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Head to timing chest cork gasket again

PostPosted: Fri Mar 27, 2020 8:47 pm
by mr.vman
On My +2 Twin Cam, Weber head, the cork gasket between the head and timing chest has split and pushed out (oil leaking). I have had this happen before on other Twin Cams. Yes have measured, used various sealants and adhesives. Considering not using a gasket. Apply some type of high build Sealant (Loctite S1-5699) to the top of the timing chest with head off, a bead of; .250 inch install head, remove excess from inside and outside areas. There is/was a problem on the end intake manifold gaskets on Chevrolet V8's pushing out. Applying a silicon gasket sealer to the ends resolved the problem using no gasket. I know the Twin Cam is not a Chevrolet, but it works. Perhaps will work on the Twin Cam? Has anyone eliminated the cork gasket between the head and timing chest? Thanks in advance, Steve V. In Arizona getting ready for LOG Salt Lake 2020

Re: Head to timing chest cork gasket again

PostPosted: Fri Mar 27, 2020 9:05 pm
by Vaughan
Where is it splitting? Is it near the bolt holes? I've had to relieve the in past to allow gasket to sit without tension.

Re: Head to timing chest cork gasket again

PostPosted: Fri Mar 27, 2020 9:43 pm
by mr.vman
Gasket pushed into the timing chain from the rear. Split on the ends, pushed rearward outside of cover. Different failure modes in the past. Have used: Gaskasynch, Permatex Aviation sealers. 3M weatherstrip adhesive (no silicon on gasket to act as lubricant). and others for an adhesive also. considering gasket elimination when I reinstall head this time.
Steve V.

Re: Head to timing chest cork gasket again

PostPosted: Sat Mar 28, 2020 12:38 am
by rgh0
Generally the gasket problems occur because the cork is over compressed due to not enough gap between the head and timing chain cover. You don't want it compressed more than 30% of its original thickness. Some of the suppliers can offer gaskets in different thicknesses to accommodate this or you can take a little off the top of your timing chain cover.

I have never done it but alternate thinner gasket materials are certainly an alternative such as cutting it from a thick paper gasket material or a thin oil resistant rubber sheet and using a good sealant on each side. Forming it out of a suitable silicone may also work with care.


Re: Head to timing chest cork gasket again

PostPosted: Sat Mar 28, 2020 2:04 am
by mr.vman
Rohan, that is I believe the problem. There is about; .038 inch of space between head and timing chest. Cork top timing chest gaskets I have on hand, measure around; .090 inch. Ken, at Dave Bean told me he stocks a thinner cork gaskets, ordered it. Will wait until arrival to measure thickness. Hopefully will solve the problem. If the gasket is once again too thick, fill with sealant or make a gasket? Thank you for the replies, any other ideas? This could be a common occurrence. Might cause head to not fully compress head gasket.
Steve V. Arizona USA getting ready for LOG Salt Lake City

Re: Head to timing chest cork gasket again

PostPosted: Sat Mar 28, 2020 8:43 am
by 512BB
I stick the cork gasket down onto the timing chest on my engine rebuilds now. Leave it with flat metal plates weighing it down overnight, not to heavy. When set, I run a bead of sealant on the inside of the cork gasket to keep oil away from it where it might pool. Then proceed with my usual head replacement method.

Since I have been doing this, I have not had any leaks on any engine I have rebuilt. Its a bit of messing about, but worth it.


Re: Head to timing chest cork gasket again

PostPosted: Sat Mar 28, 2020 1:52 pm
by 2cams70
With regards to sealants for the cylinder head to timing cover cork gasket:
The original Lotus manual (see extract attached) specifies 3M EC776 sealant on the lower face of the cork gasket which contacts the timing cover and Hylomar sealant on the top face of the cork gasket which contacts the cylinder head. 3M EC776 is still manufactured believe it or not but a more readily available almost direct substitute is Loctite 1537776 liquid Hi Tack. For the top face of the gasket a better product to use these days than Hylomar is Loctite 534 anaerobic gasket dressing stick. Loctite 1537776 is solvent based and when you place the gasket with this on the surface it immediately grips very firmly so you have to get the placement correct otherwise you'll damage the gasket if you try to reposition. The Loctite 534 on the upper face however remains slippery until it cures anaerobically. This is important because it allows time to correctly position the cylinder head during fitment before it fully cures. Lotus specifies different sealants on either side of the cork gasket for this reason. The bottom face sealant both seals and adheres the gasket very firmly to help prevent gasket extrusion. The top face sealant helps seal only (no or very little adhesion) and allows for positioning of the head during fitment.

With regards to the cork gasket itself:
The best cork gasket material to use here is one that is a sandwich construction - i.e has a thin metal foil core with a layer of pure cork either side. This is as per the original cork gasket material Ford used for sump gaskets, etc. Almost all of the cork gaskets supplied these days are one piece construction without the metal foil core reinforcement and are a composite mix of cork and synthetic rubber granules. Pure cork has better compressability than a cork/synthetic rubber mix and is better suited in this location for a Twin Cam engine.
So far the only supplier I've come across who can supply these gaskets in the correct material specification is QED in the UK. Their gaskets are supplied around 2.0mm in thickness uncompressed but can compress down a lot further than the cork/synthetic rubber mix ones

With regards to bolt tightening torques:
For the three 5/16" UNC bolts that supply the clamping load for this gasket Lotus specifies a torque of 10-15ft/lb. I recommend that you torque only to the lower range figure - i.e 10ft/lb. It's poor design here and when tightening the bolts you are practically bending the front of the head over the block (as the cork offers practically no resistance to bending load) so no need to tighten too much as you'll only stress the gasket more than is necessary to achieve a good seal.

Re: Head to timing chest cork gasket again

PostPosted: Sat Mar 28, 2020 8:45 pm
by RichardHawkins

I have used a Viton gasket in this location carefully selected for thickness held in place on the timing chest with Loctite SI 5910. I wait for the Loctite to cure, with the weight of the head holding it in place, I then remove the head and trim off any surplus Loctite. I have not used any sealant between the gasket and the head as I did not want to inhibit any movement.

I would like to say this worked, but my engine has not run yet.

Richard Hawkins

Re: Head to timing chest cork gasket again

PostPosted: Sun Mar 29, 2020 7:57 pm
by awatkins
2cam70 — what a great writeup; thanks!

Regarding loctite 1537776 hi-tack gasket sealant: it appears to be discontinued. The industrial vendors in the US who list it are “out of stock” or “unavailable” and I can find nothing similar on the Henkel-Loctite web site.

On the web there is loctite 1540591, same name, but I see it only in pints, and it too appears to be an orphan on the site (US version)

Permatex has a couple products with exactly the same name, so hopefully they can substitute