Low compression on No.4--Ideas ???

[northerner]

I've been working on an S12 Silvia that I got on the cheap which had a Blown Turbo. Well it was the worst turbo I had ever seen. The turbine had completely blown up as the bearings were shot.
Having fitted another to get it running, I have found that no.4 pot has only 100Psi were the others are about 155. Having added some oil to the bore to see if it made a difference, I have found it didnt so Not the rings. I'm now thinking HG or maybe a valve problem possibly the Valve seals. It does smoke a little but this maybe from the Turbo as it has play and was a 2nd hand one. Before I remove the head anyone got any ideas ?

[s13eater]

bent valve or valve carbond up and not seating properly or head gasket, they usually go betwwen 3 and 4.

[WM-S12]

can't say I know what the problem is but I wouldn't necessary say it's your turbo that's making the little smoke. I thought that and taking it to a performance garage I found out the smoke was due to oil in the 3rd cylinder. ( probably my piston rings have too much wear. ) also the guy noted I had something to do with compression in the 3rd and 4th cylinder....if I remember correctly one had higher than normal and one was lower than normal.

Gonna scan my email as it's in there somewere, let you know what I got told when I find it.

[WM-S12]

Inlet pipe to turbo removed - oil in turbo inlet.
Engine started, breather pipe removed from rocker cover - crankcase compression at the breather just with engine idling.
Spark plugs removed - number three plug burnt on deposits - burning oil in number three cylinder. Others burning clean.
Compression check carried out.
Compression (psi). 1 - 170, 2 - 170, 3 - 130, 4 - 100

Other turbo supplied has more play in the bearings than the one on the car.

Suggest problems are being caused by worn engine which requires further investigation / rectification before turbo is condemned.

thats the exact qouting from the guy at the garage I took my car to fix the apparant manifold problem.....turned out to be just the gasket so I bought a second hand tubby and manifold for £130....only needed the elbow and gaskets.....

As for smoke, my car barely smokes unless it sits for over 10 minutes idling below 700rpm some times nears 500rpm ( lol....chug chug ) but it's not belching out. Nor does it puff any when your belting it as the oil will simply be burnt all quicker.....really needs a new engine or atleast a rebuild.

[PukkaSilvia]

are you getting excess crankcase pressure or a pressurised cooling system?

[WM-S12]

I'd check your sparks to be sure that you ain't got the same problem I got with the 3rd cylinder. Just an idea.

well from what the guy put in the email to me he just stated crankcase pressure at idle.....no idea if theres ment to be any or what. ( plus I've no idea who your directing the question to )

[PukkaSilvia]

no idea? how about the guy who started the thread off asking the question


i would say unless it improves from driving it a bit more since its been worked on your best off taking the head off Northerner, although im sure you know that already.