L20B problem help please

[DATSUN671]

everytime i take out number 1 spark plug, its always oily

 

so i did a top end rebuild, change all the valve seals,head gasket,etc.

 

when i put everything back it will run fine, then again spark plug number 1 is oily.

 

im thinking its the piston oil rings but when i did a compression test, all cylinders are good.

 

i didnt do a bottom end rebuild

 

thanks for the help B)  B)  B)

[Eagle_Adam]

what was the reading on all 4 cylinders? 

[Rays74]

 If your compression between the cylinders is nearly the same and enough not to worry (IMO +140), then most likely yes you have an oil control ring prob in that hole.

Do you notice much oil mist in the valve cover breather hose? Feel around the outlet (valve cover) when the engine is idling......should be a slight negative pressure there but as the engines age this turns to a slight (or more!) positive pressure and will likely be the sign your engine has some blow by.....this will oil up your plugs too. Our engines are known to hold decent compression but use oil......something to check.

 

My L18 does this, but on number 4 cyl........compression is 145-155 for all of them so it still runs really well  BUT I do have that positive pressure out of the breather so my old lower end is experiencing blow by too.

 

--Ray

[datzenmike]

Are you running NGK plugs? BP6ES? If not these are the factory recomended ones.

 

If oil fouling continues try switching that one plug to a hotter heat range. Try BP5ES. A hotter plug is much more likely to burn off the oil deposits. Note that this is not a cure for bad rings, but it may help.

[DATSUN671]

I went through alot of spark plugs and still oily in number 1

 

im wondering if the compression on the cylinders are good, could the oil rings be the problem?

[ggzilla]

Have you done a wet compression test?

[datzenmike]

.... but when i did a compression test, all cylinders are good.

 

 

im wondering if the compression on the cylinders are good....

 

You said you did a compression test and it was good.

 

 

what was the reading on all 4 cylinders? 

 

So.... what were the readings you got?

[DATSUN671]

My compression reading on all 4 cylinders were 160psi

[datzenmike]

That's good!

[ggzilla]

That's good, but if the wet compression check shows 170, it means the rings are worn.

[DATSUN671]

That's good!

 

That's good!

 

so my piston rings are still good

[Z-train]

Compression rings could sghow good,but the oil ring is shot or broken.

[datzenmike]

Try one hotter range plug.

[ggzilla]

He's not listening to to us. Yes, the compression readings means NOTHING regarding oil usage.

[Rays74]

Well, yes and no, Zilla. Compression is dependent on ring seal, and if that seal is becoming an issue and there is blow by, there will be pressure build up in the crankcase that (if it over runs the PCV system) could cause the engine to start using - wasting oil. In this case it may not be, but it does happen.

 

--Ray