Head gasket query

[A80Avant]

Hi people

i would like to draw your attention in a sign we spotted the last week on the engine.

Garage did a comp.test and found that cyl 4 and 5 had 125psi while 1-2-3 had 130psi on a cold engine.
Then 4 days later redid the test with a hot engine (85C) WOT and found 130-127 on the first 3 cyls and 110 on the last 2!!!!

Car has not been drinking oil, i dont see any white smoke at the back(although if it is too little i wouldng spot it), its not misfiring or making any other weird noises so far). It does have a fair amount of blowby which im fitting 2 tanks for, but that has been there ever since i started boosting to 2bar)
Cyl head had new guides,valves resealed with seats and general treatment around 100K kms back.

Been speaking to a few mechanics about this, and i have been getting possible culprits :

1) gasket failure between 4-5
2) EX valves not sealing right between on those 2 cyl's/ valve guides playing up
3) piston rings all over being shot
4) poor compression test?

i have failed to find a shop to do a leakdown test here in the newcastle area and therefore i need to do that as well, but id like to hear your views regarding what symptoms you get on the above failures because other than the fact that i have blowby, i cannot see the engine working any differently than what it did and if i hadnt done the test i wouldnt have spotted the low compression.

trying to source a leakdown test which would reveal a lot obviously...

thanks for looking!

[anthonys2]

This is probably not the answer to your problems but my head gaskets on its way and my knowledge is crap have you tried the guys at autobahn in hexham they know there way around our engines(looked after mine now for 10 years!) they might be able to help with various tests??

[Tonks4x4]

Try a little oil down the bores of 4 and 5 when the engine is hot, and do another compression test. If the values increases it is just the rings that are tired.

[A80Avant]

thanks for those recommendations

Anthony, i may just do that. Any contact details for them?

[Knight Rider S4]

what Brian (tonks) says , oil down the cylinders trick

[A80Avant]

how do you do this oil test? pour some from the spark plug hole? how much? a few drips? or more?

i may get a new compression tester to try it out myself

[Error404]

try a capfull of oil, don't need much.

Leak down tester you can make pretty cheaply with off the shelf 1/4" bsp airline fittings, or they are like £70odd to buy

quick release plug
10bar pressure regulator with gauge
10bar prssure gauge
Female equal Tee
male to male coupling - modified with restrictor
male threaded hose tail
compression tester with o-ringed spark plug adapter.

Its important that there is an inline restrictor after the pressure regulator, you can get one custom made or you can weld or braze up the hose tail or male coupling and drill it or you can fill the fitting with araldite or similar stuff and drill it, the restrictor needs to be about 1mm diameter to stop the cylinder filling with air too quickly.

Lop the hose for the compression tester, join to the hose tail. assemble the other parts - so quick release fastener onto one side of pressure regulator. Modified male coupling / restrictor onto other side of pressure regulator. Female equal tee onto male coupler. hose tail onto opposite side of female tee. pressure guage into branch off equal tee. Done.

There are special tools for finding TDC, but you can use a long clean extension and a dial gauge, or watch when it pauses at the top of the bore it doesn't need to be massively accurate. Make sure its not in the overlap cycle where the piston is at the top of the bore but both valve are partially open. Find TDC on cylinder 1 then follow the firing order around the engine.

[A80Avant]

capfull you mean of the oil bottle?

[Error404]

yeah

[anthonys2]

thanks for those recommendations

Anthony, i may just do that. Any contact details for them?

PM sent mate

[A80Avant]

thanks!