My CA18det coupe was rebuilt not long ago and now the rings are shot, so much blowby it's crazy. It's forcing oil out the back of the turbo due to the high crankcase pressure and burning oil like you would not believe. There was a hole in the intake manifold so it ran too lean and hot - this was missed by 3 different mechanics! Ultimately it's my fault though.

It's going to cost another 3 grand at least to rebuild it so I was wondering what you guys would do? Should i keep it and rebuild it? or should i sell it in bits to you?
Any advice?
justin

It would sound as if the rings have not beded correctly. What brand of rings did they put in there? Some brands of rings are extreamly picky with the run-in process that MUST be done. If not done correctly they will allow blow by.

So you may get away with having the bore run over with a "dunny brush" and new rings fitted as the rest of the engine (bearing clearance) should not be affected by this. However, you would be best to take it to who did the rebuild for a closer inspection. They should have informed you of the correct run-in procedure for the engine and advised you of what will happen if it is not followed.

Best of luck.

Yes they were chrome cp rings and forged pistons just the usual running-in oil. It could be cheaper to repair if it's just the rings and it's pistons out, hone the bores and new rings. the leak down test showed 25% across all cylinders - the acceptable level is 12%
The rings would never have bedded in properly due to the incorrect tuning making the engine lean. In fact it lost oil from day one and the rebuilder did the valve stem seals again (as they were stuffed). This was probably due to the engine running lean and getting hot, burning out the seals.

chrome rings r #### man u need to drive the fu#ker hard n under extream loads to bed those rings in! there crap they grazy the bore if u let it idle for to long! another thing wat turbo u got on it! a true story if u have the oil feed n return the wrong way it will burn #### loads of oil thorugh the turbo its crap just something to check!

Quote:

Sounds pretty extreme blowby - perhaps more than just rings? Lean out from air leak may have melted piston/s? This gives Extreme blowby!

Don't assume the worst just yet. Pull it out, send it to a professional and prepare yourself for the absolute worst case scenario. When the results come in anything less than worst case will be fantastic news. Then consider your options.

When an engine gets hot using any sort of chr mo rings through being lean if it is found soon enough it may just be a case of glazed bores. A Torque Plate hone and a set of file back rings usually sorts out the problembut there is a chance that the piston to bore clearance will be a few thou over tolerance. Pray to the god of Forged pistons that they are o.k. They are generally more forgiving than cast.

Never use synthetic oils to run in your new engine. Or fuels either. Only mineral oils should be used as synthetic oils coat the bore and prevent bed in of the rings.

Fingers crossed. She'll be right...

Thanks, I hope the pistons aren't melted. It's strange that the airflow meter makes the mixture lean if there's a manifold air leak. Nevermind. I like the simple A series engines, new ones are a headache.
I'll take it to the mechanic and tell them to take it apart. Hopefully it won't be nervous breakdown time. If they are stuffed then you guys can enjoy my datsun bits.
As for oil lines, i have a 1mm restrictor at the engine end because the turbo is a GT25 ball bearing (S15 factory turbo). I've been told a restrictor is necessary for these turbos. Oil pressure must be 50-60psi and no more.

If crankcase pressure is high then the oil from the turbo can't drain into the sump because the pressure pushes it back up and forces it out the metal o-ring seal.
Mind you with blowby like mine, it's more likely just coming out the exhaust and fouling the exhaust turbine wheel.
I love my datsun, so i'll give it one more chance.

Nizpro in Bayswater, Melbourne would be a great bunch of blokes to get some advice on about your setup. They take their Dattos pretty seriously.

Good luck.