Post Number: 19
|Posted on Saturday, 03 December, 2005 - 00:26: |
In another thread, titled "Silver Dawn Coolant Temperature Fluctuations" there was much discussion on several topics most not very closely related to the subject title. We really should start a new thread when we begin discussion something new.
Anyway in that previous thread, Richard Treacy said this:
The last head I removed was a few weeks ago. Because it had only been on for two years and a mere 15,000 miles I didn't even need to use the cardboard spacers. I was expecting to find a burned exhaust valve and possibly reuse the gasket, so didn't want to squash the gasket, but the above pictures show that the gasket was the problem all along.
Richard and others: what criteria indicate a cylinder head gasket is reusable? When a gasket is compressed, the rolled edges around the combustion chamber are squeezed to match the thickness of the rest of the gasket, resulting in a very uniform thickness throughout. I have assumed that the squeezing of the rolled edge is necessary to achieve microscopic conformance to the surfaces of the head and block. Perhaps this is not the case.
Also, there are some cylinder head gasket sealing products offered in the auto parts stores. (Spray Cans) Comment on success with these products would be appreciated. I note that RR suggests "Wellseal" along the left edge of the gasket because the studs are inborad of the water passages that are directly above the exhaust ports. In my experience, it is not uncommon to have some water seepage to the outside along the left edge until the engine has been warmed up once cooled down and the nuts retorqued.
All comments appreciated.
Post Number: 924
|Posted on Saturday, 03 December, 2005 - 03:47: |
I have never reused one on my own car, but for some people, cost, availability and delivery time dictate that reuse is sometimes acceptable, if not exactly recommended in an ideal world.
However, a few of my used R-Type head gaskets have found their ways into other R-Types, and even into a S1. A certain club member was short of a gasket in an emergency. Coincidentally seeing half a dozen good used ones hanging in my workshed, he asked and I agreed that he use one as a temporary measuire. I understand that temporary fitting became permanent.
The main criterion is whether there is blackening between the exhaust valve apertures between cylinders 2 and 3 or 4 and 5, unless of course somewhere else is obviously shot. If the copper fold-over is split, then that's definitely a no-go.
I was even told once by a specialist unnamed that a good used gasket on a good head and block has the advantage of not needing so much retorqueing in its early life, therefore avoiding early failure risks. On the car I mentioned in the last thread, one of my old ones would certainly have stood a better chance than the failed one did when new. Given that the substrate compresses a little, the copper fold-overs don't really matter.
Even with new gaskets, using spray gasket compound with a copper substrate and a higish temperature rating will ensure a seal, and is recommended in lieu of Hylomar around the water jackets. Coppercoat brand is an old example, and Loctite make some astonishing acetate alternatives these days. Crewe always specified the use of gasket compounds in the critical places. Modern materials are so much better that you could almost cut a gasket from copper sheet and seal it, or delete the gasket altogether, both methods being used on many racing motors today.
As a complete aside, I have no sump or wheelcase cover gaskets on my R-Type, using Loctite HT Silicone RTV instead. They are leak free. I could see no reason to sandwich paper between two layers of silicone.
On my own car I now use the UE5053 S-Series/Silver Cloud steel head gasket as they don't suffer any of the problems of the C&A (rather C&Clay) ones on a 4.5. However, it is impossible to reuse a steel gasket without risking water leakage into the bores and oil.
Like my stash sump and wheelcase gaskets, my stash of genuine new head gaskets will probably never be used.
Post Number: 20
|Posted on Saturday, 03 December, 2005 - 05:29: |
Thank you for the insightful comments. I am about to attach the cylinder head to W265C a 4 1/4 L Silver Wraith engine. I have a new gasket to use, but after some of the discussion on this and other message boards, I was wondering if a used gasket I have, which appears to meet the criteria you state above, might actually be OK. This gasket has about two years use and was removed very carefully to avoid bending or deformation with the view that it might have some value someday. (Parts that are no good today may be all you can get tomorrow.) I think I took the studs out first and lifted the gasket from the block afterwards to avoid possibility of deforming the gasket.
Anyway for the benefit of experiment I have decided to use the used gasket, using the Permatex "Copper Spray-A-Gasket" high temperature sealant, which they say is for head gaskets. I used that on the last engine assembly I did, but of course I can't tell if it did anything. That gasket has not failed, but it also might not have failed without the magic sealant. Worst thing that could happen is that the head will have to come off again, and that will not be difficult in the first few years of use of this engine.
You refer to a steel gasket, which I have read about but not seen. I am guessing this is very thin metal with corregations around the places that need to be sealed, something like the exhaust pipe flange gaskets. Do I guess correctly? I believe it is only available for the 4.5 L engine, and the purpose is to raise compression ratio an incremental amount.
Incidentally, back to the subject of cylinder head removal, which is somewhat related to this current thread, my puller is designed to support the cylinder head in an exactly level plane referenced to the block surface. Raising the head straight up without any tilting is helpful even when it is not stuck. It is after all about 60 lb., and when you are reaching way out leaning over across the front wing not that easy a lift, especially considering you need to hold it level to keep from being jammed as it comes up and off the studs.