space between cylinder and head

[CHR!S/DVK]

as i was mounting the cylinder shielding on my newly built engine i noticed that there was a little space between where the cylinder "should" hit the cylinder head.

this was the case for both cylinders 3 and 4, but not for 1 and 2, after i tightened them to the right torque of course. (i haven't put any pushrods in or mounted the rocker assembly, just the bare cylinder heads)

here are some photos where you can see a little part of the tip of the cylinder in that space:









the cylinders are 88mm machine-in and the cylinder head are stock dual port vw, of which the chambers were machine for more compression by the previous owner, as i was told.


has anyone experienced this before? could this lead to loss of compression?
or can i trust on the fact that the cylinder fits tightly in the head when i have fully torques the lot?

thanks for you replies!

[richie]

The cylinder fin area must not touch the head,if it does it will leak,it only seals on the top of the cylinder inside the head,its quite common to have to machine off a head fin if it has been flycut for compression to stop the cylinder hitting that area

cheers richie

[Frenchy Dehoux]

   How much compression are you running in your heads ? May have taken too much from the heads as far as milling them at worse you will have to put in copper gaskets in the head chambers to space it out so the fins are not to close.

Frenchy

[fish]

If 1 and 2 are touching, maybe those two chambers were fly cut too much in which case pull it all out and measure everything and clearance where you need to. As per above posts, there needs to be space between cylinder fin and head. It also looks like two of your cylinders may be touching on the sides.

[CHR!S/DVK]

many thanks for the replies!

the fact that the cylinder tops should be sealed in the cylinder head and not by touching with its fins to the cylinder head casting, makes sense.


@Frenchy, I will be running around 1:8.8

the chambers have been enlarged to 46cc by helicutting, since they were flycut and the chamber volume was 36cc.


@fish, i will check to see if 1 and 2 show no clearance, if so i will measure if the cylinder head depth is not to deep to allow the cylinder tops to touch in the chambers.
i don't expect there to be a too big difference, since both the cylinders and the cylinder heads should be matching.

[dragvw2180]

   Myself I would re CC the combustion chambers on both heads just to make sure they are the same .  Like Richie said , I have had to remove multiple fins on heads that were used for high compression . Take a caliper and measure from the fin surface to the cylinder seating surface then compare it to the cylinder depth. Mike McCarthy

[DWL_Puavo]

Just a few weeks ago we built an 1600cc engine with new heads that were cutted for some more compression. The problem was that the small "round" area in the cylinder tube between machined part and first fin was contacting the head, but only such a small amount that it wasn't visible and didn't affect the torquing of the heads. That round part can also be seen in your pictures, and at least in one cylinder it seems to be in contact with the head.

Well, too bad we assembled our engine to the full before moving it into break-in "bench" - the gap between the head and cylinders top was very audible when we cranked the engine. Disassbembled the engine and popped off the heads. Then to the mahcinist that cutted 2mm deep "ring" on the 1st fin of the heads, and now it fits perfectly.

The gap between the fins of the head and cylinder was clearly bigger than in your case. I could imagine that removing the first fin from the cylinder (not from the head) could be more beneficial, but not nearly as easy to do.