Has anyone out there had

a timing chain break?

i have a 98 400 and am

considering doing one

over the winter as a

preventative maintanence measure.

am i being paranoid ,or

should these things be replaced


Speaking about 4-strokes in general (not this motor specifically), typically the timing chain failures that I have seen aren't broken chains, but are where the sprockets get worn and finally the chain slips a tooth or two. I would say inspect the chain slack, the wear blocks, the sprockets and the timing (stretched/worn chains can change the timing) and if all looks in spec then you're probably OK. Hopefully someone with more experience with this particular motor can chime in and add more info. Poor quality oil or extended periods between changes can really accelerate timing chain/sprocket wear.

Torch, I have asked the same question myself in the past and Boit recommened that the timing chain be replaced with avery top end re-build as prevention. I did just so and upon removing the original chain found that it was kinking ( like the diagram in the manual ) This kinking may cause wear on the sprokets and load the binder also. Please replace it, it ia a 45.00 part.

Thank you Sirthumpalot and Hugh

for your input. $45 is a small

price to pay for peice of mind

this is one of those things

i guess you just have to weigh

out.im going to inspect it

and probably replace it.

Somtimes in the back of my mind

i wonder if a wear item

like the timing chain or

cam gear is gonna let go when im

on the face of a big jump.

I do take very good care of my bike

I change the oil every ride and

check the chassis and suspension torque

specs service aifilter ect.

but im new to 4 stroke mx bikes and

i guess im just a little nervous.

but i must say thumper power

deffinetly kicks some serious ass!

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