Yamaha TRX850 Enthusiasts Forum

Watcha folks,

Been a while since i looked in here only to find the site had moved!! Life got in the way...

Anyways, time for a major overhaul only to find the head is fubared, inlet valves all buggered beyond recovery
and exh valves well theyre ok but the seats are shot

Question is will a TDM head straight plonk on the trixy?

TIA

Hi Steve!

Sorry to hear about your problems - and to have to tell you that basically a TDM cylinder head may fit but does miss a mounting hole for the TRX frame. So better get a TRX head.

BTW: Checking the valves is recommended every 24.000 km - and not every 42.000 km as printed here and there ...

Checked greetings from Munich!

Cheers Holertogni,

Was an idea, seeing as theres a tdm engine on ebay as well as a head, the engine had done 25,000 miles and the head only 15,000 where as mine done 55,000miles and the finish is looking tired so thought well if it fits i could have swapped the naff bits from the tdm with trx's good bits.

Would have checked it all out sooner, wanted to do it 3years ago! but as usual could get the downpipes off (well that and time/space/money etc), theyre off now but busted the collars in the process

Also doing new fork seals and a full Factory Pro kit for the carbs so should run sweet when it's all done oh and very likely a cam chain too while i'm that far into the engine!

Steve,

I've checked my TDM850 against my TRX and both have the 10x1.25mm tapped mounting lugs at the rear left and right of the cylinder head. I was under the impression that it was only the TDM900 head that was minus one of the mounting lugs.

My TDM is an early Mk1 (91-96 360/180 degree engine) that has been extensively modified. I would be very surprised if the later Mk2 TDM 850 (270 degree engine) isn't the same head casting. Obviously the cams will need swapping (for TDM 270 degree items or TRX items) if the early TDM head is to be used on a TRX bottom end.

Hope this helps.

Mark.

Thanks Mark, interesting,

my cams are ok fortunately, only considered the 1999 tdm lump as it was in much better nick than mine and didnt they improve on the valves/seats slightly? with supposedly only shot big ends and for 250, could part out the rest for tdm owners...the head was 160.
hopefully I could just swap my barrels, head and pistons for tdm's

I've fitted a complete TRX engine in a TDM and there were no problems with the head mount.

Hi!

On my first TRX a "mechanic" adjusted the valves and tightened the cam screws to much - so the crank shaft died.
Then he bought a (cheap) TDM cylinder head, swapped the cam shafts and assembled the engine again - only to notice only then that this mentioned mounting hole was missing.
So I saw this with my own eyes.

Maybe only the 3VD cylinder head was without this mounting hole and the later TDM models cylinder head were the same as the TRX one?

@sanddune51

sanddune51 wrote:My TDM is an early Mk1 (91-96 360/180 degree engine) that has been extensively modified

Hmmm "extensively modified" ... maybe with a TRX or later model TDM cylinder head?

@dandywarhol:
TRX engine in a TDM is ok but
TDM engine in TRX will disclose the missing mounting hole (at least if it's a 3VD).

Witnessed greetings from Munich!

Thanks for all the input folks, decided to take the safer route and just get the head which should be on it's way
the factory pro kit got as far as the uk in 4 days, probably take another week to travel 150miles

Hmm, well this is going well so far

Factory pro kit got snaffled by customs and the head i got from pro motorcycle salvage
according to the folks i took it too for a clean up ( yeah bein lazy, theyve got the tools etc! is my excuse)
tell me it also needs a new set of inlet valves so i'm currently a bit narked.

On the plus side i do have a good set of downpipes, fork seals and gasket set oh yeah and a tub of oil with a k&n filter
and a £550 quid hole in my bank . . . . .

AArrrgghhhh!

Rant over now

Factory Pro kit snaffled by customs, you mean they tugged it for inspection then lost it?
And a SET of inlet valves how can they tell, have they stripped the head bare?

Wish customs had lost the carby kit but they just added the good old value added to the tune of nearly 40 quid.

Not sure if the local folk stripped the head or not but know when I took it in they just rotated the cams the valves popped out and must admit they were rather black all round, wondering if even though it was a 15000mile head it'd had a hard life and wasnt adjusted up proper?

Black all round might just indicate a very rich mixture when the motor was last run. The valves need checking for their tolerances, soot cleans off no problem, unless the valves are worn or distorted in some way or their faces badly burnt they should still be serviceable.

Maybe they found tight clearances and are playing safe - what build year is the motor?

@ dandywarhol
mines a 96/97 the head was meant to be from a 99, gotta admit they looked more than just sooty, fair bit of crusty stuff around the back of the valve and on the seats too . . .

Am going in to see them after work today so get the full run down then but one bit i recall him saying about both heads was the valve seats were "umbrella" shaped ? ?
english would have been better but i'm guessing he was referring to the shape of the seats?

Now this is making some sense it terms of the early engines with valve clearances "closing up" Not valve "stretch" which I've never believed anyway but the valve seats "pocketing" which is how you could describe "umbrella"