Yamaha TRX850 Enthusiasts Forum

Being new to the TRX forum I have found many excellent threads to guide me during my engine rebuild.

Therefore I am hopeful that some of my observations will be of use to those considering the same modficiations.

My machine is an old P reg bike that has proved to be as much fun as any other bike I have owned. After 4 track days last year (Snetterton 300 twice, Mallory, Brands Indy) it is now being removed from the road for track use only. Needing more grunt to propel me down the straights as R6's/750's pass me on both sides, I have opted for the JE big bore kit supplied by TTS. Boring was also done by TTS.

I was going to strip the bottom end to shot peen the rods but it sounds as though the rods are man enough for the job and so I have left them alone.

With ring gaps set to 0.35mm I did a dummy assembly using old gaskets to check the squish using solder. This came out at 1.25-1.35mm just beyond the value recommended by TTS (1.2mm) so no barrel skim required.

JE kit is 10.5:1 CR and I will now skim 0.25mm from the head to take this closer to 11.5:1. I was going to use a burette to measure the actual CR but other members have run at 12:1 for many miles and no problems are reported. Hence a nominal ratio I think will be OK.

Standard Yamaha head gasket needed opening out by about 0.2mm on diameter. This is not so easy as the gasket is laminated. In the end I made a conical sanding block using a piece of 92mm OD nylon pipe and then stuck P80 emery to the outer conical face using double sided tape. This proved to be an excellent tool and has maintained circular holes with no burring. I did try initially on the old gasket clamping between two plates with a 91mm hole machined in them. This was no good for the new gasket which has a raised section in the profile that compresses when used.

Valves reground and a new (Yamaha) cam chain (old one stretched by 0.6 of a link over its full length; motor at about 40k miles and yes I did have trouble timing the cams when I stripped motor for reshim a few years ago) will see top end back on with stock cams. Considered YAM9 Kent cams regrind (£220) but thought cash better spent on big bore headers hopefully available through forum in Feb/Mar? I am using motad venom s'steel oval cans with no dB killers.

Was going to try Predator of Welwyn Garden City for hand made headers and will advise if they are able to do a decent job for sensible money. Made some s/steel link pipes for Yoshi RS3's on my VTR SP1 for £90.

Had to hacksaw headers off in the end which were jammed and going no where. Process was a bit brutal but necessary.

Emulsion tubes worn as expected and so new ones on order. VW T2 oil pressure switch also being added for reassurance after the cash I've spent, HEL supplying the double banjo and radial master cylinder kit (see info through forum search).

Just gotta resist spending £800 on FCR41's now. Managed to slip all costs below the radar so far but my wife may well spot that amount.

Apologies for long winded first post and hope this is of help to someone. I'll let you know how it goes when run in.

Phil

Phil,

First off, welcome aboard

No need to apologise for a long-winded post, this is the sort of stuff us TRX-geeks drool over, thanks!

Sounds like a pretty comprehensive rebuild. All tried-and-tested stuff but thats often the best way.

FCR's will boost your bhp tremendously and are the best £/bhp gain you can get. I'd start saving if I were you

Any plans for any chassis or suspension mods, or you happy with the standard set-up?

Any pics available?

Cheers,

Dave.

Hi Dave

As you say, mostly tried and tested mods which should give more power with continuing reliability.

I've got a feeling that FCR's will eventually be used for the 10bhp+ that other forum members report.

Saying that though, I had so much fun on the track with what is mostly a stock bike that I am tempted to keep it looking pretty much original. Chassis mods are limited to front blue spots + goodrich hoses, a replacement (old stock) but genuine Yamaha rear shock, Michelin Pilot Powers and not much else. fairing has been trashed due to a low side and the bike now has SRX600 clocks (temp gauge replaces SRX tacho and I use the TRX rev counter and no speedo), Diversion 600 chrome headlight and front master cylinder. It looks more retro than street fightered and uses original handlebars.

On the track the handling is so forgiving that you can really utilise the (somewhat limited) power and the brakes are great, running rings round far superior modern machinery (in the novice group to date). No fear of power slides makes for rapid exits from the turns and I am able to consistently frustrate my brother on his naked 2003 Z1000.

I will try Brembo SC front pads and may stretch to Grimeca front discs to go with these and a 520 17/40 chain and sprocket kit.

If power really becomes an issue I could simply take my VTR on the track but the thought of dropping it means it remains as my expensive ornament.

I've got a feeling the TRX will not disappoint this year and I recommend a track day outing to anyone who may be thinking that doing so on an old 1997 twin would be embarrassing.

I have not yet managed to include photos in my posts; any guidance as to how I do this would be welcome because it appears that file size is an issue. I will then add pics of work to date.

Phil

you can use these tools:
windows xp power tool photo resizer.
windows 7 photo resizer clone.
to shrink your pix.
or post them on sites such as photobucket and add links.
cheers
fung

For pics, use an online host like photobucket and then paste in the img code.

To be honest, you are wasting your money with performance mods until you get some free flowing pipes.

And FCRs rock

Also, re gearing, I'd suggest 17/42 or even 16/40.

JE pistons ain´t 10,5...standard are. JE is 11,5:1

And here are an answer i got from the source itself when providing them with the serial number on pistons:

"Hi Mattias,
Now we're talking! You'll want to set piston to cylinder wall clearance at .0030 or .08mm and your top ring gap should be about .015-.016 or .406mm. Good luck!



Tjader (Tj) Harris
Sales and Tech Support
JE Pistons Powersports Division
Direct (714)898-9763 ext.280
Fax (714)379-8213
"

Yep, the TRX is a good track bike, on the right track with not too many straights!
Done all the major UK tracks on mine, with my favourite and the ones most suiting the TRX being Mallory, Cadwell and Rockingham.
Disagree on the no-powerslide though, after highsiding coming out of Edwinas at Mallory two years ago and trashing the bike, knocking myself out and breaking two fingers and a thumb!!

I can hold my own in most groups at most tracks on a TRX (albeit a modified one) and there is no reason at all why it can't run in any group. I tend to prefer Inters but will happily run fast group at certain tracks

OK it will get swamped down the straights but should corner as fast as (if not faster) than any IL4