Headgasket not seal! Swap HG if engine in or out?

red reading

red reading

Active Member
6 bar is way too low, and were you leak down testing with the pistons at top dead centre! Because there is no way you will hear air coming past the valve stem seals either......does your friend know what he is doing because from you explanations he does not. A leak down test will give you a % of air loss from the cylinder over a given time.
 
red reading

red reading

Active Member
And the reason why you can hear air on cylinders 2 and 4 is that the cams have held the valves open, that will either be due to the valves starting to open on cylinder 1 and starting to close on cylinder 4... Long duration cams.
 
T

Thor

Member
Ah thanks now i understand it! I have fitted Tomei 272° cams. Then it is correct.

Ok, we will made a new right leak down test. By the last test he had made the pistons wasn´t at top dead centre. But is it so much different? For the leak test the engine must warm up?
 
red reading

red reading

Active Member
You need to TDC each cylinder and test, you will get higher readings if the engine is warm, and static compression readings will change depending on cams duration and overlap. Please also be aware that if it is a fresh engine build with big clearences on the piston to bore and piston rings you will have oil in the cylinders till you get some sort of piston ring bedding in.........do the tests and if they are clear get the thing running and up to temperature because the forged pistons need to expand properly to get them and the rings bedded in.
 
red reading

red reading

Active Member
And last thing when you do compression test, take all the spark plus out and have the throttle wide open, and make sure you have a fully charged battery.
 
T

Thor

Member
Ok danny thanks for your help! We will check them these days. It is so angry if the engine is new rebuild and then so sh*t result..

How much compression must it have circa if is cold or warm up?

272° Tomei cam
1.5mm cosworth HG
87mm 8,5:1 CP pistons
Head was 0.3mm skimmed!
 
P

pulsarboby

Guest
as said those comp readings are very low
sounds to me as though the block has been bored out with too big a clearance which will give you low readings on all 4 cylinders

with cp pistons you should have asked for between 35-40thou clearance any more than 45thou and you will have big troubles even when upto temp as cps don't expand as much as je pistons
for fast road use I believe the clearance should be 35
 
pulsarmoley

pulsarmoley

Member
I didnt realise that all the plugs should be out and throttle open fully while doing compression checks, made this mistake doing mine and the results were ok?
 
red reading

red reading

Active Member
Just means you are getting true readings and not affected by pumping loss from cylinders, also a closed throttle will pull a vacuum so you do not get a proper reading and if you have a duff battery as you go along the readings get lower.

Remember gtir have individual throttle bodies so that to can cause different readings between cylinders unless it is done with wide open throttle.
 
T

Thor

Member
pulsarboby said:
as said those comp readings are very low
sounds to me as though the block has been bored out with too big a clearance which will give you low readings on all 4 cylinders

with cp pistons you should have asked for between 35-40thou clearance any more than 45thou and you will have big troubles even when upto temp as cps don't expand as much as je pistons
for fast road use I believe the clearance should be 35
Click to expand...
If the clearance is too big i don´t believe because the liners was bored with the pistons:

Bore diameter: 3.425 ~ 86,995mm
Clearance: 0.0035 ~ 0,0889mm
Piston: 3.4215 ~ 86,9061mm

Pistonring gap:

1.st 0,45mm
2.nd 0,55mm

That was the bore size of the liners! The piston clearance was made with CP manual!

I think there is all right.

The funny thing is that of the head before the rebuild was ok. I can not imagine why that should now be broken.
 
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pulsarboby

Guest
red reading said:
Depends if the readings were done with plugs in and with a closed throttle bob.
Click to expand...

yes true danny but plugs in or out and throttle open or closed thats still a hellishly low reading no matter which way you look at it.
i normally do them 1 cylinder at a time with remaining 3 plugs in situ then again with all 4 plugs removed which can give you an indication if theres any blowby between cylinders due to a leaky h/g etc

sascha......the bore clearances you gave are correct so there should not be a problem with thoose and cp pistons
i know this sounds silly (has happened before) but could there possibly be a trapped wire or vacuum pipe inbetween the head and block which would stop the gasket sealing correctly???
this would also account for oil loss down back of head.......just a trhought!
 
red reading

red reading

Active Member
Cams will change static compression too and depending on timing it can be by a hell of a lot. I still stand by if it was a head gasket leaking that bad the car would be pissing water out everywhere.
 
T

Thor

Member
Ok if the HG is ok, from where come the oil on the pistons? The Block has 2 small oil holes which goes through the head i mean. Is it possible by the head work (valve guides changing) that they has damaged something?
 
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