rebuild 6 month review + a mystery
first, a bit early but a haapy new year to everyone, hopefully lots of dry warm days this year.
So... rebuilt my 929 in april, rebore and honed to +1mm, making it a 954 now. Had some issues with oil consumption at first, and it seemed to improve somewhat but still consumed more than it had before.
Fitted JE pistons, 12.5:1 instead of the standard 11.3:1.
Stripped the engine down a few days ago, I've probably done 5000 miles since the rebuild.
First thing that struck me was the oily deposit on the pistons and combustion chambers. See pic, left hand piston. right is standard from pre-rebuild. this is a soft deposit that you can remove with your fingernail. Looks like 2-stroke gunk.
First thing I checked was that all the piston rings are fitted right way up. They are, and all gaps are good. The mapping is set up is set for about 16:1 air/fuel on light load, dropping to 12.5:1 on full throttle. (Got a lambda sensor fitted). Exhaust valve stems are white, just as previously. Spark plugs are clean, very light milk coffee colour.
there is some scuffing on the front and rear faces of the cylinders, no more than usual, no deep scratches.
Hone marks are still very evident, despite me giving it a fairly hard run-in during the first 30 miles, and did not over-baby it during the following few hundred miles.
Compression pressures are good, all up in the 200-210 psi range.
So the question is...anyone else have high oil consumption with JE pistons? I note that the 6 oil drain holes from the oil control ring grooves through to the inside of the piston are completely differently arranged - they are distributed round the full circumference of the JE pistons, whereas the standard Honda piston has 3 front and 3 back, in the centre section of the piston. Want to get a few more facts before I start drilling more drain holes....