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MG MGB Technical - interchangeable Cylinder heads

I know the later cylinder heads lubricate the Rocker Assembly differently and some had different sized valves, but otherwise will all heads bolt up?
Bryan

Bryan. Yes, they will bolt up. But, they should be interchanged as part of a rebuild and the system needs to be set up as an integrated system rather than just bolting on parts. Valve sizes changed among the various cylinder heads as did the size of the combustion chamber. Peter Burgess has some information on this in his book on the MGB engine and the link that Tore has posted may provide some information that will be of use.

What are you trying to do?

Les
Les Bengtson

Les,
I am in desperation at the moment and a shoe string budget. I have found an earlier head at a great deal that just had a valve job. The Valve sizes match up to what mine have though. My existing head is needing completely reworked. I could get this one for half of a rebuild, but this one is going to be gone very soon. My head casting number is CAMII06, the one I found is 12H2389. Best I can tell all is the same except the rocker lubrication point. This one has rockers included. I did not know about the combustion size changing though.

Bryan

Bryan. Tore's post, under "Cylinder Head Casting Number" has the information you need to make your decision.

Of concern to me is the fact that the 12H2389 cylinder head has the 42cc combustion chambers while your current head as 38cc combustion chambers. Using the earlier cylinder head will lower your compression ratio somewhat. Much will depend on what size/oversize pistons you may be running and how much both cylinder heads may have been "skimmed" to raise the compression ratio.

If you question is, "Will it fit and will the engine run?" the answer is that it should. But, you may be down on performance by some undetermined amount.

Here in the US, a good, used cylinder head which has been crack tested and found good, is hard to find and can run between $300-500 depending on the specific cylinder head. Add at least $100 for a minor rebuilt, up to $250 for a complete rebuild. Rocker arms, if they are rebuilt, will add another $100 minimum.

Thus, the value of the rebuilt cylinder head is going to be at least $500. If the price is much less than this, I would want the cylinder head inspected, including crack testing, before purchase and installation. There are a lot of "rebuild shops" out there who do rather shoddy work.

Your decision and I hope this information will be of use to you.

Les
Les Bengtson

Bryan,

Since I don't know what car, engine, or pistons you have, this is only approximate. But, by my calculations the difference between 38cc and 42cc should be about 0.5 to 0.6 in compression ratio. If the budget is tight and you just need to get the car running, I wouldn't worry too much about that.

As far as getting the head crack tested, magnafluxing should be pretty cheap since it only takes a couple minutes. Pressure testing takes a bit more set up time.

Charley
C R Huff

Thanks for all the input. I did not make the purchase. The last link Tore sent helped a lot. I read up on the combustion chambers, then the difference in pistons, that head was used with the shallow dish, I have the deep dish. I was worried that would affect performance.

The reason for the hasty speed was I found a head on ebay that was only up to $200 yesterday, the bid was almost up. Said it had reground vavles, was magnafluxed and pressure checked, broze guides and hardened seats. All in all, I will just wait and have mine done properly.
Thanks for all the advice!
Bryan

Pleasure to be of help :-) This BBS is a unique source of knowledge. Donīt know how I managed before I discovered it.

Tore
Tore

Bryan,

I have a completely rebuilt CAM1106 head on the shelf. Shoot me an Email at mgbpaul at yahoo dot com if you're interested.

Paul K

This thread was discussed between 17/04/2008 and 19/04/2008

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