hanarchyrulez

I dont really know how word this right so I think I will use two questions together.

1. Would using a too thick a head gasket drop my compression by around 60psi ?
(^^^^ I Know that the answer to this is yes ^^^^)

2. What else would cause a consistent 60psi pressure drop across all four cylinders.


Has anyone ever had any problems with using a cometic gasket? I know they are particular about the mating surfaces on the block and head...

For quite some time I've been fighting with what I thought was an overfuelling issues but have learned that low compression combined with normal fuel pressure gives pretty much the same result.

Originally when I rebuilt the engine after getting my head back,I ran a compression test and vaguely remember getting around 75psi per cylinder... I just assumed that having consistent pressure

I ran another compression test today and got

1 2 3 4
DRY 68 76 76 71
WET 81 85 82 88


When I sent my head away to get skimmed and cleaned up, I measured the bore, extrusion of pistons from the block, the piston crown and the head volume (per cylinder) and gave them the figures. They reckoned I needed a 1.8mm head gasket to take it to standard compression.

I took that for granted as gospel and rebuilt my engine as such with a set of ARP studs and nuts as I am planning to run my t34.63 and greys on it.

Does anyone have any advice or suggestions? Should I just ditch the gasket and stick a group A head gasket on ? What thickness is a group A gasket and would the size be enough to give me my 60PSI back ?


Really appreciate your thoughts guys!!

stevieturbo

1. The answer is no...unless it was massively thicker....ie impossibly thick.

2. Those numbers are so low, either you're doing the test wrong, or your gauge is incorrect.

Or 3...cam timing to something like that is wrong.

Or just how low do you think your compression ratio actually is ?

Chip

iTrader: (3)

As Stevie says, no way is that thick enough to make your compression drop that much, far more likely to be a cam timing issue or similar.

Post your figures so we can tell you what your CR actually is.

hanarchyrulez

Cheers guys,


You have eased my mind a bit! I was using a Gunson gauge that I had bought from the motor factors as i was passing through and im pretty sure its accurate enough I did buy a snap on compression tester but in my haste, couldnt wait for it to arrive before I had pulled the head back off it.

the compression should just be standard cosworth. Thats all i asked when I sent the head to get refurbed.

Sorry chip but i didnt keep the figures as it was nearly a year and a half since the head was built

Im clutching at straws with this now.

I timed it to just behind the lug on the crank pully and both pointers facing each other on the cams.

I have just re used the cometic gasket and dropped the head on but cant find my torque wrench so will have to do that tomorrow after work. Then Im going to fuck about with the timing again

Turbo Zetec

iTrader: (1)

try a cylinder leakage test, you should be able to identify where your leak is then

stevieturbo

So is the cam timing correct, and did you open the throttle during the test ?

hanarchyrulez

I have just been playing with the timing and moved the crank pulley one tooth so that the timing line now points to the groove across the crank pulley and I am now making about 125 psi dry across the board and around 13 - 135 wet. Im a bit mythed at this as Im sure the marking was pointing to the other side of the lug on the pulley.

The oil is stinking of petrol so I am going to get some 10 50 tomorrow and hope that the oil isnt running from the buckets.

The engine hasnt ran in a good while so I would imagine that the buckets would only fill correctly when the engine is running ??

stevieturbo

sounds like more sensible numbers.

Buckets will be fine.

hanarchyrulez

but what about the timing mark on the crank not matching up? the mark on the block is in line with the 16 degree btdc groove?

stevieturbo

All timing marks should match up as per manufacturers instructions.