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2000 Honda trx250, 1986 Honda trx 250
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Discussion Starter · #1 ·
Hey guys, new to the forum thing. I’m a automotive/heavy duty mechanic and really only work on 2 strokes, but I’ve got a 2000 Honda trx 250 and I bought it not running. And after running a Compression test I opened up the top end and found the piston to be slightly melted so I replaced the piston, jug and re ran the compression test and got good compression but still not starting, had good spark, fuel, air and compression so I popped the clutch cover off and found this
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Not really sure why the chain would pop off and not really sure what parts need replacing. Tensioner for the other chain looks fine but there’s a little chain slack, not really sure how much there should be though. not really sure what this chain does ? Maybe an oil pump ? Any help would be greatly appreciated. Thanks in advanced!!
 

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Yes, that is the oil pump drive sprocket and drive chain - it only 'pops' off if the chain is worn out or the snap ring that retains the sprocket comes off the oil pump shaft
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To replace the chain, you need a clutch puller
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If I had bought it not running and found a problem with the piston, I would have removed the engine and performed a full rebuild - but that's me
 

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2000 Honda trx250, 1986 Honda trx 250
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4 Posts
Discussion Starter · #3 ·
Yes, that is the oil pump drive sprocket and drive chain - it only 'pops' off if the chain is worn out or the snap ring that retains the sprocket comes off the oil pump shaft
View attachment 4837

To replace the chain, you need a clutch puller
View attachment 4838

If I had bought it not running and found a problem with the piston, I would have removed the engine and performed a full rebuild - but that's me
So will the oil pump chain coming off cause a no start ? I feel like it would start but obviously have no oil going through out
 

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No - it should run until the engine burns up from lack of lubrication - since you rebuilt the top end, what was the valve lift? There is no spec for the lift in the service manual, but it should be apprx. the same for both the intake and exhaust - if you check duration, the intake should begin to open 8* BTDC and close at 37* ABDC - the exhaust should open at 38* BBDC and close at 7* ATDC. With no oil pressure I would suspect the cam and lifters may be damaged.
 

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2000 Honda trx250, 1986 Honda trx 250
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Discussion Starter · #5 ·
No - it should run until the engine burns up from lack of lubrication - since you rebuilt the top end, what was the valve lift? There is no spec for the lift in the service manual, but it should be apprx. the same for both the intake and exhaust - if you check duration, the intake should begin to open 8* BTDC and close at 37* ABDC - the exhaust should open at 38* BBDC and close at 7* ATDC. With no oil pressure I would suspect the cam and lifters may be damaged.
Unsure of valve lift but I will look into it, I did adjust valve lash but again I was able to see intake and exhaust valves open and close when turning over and it also backfired out the carb, indicating timing is probably off right ? Should I check cam crank timing to make sure that chain hasn’t slipped ?
 

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2000 Honda trx250, 1986 Honda trx 250
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Discussion Starter · #6 ·
Unsure of valve lift but I will look into it, I did adjust valve lash but again I was able to see intake and exhaust valves open and close when turning over and it also backfired out the carb, indicating timing is probably off right ? Should I check cam crank timing to make sure that chain hasn’t slipped ?
the cam crank chain has about 1/4 inch of slop is that normal ?
 
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