Shim shimmeny, shim shimmeny, shim shim - to do?

Discussion in 'Mech Tech' started by Jonboy_t, Jan 25, 2020.

  1. Just about to fit the new pistons and barrels on my 1.8 type 4. Have a new gasket set from VWH which comes with 4 seals and sixty bazzilion shims. I’m fitting the same heads back on, but have heard conflicting reports of whether shims should be used on the head/either side?

    was planning on using the case-to-barrel seals with a dab of hylomar on to shore it up a bit, but do I need shims on the barrel-to-head side? I have limited tools (and knowledge..) so not sure how to check whether I need shims or not?

    (The new pistons are from VWH too and are AA Performance, I think)
     
    Deefer66 likes this.
  2. New stock B&P?. Usually nothing between heads and barrels now in most cases and shims under the bottom to get your deck height (gap between top of barrel and top of cylinder ) in the 1 to 1.5mm range.

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    Jonboy_t likes this.
  3. they are new, but not sure how the AA Perfomance compare to stock. Would you add liquid gasket to either side too, or not worth it?

    Makes perfect sense about the deck height though, thank you :thumbsup:
     
  4. You need to look up checking head capacity from sealing face upwards, and deck height being the distance from piston at TDC to the top of the cylinder with the cylinders being pressed into the engine block by some arrangement involving nuts on the studs without the cylinder heads.

    From the head capacity, the deck height and the swept volume of the cylinder you can calculate compression ratio. Depending on petrol octane rating and your desire for power you can tweak the target numbers.

    Originally VW quoted e.g 7.3 CR for a 1700 or 1800 engine 91RON octane fuel. Or about 140 psi compression tester pressure.


    In the best case there should be about 1mm between the top of the piston and the cylinder head flat portion at TDC.. more than 1mm can be hotter running and at the same time produce less power, less than 1mm is risking contact.

    Its all a compromise but getting it wrong can affect cylinder head life and power output.

    Typically the Type 4 engine had a copper gasket at the top of the cylinder. Typically these provided twice as much chance of a leak as the type 1 direct head to cylinder contact seal.
    You can put shims under the cylinders instead of the copper rings, but you do need to measure the deck height.
    Almost certainly the AA cylinders will be slightly different height to originals so you need to measure.

    If everything is clean you should need very little sealant between the block and cylinder.
     
    nicktuft likes this.
  5. If they're the AA 1800 B&P I think they made them to match the stock with regard to dishing etc, If your heads are still stock chances are everything will work out to meet recomended compression ratios. I'd chech volumes for compression ratio but check deck height as a min.. see the other thread nearby..

    Edit: you don't need plates and dials to get close.. fill the gap between top of cylinder and threaded part of head stud with sockets from a socket set and bolt ot down.. just snug not too tight as you're pushing on a fin like this. Rotate the fan until piston is as top of stroke.. it doesn't move much for a while at this point. Pop a ruler across the top of the cylinder on edge and measure the gap with feeler gauges.

    Personally I'd stick sealant around the bottom as long as it's not a silicone sealant type as they can end up in your oil. The Curil ones are good.. Dirko I think is the standard one but I just used Curil T.

    ..and like the song thread name..
     
    Last edited: Jan 26, 2020
  6. Don’t use head gaskets. You really should check the deck height, measure the combustion chamber volume and work out the compression ratio but if you’re not confident doing that at least look at the heads. If there is a step where the barrel fits you just need a smear of sealant on the barrel to case face. If there isn’t a step you need to fit a shim at the bottom of the barrel.
     
    snotty likes this.

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