Yamaha TRX850 Enthusiasts Forum

Just a quick one one trx engine reliability.

I am searching for some history on this track bike we are bringing back to life, and have seen quite a few posts that question the reliability of the trx engine, saying they are prone to let go.

I have had no personal experience of one going, just wondered what other peoples thoughts are?

pretty damn reliable coxy, if the class permits though, one of Cobba's ignitions would be a good investment to hold the rev limits.

Only prone to letting go if sloppy with watching the oil level - left big end goes first

Over rev is the killer. The fellow who did my head work explained it to me about the TRX from years working for Yamaha as 1 of their race mechanics.
It stresses the rods and the cap on the bottom begins to stretch out of shape . This is only amplified with higher compression.
Bearing clearance and oil pressure go hand in hand.
Yamaha beefed up the oil pump on the TRX too as the earlier tdm's suffered problems with lack of oil pressure but it is still limited by the RPM.
Std trx torque and power curve will usually drop off from 6700 and 7500rpm respectively and mine for example drops off at 7500 and 8500 with the Nojima system. But with the Akra system it holds it's peak HP from 8500 to 9500rpm.
Even with the Carrillo rods I set the rev limit light to go Amber at the peak torque at 7500 and red from 8500rpm to limit stress. ( rev limiter at 9500rpm )
Weight is another killer , 48 gram heavier JE 878 pistons don't help in that respect on a std rod.
I've lost 85grams in reciprocating mass from Std on each piston /rod set up to take a little stress of things too.
Cams and cam timing will dictate your torque and HP curves .

the engine we have has got (allegedly)an 878cc overbore, (allegedly) kent cams, and (definitely) FCR41 carbs.

It should be a really good setup, just wondered if there is anything I can do to improve the reliability.

I will be definitely be purchasing an ignition module, as I want the added features of shift light and quickshifter on the bike, its a no brainer really.

Pull the pistons out weigh them and remove as much material as possible or just limit your revs.
You can pull the cam cover off and you should be able to see and measure where material has been removed from the base circle to give the extra lift against a std set of cams.