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MG MGB Technical - 3 main 1800 engine rebuild help.

I am rebuilding a 3 main 1800. I have two engines to choose from. Both engines have std. pistons. The numbers stamped in the top of all pistons is 493506/1. In one engine the pistons look like they have been knurled on the sides located 90 deg. from the wrist pin. The max cylinder bore on one block is 3.162" and the other is 3.163" Assuming a std bore of 3.16", do you think I have to install .010" over pistons or could I reuse the old pistons with new rings and hone the bores. Also I have 3 cams. The cam lifts are: .264"-.268" on one cam, .260"-.263" on another and .233"-.236" on the last. One or more of these cams may be from an MGA. I do not know the history of either engine. Both cranks are .010"under on all journals and I am having them both checked for cracks and journal condition to determine which I should use. Should I replace the head studs, main studs, and con rod bolts and should I buy from Moss or from an aftermarket like APT. Thanks for your help and have a good day!

John
John Progess

Cylinder bore wear of only .002" or .003" is perfectly acceptable. I would choose the pistons which have not been knurled, providing there are no scuff marks on the skirts and the ring grooves are sound. Hone bores with a 45" crosshatch. Cams are a bit more difficult but I would tend to go with the highest lift , using that as a guide to least wear, I always use APT,studs the quality is so much better.
jim soutar

John, the higher lift camshafts are consistent with MGA/MGB cams. The lower lift one probably comes from one of the Austin / Morris saloons. How do I know? - The PO of my MGA had put in an Austin A60 engine, and I had to swap cams to convert to MG.
Art Pearse

There is no need to use APT studs and bolts for a normal road going engine. Provided that they are all original equipment items their quality is fine for re use.
Iain MacKintosh

O.K. if you dont mind using fasteners that are 30+ years old and may have been overtightened more than once
jim soutar

Jim-
And have expanded and contracted so many times that metal fatigue may be setting in! Actually, with the three-main engine having gone out of production in October of 1964, that would be 47 years old at best! And after all these years who's to say that they aren't substandard aftermarket replacement parts? I'd play it safe and toss them in the bin.
Stephen Strange

"...may have been overtightened more than once"

Or never actually overtightened?

"...who's to say that they aren't substandard aftermarket replacement parts?"

Who is able to say they are?

As significantly, who is able to guarantee replacement parts will not fail?

In fact, who among us mortals is able to answer any of these questions?

Other than for obvious wear or stress, I think I'd go with Iain's advice for a road going engine.

If something fails then deal with that when/if it happens.

My 69 roadster went out of production 43 years ago. Would anyone seriously suggest I should replace everything with contemporary parts?

An MX5 perhaps?

I do wonder when otherwise calm and rational men start punching at shadows!
Roger T

Roger-
You said "who among us mortals is able to answer any of these questions?" Exactly my point. You also said "If something fails then deal with that when/if it happens." The rational approach is to build an engine properly from the outset so you probably won't have to deal with problems later. An engine is just too expensive an item to gamble with.
Stephen Strange

My view is that original is OK, if you are able to apply the required torque, which will be obvious at assembly time. I doubt that head studs will ever fail after a successful assembly.
Art Pearse

Art Pearse

Headstuds breaking on applying torque.
headstuds breaking when retorquing after first heat cycles.
Headstuds breaking on original never touched engine's leaving a dent in the bonet from below!
On A and B series engine's are all possible problems.
Ask me how I know........

Building an engine that will just be used to drive to the field for a picknic and never go above 3500rpm would be fine with almost any bolt.

But when the use gets more intensive you have to ask yourself what is needed?
What failure is catastrophic.
And what is the likelyhood of failure.

Take those points in to account and you get the following list of fastners with the most important to use first.

-rod nuts and bolts
-flywheel bolts
-head studs and nuts
-mains bolts




Onno K

At the very least, replace the head studs with ARP fasteners. After a thorough rebuild, in the early '90s, the only thing to fail were the head studs, on my '67. After replacing them 3 years ago, there have been no problems since. RAY
rjm RAY

Of course it is a pain if a head stud fails but it does not lead to a catastrofic engine failure.
Where a broken rod or flywheel bolts can lead to either a hole in the block or your legs in pieces.

Again add:
Chance of failure to result of failure.
Onno K

Onno, I was referring to head studs.
"Headstuds breaking on applying torque.
headstuds breaking when retorquing after first heat cycles".- My point was that failure in this instance is not catastrophic and can be fixed with a new stud.
"Headstuds breaking on original never touched engine's leaving a dent in the bonet from below!'- What are you talking about and how could new studs have prevented that? Presumably a new engine has new studs. Are you saying that a broken stud was ejected as a projectile?
Art Pearse

Onno, I think your shadows are lengthening just a tad!

We'll probably not resolve this to a single position. Why should we expect to? We all come from differing background experiences.

Mine includes a knowledge of a number of engine rebuilds among our Club drivers (including some with mild sporting applications) where inspected OE fasteners are routinely successfully used. I've reused inspected head studs (substituting a couple from used OE stored pieces) when installing two heads on my car.

So, "used" does not of itself need to mean unreliable.

A Google of "ARP fastener failure" gives four sites of discussions of the failure of ARP fasteners in the first three pages of results. So, new does not necessarily guarantee reliability.

Yes, I acknowledge that questions of the competence of the engine rebuilder, the use (abuse) of the engine et al are all probably more significant than the factor of newness. However, such cases do demonstrate that "new" can be unreliable.

I am still with Iain and Art on this. I think we can overdo the investment in a road use rebuild. After all, these engines (in there entirety) are somewhat renowned for their agricultural toughness.

In the case of a significantly stressed rebuild, intended for frequent hard use, a different set of criteria need to be addressed.
Roger T

John, I race my MGB at club events, I do see on occasions 7250 rpm. Even if you don't go anywhere near these revs for the price of ARP bolts it is worth the cost verses worry of things flying off! All my engines have at least new con-rod bolts.
Don in the hot hills of Adelaide Sth. Oz
TF 4887
Twin Cam YD2 2448
1971 MGB (boy racer)
D J Walker

This thread was discussed between 24/01/2012 and 28/01/2012

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