Yamaha TRX850 Enthusiasts Forum

This one is bugging me. I've now spent 4 afternoons messing about with this bike.

The TRX I bought last month advertised as having a "noisy cam chain. Well it has a clattery, cammy, tappy, rattling noise at 2800-3000rpm. Which isn't there at idle, and isn't that bad above those revs.

I've changed the oil and filter, it was disgusting, hadn't been changed for a while.

Whipped the rocker cover off, took the cams out, very worrying damage to the inlet cam and it's bearings. Had to go back to my old school fitter training to restore the bearing suffaces and get cam to actually turn again! swapped in the cams, sprockets, cam chain and oil pumps from my 15K TRX engine, which are like new as the 28K ones were well out of spec. Valve clearances are now within spec. (no point in putting new parts into a bike I'll be selling on, might as well stick them in the one I'm keeping).

Got it all back together, it's exactly the same, a horrible ticking, rattly sound at 3000rpm. I'm worried it might be something worse than timing gear now as the oil was real bad, there were metal particles in the oil filter (which I was hoping had come from the cam bearings/head but probably not) and the pumps are very badly worn.

I had oil pressure, oil drips out of the bolt in the upper gallery like it says it's meant to in the Haynes manual so I know i have oil pressure to the head (well, i do with the new pumps)

Then had a heart attack when I ordered 2 new oil pumps today....one was £88, the other £107!! still, good to know that they will last me a good while,

My next step is looking to be a head off job, or possibly drop the whole motor out for strip and inspection. I'm fearing the worst that it is in fact completely knackered all because some twunt hasn't serviced it.

Any ideas? anyone got a spare head?

Sure does sound like a loose timing chain, have you verified that the adjuster still has some notches to go? Even maybe take the little bolt out of the centre of the adjuster, withdraw the spring and use a small allen key or similar to try and push the adjuster out one more click. If it was bearing knock or piston slap or some other terrible thing it would be there at idle. Also while you were fitting up the bearing surfaces, did you bolt the cam caps on and measure the cam bores for size and out of round?

yep, tried all that with the tensioner, even so far as taking it out and adding an extra click to get that little bit more, but it still makes a racket.

i measured the cam, not much point in measuring the head, the bearing surfaces are visibly damaged and out of shape, they aren't going to be anywhere near the right shape or size.

I think you answered your question right there, if the cams are loose in the bearings they may "whirl" at certain speeds, which would shake the sh*t out of the cam chain, I think you were right when you said you need to chuck a new head on it. If you live near a good machine shop you could get the bearing bores tigged up and re bored, but if it's just a chuck together motor to sell the bike I don't know if that would be worth it.

i hear you. line boring the head has been considered, at this stage i didn't want to remove it, but i think that has to be my next option.

it's more of a case of the cam being tight in the head rather than slack though.

also, it doesn't do it when the engine is cold. only about 30 seconds after it's been fired up??

Make sure you put your location on Evilbay when you sell it Phat...........that way we can avoid bidding on it.............

hey, I'm one of the few honest sellers out there! I could have quite easily just stuck it straight back out there with a "noisy cam chain"......which i suppose a lot of people would do. But I like the challenge, and it's not a bad bike so it deserves fixing rather than bodging or breaking.

I bit the bullet today. Head off, barrels off, pistons and rods out (which wasn't easy with the engine still in the bike!. Sump off to be cleaned. strainer had a few bits of crap in it, filter must have caught most of the debris.

Number 2 bore has had piston contact and is damaged up near the top on the front side. Lots of play in the gudgeon pins and big end bearings, but they haven't spun and damaged the rods. Thankfully the crank looks OK, yet to mic it up to see. The bearings must be very soft, I've had car engines go before and they have always wrecked the crank and spun the bearing shells in the conrod.

Looks like I'll be swapping in the barrels and pistons from the other lump and going for an overbore on these barrels with new pistons for the original motor. Unless there is a cheap way to hone out the barrels and re use them and the pistons?

Still looking for a head in the meantime. I can get it welded, but don't know of anyone I can think of right now who could line bore the inlet cam bearings out.

Going to cost me more than I really expected, but the money will be going into upgrades for the bike I'm keeping so I don't mind too much.

Best of luck Phat. Wish we had more honest "doer-upperers" in Aus!