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Rebuilt BF90 SMOKES!

J

jakepitsville

Member
Hey all. Recently my Honda BF90 (carb) (approx. 1600hrs - probably not genuine) ran into some issues. Cutting a long story short, it was hard to start, would not idle (regardless of what we did to change this) and was using oil and NO 4cylinder was not firing despite having fuel and air. -it was using quite a lot of oil (1-2 L per 10hrs). After some diagnostic tests it was found to have burnt exhaust valves and worn valve stems and the head gasket(despite being new 300hrs ago was leaking). I have since restored the head - new valves, and stem seals, new head gasket etc.

The engine now runs very nicely, starts first time and idles like a dream. But when you power up (in or out of gear) the engine smokes a lot out of the prop and exhaust bit by the rear cowling cover clip and uses more oil then ever

I have since pull the spark plugs, cylinder NO1 plug is pretty dirty/oily the others seem mostly fine with maybe slight oily residue on threads.

My thoughts are that now the head and valves etc are holding compression there is significant blow by and my rings are shot.

Is there anywhere else that could be causing the problem?"??]
as the plugs dont seem to be black enough to be burning that much oil.

kind regards

jake
New Zealand
 
This is kind of basic, but could the oil level be too high? Is it about 1/4 inch below the full mark?

Perform a leakdown test. That will tell you it you have a ring problem.

Other than....was it reassembled and torqued correctly.......it is back to basic trouble shooting.

Mike
 
So the oil has burnt off or leaked out so none is on the dipstick at all. The head was torqued correctly and was double checked- ive rebuilt quite a few honda heads and during this rebuild I refered back to service manual and video of disasebly .the valves were seating nicely before the head was put back on.

Will do another leakdown test
 
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