Hi,
I am baffled, first this happens to a friend's Mc91B with a standard McCulloch brand piston and now this on a 101 piston built by Burris that was also a new part.
I have never had a ring pin failure on a Burris or McCulloch piston and now I had both.
Anyone want to weigh in, these pins cause a mess when they let loose. Anyone have a work around?
wiseco .005
I blamed this on a duck bill failure ..caused lean conditions then excessive heat spots ..??
now I file them back .002 or so ..??
[
attachment=3055]
Mr. Kniesel......
We've never met, but I'm aware of your reputation......Is any of the pictured carnage
and related damaged parts salvageable of capable of being made usable?
Any suggestions to us novices and wanna be's so we as newby's don't end up in the
same predicament? I HATE spending $$$$$ for parts, labor, etc, only to end up with
another addition to the scrap bucket.................
Chuck
(02-24-2018, 09:10 PM)Chuck Lipka Wrote: [ -> ]Mr. Kniesel......
We've never met, but I'm aware of your reputation......Is any of the pictured carnage
and related damaged parts salvageable of capable of being made usable?
Any suggestions to us novices and wanna be's so we as newby's don't end up in the
same predicament? I HATE spending $$$$$ for parts, labor, etc, only to end up with
another addition to the scrap bucket.................
Chuck
piston is junk.bore can be recut to bigger size so block savagable, head not the best but usable removing any lifted aluminum is advisable o keep out hot spots.
Scott k. ,
i think steve m may have a point about a slightly tight ring pushing up against locating pin and loosening it over time.
Additional information...
Neither engine over heated, plugs were wet and dark brown and no evidence of sticking on the pistons or cylinder walls.
I always am conservative making ring gaps a minimum of 0.080" and make sure to square the ends of the rings and also deburr them.
I went thru this a few years ago and am super careful how I set up the rings and pistons.
The 91B had run at least 3 seasons before failure.
I think these were not caused by anything except poor fit of pin into piston which I have no way of checking.
On pistons where I pinned the rings myself, I have never had a failure (So far)
On using Wiseco pistons, I have had several ring pins fail but on Steve O's recommendation I now grind the outer surface of the pin a bit so it does not contact the bore and that has helped. I may start doing that on all pistons now.
I was able to save the block on the Mc91 engine with a 0.010" overbore.
The 91 head cleaned up nicely removing around 0.020" off the head which reduced the size of the combustion chamber around 1cc which will up the compression a bit so I installed a 0.005" thicker head gasket to compensate because it is a gas engine.
I have not tried to mill the 101 head and have not done anything with the block as yet but there are two scores and both are deeper than the 91 had. It was already real big so I may not move to try and save that.
I don't know Scott, I had the same thing happen to me last year. I know the ring gap was good, plenty rich enough, no detonation, timing ok. I blamed it on the piston.
2 diff pistons is freaky!
Well the piston is drilled and the pin driven in. At some point there is going to be a percentage that come out. Probably not a good time to go to 'Vegas.
Hey Scott,
I'm sure everyone is tired of me quoting The Two-Stroke Tuner's Handbook... I know, I know, I gotta widen my horizons...
Anyway, on page 24 and the top of page 25, Gordon Jennings describes his theory for how this can happen.
See what you think. Did these motors have work done on the exhaust ports?
Doug
http://www.vintagesleds.com/library/manu...ndbook.pdf