Blue smoke on Decel, Think I understand now Geoff Options

[DNHunt]

Got the bad news yesterday. Geogg Bleyseng followed me to lunch from the AX and said "Blue smoke when you slow down, bad rings or valve guides".

I calmly say "Thanks I was wondered where all the oil was going". Meanwhile I'm thinkin "Aw $hit, more $$$".

He says "Do a compression check then do another one after you squirt some oil in the cylinder. If it improves its bad rings if it doesn't it valve guides".

I proceed to ask several questions that show how little I really know but, I got to thinkin about it last night at a wedding reception (damn this 914 thing is an obsession) and I think I understand it now.

2 ways for oil to get into the cylinder, past the rings from the crankcase and past the valve guides from the valve covers (from crankcase via pushrod tubes). On decel there is a high vacuum in the cylinder (and intake) therefore oil is sucked into the cylinder from one or both worn parts and burned leaving blue smoke from the exhaust and extra oil usage.

Compression should be lower than desired because of leakage past the worm parts. Squirting oil in the cylinders will help seal the worn rings & cylinders and result in improved compression. But, if the valve guides are worn it will not help compression.

Low oil pressure at idle results from more oil escaping at the bearings and therefor less oil reaching the sending unit at the oil cooler.

Guess I'll do the compression checks Wednesday. More to follow.

And I repeat "Ah $hit more $$$".

Dave

[DNHunt]

Its gonna take some figurin. Besides the blue smoke the oil pressure is low at idle at least according to my gauge and light. I added the gauge last winter and changed sending units. Prior to that, I had the light only and I only saw it on a couple of times when the oil was low so, I suspect that the new sender might be wrong. Keeping my fingers crossed

The interesting thing is the car really runs very well and just dyno at 80.5 hp so the performance is not that of a tired engine. True the fuel injection was just "upgraded" to Megasquirt, but, it ran well with old D-jet and I'm convinced that the new fuel system isn't masking problems. Still I remember a old saying "They run the best just before they bust".

So my plan is this. First, change back to the old sender and see if the idiot light still comes on when warm at idle. If so according to Geoff, I should suspect the bearings and so it looks like rebuild time in the not to distant future. If the idiot light doesn't come on I'll try to find a way to check the pressure with and accurate gauge and see if there is a way to recalibrate the VDO unit. Second, do the compression check and find out the source of the smoke. Either, redo the heads or rering or rebuild.

This may rearrange my plans since I wanted to do the suspension this winter. I've got a lot to consider. Should I stay with a suspect engine and try to stall big engine work while improving the handling or put off the suspension and do a new engine. Hopefully, I can find some kind of compromise, I doubt I can do it all.

Dave