What would cause a 250R to keep blowing crank seals?

[RUNMYTA]

What would cause my Big Bore LRD 300R keep blowing crank seals? Last month I had to replace the left side crank seal and I have only rode it about 2 hours since it was replaced. Now it has blown another crank seal and is sucking in the tranny oil. Would a loose bore cause this?

What brand of bearings and seals do you recommend? Honda or aftermarket? TIA MIKE

[INFANTRY RACING]

too much crankcase preasure.. maybe a bad crank

[powerslider]

If you didn't you should have went through the bottom end when you installed the big bore cylinder. For reliability the crank and counter balancer should be rebuilt with new bearings. With the increase in power your new top end produces you may have parts failing from age/wear so it's best to freshen everything up to avoid these problems.