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Discussion Starter #1
Hello,
I recently got my hands on a 96 TRX in good shape except non-running with no compression. I pulled the head and it had a bent valve. It had touched the piston, but there was no evident damage to the piston and the cylinder wall looked good too. So I bought a used head off ebay and bolted it on.

The first thing I did was check compression. It came in at a little over 180 psig, so I'm happy with that. I went to start it and if fired right up. It runs good, has plenty of power and shifts through all the gears (including reverse) like it should. But there's LOTS OF SMOKE out of the tail pipe. Clearly oil smoke, not fuel.

So, my first suspect is the rings. Even though I've got compression, the oil ring could be stuck. But, I didn't replace valve seals either. I can't imagine this much oil making past the valves, but who knows. Either way, looks like I'll be pulling it back apart. Is there anything else I should be looking at?

Thanks
 

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Yeah, keep checking the motor oil dipstick and see if it is actually burning any oil, or just burning excessive oil out of a previously saturated exhaust and muffler..? Previous history of it is unknown right? Got FSM?

Welcome to the forums!
 

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Discussion Starter #3
Thanks for the reply.

Right. Previous history is unkown. I bought a good running TRX300ex for $1100, but had to take this one (free) as a package deal. I figure I can afford to put a little money in it without getting hurt. And yes, I do have the service manual.

I don't think the smoke is from a saturated exhaust system. It's instantaneous, before the exhaust has a chance to heat up.

As an update, I went ahead and pulled the top end back off. Piston and rings look good, but I went ahead and ordered new anyway. They're pretty inexpensive, and I don't want to do this again. If I get a little time this weekend, I'll rent a spring compressor and take the valves apart so I can check the guides, and I've got seals I can install.

So far, no smoking gun, but I'll keep looking.
 

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Hi guys, again my trx 300 is giving me trouble. Riding one day, no issues. Next day, no fire to the plug, what is the most common issue that can cause that? Also the solinoid clicks on the start button but no spin. Tried the old jump across to no avail, it had what look like electronic switch wires could they cause a no spark issue? Thank you for any and all info. Safe riding, and happy holiday.

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Discussion Starter #6
A lot of travel for work lately, so progress has been slow. But I was able to get a new piston and rings installed as well as new valve stem seals.

While I had the head apart I noticed a lot of carbon build up in the exhaust ports and on the exhaust valve stems. I also found that the intake valves were nice and solid in their guides, but there was a slight bit of play on the exhaust valves. Barely perceptible, but it was definitely there.

I started it up, and initially there was no smoke. As it warmed up however, it started to smoke a bit. Nothing like before, but not good enough. In hindsight, I should have replaced the guides while I had it apart. Looks like I'll be pulling the head one more time. I'm starting to get good at this, so it won't take long ?
 

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It shouldn't be smoking oil at all. Did the cylinder measure within specs? Piston clearance within specs? Piston rings all gapped OK? Fresh hone in the bore?
 

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Discussion Starter #8
I've put a few more miles on it, and the smoking has completely cleared up. Either the rings needed to seat or there was some old oil in the muffler, but whatever it was has healed itself. Runs great and looks good (for a 21 year old quad). All that's left is to take it out and run it!! Thanks for all the help.
 
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