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Old 05-03-18, 16:00
Lolat492 Lolat492 is offline
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Inlet manifold gasket material?

Found two inlet manifold gaskets are leaking on my Lola's Porsche engine.

The gaskets from the company PMO, USA (who make the carbs used) seem to break down when exposed to petrol(!).

This is the 2nd time I've had this issue with their gaskets. The gaskets are between the base of the carb's manifold and the cylinder heads. The two items are heat insulated by a special phenolic plastic and the gaskets I need to replace are sealing both sides of this heat spacer.
The port size is 40mm and fastened by 2 M8 studs/cylinder, all very classic design.
Nobody has them in the UK. I have asked PMO for a set of 12, but considering if there is a better gasket to be had.

I have found a proto shop who can CNC cut a set, but not sure what material to specify.

It is a dry seal. The American 'grey, greasy feeling' gaskets are pictured below when new.

Any ideas on material spec please?
Graham.
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Old 05-03-18, 17:14
mikegleaves mikegleaves is offline
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I have recently purchased a car that has set up to run on Shell v power and cvl I was told not to deviate on this and that I would need to change some of the gaskets in the fuel pump and carbs every couple of years or so, due to them not being able to handle the ethanol in modern fuels. I did some research a few months ago and came across these people James Walkers https://www.jameswalker.biz/ who make specialist gaskets for industry. In my case it is most likely cheaper to change the gaskets on a regular basis. The only other advice I was given for this fuel was to buy it from a garage that has a regular / high turn over and replace unused fuel after a month. I am interested if any of this is not correct, as most is passed on info.
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Old 05-03-18, 19:52
MX5 novice MX5 novice is offline
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Would it be possible to machine a groove into each side of the phenolic and fit a large o ring?

Alternatively I sealed my home made manifold to the head with Wynns black gasket maker. My method is to apply the gasket maker to the surfaces then assemble but only for the fixings finger tight. Leave it 24 hrs to cure before tightening properly, this allows the rtv to create a slightly compressible gasket which will be compressed once fully tightened.

D.
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Old 05-03-18, 22:05
Lolat492 Lolat492 is offline
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I have the O rings and the lathe Dave, but the groove is not circular!
Will try for 'paper' gaskets.
I think the ethanol is the reason for this second degeneration of the gaskets as suggested...
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Old 06-03-18, 19:46
Darvie Darvie is offline
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If you do use gaskets tha tare near fuel make sure that they are made from viton, more expensive but worth it.
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Old 06-03-18, 20:47
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tr7v8 tr7v8 is offline
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Shouldn't they be Mishab gaskets? Various ones on a google but like this http://crosthwaiteandgardiner.com/parts/weber
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Old 06-03-18, 21:30
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Biggles Biggles is offline
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Quote:
Originally Posted by Lolat492 View Post
I think the ethanol is the reason for this second degeneration of the gaskets as suggested...
Higher percentages of ethanol and some rubber seals are a bad combination but I've never heard of ethanol affecting gaskets on a petrol engine. In either case, the fuel we get in the UK is max 5% ethanol which, allegedly, has no compatibility issues. It's only when you get to E10 (like on mainland Europe), that you start to get issues.
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Old 06-03-18, 21:42
Lolat492 Lolat492 is offline
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I've only used Shell V Power petrol on this engine and this is the start of the second set of gasket failures.
All gaskets are from the carb supplier, PMO in California who cannot be contacted by email.
I'm taking 2 actions, first is to make my own from inlet manifold application paper gasket, 0.8mm thick.
Second is a supplier Atlas who I have emailed tonight following a phone call from a trusted UHR member.
Carbs coming off on the side that is leaking tomorrow.
Will be interesting to see how the gaskets look.
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Old 07-03-18, 09:03
asklepios asklepios is offline
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Graham, your image of the failing gasket vs new is confusing(to me). The inner tear drop seems extremely regular and looks as if this was the way it was formed. The failure at 5 O'clock could be simple chaffing if there is a high spot on one of the surfaces.
As an aside there appears to be a crack visible in the bottom right of your pic. behind the hose. Sure you know about it but just incase you have become target fixated on the blasted gasket.
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Old 07-03-18, 14:30
Lolat492 Lolat492 is offline
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Thanks for the comments.
Let me explain though:
The picture is of the new gaskets from the USA fitted 3 years ago due to a failure of 4 of the 6 cylinders for air leaks.
The gaskets are new except the one on the right. That is a Porsche gasket with a cut-out for the injector used on the original engine induction system.

I was the only picture I had of the gaskets, hence using it.
The large flat area of black painted sheet aluminium is part of the ir cooling shroud of this special engine, hence the 'crack' which is a it of over cutting of the alum sheet.

Today I pulled the carbs off.
The gaskets had indeed started to break down, all 12 of them, so all now removed and all mating surfaces clean.

The plastic heat spacers are not really flat enough to simply re fit using Blue Hylomar, so waiting on the gasket material to arrive.

Everyone I've contacted to ask if they can make me 12 gaskets have failed to respond...
So, making by own.
I hope the paper arrives tomorrow so I can get the job done and the engine tuned using my air meter and trusty Colour Tune. (remember them?)

Here are today's gaskets showing rather clearly the degeneration of the gasket material from the side that was leaking air.
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