Yamaha TRX850 Enthusiasts Forum

Well after collecting bits and pieces over the past few years it's time to put all these things together and upgrade the TRX.
I've given the raceglass a new look and resprayed the tank from red to black which should be complete tomorrow.
Next week the suspension will be upgraded with R1 forks and billet trees to get the same offset as the std TRX and will be dropped to bring the shorter R1 front end back to the same height also.
Forks will be rebuilt and resprung, gold valves all revalved to suit the TRX and my weight and same to the Ohlins rear shock.
And then out comes the motor and time for a rebuild there too.
Bottom end rebuild and tossing up (budjet) on just having the std rods shotpeened or Carrillo rods fitted. JE 878 pistons and 1mm oversize valves with the head ported and flowed with Kent cams, 41mm FCR's and Akrapovic 2 into 1.and to finish it off a Sigma slipper clutch and lithium battery ..
Hopefully all will be finished just in time for my licence handed back to me on in 17 days...
The YZF750 rear end can sit in the garage a little longer , I'll see how the Std swinger goes and I wear out the tyres fitted on the track and road rims and toy around with the modded YZF bellypan..

Coolio, just about to fettle me new forks meself, ones got a leak and I want to anodize them a nicer gold. Don't know whether to do it meself or send them to Kias.

What's that tail piece ?

Have an idea it may be a Honda 250 tail end

Sounds like fun with all that new gear. Not sure bout that belly pan though. Try Geelong carbon craft on the coast. Bit Exxy it is but great quality. Bet you can't wait to jump on the bike and blast along that redcliffe bridge!

Can't wait for a day at Lakeside all I need to source are some raised clip ons . I just hope When on full lock and don't foul the fairing subframe .. The belly pan is still an experiment at present and may be able to be used as a mould to build off.. Something to tinker with over the next few months

Dammit, I want another Rex now

I'll be happy if I can get close to 100 hp to the rear wheel so I can blast out of those corners a little faster. At 87 hp now and they get me on the straight so I need to make up a little more time between the corners where I'm relying on braking to reel them in..

cobbadiggabuddyblooo wrote:



Well after collecting bits and pieces over the past few years it's time to put all these things together and upgrade the TRX.
I've given the raceglass a new look and resprayed the tank from red to black which should be complete tomorrow.
Next week the suspension will be upgraded with R1 forks and billet trees to get the same offset as the std TRX and will be dropped to bring the shorter R1 front end back to the same height also.
Forks will be rebuilt and resprung, gold valves all revalved to suit the TRX and my weight and same to the Ohlins rear shock.
And then out comes the motor and time for a rebuild there too.
Bottom end rebuild and tossing up (budjet) on just having the std rods shotpeened or Carrillo rods fitted. JE 878 pistons and 1mm oversize valves with the head ported and flowed with Kent cams, 41mm FCR's and Akrapovic 2 into 1.and to finish it off a Sigma slipper clutch and lithium battery ..
Hopefully all will be finished just in time for my licence handed back to me on in 17 days...
The YZF750 rear end can sit in the garage a little longer , I'll see how the Std swinger goes and I wear out the tyres fitted on the track and road rims and toy around with the modded YZF bellypan..

Had the same dilemma with my rods recently. My thought was to shot peen them (cheap and quick) but ended up doing nothing at the advice of the guy who did my crank regrind. He knows TRX motors pretty well and told me they very rarely throw rods (same comment from PHUK elsewhere on the forum I recall).

Couldn't justify high cost of Carillo rods.

Was also told that polishing after shot peening is a definite no-no because all of the benefits of the induced surface compressive stress from peening is lost (or at best no longer uniform).

Mine now revs cleanly to 9k in every gear (17/42 - 148mph in top approximately) having planned never to exceed the red line but I can't help myself. The stock motor did not benefit from over revving but 878, FCR and Akra makes quite a different motor. Now I wonder whether I should have had them peened!!

Got a price today $750 for Carrillo Rods so its a big bite into the budget..

cobbadiggabuddyblooo wrote:Got a price today $750 for Carrillo Rods so its a big bite into the budget..

A lot of $ to spend with no real gain in HP. Get the rods crack tested and then shot peened, money well spent on peace of mind

cobbadiggabuddyblooo wrote:Got a price today $750 for Carrillo Rods so its a big bite into the budget..

Cobba

Did you make a decision on Carrillo rods or peening in the end?

What's the schedule for your engine build? Will it be done this year?

I'll dyno mine when I've swapped the head and upped the compression a bit and see how close I am to the 100rwhp. Have not gone for big valves or cams though.

Rods where shot.. As in no good so I found out when all pulled apart. The motor had been rebuilt sometime in the first few yrs(pre 50,000km) when I bought it 8yrs ago.
I've just bought new std rods but with the extra weight of the JE pistons I had decided to balance it all up again and knife edge the crank while at it.
The guy who has the head at present doin the work on the valves has made me aware the yamaha cranks are pretty good as I found with mine in excellent condition.
The thing he made me aware of is the caps on rods may stretch a little at that point from over revving or if you miss a gear. He also told me that it's always best to try to keep within the middle of your tollerences on the bearing shells so stick with the numbering/colour code as sometimes when you start the bike after a resting it a few minutes some yamahas he has works on suffer moreso than the trx is is sounds a little tight on turning it over with the starter. This is from the alloy case cooling faster and shrinking more than the heavier steel crank which holds it heat a little longer.
Once the head is back and pistons rebalanced I'll take the piston, head ,valves n springs off to get ceramic coated.
I've been questioning the different design on the STD TRX pistons and rings compared to the JE ones and found the answers there too.
The std trx pistons dont have a full skirt like the JE pistons . The stock piston also has curved rings and all this was factored in for the piston rock so as it reaches top of its stroke and about to pull down the piston rocks a little and the curved ring allows for this and the skirt design stops piston wear while this happens.
But with the square rings on the JE piston this rock is actually taken up in the ring groove on the piston rocking up and down in the groove and allowing to keep the square edge of the ring flat against the bore so the skirt doesnt become an issue. I've also learnt that the seal against the piston and the top ring is actually improved here also because of this.
I have looked into coils and programmable timing units too so I'm going down the route of less friction, less heat ,less wear and all those little things just adding up to the useable gains .
I'll be using a set up with a couple of bungs drilled/ welded on the pipes so when running we have O2 sensors in there and a meter mounted on the tripple trees. A cam set up to record the meter/taco/ throttle as I'm off for a ride and get the carb's running to their optimum.. So I would say by xmas I hope to be up n running. Suspension sorted and 320mm brake disc set up.
I'll stick with the std swingarm and 170 rear tyre for now and get a feel on things.
So thats where I'm at and what I'm up to.


AS FOR THE PISTONS ,THESE PHOTOS WILL GIVE YOU BIT OF AN IDEA OF THE DIFFERENCE. ALSO NOTE THE OIL HOLES UNDER THE YAMAHA PISTONS TO AID IN COOLING AND LUBRICATION OF THE PIN. THESE ARE FED BY THE HOLES IN THE PISTON WHERE THE OIL RINGS SIT IN THE GROOVE. ON THE JE PISTON THERE IS AN OIL HOLE THAT FEEDS THE SEMICIRCULAR GROOVE ON TOP SECTION OF WHERE THE GUDEON PIN SITS. THERE IS ANOTHER SEMICIRCULAR GROOVE OFFSET AT THE BOTTOM TO RELEASE THE OIL AFTER LUBRICATING THE PIN ALSO FED BY THE OIL RINGS.