Yamaha TRX850 Enthusiasts Forum

How do.

Well looks like I was sold a dog as just checked the engine number and it's stamped 4TX.

Can someone who know more than me please confirm that this is a TDM lump.

I wondered why it was so gutless.

Cheers, Adam

Hi Adam

4TX is tdm850 from 1997 onwards.. exactly the same engine & 270 degree crank as the TRX.

Seems you’ve bought a built up Trx.. nothing too wrong as long as it’s done right.

Cheers
Adrien

Hi Cloot!

4TX is a TDM-engine - and according to the information that I have, not identical to a TRX-engine.

Differences are in HP and torque.

4TX: 59 kW/80 HP
4UN: 61 kW/83 HP

4TX: 80 Nm
4UN: 87 Nm

No big differences but not identical.

I suppose the differences result from different camshafts (lobe) or carburettors (jets).

Found out greets from Munich!

If it's gutless it's not because of the 4TX engine itself. Without a side by side comparison you wouldn't notice a difference. Something is amiss that shouldn't be. 96-98 TDM and TRX 4UN have identical carburettor setup btw.

Read your other thread, someone didn't know or wasn't honest. But you are not missing out on anything. 'Specially not with the engine replaced and the speed limit removed.

Cheers for the info chaps

Shame I'm missing out on sooooo much torque, just have to rag it more and lower the gearing a tad as in top it won't go near the red line.

Thanks again, Adam

Hi Cloot!

Forgot one thing:

A 4TX-engine can't be just mounted in a 4UN-frame - the fixing eyelet, which is cast onto the 4UN-cylinder head*, is missing on the 4TX-cylinder head.
(* where the crash bung is fitted on the frame)
This means: Your 4TX-engine must have a 4UN-cylinder head.
If not, you really have a severe problem ...

Whether using the 4UN-cylinder head on a 4TX-engine makes any difference in power and torque, I can't say.
Comparing the part nunbers of the camshafts for both engines should bring some light on this matter.

Remembering greets from Munich!

PS:
As jpe70 already said: There must be other reasons for the "gutless" impression of this engine.
Maybe checking compression can help finding out?

You may find the difference is power output is all to do with ignition timing..
So look at the number on the TCI under the riders seat and find out from there if it’s still the original 4NX ( Japanese ) or 4UN . If it’s 4UN you should be able to contact a Yamaha spare parts and quote the number to find out if it’s from a trx or tdm.
Tdm will have a lower 1st gear ratio too so no real drama their and won’t have to use as much clutch off the start... it’s about the only time 1st is used with so much torque on tap from the trx/tdm/xtz motors...

That's the later TDM900 engine....

HolerTogni wrote:Hi Cloot!

Forgot one thing:

A 4TX-engine can't be just mounted in a 4UN-frame - the fixing eyelet, which is cast onto the 4UN-cylinder head*, is missing on the 4TX-cylinder head.
(* where the crash bung is fitted on the frame)
This means: Your 4TX-engine must have a 4UN-cylinder head.
If not, you really have a severe problem ...

Whether using the 4UN-cylinder head on a 4TX-engine makes any difference in power and torque, I can't say.
Comparing the part nunbers of the camshafts for both engines should bring some light on this matter.

Remembering greets from Munich!

PS:
As jpe70 already said: There must be other reasons for the "gutless" impression of this engine.
Maybe checking compression can help finding out?

Afternoon all.

Maybe I'm just expecting too much from the engine as have just come down from a 955 Triumph and that had some motor.

Just the rest of it was HUGE!!!

Got 130 out of her on a private track so not too shabby

Thanks again for all your help

Do a compression test may give you a clue if it’s just to much expectation or not enough compression... lol.. the trx is more about corner speed , braking and agility as anyone can go fast in a straight line.
The std trx should get you to 180kph and will peak at 200. Speedo is only accurate once you fit a 70 series tyre on the front otherwise it reads 6kph/100k faster than what it’s doing

cobbadiggabuddyblooo wrote:Do a compression test may give you a clue if it’s just to much expectation or not enough compression... lol.. the trx is more about corner speed , braking and agility as anyone can go fast in a straight line.
The std trx should get you to 180kph and will peak at 200. Speedo is only accurate once you fit a 70 series tyre on the front otherwise it reads 6kph/100k faster than what it’s doing

200kph? Is that all?

My speed was in mph so should be happy

Cloot wrote:200kph? Is that all?
...

Hmmm ... what did you expect from 83 HP?!?

Braking the sonic wall may well be reserved to other mopeds.

With the TRX you have fun in the twisties, with the oomph from (quite) low revs and create your own wall of sound!

BTW, even on the race track my TRiXies never see the red line - I usually switch to the next gear at 7500 rpm at the latest.

"Hoping that you find a riding style fitting to the TRX"-greets from Munich!

Ditto on that... Std motor peak hp is around 7500 / 8000rpm and the gear ratios allow you to change at peak hp and sits you nicely close to peak torque once again. The trx neutral handling is its forte and sort the Front suspension with emulators/ spring to weight to suit your riding style and rebuild the rear shock and spring to your weight , you’ll give any rider on a 955 triumph a run for his money through the twisty roads.