Trials Australia Forums

Hello,

A while ago I replaced the crank seals on my TY175. Today, in our club trial the bike developed an electrical fault - misfiring badly. It was raining heavily so I thought water had got into the points (I checked the kill switch). When I got home and removed the flywheel cover there was a puddle of crankcase oil in the bottom of the casing. I'm thinking this oil might have got flicked around by the flywheel and caused the points to short. Question is, where did the oil come from? It must have come through the seal, I can't see any other route. When I installed it I seated the seal about 5 mm into the crankcase casting, thinking the seal would run better on an unworn part of the crankshaft. Was this too deep? Should it have been flush with the casting? It was not a genuine part - just an ordinary oil seal from the local bearing shop (dimension 25-40-8).

Thanks in advance,
Adrian

The oil is probably in there because you used an off-the-shelf seal. Two stroke crankcases blow as well as suck so the seals have to hold pressure in both directions alternately.
If you have used the same type of seal on the drive side you may get problems there as well.
Genuine Yamaha crank seals work great, last for ages and are readily available.
A few years ago I bought a KT250 in pieces and the motor had been worked on a bit by the previous owner, but not run. I put the bike together over a period of months and when I finally started the motor, it started emptying gearbox of oil at a rapid rate (and trying to burn it on the way through). Suspecting the drive side crank seal, I waited till my workshop cleared of smoke and pulled the clutch cover off and found that the crank seal had completely popped out of the crankcase half. It was nowhere tight enough in the hole to have stayed there, and yes it was an off-the-shelf oil seal. Luckily for me, proper KT250 crank seals are available too.

iam with david ! go the genuine seal. they are cheap and last for ages! some after market seals dont handle the heat to well. from my past experance its always the dry side[stator side] that goes, not the oil side[clutch side]...

Thanks for the advice. I've ordered some genuine seals and will see how they go. At least my non-genuine seals were better than what was in there before - the previous owner had replaced the seals but put them in the wrong side, then wondered why it wouldn't idle!!

Cheers, Ade

Gday, dont forget to lubricate them around the lips when fitting. I use some grease.

Cheers,


Stork