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Old 22-07-2008, 09:38 PM   #1
whippetman
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Default new heads,pistons,barrels. do i need metal shims

hi guys
I've bought an engine rebuild kit for my 71 camper 1600cc.
new heads, new barrels new pistons etc, when i took the old heads and cylinders off there was metal shims between the cylinders and the crankcase, and also between the cylinders and heads. Do i need to put these back on? or do i just use the paper gaskets between cylinders and case and then grind the cylinders into the heads? Also do i need to use a gasket sealer on the paper gaskets and on pushrod tube seals. Any help would be much appreciated. thanks
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Old 22-07-2008, 10:55 PM   #2
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If it has shims fitted, put them back. It would also be wise to check the end float on your engine. if it is more than barely detectable, you are probably wasting your time.
You would be wise to rebuild the bottom end or at least fit new big end shells.
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Old 22-07-2008, 11:03 PM   #3
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ok thanks. any idea why they have shims and some engines dont? Do istill need to grind the new cylinders into the new heads and use the paper gaskets as well, or just use the shims? thanks
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Old 22-07-2008, 11:24 PM   #4
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This topic probably stirs up more argument than any other. In the 1990's VW released a tech bulletin that among other things recommended the removal of the shim gasket between the head and the cylinder. This gasket is actually made from several thinner gaskets pressed together and when one layer shrinks and burns through a gap forms that allows the combustion gases to escape resulting in eventual head failure.
The concensus on this issue, after much photographic evidence depicting burns in this area, is to remove the head gasket and lap the head to the cylinder and rely upon a carbon build-up to help maintain the seal. Now there is no gasket to fail because there is one less sealing surface but it means you have to get the contact surface absolutely flat because there is no gasket to crush and make up for inconsistencies. It also means that you need to recalulate your compression ratio but that is a necessary part of an engine rebuild anyway.
The gasket (~0.80mm before crush) in not the same thickness as the 1.6mm spacer VW recommends using which begs the question: has VW also recommended lowering the compression ratio or were there further instructions? Well, first consider there is was also a paper gasket at the base of the cylinder and if that measured 0.80mm also then there should be no change to the CR but Wilson says the paper gasket should be 0.20mm thick and so is the metal base gasket included with the rebuild kits so it appears VW did recommend a slight reduction to the compression because overall the deck height has increased by 0.6mm (approximately 7.3:1 to 7.0:1).
AMC has solved the problem of the head gasket by eliminating it as well. They have machined a step into the head in place of the original gasket and this serves to provide a corner and mating surface that obstructs any escaping gases after sufficient carbon buildup which is promoted by the gasket sealer used. The step is about 0.80mm thick (incorrectly shown as 1mm in photo) which is about the same as the gasket that was removed. The head combustion cc is about 50cc on a 2.0L AMC head below the step. Above it's about 57cc.
To summarize, if you elect to remove the gasket you've got some machining to do to your head and some math in order to add the step. If you have an AMC head you don't need the head gasket (AMC even gives you a warning notice with your head). Electing to use the gasket is an acceptable practice on a VW head if you cannot guarantee the seal but only if there is no step cut in place.
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Old 22-07-2008, 11:33 PM   #5
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Since when did they use a gasket between head & cylinder??

Go with what mucky green has said-hes a well known & respected engine builder!

i think the above post is talking about some other kind of engine!
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Old 22-07-2008, 11:34 PM   #6
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ok thank,s sounds a bit complicated. the kit ibought was from just campers and the heads are vw mexico, came with an engine gasket set which just have the paper gaskets between cylinders and crank case. cheers
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Old 22-07-2008, 11:34 PM   #7
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Fook me thats an answer
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Old 22-07-2008, 11:38 PM   #8
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the shims were used when a case had been spotfaced-so if youve got shims re-use them!
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Old 22-07-2008, 11:38 PM   #9
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so is the shim for spacing rather than a gasket, what about other end of cylinder, use the shim and paper gasket or just shim? any sealer needed?
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Old 22-07-2008, 11:46 PM   #10
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re-use the steel shims at the cylinder base,& a new paper gasket,plus hylomar,is what i'd say.
yes,lap the barrells to the heads
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