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kevin_c

trx350 mystery

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Hi All. Hope someone with more experience has some insight.

 

I was gifted an 86' TRX350 Foreman that is in great shape. The previous owner said one day the oil temp light and fan turned on when he fired it up. He decided it was probably just a bad sensor and ran it anyway. After a while it seized up. He didn't want to work on it so he gave it to me. I was able to free the piston with some penetrating oil in the spark plug hole and a good push on the kickstarter. I decided something was probably really wrong with the piston or cylinder so I took the top end off for inspection. Trouble is, I can't locate the problem. The piston, rings, cylinder, valves, cam shaft, and springs all measure within the service limit. Nothing I can see indicates there was ever a problem (in my limited experience with small engines). I can't "hear" anything that sounds troubling in the crank case but I'm a total novice and new to ATV's. Any thoughts would be greatly appreciated. 

honda2.jpg

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Good job for taking on a first year Honda 4x4.

if it’s an 86, it’s a TRX350A Fourtrax base model. TRX350A ran 86/87.
its not a Foreman; the TRX350D came out in 87.

every year has model variations so don’t think every part will swap out. Carbs are all the same. Ignition systems are not.

 

Will it turn over? you must do a compression check besides examining Bore and piston.

 

BTW mine stopped while overheating once but continues to run with no problems. 

Edited by Goober
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Hi Kevin , welcome to the forum .  Good score on the 350 for free and cool dog ..... some pics of the piston and bore might help 

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Welcome aboard.  You're definitely in the right place for the old 350's. 

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welcome to the forums.

 

21 hours ago, kevin_c said:

The previous owner said one day the oil temp light and fan turned on when he fired it up.

 

did it does this (cold engine) just as soon as he started it ? we need more detail. 

 

21 hours ago, kevin_c said:

I was able to free the piston with some penetrating oil in the spark plug hole and a good push on the kickstarter.

 

or it been over heated then shut off. without time to cool off. 

Edited by _Wilson_™

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Thank you all for the welcome and wise questions!

 

20 hours ago, Goober said:

Will it turn over? you must do a compression check besides examining Bore and piston.

 

Thanks for pointing out the correct model. It is a TRX350A. I did not try to run it - just went with the top end inspection. Compression test is a good idea.

 

10 hours ago, Fishfiles said:

some pics of the piston and bore might help 

IMG-2978.jpgIMG-2976.jpgIMG-2975.jpgIMG-2974.jpgIMG-2973.jpgIMG-2972.jpgIMG-2971.jpgIMG-2968.jpgIMG-2967.jpgIMG-2966.jpgIMG-2965.jpgIMG-2964.jpgIMG-2963.jpg

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1 hour ago, _Wilson_™ said:

did it does this (cold engine) just as soon as he started it ? we need more detail. 

 

 

1 hour ago, _Wilson_™ said:

or it been over heated then shut off. without time to cool off. 

 

Thanks for the questions. The best synopsis I have is that the temp light and fan came on during a cold start. He drove it for ~10 minutes, walked away and let it idle and when he return it had seized up. I didn't try to turn it over myself. I checked the temperature dependent resistance of the oil temp sensor and it checks out fine (10.9 kohm at 75 F and 2 kohm at 187 F). 

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got any pics of the head cam shaft, valves, and rockers ? might need to clean the sides of the piston, and take some more pics ..

Edited by _Wilson_™

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34 minutes ago, _Wilson_™ said:

got any pics of the head cam shadt, valves, and rockers ? 

 Yes sir. I haven't taken the rockers out yet. Here's a valve before and after a quick clean, and the lifters, and cam shaft...

IMG-3001.jpgIMG-2999.jpgIMG-2998.jpgIMG-2997.jpgIMG-2996.jpgIMG-2993.jpgIMG-2992.jpgIMG-2990.jpgIMG-2989.jpgIMG-2988.jpgIMG-2987.jpgIMG-2986.jpgIMG-2984.jpgIMG-2982.jpg

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was the engine oil changed lately ?, is the oil filter in backwards ???. from looking at the rockers and cam journals ^^, it looks like no oil was getting to the top end ?.

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Does the motor turn over fine with the top end removed? A uncommon thing that can lock up a motor are the bolts on the flywheel coming loose and hitting the stator.

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The piston looks excellent, the knurled grooves around the circumference of the piston (that hold oil) look like new. No evidence of scuffing or seizure either, it appears to be a low mileage motor. Everything on top looks great to me.

 

I'm with toodeep... I'd take the left side cover off and check the flywheel & stator next.

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3 hours ago, toodeep said:

Does the motor turn over fine with the top end removed? A uncommon thing that can lock up a motor are the bolts on the flywheel coming loose and hitting the stator.

 

2 hours ago, retro said:

 

I'm with toodeep... I'd take the left side cover off and check the flywheel & stator next.

 

Thanks folks. It turns over beautifully with the top end off. It sounds very smooth (to my untrained ears). At this point I'm almost inclined to replace all the top end consumables and put it back together and see if it runs okay🤷‍♂️

 

 

2 hours ago, retro said:

The piston looks excellent, the knurled grooves around the circumference of the piston (that hold oil) look like new. No evidence of scuffing or seizure either, it appears to be a low mileage motor. Everything on top looks great to me.

 

 

👍

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would this be a rebuilt engine, or the head being taken off ... i see sealant to the inside, that might have eventually caused an oil starve issue  to the top end ? but this doesn't explain you freeing the piston up with penetrating oil, unless the decompression wasn't working, or if is out adjustment, and it was never said you used the electric starter, just the kicker, and from shade said does look very much lke the top end was starved for oil, and or was long over due for an oil change. 

image.jpg

image.jpg

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Maybe the lock up was caused from a overflowing carb and it was hydro-locked and that temp light and fan issue is a separate issue 

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10 hours ago, _Wilson_™ said:

would this be a rebuilt engine, or the head being taken off ... i see sealant to the inside, that might have eventually caused an oil starve issue  to the top end ? but this doesn't explain you freeing the piston up with penetrating oil, unless the decompression wasn't working, or if is out adjustment, and it was never said you used the electric starter, just the kicker, and from shade said does look very much lke the top end was starved for oil, and or was long over due for an oil change. 

 

Thanks _Wilson_. I was told that I'm the first to work on this bike (it only had one owner). I did forget to mention that the owner said the electric start stopped working so he just used the kickstarter, and then it froze up. Should I be thinking about the oil pump at this point? The oil path pipe isn't occluded or anything like that. I think I will have a look at the flywheel and the starter. 

 

This is what I've ordered so far for the rebuild...

 

Wiseco Powersports Piston Kits PK1015

https://www.summitracing.com/parts/WIS-PK1015

 

Tusk - Top End Gasket Kit - 1032020077

https://forwardpowersports.com/index.php/top-end-gasket-kit-tusk-1032020077.html

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image.png

Is it just me , or does the bottom edge of the piston skirt look bent / deformed in this pic ? 

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yeah, kind of does. 

 

 have you confirmed the oil filter was in the right way ? 

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42 minutes ago, _Wilson_™ said:

yeah, kind of does. 

 

 have you confirmed the oil filter was in the right way ? 

Yes it was in the correct way

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2 hours ago, kevin_c said:

 

3 hours ago, _Wilson_™ said:

yeah, kind of does. 

 

 have you confirmed the oil filter was in the right way ? 

Yes it was in the correct way

 

 

9584BEC9-D625-4025-A4E4-B5FAC6F2BF1D.jpeg

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Well I found that one of the intake valves is slightly bent, going to replace. I noticed it while cleaning. It has a slight wobble on the drill. Also the outer springs are out of tolerance, probably not surprising given its age. 

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thanks for the update ....ill add not a bad deal being gifted that classic old girl, with some more work, and help from the guys, you scored good! IMO.

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22 hours ago, kevin_c said:

Well I found that one of the intake valves is slightly bent, going to replace. I noticed it while cleaning. It has a slight wobble on the drill. Also the outer springs are out of tolerance, probably not surprising given its age. 

if a valve is bent as you say ?, chances are..it smacked the top of the piston !. when this happens?, most times its because the cam chain is stretched , and allowed the valve to jump time, and hit piston. you can check the cam chain without tearing the motor apart.

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1 hour ago, shadetree said:

if a valve is bent as you say ?, chances are..it smacked the top of the piston !. when this happens?, most times its because the cam chain is stretched , and allowed the valve to jump time, and hit piston. you can check the cam chain without tearing the motor apart.

 

Thanks shadetree good point. I've read in other parts of the forum how to check for stretch in the chain while the top end is still on the motor. Is there also a way to check when the top end is disassembled? Right now my chain is just hanging there above the crank case while I work on the top end.

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