[Exaviator]

When I first introduced myself, I wrote a bit about my NTM TRX 350.
I was warmly greeted and promptly treated with much kindness and generosity.

When I went to buy this machine, it would not start, but had fuel and spark---but no compression. So, I suspected valves or rings. When I got it home, I put my comp guage in the hole and with the carb already off, I guess I would have had WOT. Nothing would register on the guage. So I tore into it, expecting to find lots of problems and horror stories. The one thing I did not do was take a look at the cam timing before I removed it. I gave myself a hardy kick for that oversight. Anyway, the upper part looked great, and when I pulled the head to look at the piston and valves-but for a bit of carbon on the head part and around the ex valves, the piston top was nice and clean and even shiney(what gives here??---can an engine that has been run for any time at all still have a clean piston top. The wall is nice and smooth if a bit glazed with no marks whatsoever. So I stopped right there in the teardown. I removed the ex valves and cleaned them up and looked at the guides and seals--great shape---WTF--- no need to even remove the intake valves, they looked so good, and were absolutely air tight.
So--I decided to put it back together--even using the same head gasket because it is a holiday weekend and I could not get one. Comments on that please--I just want to get it together and see if I have any compression.

Now, when I removed the cam chain tensioner, I noticed that it was run full extension--so I am assuming that the chain has reached its wear limit and MAY have been loose enough to let the cam jump out of time. Either that or the PO, or someone did not get the timing correct the last time.
This engine has definitely been apart and put back together, and it may have had a new piston. The two sides do not match the texture of the long block, and I may have a much younger(or older) engine than the 20 year old ATV itself.

I am going to put the top cover on and then do a compression check to see if my theory is correct. If I get compression, then I need to ponder about getting a new cam chain and possibly a new head gasket.

Sorry for the long disortation, but I would be most interested in any comments. I want to do this right and will welcome any suggestions.
Thanks

 

[Helmut]

the piston top was nice and clean and even shiney(what gives here??---can an engine that has been run for any time at all still have a clean piston top.

Either it's been running lean or someone just changed the piston not long ago.

So--I decided to put it back together--even using the same head gasket because it is a holiday weekend and I could not get one. Comments on that please

I usually like to replace the head gasket, but I have reused the old one before when working on one when I was in a hurry and I didn't seem to have any problems. I would try to replace it, just in case or at least, later.

Now, when I removed the cam chain tensioner, I noticed that it was run full extension--so I am assuming that the chain has reached its wear limit and MAY have been loose enough to let the cam jump out of time. Either that or the PO, or someone did not get the timing correct the last time.

You do realize that when you pull the tensioner out of the cylinder, it will automatically extend all the way out since it is spring loaded, right? If you took that in to account and determined that it was still extended all the way out before you pulled it out, then yes, the timing chain is stretched beyond the ability of the tensioner to tension it and needs to be replaced. And that's probably why it jumped time. Unless the timing chain has been recently replaced, it probably needs one.

 

[Exaviator]

Yeah, I thought of that after I spoke. It may have just automatically extended when I removed it. Is it OK to just remove the end bolt and screw the plunger back and then just let it extend again onto the tensioner plate--or should I simply remove it again and install it with the wire wedged inside to keep it retracted until the two bolts are tight.

I got the thing back together and before I even installed the carb or the exhaust pipes, I did a finger test and the thing near blew my finger into space. Put the guage on and after only 3 seconds of starter cranking, I had almost 190 psi of compression.
It was either improperly timed or it jumped timing due to what we talked about.
Is this a non interference engine??? I would guess it is.

 

[Helmut]

Yeah, if you already have it bolted on, there's no need to remove it. Just take the bolt out of the end of it and use a small screwdriver to turn it clockwise to retract it and then release the screwdriver and it will automatically extend out and tension the timing chain. That is, if the timing chain isn't stretched too much.

If you want to test it to see if the timing chain is stretched too much, unbolt the tensioner and take it back out and let it extend all the way out. Now, just stick it back in the hole and if the base of the tensioner goes in and touches the cylinder, the timing chain is stretched too much for it to properly tension. When the arm extends out, it locks out, so it won't go back in until you use a screwdriver to retract it.

 

[Exaviator]

That is essentially what I did when I put it back in. Looks like the chain may be worn to beyond its limit, and that may be why it was out of valve time.
you did not say if the engine is non interference --ie, the valves will not contact the piston when out of timing.

How much does a new chain cost, and fromn where?
Thanks

 

[Helmut]

That is essentially what I did when I put it back in. Looks like the chain may be worn to beyond its limit, and that may be why it was out of valve time.
you did not say if the engine is non interference --ie, the valves will not contact the piston when out of timing.

How much does a new chain cost, and fromn where?
Thanks

Yes, the valves can hit the piston, but you can get lucky, it depends on how far out of time the engine is when it jumps time.

 

[Exaviator]

Because of my oversight, I do not know how far off time it was--if it was even off any. Well, if the valves can hit the piston, then I surely did get lucky.
Anyway, I put the carb on and fired her up without any breather or filter. I gave it a shot of quick start and she fired right up and smoked like a chimney. I hoped that it would soon burn off the oil I had put around the rings, but alas it kept pumping out the smoke. So it looks like some new rings are called for, and while I am back in there, I will get a new head gasket and a new chain. Hopefully, that will be all I will need to do. I will probably need to have the cylinder checked for run out and wear. Hope I don't need to bore oversize and get a new piston. Can't be that much worn with 190 lbs of compression.
Don't want to put a lot more money into this machine--just want to get it running well so I can play a bit this winter.

 

[Helmut]

Yes, that's good compression. Maybe the valve stem seals are bad or did you already check them? If I were you and I replaced the piston rings, I would go ahead and replace the valve stem seals too, as they're cheap and easy to change.

 

[Exaviator]

When we cleaned up and lapped the ex valves, the seals looked OK and they had good seal as indicated by that little suction pop when they were pulled out.
I do not know any of the history of this engine--it may already have been redone--it sure looked like it as indicated by the newish looking piston, and the nice firm fit it had in the cylinder. But the walls were pretty glazed.
The pipe was pretty black and wet looking, so if the top end has been done already, and it has never been run due to the timing issue(why the guy sold it), do you think that all the smoke is coming from the pipe and may eventually burn off?? How long is long enough to try that?? Hard to fathom bad rings and or valves with 190 lbs of compression. That was a wet check reading though. I will try it again tomorrow, and see if the smoking subsides as the pipe stays hot for a spell. Can't hurt it what???

Where can I get parts online?? I looked at several places, including Bike Bandit and found not much.

 

[Helmut]

I don't really know how long it would take for all the oil to burn out of the pipe, but I would run it for a while and see if it cleared up. It won't hurt anything and that might be the only problem, considering the compression is so good.

As far as parts, I usually buy all my parts at the dealer and order some from Ebay. I don't know where the best place to find parts for the 350 Fourtrax/Foreman would be. Shadetree probably knows and should be able to tell you when he gets back on.

 

[Helmut]

How much does a new chain cost, and fromn where?
Thanks

Sorry, I just saw this. A timing chain would cost around $125 from the Honda dealer.

 

[Exaviator]

I went out this AM and did a dry compression ck. It showed about 125 psi. I then started it up(after taking it out of the garage) and tried to see if the heat would burn off the oil in the pipes. It did not. So I removed the pipe and heated it with a torch and got no smoke. Therefore I assumed the smoke was coming from the engine. So I tore it down to the bottom. The rings and cyl wall look good and it all measures out as std., but I have only a cheap guage.The ring gap spacing was OK I guess I will need to take it to a shop and have it examined. If it is reasonably OK, I will hone it to get a good cross hatch and put in new rings. Might as well look for a reasonably priced cam chain and some valve seals too.
Hopefully that will break it of its bad smoking habit. LOL

 

[Exaviator]

Bit of an update. I took the jug to a guy near me who does repairs on many machines. He has a fairly nice shop and has quite a number of parts. He looked at the jug and then tossed a stock piston inside and declared the jug to have been very recently bored to 20 thou over. He had a head gasket and a lower jug gasket, and loaned me his valve spring compressor and a honing tool. He suspected that someone had put std rings into a 20 thou oversize piston.
I came home and tossed a ring into the jug and the end gap was over 40 thou, but remained constant thru the entire length of the wall-telling me that there is no wear or egg shape. I pulled the seals off and will be off at first light to Mother Honda looking for parts.
I am encouraged.

 

[Helmut]

Yeah, the ring end gap shouldn't be over 0.020 in, so he might be right.

 

[Exaviator]

Funny thing, but the ring with the 50 marked on it-which I have been told is the top compression ring, and is an oversize ring, is the one that has an end gap of over 40 thou, while the second ring is only about 20 thou. I cannot understand that, unless there is extreme wear on the top ring. I will know when my new 50 over rings get here on Friday.
Also, if the end gap stays constant while you push the ring down thru the bore, does that not indicate even wear and no egg shape. I can think of no better test for even wear on the walls.
Anyway, I installed the new seals and did a good cross hatching to the cylinder wall today while awaiting my other parts.

 

[Helmut]

Also, if the end gap stays constant while you push the ring down thru the bore, does that not indicate even wear and no egg shape. I can think of no better test for even wear on the walls.

That would indicate no taper, as long as the ring stays square with the bore. To check for egg shape or out of round, put the ring in the cylinder and hold it up to the light and make sure the ring touches the cylinder walls all the way around. Look for light coming through between the ring and cylinder walls.

 

[Exaviator]

No light shineth thru. Hopefully I have a good jug.
I had some fun reading about the great contraversy over the use of a 3 stone honer vs the balls honer. Anyway, I used the stone honer and got a nice chross hatch pattern where the glaze was before.

 

[Helmut]

Yeah, I use the 3 stone honer, too. The cross hatch pattern helps hold oil on the cylinder walls so the rings can seat properly.

 

[Exaviator]

I probably should start another thread, but since I seem to have your undivided attention, I am going to present you another of my little problems.
During the first time that I put the engine back together, when I was torquing down the rocker cover, I was not able to get any torque on the two 7 mil bolts that straddle the cam shaft bearing. Looks like the PO, or somebody had overtorqued and pulled thread. When I turned the bolts out, thread came with them. There is still about 3/8" of good thread at the bottom of the hole, but I cannot find any 7 mil bolts that are 1/4" longer. 7 mil seems a rare size. I may be able to get away with having those bolts just snug, but I would like to somehow get the proper torque applied.
Helicoil may be too expensive. I bought a couple of 8 mil bolts the same length and may try to tap the head holes out to fit those bolts. I would then need to drill out the two holes in the cover to allow the bigger bolts in. It may work, but I am very open to any suggestions.

 

[Helmut]

Yeah, 7mm is an odd size. It would be best to get longer 7mm bolts, but if you can't find them, you can't. I don't see any problem with using 8mm bolts and tapping threads for them, as long as you can tap good threads in the aluminum. Aluminum is so soft, sometimes it's hard to tap good threads, but it can be done. The hardest part is getting the tap to start good and straight.