Yamaha TRX850 Enthusiasts Forum

I just cannot believe what has happenend. I was going to post the other night saying how I thought the bike was feeling a bit flat. It was really struggling to pull, and at 100mph I was finding in order to get it to go any more I was havng to kick it down a gear. This has been getting worse over the past few days but i just put it down to the carbs being worn out and needed new emulsion tubes. It's never really ran right since I put it back together (the bike, that is, not the engine).

I checked the oil last week, and it when i topped it up it seemed to take a fair bit, like half a litre before it started showing on the glass. But, my main worrry is the oil itself, it looked a bit funny, and I'm now kicking myself for not changing it like I'd meant to. Used the bike on Tuesday, seemed OK, but again, a bit flat, it got me to work fine yesterday but on the way home just felt totally lethargic, really struggling and underpowered. Then, i started to hear a strange rattling noise, so I pulled in as soon as I could to check it out. Removed my helmet and earplugs and fired it up....nightmare....the same knocking sound at 3000-4000rpm that the 2 other knockered engines I've heard had. Straight away I knew it, the bottom end had gone. Resigning the engine to scrap I just got on it and kept going as far as I could. It broke down a further 2 times, then got so bad I could fell the knocking through the handlebars and footpegs. It eventually gave up completely a mile from my house. Another biker stopped in his car and towed me the rest.

The noise from the engine is now truly horrendous, it is catastrophically damaged, and will barely even turn over, but when it does catch the clattering noises are just awful. It's safe to say it's complete and utter scrap.

I cannot understand why this has happenend, unless the oil i used was no good, but i don't se why not. both oil pumps were replaced early this year at a cost of £300 for genuine yamaha items. It's always been a really quiet engine, but for some reason never felt quite as fit as it did last year.

I'm now in the dilemma of having 2 TRX's, both with scrap engines, and I know you just can't find engines anywhere as I've looked before, and the only one I found and bought turned out to have a knackered bottom end too!! I have just changed jobs to a place 34 miles away. Doable in a car, but there's a lot of slow moving traffic to overtake if you dare, no dual carriageway (well, there s another route but that's just too busy to use) and my car is a 3.2 so only does 20mpg. In other words, £60 a week to run, not an option.

So, I'll probably be breaking both bikes now, as I simply cannot be arsed anymore. Looks like I'll just have to go buy a brand new bike on 0%, sod it. I'm meant to be going away for the weekend now, so I'll contemplate my options over a few beers and decide what to do when i get back. right now, I just want to get a big hammer and smash it to pieces.

ok.. This is gonna sound CRAZY, but ive seen it done.. hang with me here.

When you say the bottom end died, do you mean the main bearing journals ? if so.. ITS FIXABLE... its crazy and you REALLY have to have faith,, but its possible.

Send the crank to a re-grinder, get them to cut it back ~2mm (80thou) undersize, you should have nice, clean new metal..

Go to some machine / general fab shop and get them to machine up some rings.. That are a touch oversize of what your original crank SHOULD be, and the inside diameter size for size (maybe 0.05mm smaller than your new ground crank). Drill 4 holes evenly spaced aronud it.. fairly big.

Cut the ring into 2 pieces.. so each piece has 2 holes equally spaced.. Take the lot to a welder.. get them welded in place, fill up the holes and weld the seams so its all one piece... Send crank back to regrinders and grind the lot back to original size.

Many ppl think this is a CRAZY idea, but it does actually work on old hard to get items.. Think 1900`s diesel farm stuff thats on show.. but you cant buy new parts for it anymore. This is one method that is used to replace parts.

Im not saying its perfect, nor is it stronger.. its honestly a touch smaller.. BUT the grinder can compensate by putting a radius on the side of the lobes.. it actually strengthens it..

ALso, where your conrod connects to the crank, you can off-set grind the lobe... in effect stroking it.. do the same process of making a new pad / filling it up.. you can get more CC aswell without having to bore / new piston kit it..

Yes it all costs money to replace / do this.. But im confident in my welding and machining skills so i would do the whole lot and it would only cost me time.. For someone without machines you are at the mercy of who you are paying.. Ask around there will be someone crazy enough to do this for you.

goodluck and if you pull the motor appart, please take pics and post online.. Id like to see the exact places it fails.. Would be some good info for rebuilding an engine.. IE: under / overcutting oil ways etc...

I've already got the crank and rods out of the other engine being done at the moment. It's been away for 2 months now.

Unfortunatley it's much much worse than that. You have to hear it to believe it, it's cringeworthy. I can't even be bothered to strip it down, what's the point, it's scrap.

I may put the other engine in when it eventally comes back (if it ever does) . I dunno, I'm just fuming at the moment and I deperately need another bike or another job.

Just been offered the loan of a GS500 to keep me on the road for the time being. It's an option anyway.

and that TRX looked so good aswell...

Lets hope something good comes out of this.. Doesnt the TDM900 crank fit straight in or is it different ?

I only say this because the heads are same, which means the lobe spacing must be identical, and the stroke is also the same.. so shouldnt that be an option ?

I've had that other bike for nearly a year now, and I've looked on ebay every week for engines. I think i've seen about 2. and the TDM engines on there are silly money, it's just not worth it.

Phat,

You sound might pissed off, and I can understand why!

Phuk72 was selling a bottom end to a motor I believe: look in stuff for sale... just a thought.... doesn't get you a running TRX immediately for your commute tho.

Dave.

Commiserations Phat - it's a really sh!tty feeling I know...

I think Quant's on the right lines, if it's the crank you can have it welded and re-ground by a competent engine machine shop (Do Alpha at Dudley still do it?) but the worry is what else might be causing the noise you mentioned... Without stripping it down to see what's f*cked - the first thing to go on the crank is the RH crankpin journal (I think) but if the mains have gone too then the crank might have oscillated enough to knock off the balance shaft as well.

Thankfully these lumps aren't too difficult to work on, it might not be so bad after all. Could you not chase up the guys with your other crank and ask them to get their fingers out??

Best of luck

Greg

i'd already bought that whole engine off phuk, the crank needed a regrind in that one too! I've kept the barrels and head off it.

the machine shop are being pestered as we speak.

just dropped the oil, it stinks, it's black, thin, and the oil filter housing is full of bearing shrapnel.

i've worked out the problem. the oil i've been topping the bike up with isn't new....i've got my containers mixed up, and i've pured in the oil i used to flush out the other motor......which is basically like thinners. stupid, foolish, idiotic mistake, but it's my own fault. and the daft thing is, i thought it smelled funny when i topped it up last week, but used it anyway....i feel like a right chump now.

2 tdm lumps on ebay. an 850 for about 680, and a 900 for 900!! too much for me.

looks like i'll just borrow the gs, rip the lump out and strip it. I've had a few in bits now so i'm not scared of pulling them apart. will post up progress in here when we see what damage has been done. i don't hold out any hope for any of it really after seeing the state of the oil and knowing what i've done.

Greg wrote:Commiserations Phat - it's a really sh!tty feeling I know...

I think Quant's on the right lines, if it's the crank you can have it welded and re-ground by a competent engine machine shop (Do Alpha at Dudley still do it?) but the worry is what else might be causing the noise you mentioned... Without stripping it down to see what's f*cked - the first thing to go on the crank is the RH crankpin journal (I think) but if the mains have gone too then the crank might have oscillated enough to knock off the balance shaft as well.

Thankfully these lumps aren't too difficult to work on, it might not be so bad after all. Could you not chase up the guys with your other crank and ask them to get their fingers out??

Best of luck

Greg

having stripped 2 of these engines already i think it's safe to say that the main bearings are pretty tough, and it's the big ends that go as they are very soft. unfortunately they nearly always score the crank.

expensive rebuild coming up, or i may even sell it as a rolling chassis if anyone is interested?

Bad luck dude. Looks like you have had a heap of advice. Think about it for a while. The answer will come to you.
Sarg

So what oil do you use??
Dave

It was Motul 5100 4T Ester SAE10W40, bought from the Yamaha main dealers, and it wasn't cheap.

You said you had to top up the oil by quite a volume. ZDid the engine run short of oil presure?

sorry your bike is dead looked the dogs bollocks to

cheap engines for TDM do occasionally turn up on ebay, keep your eye on the forsale area on carpe-tdm.net
might also be worth posting in the wanted section

hope you get it sorted mate