I own several "classic" jap cars, as such i have had to visit other web sites in the past, let me tell you that Datsun1200 dot com is by far the best.
I have been building up a turbo conversion on my datsun motor recently, before the conversion it only had a few problems, a couple of extra pistons and the cam in the wrong place (L28).
After buy a chinese turbo for my B10 sedan (I realised it was waaaay too big), I thought id put it on uncle cedric (280c).
Now that it all together it has started a rather embarrasing smoking problem I have reduced this problem by replacing the original chinese turbo compressor (dynamic seal) with a compressor and cover from an 13B mazda (positive carbon seal) as this is a draw-thru carby setup on my car ,So there should not be any oil entering from the turbo.
On start-up there is no smoke, occasionally on take off it blows a bit of blue smoke, there is no blue under heavy throttle, but it blows monumental amouts of blue smoke after long periods off throttle (maximum vacuum) it only blows for about a second or so but thats all it takes to make everthing in my rear view mirror to disappear (very embarassing).
When I pull the plugs it appears that its only one clyinder is oil fouling.
I`v replaced all the stem seals (using the old rope trick).
I did a dry compression check and no obvious problems there.
If it was the turbo seal leaking I would assume it would foul all the plugs.
Im leaning toward worn rings but this would not explain the relative similar compression test figures (I repeated the test 3 times) and the suspect cylinder showed the second highest compression every time.
I dont realy want to replace the rings if they are not the problem but I cant see any other option.
So please any comments or thoughts would be appreciated

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Your oil control rings are seperate to the first and second rings.

so you would asume the rings are the culprit then?

I suspect a bad oil control ring on the one piston. This won't affect compression at all. It only affects oil use.

There should be a way to test this without tearing down the engine?

Did it smoke before the turbo was fitted?

On a compression check, is that cylinder a bit higher than the others?

I usually suffer from the reverse. Doesn't burn oil, but has fisted ring lands and blows by like a bastard.
The rearmost cylinder is farthest from the cooling, so on many engines this cylinder experiences problems.

Off topic, I sent you a PM ages ago, and never heard back dude. Why no reply? It's been so long that I've forgotten what I was asking in the first place. Might still be in your inbox though..........

A bad oil controll ring would make sense is this the bottom ring?

I would be very interested to find out if I can test for this before commiting to buying parts.

The motor blew very little before the turbo install.

On the compression test the suspect cylinder (no.6) had about 5 psi less than the best one and about 5-10 psi more than the rest.

The oil controls rings are those flimsy things at the bottom. They look like they are made out of sheet metal.





If they are put in with the wrong tension, they won't control oil correctly. But your compression test doesn't indicate what the problem is.

Jury's still out.

If a bit of oil is getting past the oil control rings, it can actually improve your static comp test by allowing oil into the chambers creating a false sealing for the top ring. If you comp test a motor which has Sh1t comp, then squirt a bit of oil in the spark plug holes the comp can then read higher.
Still, 5-10 psi difference isn't too bad though.

A full compression test is done twice. First time round it it done 'dry' & results recorded.
Second time each cylinder should have a few good shots of oil & enough time allowed for it to run around the top ring of the cylinder under test & seal it.

A comparison of the two figures against factory published specs gives a guide to ring &/or valve condition.

It's possible to have good compression while still suffering from a failed or stuck oil ring.
If testing doesn't find the problem then the only recourse is a partial teardown for inspection.

Okay Iv now done a complete compression test, there seems to be no more than 10% differance between highest and lowest cylinders on tne dry test, on the wet test all cylinders showed about 5% higher comp. but still less than 10% variation between highest and lowest cylinders.

I started tearing down the motor for an inspection, after removing a vacuum line to the auto a bit of automatic transmission fluid appeared to dribble from the hose to the manifold.
This automatic transmission vacuum line is plumbed right next to no.6 (back of motor) and im thinking that maybe its pulling A.T.F. from the auto and then dumping into no.6 cylinder thus fouling no.6 sparkplug only.
So if this is the case have I neglected to put some sort of one valve or somthing in the vacuum line between the auto and the inlet manifold?
If anyone has any ideas i would be very greatful as i would be mighty unimpressed if I sripped the motor, replaced the riings and have no change in its smoking habbit.
I have no workshop manual for this car and I have no idea when it comes to automatic transmissions. I do know that it does not drop any ATF but it goes through a bit so maybe there`s my problem, but how do I stop it?