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Con rod not sitting central in piston.
Posted: Wed Aug 13, 2014 1:36 pm
by corrado
Just fitted a SIL crank re-rodded with Yam rod. Crank isn't rubbing on driveside seal plate so clearance there but the rod is more or less flush with the piston on the small eye. 20mm small end bearingis a nice flush fit into piston but rod has about 3mm gap on mag side and flush against piston on driveside. No shims at big end both web width is the same as it was when it had SIL rod. Even if the big end had half mm shims it still wouldn't be sitting central. I'm about to pull it all out again just wondering what the issue could be?
Posted on LCGB too.
Re: Con rod not sitting central in piston.
Posted: Wed Aug 13, 2014 1:57 pm
by fastfrog
Mag house not completely shove in place? too large gasket on mag/casing?
Re: Con rod not sitting central in piston.
Posted: Wed Aug 13, 2014 2:10 pm
by corrado
Ah, that got me thinking .... I haven't yet fitted the flywheel, so maybe fitting the flywheel pulls it into position? Mag housing is home ok with standard thickness gasket.
Re: Con rod not sitting central in piston.
Posted: Wed Aug 13, 2014 3:02 pm
by fastfrog
A pic?
Re: Con rod not sitting central in piston.
Posted: Wed Aug 13, 2014 3:24 pm
by belly
Flywheel wont pull it over as crank tightens against drive side bearing. Have you tried piston round tother way to see if bearing cutout is central?
Re: Con rod not sitting central in piston.
Posted: Thu Aug 14, 2014 12:41 am
by corrado
I've used the piston before, mind you I probably never noticed the conrod on the last crank. I've taken the crank out now and I'll compare it with other cranks, plus I'm going to fit a different crank and see how that lines up.
Re: Con rod not sitting central in piston.
Posted: Thu Aug 14, 2014 11:56 am
by Special X
Both big end shims on one side of the big end boss?
Re: Con rod not sitting central in piston.
Posted: Thu Aug 14, 2014 1:58 pm
by coaster
Special X wrote:Both big end shims on one side of the big end boss?
corrado wrote:....... No shims at big end both web width is the same as it was when it had SIL rod. .
Re: Con rod not sitting central in piston.
Posted: Thu Aug 14, 2014 3:59 pm
by Special X
No shims . . . . surprising.
Re: Con rod not sitting central in piston.
Posted: Fri Aug 15, 2014 12:21 am
by corrado
Special X wrote:No shims . . . . surprising.
It's what you get when a bike builder builds your crank, he can't understand why we need shims, he says bikes don't need them so why do Lambrettas? I couldn't answer his question. He's probably the biggest UK supplier of cranks and pistons for 2 stroke bikes.
I've changed the crank now, I'd tell you what the new one is but too scared of all the "they're s**t they all break" replies.
I know it's going to break ..... I break everything given time.