Yamaha TRX850 Enthusiasts Forum

Hi all, I have a spare head and cams, which I want to send off for porting reprofiling, however I am now wondering if it is a TDM head, it looks identical to my TRX head. The mounting lugs are the same, how do you tell the difference, is there a difference? The cams probably don't matter as they will be reground by Kent cams.

TRX has a mounting point off the head and I have an idea the tdm's differ in that respect..

I have 3 or 4 Trx and Tdm cylinder heads, and I can tell you that Tdm 850 heads are identical to the Trx heads.

When I was looking around for cylinder head to port and modify to accept big valves, I paid a lot to get hold of a Trx head as I had read a lot on the internet (here in all likelyhood) that Tdm 850 ones differed..... Another internet propagated falsehood. They are the same, only the camshafts differ on the early 360 degree Tdm 850 engine (3vd). They can be quite happily mixed and matched as long as the correct camshafts are fitted for the particular crankshaft (ie.360 degree or 270 degree)

I hope this clears up any confusion once and for all. (...... ....again )



Mark.

Cheers can now happily send head off for porting!

One more question TRX / TDM 270 cams thecam lobe will be roughly 90o apart from one cylinder to the next?

onya Mark.. you ever stop learning

SDN wrote:One more question TRX / TDM 270 cams thecam lobe will be roughly 90o apart from one cylinder to the next?

Quick sum, what does 270 + 90 equal?

I do know that thank you Chris, however was just having a bit of a panic, that I was about to spend a couple of hundred pounds modding cams that were no good to me! I hate wasting money, also as the cams rotate at half engine speed 1 whole rotation for ignition and exhaust strokes would 90o be for a 180 deg crank! at thats not considering overlap etc no wonder I was confused. I eventually resorted to checking pictures of TRX cams of Ebay

sanddune51 wrote:I have 3 or 4 Trx and Tdm cylinder heads, and I can tell you that Tdm 850 heads are identical to the Trx heads.

When I was looking around for cylinder head to port and modify to accept big valves, I paid a lot to get hold of a Trx head as I had read a lot on the internet (here in all likelyhood) that Tdm 850 ones differed..... Another internet propagated falsehood. They are the same, only the camshafts differ on the early 360 degree Tdm 850 engine (3vd). They can be quite happily mixed and matched as long as the correct camshafts are fitted for the particular crankshaft (ie.360 degree or 270 degree)

I hope this clears up any confusion once and for all. (...... ....again )



Mark.

I've been preaching that mantra for yonks Mark - good to see someone else getting it right The difference of less than a couple of horsepower is in the less restrictive pipes and different jetting in the TRX IMO