Valve train advice

[andy230]

Hello all,

Yamaha seals fit better than pattern parts   

If anyone can still continue with possibly the worlds most pedantic community project, could you have a read please?

www.team-thumper.blogspot.com

Whats the collective opinion on my thoughts of taking just a smidgin off the bottom of the collets very carefully to give just a bit more clearance at full lift?

Are they case hardened?  They are not all exactly the same size incidently...

The motor ran well with this cam, (presumably) standard Yam seals, and the  same modified guides.  Go with it??  Boyd's down in just over a week and time and tide and all that.

ta...

a   

[guest146]

Andy

If your valve collets are so close to the guide or seal that you need to remove some your pushing your luck. If you over rev it and the valves bounce thats bad enough but if a collet strikes the valve guide while the rest of the valve and spring are still on the way down it will fire them out and you have a very expensive rebuild. I would try to remove from the guide if anything.. Andy do you guides have a stop or are they just pressed in? Why not press them through a couple of mm or remove  the same.

Ken

[Steve Lake]

OK...might be a silly suggestion....but.....probably b4 you were born Andy.....and i think i mentioned this at snetterton.....i raced an imp engined (coventry climax) outfit....and....like you, the only way we could afford to compete was to do all the work ourselves, and i ended up tuning the motor....now......i saw problems on the horizon once the cam and valves had been changed...similar to the ones you are experiencing.....so....i chucked the seals in the bin!.....it's a racing engine ffs!
who needs silly little things like valve stem seals??......the ones on the imp engine, similar to the ones on my old Cooper S, would go as hard as walnut shells (and about as much use) in 500 miles (or less at the sort of temperatures they got up to when the engine was tuned)....I still have my 'Tuning the Mini engine' by Clive Trickey.....and i'm sure he suggested doing the same thing....ask you guru at the bike shop

And you should know...that some of the imp engines i tuned.....lasted a WHOLE meeting :-)

pip pip

[andy230]

Hi Ken,

Andy

If your valve collets are so close to the guide or seal that you need to remove some your pushing your luck. If you over rev it and the valves bounce thats bad enough but if a collet strikes the valve guide while the rest of the valve and spring are still on the way down it will fire them out and you have a very expensive rebuild.

Granted, thats my fear, but its run hard and well for many moons with this cam and guides etc, suggesting to me that either my measurements are out, or else I may be worrying about nothing.  I am known for that...!  Its a slipstream head, done for this cam, I've spoken to martin Sweet about it, and the guides have been already shorthened to suit.

Andy do you guides have a stop or are they just pressed in? Why not press them through a couple of mm or remove  the same.

Nope, looks like they have a stop.  But I hear what you're saying, it would be a catastrophic disaster!

(thanks for the vac pump btw, did i email you to say received?? think so...)

who needs silly little things like valve stem seals??

True steve, I know what you're saying but the consideration is not just performance.  The scrutineers will pull a smoking bike off, for fear (perhaps not unreasonably... ) that its just about to blow.  And I'll bet you that these "modern" jap engines will smoke like buggery without stem seals !  Quite a lot of oil around that top end, and wouldn't it really pour down the guide??

I think I'll get on the blower to Martin Sweet....

 Anyone run a modern single without stem seals?

a

[Steve Lake]

I bet you a tenner it won't 

[Steve Lake]

Seriously (not for one minute suggesting that a tenner isn't seriously serious!) if oil is going to 'pour down the guides' it means either you forgot to fit the valves, or they are such a pi55 poor fit that you'd better stop building the lump right now and check all your other tolerances!.Now....on the inlet side I grant you that the tendency is for oil to migrate DOWN the guide due to the partial vacuum in the inlet tract between the carb and combustion chamber....it will be infinitisimal...and in the worst case evident when the throttle is opened after a period of overrun (into and out of a corner say) by a puff of blue smoke, barely visible. On the exhaust side the tendancy is for exhaust gas under pressure, to force its way UP the guide.....and result in drying out the valve stem in the guide and, in the worst case stuck valves and a big bang! ........but the wear (and thus the valve stem to guide clearance) has to be very bad, and by the time you get to that position the engine will be knackered in other areas anyway.....i'd be interested in what Martin says about it.....especially as he built the head

[guest146]

Andy

I was thinking what if you did not fit the seals. I bet if your guides and valves are a good fit it wont smoke a lot, and the extra lubrication wont hurt. Just out of intrest how high does this rev. Do the valves bounce or has it a rev limiter or is it when changing down it over revs.

Ken

[andy230]

Andy

I was thinking what if you did not fit the seals. I bet if your guides and valves are a good fit it wont smoke a lot, and the extra lubrication wont hurt. Just out of intrest how high does this rev. Do the valves bounce or has it a rev limiter or is it when changing down it over revs.

Ken

Ken,

Ok, I'm coming round to the idea...  Anyone else care to coment?  At worst I only take the head off again and put the seals in...   Will speak to martin and post.

Will try to stick to 8?  Maybe 8 and a half at a push?  But I think it should be ok with that (red line a 7.5 on standard engine.  The valves shouldn't bounce with the uprated springs, but there is no real definate "red line" as such, as a non-standard engine.

One ignition system I have has a programmable limiter, the simpler one i fancy doesn't (I dont think).  Down changes will just have to cautious!

[guest27]

My 2p worth.

Stem seals to me are there for road use where there is a definite need to restrict the hydrocarbons in the exhaust gas.  The fit between the valve and the guide is supposed to be really close but sliding (good engineering terms) to a point where if you can feel a wobble in the valve at 'full lift" either the valves, the guides or both are knackered.  I would be surprised if there was any real migration of oil down the guides - over and above the normal amount for lubrication.

It may be that slightly more oil running down there - we are talking minor amounts mind, will make the valve/seal interface better and thus be better for cooling.

John Robinson does not see fit to mention them.

A quick look through the net via google gave no real answers, but the E-Type peeps suggest fitting them to cut oil consumption - but not on the exhaust as this hinders cooling and probably not if you have a hot cam as they get in the way.

Throw the buggers out.

Apparently you can get guides modified with an internal groove to hold an O-ring if too much oil gets past, but this sounds like a desperate measure...

R

[Steve Lake]

and another thing!!.......less friction! :-)  = more power at the back wheel

[andy230]

Hi,

Mr Sweet says running without stem seals is a no-go.  It will indeed smoke heavily, seals are necessary.

He reckons its probably not one of his heads...

2 options:

Use alternative seals (yamaha model 26H, possibly XJ900 or something?) with a lower profile. I will investigate.

Or (he's never done this) heat the head, lift the guide, remove the circlip and knock it thru 40 thout (1mm).

He said not to run with less than 40 thou (collet to seal clearance) to allow for over revving, valve float, missed gears etc.  40 thou is also as recommended by the RD paperwork.

Ok, on the fone to fowlers again then...!

a

[guest27]

Damn shows we all know bugger all...

R

[andy230]

Hee hee     I wouldn't say that!!

The seals are for an xvz1200.  I think!  thats the only yam stem seals starting 26H-xxxxx-xx-xx

But, none in UK!  so, they're on order....

I may yet try it...

cheers, further discussion welcome!

a

[Steve Lake]

ah well.......thats plan A out the window.....what's plan B then Doc?

[guest27]

M&S sponsored this one - Plan A because there is no plan B

R