.

Pulling the pan and pistons today. Will post more pictures tonight.
Bruce Cunha

Bruce,

You were probably typing when Dave made his comment. Without having the bottom end opened up to measure as he suggests, your ridge at the top is probably the better indication of wear. But, when is is torn down you can have it measured.

Sorry to speak ill of your relation's town. I have only stopped there for fuel, and it always seemed kind of dusty and wind blown.

Charley
C R Huff

Got the cam out. Have no grossly worn lobes, so may be a candidate for a regrind. Crank and pistons tonight and the off to the machine shop for inspection.
Bruce Cunha

Got the bottom end open and the pistons out. I was very pleased that I did not find any obvious major issues. The engine shows what I would expect from a 47 year old engine with 100,000 miles. Rod bearings have a little brass showing. Crank Journals are smooth and no scoring.

Cylinders are without any scratches. All the piston rings are intact and moving freely.

Cam lobes appear to be all the same, and no
lobes that are flat.

CR. Not thinking of using the head gasket again, just happy that it was as clean and in good shape. That makes me feel better that the head is in good shape.

Still going to have it magnifluxed, but given that the temp stayed normal, I am hoping the burnt valve is the only issue with the head.

I was also pleased that the engine inside is very clean. All the oil gallery plugs our out and I did not find any gunk.

Same for the cooling system. Very clean and open.

So from what I see so far, this should be a pretty straight forward rebuild.
Bruce Cunha

Bruce: Glad to know the engine fared well for 100k. I would still consider a fresh cam.

My engine needed a new oil pump as well. When #2 piston was removed, the rings literally fell off. The rod bearings had a good amount of brass showing. Suffice to say it did not have an easy life in the hands of previous owners.

Cheers

Gary
79 MGB
gary hansen

Bruce, when I first purchased my '67 B, back in '72, it also had a burnt valve. It was due to a ruptured PCV valve diaphragm. I wouldn't worry too much about the head being bad. This was mainly an issue with the '68 and later heads that incorporated the holes for the Air Injection Reactor System. It considerably weakened the heads between the valves. It would seem that you dodged a bullet. RAY
rjm RAY

Got the motor to the machine shop. Should know what the find and recommend behind done in a few weeks.

A couple of questions.

If the can is regrindable is it better to have it reground or just buy a new cam? Sounds like either can get me a bit more mid range power.


When I took the pistons out I found the wrist pins are the newer type without the bolt. Anyone know when the changed to the newer version? (Away from home and don't have all my reference material).
Bruce Cunha

Ready access to a cam re-grinder is the biggest hurdle to your camshaft question. When I overhauled my '67 GB engine, back in '93, I went with a Kent 285 cam and lifter kit as well as the later longer pushrods. This has proven to be an excellent re-grind over the years and I rarely have to adjust the valves indicating that it was properly hardened. If your engine is indeed a GB series, it should not have the clamping bolts on the connecting rods. This was last used on the GA series engine around late '65. RAY
rjm RAY

Thanks Ray. There is a cam grinding shop in town. Machine shop says they are very good. I will check cost of regrinding mine VS a new one.

Appreciate the information on the wrist pins. This car is close to the end of the MK I production run and it has other items that are from the MKII, so I was unsure if it was a similar situation. Your numbers of 1965 would clarify this.
Bruce Cunha

This thread was discussed between 11/08/2014 and 24/08/2014

MG MGB Technical index

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