[joandemma]

Just finished stripping my mates bike down with him, to replace the main bearings and seals for the second time in 6 months. Both times it has been the bearing on the flywheel side that has gone. When we took off flywheel cover we noticed liquid inside it which looked like engine oil and water, could the problem be that this plastic cover is not sealing properly and letting water in and then this is somehow getting into the bearing. We have been told that these bearings usually need replacing after 6 months, but surely they must last longer than that. Bearings and seals were bought direct from Gas Gas so were genuine articles. Anyone had similar troubles, or could shed more light on the subject, any help appreciated-cheers.

[max1956bikes]

could be crank not balanced properly,or fly wheel out of balance,hard to find out unless you can find another fly wheel

[JSE]

joandemma, on Jul 18 2009, 12:51 PM, said:

Just finished stripping my mates bike down with him, to replace the main bearings and seals for the second time in 6 months. Both times it has been the bearing on the flywheel side that has gone. When we took off flywheel cover we noticed liquid inside it which looked like engine oil and water, could the problem be that this plastic cover is not sealing properly and letting water in and then this is somehow getting into the bearing. We have been told that these bearings usually need replacing after 6 months, but surely they must last longer than that. Bearings and seals were bought direct from Gas Gas so were genuine articles. Anyone had similar troubles, or could shed more light on the subject, any help appreciated-cheers.

Two sets of crank bearings in 6 months is not normal, by any standard, except if Raga rode it maybe . I have the original set in my 02' Pro 280 and no signs of a problem.

The water in the sidecover is not unusual (for any bike) if the seal is compromised. Some riders drill a small hole in the bottom of the sidecover to drain water, but this will cause the engine to suck in water through the hole if in a creek, as the sudden cooling of the case creates a vacuum (which, hopefully will drain out later). The oil in the sidecover, however, is unusual and you might look for the cause. Maybe a scratch on the sealing surface of the crank that has worn the seal or the copper washer left off the case capscrew that has an oil passage inside the hole?

As for the bearing failure, you might expand the search for the cause to something beyond the bearing itself, like installation preceedure or crank misalignment, for example.

Jon

[JanDyb]

joandemma, on Jul 18 2009, 07:51 PM, said:

Just finished stripping my mates bike down with him, to replace the main bearings and seals for the second time in 6 months. Both times it has been the bearing on the flywheel side that has gone.

If the bearing is gone are You sure You put one in? (Haha... funny me... )

No seriously are the bearings actualy damaged or is it "just" the seals? If the bearing is damaged I would go for the unbalanced or misaligned crank theory.

What kind of bearing does the 05 have? The early narrow bearing with the big seal against the crank or the later wide bearing with the seal inside the bearing and O-rings on the outside and inside?

-Jan

[joandemma]

It was the wide bearing with seals, how can we test crankshaft to see if its ok?

[JanDyb]

joandemma, on Jul 19 2009, 08:21 PM, said:

It was the wide bearing with seals, how can we test crankshaft to see if its ok?

Most motorcycle workshops have equipment to measure the crank.

I just remembered something. The left bearing is lubricated by gear oil coming in from the gear case through a narrow passage and going out through a hole in the bearing that again have to be aligned with the hole in the casing. If one or both of theese are clogged naturally the bearing wont last long.

-Jan

[trialsnutterman]

It is very easy to damage a bearing when installing it, this could be another reason.

[PeterB]

Hi joandemma,
These bearings usually last for many years, unless water finds its way in. Are you sure the water pump shaft/seal is not passing coolant? The water settles in the well of the bearing while the bike sits for a week or two and corrodes the bearing surfaces. Similarly, any water egress from drowning the motor and not cleaning out immediately gives the same results.
Never heard of the GG crank being out of balance.
Are you sure the LHS drain hole in the bearing/crank case is aligned properly?
Is the LHS teflon oil seal in the right way around?
Bye, PeterB.

[joandemma]

Which is the right way round for teflon seal?

[PeterB]

Hi Joandemma,
The seal has a spring to tension the seal lip, it is the open side of the seal, this side should face the pressure area, in this case, it would be the crank case. Also, the teflon seal usually has a steel outer casing, the closed part of the casing goes into the housing first. It's not an easy seal to fit and it is easy to damage the steel case when fitting. I turned up a steel mandrel to mount the seal onto to allow the seal to be fitted squarely into the housing.
Bye, PeterB.