Yamaha TRX850 Enthusiasts Forum

Just tried firing up my recent rebuilt 878 before Snetterton this coming Thursday.

Observed two things that may be of help to others.

Started readily even when cold but refused to idle and lots of back firing when held on the throttle before dieing.

Much cursing, plugs out, check for inlet leaks, vacuum tap and pump OK. About to strip carbs but before doing so lifted FCR overflow from catch tank. Ran perfectly.

The cause was the end of the overflow being immersed in the small amount of fluid in the catch tank. Must have been stopping fuel flow to the motor (pulling a vacuum in the float bowl???

Relieved its a runner with 4 days to go.

Second thing was potentially dangerous.

Drive output shaft oil seal was changed when I stripped the motor.

Noticed oil below bike after short run time and traced this to the output shaft seal.

Again cursed as not an easy fix with the motor in one piece. Thought of burning it, selling the FCR's and getting a KTM.

Then noticed on close inspection that the inner seal lip had flipped when the seal was put on the shaft and was facing outwards. Care with a small screw driver pushed this lip to face inwards towards the cases and now oil tight.

If I had not noticed this before Thursday, leaking oil would have ended up all over my 180 rear Diablo and I may have ended up on my arse. Maybe comes from rebuilding over 3 weeks and not enough asttention to detail.

Pleased I am ready to go and will be checking the seal regularly during the day so that I do not worry about it as I scream round Corams at 100mph.

Will let you know how the day goes.

Blimey what a kerfuffle. Fingers crossed mate.

Yup. Bit fed up of working on the thing and not riding it.

Need to think carefully about the oil seal lip.

Have an old one outside and so will check lip direction. Probably worth buying a new one on Monday just incase I have to swap it on the day.

Will google lip seals and try to gather info.

Crap.

Looks as though outer visible lip is a dust seal and the functional lip is further inboard.

Suggests I may have a problem.

Will see if I can pull the steel sleeve out and check lip condition.

Why are things rarely straight forward?

Hope you get it sorted before your trackday at Snett tomorrow.

I'm still messing about with mine too,before a trackday at Brands. Simultaneously trying to fit FCR's,a homemade quick action throttle and do the throttle position sensor bypass mod and its now nearly 5:15pm

Mark.

sanddune51 wrote:Hope you get it sorted before your trackday at Snett tomorrow.

I'm still messing about with mine too,before a trackday at Brands. Simultaneously trying to fit FCR's,a homemade quick action throttle and do the throttle position sensor bypass mod and its now nearly 5:15pm

Mark.

Are you at Brands this week then?

I'm loading up tnt for Snetterton. Motors running well now breather not obstructed. May drop to 150 mains on the day as it seems rich on 160's.

Just got to keep a careful eye on the gearbox oil seal.

Hope you miss (or missed?) the rain.

Looking hopeful for me but will be out enjoying the wets if not.

Still got your gearbox bits etc boxed up waiting for when we next meet up.

Trackday tomorrow at Brands. Road bikes only day in conjuction with Bike magazine. The plan is to ride it there, thrash it all day and then ride back home. Copious supplies of top up oil after every session

Hope your seal hangs in there for you at Snett.

Mark.

Ps. Thanks for holding on to the bits for me. Well meet up for sure this summer.

So is this with your rebuilt motor and OEM oversize pistons and larger valves? Still haven't heard any feedback from anyone who's completed 1mm larger valves rebuild...

cobbadiggabuddyblooo wrote:So is this with your rebuilt motor and OEM oversize pistons and larger valves? Still haven't heard any feedback from anyone who's completed 1mm larger valves rebuild...

Cobba

It's not me with the big valves.

Mine blew its crank in April and today was my first track outing with full engine rebuild (FCR41's, JE878 and Akra, stock head and cams).

Pleased it was reliable and fast, much time being spent trying to pass litre missiles that are slow in the turns without being black flagged and sent home for being dangerous.

A good day.

Cobba,to be honest I've been that busy lately I just wasn't able to find the time to strip the motor to build it with all the good bits that are ready to go on. Have gotten pretty involved with my Sons old FZR600 (3HE). Six broken exhaust studs when removing the rotten std downpipes and collector meant a head off job to carry out the repair. As we had gone that far,we dropped the valves out for a look and found the worst finished ports I've ever seen Of course I couldn't leave them like that so did a full port cleanup job. Worth noting was that I got away with re using the original head gasket and and exhaust gaskets. Used stainless headers fom ebay and the job was a goodun

With my Trx I took the easy way out and just did the less intrusive work to see me right for the trackday today.I hope to be able to find time to get the big valve head fitted in the next few weeks and will of course report back with the outcome including any problems encountered along the way

The trackday today went like a dream. The bike pulled strong and hard all day and completed just over 100 miles on track and another 100 to and from the circuit. I'm well chuffed to say the least.

Mark.

Ps. Glad your day went well too Phil, all that work was worth it after a day like today.