Block to timing cover step

[JATLAN4]

Simple question but its proving difficult to get answer. My twin cam block has been decked and the amount of metal removed means that the head now won't seal because the plates at the front of the engine are too high.
I am going to machine them back to obtain the original clearence. Does anyone out there know the dimension originally used by Lotus for the clearence between the plates and the head. In other words what size should the step up be from the plates to the block so that the cork gasket can be used?
Cheers
John

[john.p.clegg]

John

You have a problem there,either you have a tall front cover,in which case flog it on ebay and purchase a smaller one or your cank/rods/pistons have a problem re. deck height

More info will surely follow from those who havent opened the red wine yet...

John

[JATLAN4]

John
Thanks for comment. It is actually the standard height front cover.
If all else fails its a case of calculating the difference between the front gasket compressed and the head gasket compressed I suppose?
I just hoped that this might be a bit of general info that someone might have
John

[bill308]

OK, I hitting the red wine too. Doctor's orders.

On my engine, with no decking of the block, the case is the same height as the block, by eyeballing it. So, if your case stands proud of the block by half the thickness of the head gasket, then the timing case gasket should be half the OEM thickness, IMO.

How much did the mill off the block?

Cork compresses quite easilly so if the mismatch is less than half the thickness of the timing case gasket, I'd consider, but not necessarily accept, a full thickness cork gasket.

Bill

[rgh0]

The sealing of the timing cover to head gap is a challenge for many twin cam rebuilds these days for a range of reasons

eg
Tall blocks and variable front cover spacer thicknesses and block decking practices to match pistons used.
Block decking on standard blocks to fix distortion and corrosion problems
Machining of front covers to fix distortion and cracking repair problems
Proper alignment of front cover to crank affecting front cover to block alignment, this is also affected by block line boring moving the crank location versus the block.
Different head gasket thicknesses due to compression ratio problems or changes to utilise modern gasket technology

The Elan Factory can supply the cork gaskets in three thicknesses to better cover the range of possibilties and if you have ended up with a non standard gap consideration of a different gasket thickness to match is warranted. Dont know if other supplies do the same but I would expect quality engine rebuilders in US or UK to have faced the same problems and addressed the issue.

cheers
Rohan

[JATLAN4]

Thanks for the comments and thoughts.
I have been advised that the step now was originally 40 thou (inches).
My front cover is about 10 thou higher than block. When head is fitted with standard gasket it will not seal because of front cover lifting the front of the head. In theory this should not happen because the head gasket is probably around a minimum of say 20 thou when fitted and compressed so there still should be clearence.
Anyhow plan is to remove as much as possible without interfering with the top 2 through nuts and bolts.
I wonder if the problem I've got and the apparently large standard step is all to do with the relative expansion of the cover versus the block?
John