Yamaha TRX850 Enthusiasts Forum

does anyone know if stainless valves are about for the trx? slightly bigger or 3 angled or both?

kookimonsta wrote:does anyone know if stainless valves are about for the trx? slightly bigger or 3 angled or both?

Only thing i´ve seen is titanium valves for XTZ750....cost a fortune used!

any ideas where these are avaliable from? sounds interesting, were they a direct replacement or bigger?

tom

What about bits for the xtz850 desert monster, If you could get anything that is?

Dave E

kookimonsta wrote:any ideas where these are avaliable from? sounds interesting, were they a direct replacement or bigger?

tom

Don´t know if bigger....would last longer anyhow!
Saw them on ebay over a year ago....

its normaly the valve seats that get the three angle or five or radius

cheesie wrote:its normaly the valve seats that get the three angle or five or radius

thankyou i didnt know that! i assume its to get the best contact "seal" between the valve and head.

i thought the valve was machined rather then the seat.

cheers tom

once valves are machined to the size you want, (angles, back cut, stem collar etc) they are "lapped" into the seat. You do this manually, it gets the best seal.

As for buying new valves, you can buy new stainless ones, they are a touch oversize. If you have access to a lathe, you can cut em down and put on the correct valve angles. If you go to most any specialist "head porter" they can do it all for you.. Replace your seats, make new valves and lap them all in, new retaining collars and springs. It is inherently expensive tho.

$2000 AUD is not unheard of for a 4cyl head (thats with a minor port clean, not a full port job, a "full" job can cost you $5000 depending how far you want to go.. it takes time to find the "best" flow for a head).
If its a common head, such as a V6 buick engine, they quite often have "exchange" programs.. $1000 exchange for a pair of heads (well here in some places in australia anyway). Since the TRX is a bit exotic, dont expect that ! Standard valves are actually very good quality imo.. I cleaned a set up on a wire buff (brass type, so it didnt damage anything) and they came up great, and the stock flow isnt that bad at all. Could use a back angle tho to help stop surge, but otherwise quite well designed.

Quan-Time wrote: Standard valves are actually very good quality imo.. I cleaned a set up on a wire buff (brass type, so it didnt damage anything) and they came up great, and the stock flow isnt that bad at all. Could use a back angle tho to help stop surge, but otherwise quite well designed.

Except the '95/'96 inlets elongate stems... result: excessive oil consumption, impossible to shim for clearance, loss of compression, difficult starting, slanderous rumours of valve seat recession.

Cure... post '97 inlets.. different part number. These are well designed and cure all of the above. Made my TRX like new again

DFH

Killerwhale wrote:

kookimonsta wrote:any ideas where these are avaliable from? sounds interesting, were they a direct replacement or bigger?

tom

Don´t know if bigger....would last longer anyhow!
Saw them on ebay over a year ago....

Not so sure about that... But as they're lighter, one can rev higher (as long as the crank and con-rods etc are up to it...)

how far is safe to rev it to as mine now pulls 9000 rpm without any show of reduction in power

cheesie wrote:how far is safe to rev it to as mine now pulls 9000 rpm without any show of reduction in power

Well, 9500 is the limiter so rev on!! ....or do the CDI mod and get 10k....

wasnt really saying bigger valves would last longer or rev higher, just get the gasses in and out faster, something ive always been told about tuning 4 strokes theres no point putting a big bore and bigger carbs etc if you can't get the gasses in and out faster. trx might be fully capable at the mo my thoughts really being that it started off as a 750 back in the day.

cheesie wrote:how far is safe to rev it to as mine now pulls 9000 rpm without any show of reduction in power

no worries with the low revving TRX engine. If You've had Your bike on a dyno, You'd probably change gears a lot earlier though, unless you have really really hot cams. That's the main reason for titanium valves,reducing the mass of the valves so they still follow the cam profile when the speeds increase. But of course more high revving causes more wear ultimately, but to what extent is hard to say. I know some bikes that have touched the rev limiter a touch to often, and I am not interested in buying them...

kookimonsta wrote:wasnt really saying bigger valves would last longer or rev higher, just get the gasses in and out faster, something ive always been told about tuning 4 strokes theres no point putting a big bore and bigger carbs etc if you can't get the gasses in and out faster. trx might be fully capable at the mo my thoughts really being that it started off as a 750 back in the day.

my thoughts exactly, but 'my' tuner had a look at the valves today, and figured the total inlet area looks to be sufficient. He'd do some calcualtions and thinking, I'll let You know the outcome. I don't know if TRX engines have the same valve sizes as the XTZ though, that would definitely be interesting to know.