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- Dec 27, 2008
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OK Lads, need collective Norton grey matter applied to this one!
Bike: 1975 Norton MK3 with 920 conversion (Norvil)
Head rebuilt by THE best, you know who he is This has only a few miles on the head, so brand new.
Approx 12K miles on the bore.
Problem, oilly plug RHS, smoke after 3-4 minutes after warming up on bench. Had bike out, pulls like a train, great acceleration, ticks over like a clock but lots of smoke from RHS while blipping the throttle.
Did a compression test, 180 both left & right.
Just did a leakdown test, both left & right about the same (see pics).
I have cheap Chinese gauges & a crappy compressor (that's the don't laugh moment!!) but I'm using this setup for comparison rather than 'accurate' data. There is a bit of 'gurgling' from the breather tube in the oil tank (I have Jim C.'s lower crankcase breather fitted) from both the LHS & RHS, same sound from both.
So, my thinking is this:
Compression is fine & leak down is fine on both left & right hand side. My limited knowledge is telling me that this indicates that the valves, seals, guides & top rings on the pistons are all OK.
It points to an oil ring issue on the RHS, would anybody agree or disagree with this diagnosis???
OK, IF it's the oil ring on the RHS has anybody used any 'snake oil' concoctions in an attempt to 'loosen' the oil ring if its stuck from carbon build up?
Could running the bike on a good spin, 100 miles, have any chance of 'loosening' up the oil ring so it gains functionality again?
My theory obviously presumes the oil ring is stuck as opposed to broken, When I had the head off both of the bores looked the same i.e. no gouge's on the RHS bore etc.
I'm obviously trying to avoid taking the entire top end apart, head, barrels etc. just checking if I have ANY other options?
Is my thinking sound???
LEFT HAND SIDE
RIGHT HAND SIDE
Bike: 1975 Norton MK3 with 920 conversion (Norvil)
Head rebuilt by THE best, you know who he is This has only a few miles on the head, so brand new.
Approx 12K miles on the bore.
Problem, oilly plug RHS, smoke after 3-4 minutes after warming up on bench. Had bike out, pulls like a train, great acceleration, ticks over like a clock but lots of smoke from RHS while blipping the throttle.
Did a compression test, 180 both left & right.
Just did a leakdown test, both left & right about the same (see pics).
I have cheap Chinese gauges & a crappy compressor (that's the don't laugh moment!!) but I'm using this setup for comparison rather than 'accurate' data. There is a bit of 'gurgling' from the breather tube in the oil tank (I have Jim C.'s lower crankcase breather fitted) from both the LHS & RHS, same sound from both.
So, my thinking is this:
Compression is fine & leak down is fine on both left & right hand side. My limited knowledge is telling me that this indicates that the valves, seals, guides & top rings on the pistons are all OK.
It points to an oil ring issue on the RHS, would anybody agree or disagree with this diagnosis???
OK, IF it's the oil ring on the RHS has anybody used any 'snake oil' concoctions in an attempt to 'loosen' the oil ring if its stuck from carbon build up?
Could running the bike on a good spin, 100 miles, have any chance of 'loosening' up the oil ring so it gains functionality again?
My theory obviously presumes the oil ring is stuck as opposed to broken, When I had the head off both of the bores looked the same i.e. no gouge's on the RHS bore etc.
I'm obviously trying to avoid taking the entire top end apart, head, barrels etc. just checking if I have ANY other options?
Is my thinking sound???
LEFT HAND SIDE
RIGHT HAND SIDE