Yamaha TRX850 Enthusiasts Forum

Hi there. I've joined up here looking a few pieces of information. I'm not a TRX owner, I belong to the other side, yes, I'm a TDM owner I've noticed a few folks on here from the TDM forum but I was wandering if anyone can help me.

Recently I did what I thought was a routine valve clearence check and it turned out I had to change a few shims but thanks to my ignorance and in-experience with chain driven cams (gear driven V4's are so much easier to work with ) I've gone and put the bike together with the timing off so low and behold I've bent both exhaust valves on the right cylinder when sitting on the bike.

How similar are the engines and their components? I have the opportunity to buy a TRX head and I wanted to make sure the components from the TRX head are compatable with the TDM. Also, on the topic of similarities in of the engine, what makes the TRX put out more power than the TDM. Granted I've not dyno'd mine yet but I'm running a set of cans and s/s link pipes with standard steel headers, 165 mins and the e-clip on the 2nd groove from the top of the dyno needle (as recommended by Dyno-Jet themselves) and I've a K+N to fit once the valves are sorted. Are the carbs different or is it in the CDI? I've also read a few topics that say disconnection the TPS can unleash a few more ponies. I'm not looking triple bhp figure but definately a few more wouldn't go amiss

Thanks for your time, help and info.

The head is the same.

The difference in power is primarily attributable to the differing piston profiles. Other than that, the motors are fundametally the same (although the gearboxes are different). Also believe CDI is different.

The TPS mod on the TRX is worth between 1 & 2 (dyno proven) bhp through the range and also increases the rev limiter.

Hi viper_biker!

There are very well different heads - there is a TDM head which lacks a mounting hole for the TRX frame.

So this would cause no trouble using a TRX head in a TDM - but I don't know where the head is mounted in a TDM frame ...

The (manic) mechanic from an independent work shop fixed such a TDM head (with the lacking mounting hole) on my first TRiXie after he had caused engine trouble (crankshaft lost the teeth for the timing chain and all valves were bent) after adjusting the valves by most likely fixing the camshaft support screws too tight (only 10Nm are correct).
From there I know there are different heads.

But from memory this TDM head was built before 1996.

Hope this helps.

Greetings from Munich!

yes indeed, the head, crank, clutch, cams and timing chain are infact identical items..

The main difference is the 900cc.. I can actually tell you from experience that the main cylinder block is the same, its just the sleeves that differ (i have a spare motor and actually fitted 900cc pistons / sleeves in).

TDM is obviously injected (the 900 variety) so all teh pickups and things are actually different on the electrical side of things.

Hope that this helps you !

Good point well made

My comments are based on the 270 (post 96) TDM head

Don't know about the 180 head

The similarity between your engine and a TRX engine depends on what TDM you have. If it's a pre-96 you can't just bolt on a TRX head, intact with cams and valves.

If you have a 96-02 TDM850 on the other hand, you may just go ahead and change. The TRX engine after all is a -96 TDM engine (more or less).

This from an x-tdm-owner who apparently agree with what phuk & HolerT said

Thanks for the replies guys, it's been very helpful. My TDM is the 4TX II model (or '97 if you so wish ) so I gather from what you are saying, it's a direct replacement. SWEET!!! I really don't have a need to buy the head as it's only 2 exhaust valves that are bent but at £22 each per valve I think buying the 2nd hand head from the TRX and taking the best from both heads (plus de-coked piston heads) ie valves, springs etc plus a few extra shims won't go amiss either.

I'll keep you posted with the progress. I just need the guy with the TRX to get the head off and posted accross to me