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Did you check the deck height when you were putting it together. I would question everything about that TRX70 crankshaft. It is a pretty odd duck IMO. It is SAID to be a short rod, it has a 12v taper on the flywheel end, and from 1987. They sell(sold) you a regular big dome, short rod, CT70 piston. If you didnt verify that the piston wouldn't hit the valve, I'd guess that was the problem.

But the timing chain DOES look like it could be loose in there...and that is the easiest thing to check. Pull that stator plate off of there for a look.
 

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If you didnt verify that the piston wouldn't hit the valve, I'd guess that was the problem.
That was the reason why I asked for the piston part number on the box. The TBW0219 is for the 6V short-rod engines, the TBW0365 is for the 6 and 12V long-rod engines. Installing the 0365 piston on a short-rod would leave the piston 2mm short in the cylinder at TDC.
 

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And if the trx70 crank is actually a LONG rod, instead of a short rod, the 0219 would put the piston high, and hit the valves.

It's odd that a crank with the 12v taper, would have a short rod. But that's what they're saying it is.
 

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Discussion Starter #27
Little update,
Talked to Spanglers, he talked me into pulling the head back off, i see no signs of piston to valve contact. He (Logan) at Spanglers really thinks it is something going on with timing chain and or tensioner. He's sending me new chain and gasket kit. Might as well change the chain if im talking it that far apart.
So for your info, do you feel I have the right piston??
My fly wheel puller came in today so I hope to work on it tomorrow.
I noticed some oil in the exhaust when i removed, hope it's not a valve seal or something, he told me to double check the rings that the splits are not lined up
 

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So for your info, do you feel I have the right piston??
Yes, the 0219 is the piston for the short-rod engines, I also think the issue is the timing chain being stretched beyond servicable length and rattling around inside the cam chain tunnel.
Once you've removed the stator plate, make sure you post some pics of the whole area that is underneath the stator, right after you open it up.
 

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Kirb, I think I may have a stock TRX70 crank somewhere in the catacombs, I'll see if I can dig it out and get an overall length measurement over the next few days.
Okay, after doing some very UNscientific research & development, I measured the overall length of a TRX70 crank assembly. Using a set of digital vernier calipers, I came up with 120.27mm, top to bottom. I then measured an XR/CRF50 stock crank assembly and it was 122.56mm, top to bottom. To be sure, I measured an '83 ATC70 crank assembly I just came across, it measured 120.22mm top to bottom.
 

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Well that certainly goes along with the TRX70 crank being a "short rod" type. Or...short rod, 12v type.
I'm committing it to memory.
 

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I would start checking the size of the chain first. Maybe it's the wrong length. Then the rest.
 

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Discussion Starter #32
Finally had some time to work on it. After breaking a snapon #3 Phillips socket, I finally got the cover off and yes, timing chain was indeed stretched. Hard to believe it was stretched that much. I got it all back together, fired it up. And no more chain slap. Yes!
But I now have another issue. It's running bad. Last time I started it, yes it had the chain slap, but it rain smooth as can be. Idled perfect, revved up smoothly. I thought great this will be easy to fine tune it. But this time I had to pull 10 times to get it started, once it did it high idled really bad, could barely take choke off, and you had to ease into the throttle very easy or would die. Just ran awful. Is there anything I could of messed up? If I would of damaged anything in the stator/alternator it wouldn't run at all correct? It seem like a carb issue, but it ran perfectly fine before. Could it be a spark issue? What with the coming and going of the high idle.? I ran awesome before. What are some things I should check for? Maybe I need to triple check my timing, if I'm off 1 tooth could it run like crap?
 

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Discussion Starter #33 (Edited)
Could my timing be 180 off? I read another post guy was 180 off and ran like crap, how do I know or check if I'm 180 off? Shouldn't it send spark every revolution anyway? So 180 off shouldn't matter. Also I noticed it's smoking some. I hope it just assembly oil or something. This sucks, I thought this would be pretty straightforward and I have problem after problem. The running issue has to be carb related. Shouldn't I of gotten some other jets along with this kit
 

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Timing can't be 180 degrees off. It's a wasted spark ignition, so cam timed at TDC is cam timed at TDC. (Minor correction for an earlier post, starting at TDC and turning the crank one full revolution brings you back to TDC, not BDC. You're on a different part of the four stroke cycle, but the piston is at TDC. Turn it again, TDC again.)

If the motor ran well before, and all you've changed is the cam chain, I'd recheck your cam isn't one tooth advanced or retarded. You can use a screwdriver in the plug hole to feel exactly where TDC is, and then set the cam timing based on that.
 

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Discussion Starter #35
Finally had time for testing today, definitely need to rejet there carb.still getting smoke. Does anyone have any tricks on how to trace how its burning oil? I guess I'll run it a bit more and tear it back down see what looks worn? I've got more hours in this little thing than I'd ever dream of, disappointing that's its burning oil still. This was the sole reason for buying a 88cc kit. The oli top end was burning oil bad! Its definitely not as bad as before but still burning.
 
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