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87 trx 250 Fourtrax Rod Knocking or Wristpin?

16842 Views 11 Replies 8 Participants Last post by  Here 2 help
I have a 1987 fourtrax 250 with a slight metal to metal knocking sound in the head when at idle. I took the head apart to check the rod but found no play in it. The wristpin also seems to be fine. There is no up , down looseness I can find that would cause the knocking. Any idea? The knocking is only heard at idle and sounds like metal to metal slapping. Like a rod knocking but not as loud or hard.Not a tapping like a cam chain more of a slapping of metal. As far as I know the engine is all stock with maybe new rings.
Thanks for any Info.
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Man I am not real sure except maybe also check valves. You did not mention that and I am not there to here it. I know of a site that I mod at that is alot more active you could check out.
Don't forget us here though. I mod on both forums. You may get some more answers there. Look me up.
I'm going to agree with tom you might need a valve adjustment
Hey, I checked the valve adjustment before I broke down the motor hoping that was it, but it was set right plus the knocking was more in the bottom end. I think the previous owner checked the valves too. They were set right on .007 mm . Let me ask you guys this: Should the wristpin have any play in it? Thank you for reading and trying to help. I know its hard to tell someone what the problem is without being there, but yall give me new ideas as to where to look.
Check your Decompression lever adjustment if you have one? is this a 250X? and does it have a backup kickstart or pull rope?
I had that on mine when I rebuilt it. It turned out to be the valves. Make sure you put it on the right mark when you adjust them theres a "t" then an "f" notch on the flywheel and another "t" 180 out. put it on the "t" thats before the "f". . It still ran decent but when I adjusted them properly it was night and day! Until my intake valve stem broke......haha
If its coming from the bottom end you may have a rod knocking. The wrist pin should not have any play in it or you would be getting piston slap You may also want to look at the wrist pin to see if the lock rings are still in place
Ok. Sorry for the late,late reply. I got it back together. I honed the cylinder, new rings, and timing chain. It run great. I'm thinking the timing chain had more play than I thought and was hitting the head. I did put a new wristpin in it which got rid of the little play I was having. I still have one more problem I think. Do they always run so hot? We were riding them in the woods and at a idle I heard a hissing sound. I turned it off and the sound was coming from the gas tank. When I open it the gas was boiling. We now have 2 of these 4wheelers a 87 and 85 both get hot like this. What do you guys think could be causing this or is this normal?
i have a 87 honda fourtrax 250, brand new stator, now when i kick it over it kicks back like its out of time? any ideas on what i could try? have already torqued the valves and checked the timing chain
over heating

any atv without a radiator will get hot as hell if you dont let them cool off every 30 min of riding or so. it also depends on how fast you go becouse thay are air cooled so if you like putting around do it in a higher gear so the engen dosent have to work as hard and get as hot. if you dont let them cool off thay will start sputtering and if you dont stop thay will crack the block or the head from exessive heat. I have to let mine cool off or it will start burning my leg. I own 2 trx250x as well a 87 and a 92. the 92 had a knocking like yours and gave blue smoke out the back soo im going to bore it as well and new pistion rings and ill also check the bearings in the camshaft for ware. I'm glad you figured it out!! this is my second one and I just joind the forums or i would of helped you sooner.
i have a 87 honda fourtrax 250, brand new stator, now when i kick it over it kicks back like its out of time? any ideas on what i could try? have already torqued the valves and checked the timing chain
More info please. In 1987 there was a 250A, a 250R and a 250X - which do you have? Also; kicking back is usually an ignition problem. Timing is set by the crankshaft. Either a sheared flywheel key or a fouled spark plug might be a good starting point for finding the problem.
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