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MG MGB Technical - Shims, Head bolts, & Head gaskets, etc.?

Yes, its me again!

I've just picked up the head for my 72B from the machine shop. The major work was replacing all 4 Exh valves, guides and seats. But receiving the head back has resulted in more questions.

1. When picking up the head, the machinist handed me 2 2-1/2" x 1/2" metal shims. He explained they came from the center 2 posts on the rocker assembly. He didn't understand why they were installed as the assembly appeared level/straight. I tucked them in my wallet for safe keeping. So, why would such shims have been needed and should I reinstall them?

2. When removing the head originally all the head bolts appeared to equally torqued down. I had no difficulty in removing the bolts. I am planning on reusing the bolts. However, some feel I should replace head bolts as a standard practice. Thought is that they will stretch over time and may be weak or too long now. I've never replaced head bolts unless they were broken. So, how routine is the replacement of the head bolts, or is it normal to just use them?

3. The head gasket that came with the valve job gasket set is copper, based on recommendations by others. Now I'm hearing some don't like copper head gaskets, why I don't know - but there is a concern they are more tempermental than original material gaskets. So, how do people feel on using copper and should I take any extra care in torque process?

Thanks for all the help. I'm looking forward to getting things running again and being too busy to keep making inquires.

BobA
Stillwater, MN
R.W Anderson

The shims are there to put a very slight bend *in* the shaft, or more correctly make sure it is held stiffly by putting the four mounts very slightly out of line, so it can't itself twist back and fore which wears its mounts. They should be refitted, it was issued as a mod to earlier engines that didn't have them originally, to be applied when the rocker shaft was removed for other reasons.

I thought copper *was* the original material - on the 4-cylinder at any rate. Mine is, although it is a gold-seal engine which may heve been rebuilt.

Should be head studs and nuts - again on the 4-cylinder, and therefore can't be too long - unless they have stretched so much the end of the threads is above the top of the head! Stretching *is* an issue with bolts, as they can bottom in the block holes before applying full torque to the gasket, but as I say that shouldn't apply to the 4-cylinder. The seal between 2 and 3 can be problematical as it is so narrow. John Twist writes this "MGB WEEPING CYLINDER HEAD: The rule is, all rebuilt B series engines weep between the block and head, between the 2nd and 3rd spark plug. Some actually piss. To remedy this problem: That center exposed head stud, RH side, between #2 and #3 is the guide stud -- the hole in the head is 3/8 whereas the other holes are 7/16. Clean out the stud hole in the head with a 3/8 drill. Polish that stud, at least. Ensure a chamfer at the threaded hole in the block. Chase the threads on the stud, nut, and block (3/8-18 and 3/8-24). Ensure the head is planed to 0.001." Ensure that the top of the block is cleaned to a SMOOTH finish. Fit the studs back into the block with only about 5 lb-ft torque. Place a THIN film of clear silicone, RTV, sealant on the RH side of the head gasket. Into that EXTREMELY THIN film, place two strands of stranded, flexible wire about six inches long, twisted together, along the outboard side of the gasket, between its edge and the water jacket holes so that the thickness of the head gasket is effectively increased by several thousandths. Goodbye leaks."

Paul Hunt 2

Bob. As Paul notes, the shims were used to stop "fretting", a form of wear associated with slight movement of parts causing a wear pattern on the rocker arm shaft.

I normally re-use the solid washers and nuts on the cylinder head unless a visual inspection shows them to be bad. As to the cylinder head studs, our opinions vary. I have to respect the ability, experience, and knowledge of some of those who do not replace the studs. But, I do it on the engines I rebuild. Chris Betson sells an upgraded stud set that is stronger than the factory studs, not quite as strong as the ARP studs, and is reasonably priced. I use his product for my rebuilds.

I am not sure what you mean by a "copper" gasket. As Paul notes, all of them use some copper in them. The original gasket was thin sheet copper with asbestos (called a composite gasket), there is a solid copper gasket, sometimes recommended for high performance use, and there is the modern composite gasket made of copper and resin. This latter is available as part of the upper gasket kit from Fel-Pro. It is the gasket I have used on my last three rebuilds and will be using on the one currently taking place. No need for strands of copper wire or other tricks to make it work correctly and hold up well.

Yes, you should torque carefully. Fletcher (FRM) recently had some comments on how to properly use a torque wrench--consistent, medium speed movement with torque being taken as the wrench is moving. I torque in steps--i.e. 20 lbft on each nut, 30 lbft, on each nut, 40 lbft on each nut, then to 45-50 lbft as the final reading. In theory, that should make sure that you do not have nuts at full torque and nuts at zero torque causing a problem with the head or gasket sealing. This may be extra work. But, with the cost of rebuilding an engine, I am willing to spend a little extra time and I have never had a cylinder head gasket leaking after being installed.

Les
Les Bengtson

Paul is correct on the rocker shims.

"Copper" can be misleading. The OE gasket on early cars was asbestos faced with copper on one side, and either steel or copper colored to look like steel on the other. They work very well if correctly installed and retorqued. A bit of looking will turn these gaskets up - Clough & Wood make them in the UK, and TRF sells them here.
These gaskets seem to be referred to as "copper"; it would be less confusing and more accurate to call them "copper faced".

There are solid copper gaskets, also called "copper". It is an old racer trick used for expedience, quick head changes, compression changes, and lack of a "real" gasket. They work fine if done right, but only for a short time, after which they leak, but rarely fail totally - good for racecars. The hucksters sell them as "competition upgrades" - "...a secret ingredient of many high performance racing engines" Gets the suckers every time! And after the thing leaks, then they get to sell more gaskets, "upgrade" or "Regular" or "Premium" - or all of the above, since NOBODY seems to know how to do it correctly anymore.

Finally we have the Payen or similar resin faced fibre gasket. It lasts longer without retorque than the copper faced ones, but will invariably leak after a while. And it is a PITA to get off the block and head when it dies. In situations where the gasket has not been in use too long, the copper faced gasket can be reused by cleaning and a thin coat of Permatex #2 sealer, though it's not "good practice"; you ain't a'gonna do that with a Payen.

I am quite surprised and disappointed by Paul's quote from John Twist on seepage and the cure thereof. NONE of my rebuilt/repaired/patched together engines seep, leak, or blow gaskets, EVER, in 40+ years. And I don't go through all that rigamarole either. The procedures given are good for rescue of really screwed up parts or maybe blower motors; I've just recently salvaged a horribly machined Spitfire block with appropriate copper wires in strategic locations. I've never planed a head or block just for flatness in a bad gasket situation - only when I was doing other stuff that required true surfaces or for compression increases. Everything clean and dry, head and block reasonably flat, put it together and follow my correct retorque program, as handed down to me by real Mechanics from the days when men built and fixed machines based on reality and knowledge, not rumor and laziness.

My procedures and real world successful experience with such things are detailed in "Boltbabble.doc" available by emailing me and asking.
FRM
FR Millmore

Didn't mean to step on you Les - I was without access for a while there, written but unable to submit!
BTW, I am still looking for some good OE used studs, for both A & B series engines, so you guys who replace them please tell me what it takes to get you to send me your "junk"
FRM
FR Millmore

FRM

How many OE used studs would you like?

Chris at Octarine Services

Very timely thread bob, as i am just waiting for my "new" head to ocme back from the mechanic. Newly machined, new exhaust vales, guides, seats, etc.

I don't recall any shims when i removed the head? Should i be looking to by them? As for the gasket, in the moss catologue, for the cylinder head gasket, it shows, "copper" for engines 62-74, adn "composition" for 75 - on. Going by Les' answers i should be using the composition, as i do have the leakage deescribed by Paul.

One lasty question regarding cleaning the block top before replacing the head. is there anything special that i need to do to make sure it is clean and smooth?

Thanks

Ken
70 B
Ken Harris

Chris-
I need one short one for a B, since I robbed from an engine set to fix the wretched Spitfire. I am, I hope, going to be doing a couple of Magnette/A engines and would like a couple of sets of the "22" or center drilled ones to replace the early type. Any more than that is just backup, since I have never broken, stripped or stretched one yet - I do like to replace those that are corroded. OE nuts likewise, since the replacements are no longer correct either, and I replace Triumph rubber nuts with B ones.
It seems a bit much to have to get scrap studs shipped from the UK, what with guys here throwing them out, and the response from this side might be overwhelming! If it comes to that, I will endeavor to get some other stuff from you to make it worthwhile.

Ken - It's all in my article.
FRM
FR Millmore

Jeez- For years I've credited that strand- rig-in-the-goo" to Lawrie Alexander, Cameron Park, California. At least that's where I "learned" the trick, when Lawrie finished the build on the 1977 stage 2.78542 roadster. I saw him laying in the strands, and asked for the full monty on explain. Sounded good to me, and over, oh, 15-20 heads, using the "trick" each time, I've not had weeping nor pissing. And, yes, I did have leakers just as Les notes, between 2 and 3. Now it's the urban myth I use to look really qualified whenever replacing the head gasket( just as Lawrie did to me 6 years ago): always the black sticky Payen head gasket FWIW.
MFR, thanx for the reference info on the torque, sounds right arm.
Cheers, Vic
vem myers

Did anyone change to harden seats?
Rich Osterhout

Rich. Yes. As a minimum, hardened exhaust valve seats. The hardened intake seats are a matter of opinion. The hardened exhaust valve seats are a matter of necessity.

Les
Les Bengtson

Rich-
I always install hardened valve seats on both the intake and exhaust valves. When valves are reground and their seats in the cylinder head recut, the old deposits of Tetra-Ethyl-Lead remaining from the era of leaded fuel are removed. Without Tetra-Ethyl-Lead to both cushion and lubricate the valve seating surfaces, the head of the valve impacts upon the raw cast iron of the valve seat and forms a series of micro-welds which are torn loose the next time that the valve opens, resulting in the erosion of both the cast iron valve seat and the and the valve. This also occurs when a cast iron cylinder head that was induction hardened has had new valve seats cut into its surfaces, removing the layer of hardened metal. This is because in induction hardening, the surface is heated by a high-frequency alternating magnetic field that generates heat in the surface of metal before being quickly quenched, resulting in a hardness penetration of 0.060-0.080 inch below the surface. The ease and speed of this process makes it the favored technique of Original Equipment production. A lead-free fuel compatible hardened valve seat insert eliminates these problems.
Steve S.

FRM,

I have no shortage here!
A full set with nuts and the correct hardened washers weighs in at 915 grams

Two full sets plus 1 odd one should just get in under 2 kilos when packed - cost of £20.72 by air (5 days) or £10.66 by surface mail (56 days!!)

Next time my brother is flying in from wherever and going back to the states, I'll give him a few to carry with him!

What are postage costs like in the US?

Whereabouts in Pennsylvania are you?
Chris at Octarine Services

56 days surface mail??? What the heck are they doing, bringing it over in a canoe??

Ken
Ken Harris

Pack donkey, I think!
Chris at Octarine Services

This thread was discussed between 06/04/2007 and 11/04/2007

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