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MG MGB Technical - Head question

Hello All,
I have a 18V engine with an aluminum head presently. Some may remember awhile back i was experiencing oil loss and I saw problems coming from two of my studs that hold the head in place. I have recently purchased a parts car with a intact engine and trans. The engine markings say it is a 18GB, from the late sixty's (I suspect), Now the question, Can I put the steel head from an 18GB on a 18V and what are the potential consequences?
Thanks in advance.
Peter Murray

Hi Peter:

As far as I know, an older head should fit on a newer block. The newer heads have a water choke port I believe, which would present problems in that direction, but not in the direction you are going. However, there are some things to consider:

Some 18V engines had heads with bigger intake valves, which may offer alittle better performance than the smaller valve heads. Not sure which valves your alum head might have, but there might be a small difference in performance (some might argue the smaller valves are better for fuel mixing or something like that).

Do you know your compression ratio? Often with alum heads, the CR is higher, as you get less detonation at higher CRs with aluminum. It may be that the alum head has a different combustion chamber volume than the standard one did, to achieve this. You will need to make sure the combustion chamber volume of the GB head is going to result in the correct CR for your engine - CR is dependent on chamber volume and piston design. Low CR would result in poor performance, and higher CR can lead to detonation problems.

Use a Payen gasket and consider ARP head studs (at least get new stock ones) when you make the change.

Erick
Erick Vesterback

Hi Peter-Erick
Just be a bit carefull which rocker gear you use' If using the set that is with your new head all is ok but if using your original set just make sure the oil feed hole in the post lines up with the hole in the cyl. head. It all depends on what model posts have been used when your alloy head was fitted. Cheers Gary.
Gary

Gary,

I think there may be an issue regarding the pushrod lengths to be cleared as well. I understand that, depending on the geometry of the alloy head, the rods from that may not transfer to the old head without stressing the rocker system.

Others on here will have more experience than I have with this sort of change so I offer my comment as a caution for Peter.

Regards
Roger
Roger T

Peter,

I'm not sure what the problem is with your aluminium head. You said an oil leak.

If you do change for the other one, and you don't have any plans for the aluminium one, I'll happily pay for the postage...

David
David Balkwill

Thanks all that responded,
I am thinking I will use the steel head and the rods from that engine to ensure proper clearances. I will also install new studs in the block to resolve the seemingly stretched studs that I have now, again I believe a result of mix matching on this alloy head.
Peter Murray

This thread was discussed between 07/06/2008 and 09/06/2008

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