congatulations to whoever created this new site...
on the old yahoo site i wittered on about disappearing valve collets - i wondered if they were weraring excessively due to the 8900 rev limit of the bb chip.
well, i've made a proper job of wrecking things this time: i've dropped an inlet valve and smashed it, the other valves, the piston and bent the rod - i daren't check the crank yet. this was after a healthy 30 mile blast at or near the rev-limiter with a shameful exhaust and the bb chip on stage 3. the valve collets were fine before i went, so, in the space of 30 miles the collets on the upper left hand inlet valve have gone from being there, to not being there. the other inlet valve collets are going the same route also. the first time that it happened, i put it down to crummy collets from the production line. but after rebuilding it and now suffering a much more calamitious version of the same problem, i wonder if the problem is the increased rev limit? any wisdom out there would be much appreciated, thanks
chris
bb power-dropped valve - half an engine left
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bigblackfalco
- Posts: 1922
- Joined: Wed Feb 18, 2004 10:05 am
- Location: Darkest Aberdeenshire
Chris,I've recently done some work on one of my heads(LHS).It was drinking oil and running rough.When i took it to bits I found one bent inlet valve and four worn valve guides!The collets looked worn so I replaced them all.
The problem with the collets is a recurring one.Firstly they are not really heavy enough;there should be more than one shoulder.I remember in the past that there were numerous cases of dropped valves when I worked at Courier Systems who run a 100 strong fleet of 850R's.The collets were found to be too soft!
I am running a standard chip/K&N/Arrow system so can't help with your BB chip/high revs theory.But it stands to reason,the faster you rev it the more chance of valve bounce and impending disaster.
My bike is high mileage so this type of thing is half expected on an air cooled bike.I also think my cylinder heads were off another bike as `I bought it as damaged repaiarble and it had numerous bits missing etc!
At high mileages the cam chain question comes into play too if the tensioner can not keep up with the slack.
If you go for a rebuild,I think BB or someone do special valve/springs/rocker assemblies for this purpose.
Be interested to learn about the con rod/crankshaft/big end shells etc.
Best of luck.
Bailey.
The problem with the collets is a recurring one.Firstly they are not really heavy enough;there should be more than one shoulder.I remember in the past that there were numerous cases of dropped valves when I worked at Courier Systems who run a 100 strong fleet of 850R's.The collets were found to be too soft!
I am running a standard chip/K&N/Arrow system so can't help with your BB chip/high revs theory.But it stands to reason,the faster you rev it the more chance of valve bounce and impending disaster.
My bike is high mileage so this type of thing is half expected on an air cooled bike.I also think my cylinder heads were off another bike as `I bought it as damaged repaiarble and it had numerous bits missing etc!
At high mileages the cam chain question comes into play too if the tensioner can not keep up with the slack.
If you go for a rebuild,I think BB or someone do special valve/springs/rocker assemblies for this purpose.
Be interested to learn about the con rod/crankshaft/big end shells etc.
Best of luck.
Bailey.
do the collets just give-up or do they pull through the upper spring cup? on Vincent's it's a problem that they pull-through the duraluminium upper valve cup, only answer then is to fit titanium cups or thicker cups which solves the problem for high revs upto 8k ish on racing vincents
Classic Motorcycle Magazine, Young Motorcyclist of the Year 2003
falcoperson;
boy am i relieved to know that someone else knows about this problem - i thought my bike was spooked or something. when i go on about the collets disappearing, i mean just that - they get progressively smaller and this allows the valve stem to work its way down throught the tapered hole in the top spring seat - like you say, it's just as if the collets are too soft, they thin out with wear. now that i keep a close eye on them (obviously not close enough) it seems that it's the inlet valves that really suffer - and the upper ones particularly so. my bike is a 98, and i've only ever fixed it with second hand parts, presumably of a similar age, so hopefully they now make the collets harder - cos i'm putting new ones in this time!
boy am i relieved to know that someone else knows about this problem - i thought my bike was spooked or something. when i go on about the collets disappearing, i mean just that - they get progressively smaller and this allows the valve stem to work its way down throught the tapered hole in the top spring seat - like you say, it's just as if the collets are too soft, they thin out with wear. now that i keep a close eye on them (obviously not close enough) it seems that it's the inlet valves that really suffer - and the upper ones particularly so. my bike is a 98, and i've only ever fixed it with second hand parts, presumably of a similar age, so hopefully they now make the collets harder - cos i'm putting new ones in this time!
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bigblackfalco
- Posts: 1922
- Joined: Wed Feb 18, 2004 10:05 am
- Location: Darkest Aberdeenshire
All the collets suffer because(as I said) they are inadequate for the job they are doing.They should be about twice the size.
It wouldn't help putting secondhand items in during maintenance.The collets are so cheap and so vunerable that if you ever do anything on the heads they must be renewed.
The bent inlet valve could just be a coincidence.
I wasn't really that surprised with the mileage my bike has done.
I quite often find I'm bouncing off the rev limiter which probably doesn't help!
Bailey.
It wouldn't help putting secondhand items in during maintenance.The collets are so cheap and so vunerable that if you ever do anything on the heads they must be renewed.
The bent inlet valve could just be a coincidence.
I wasn't really that surprised with the mileage my bike has done.
I quite often find I'm bouncing off the rev limiter which probably doesn't help!
Bailey.
I would hazard a guess at higher lift on the inlet with regards the exhaust, typical thinking is that you need more lift on the inlet to help that extra bit in, while the exhaust gets rid of alot of the gases in the first part of opening.... or something like that.....gus wrote:BB power have all the gubbins,hardened valves,lightweight cups etc.What sort of mileage you got on your bike?Funny how its the inlet and top colletts which suffer most,could this be a possible oil starvation situation?Your thoughts please Mr bailey.
gus
Classic Motorcycle Magazine, Young Motorcyclist of the Year 2003
Sounds bad! From a completely numpty point of view with absolutely no idea as to what I'm talking about, could the problem be the valve springs not being up to those sort of revs and starting to bounce leading to the collets rattling and wearing - I can't see how they would 'wear' as they don't (shouldn't) move at all should they. I can see that the say (numpty calculation again) 12% more revs means an equivalent increase in acceleration of the valve when it's twatted by the cam might cause it to push through the cap - I dunno - just thinking aloud.
Hope you get it sorted anyway - you sound like a good source of knowledge!
Jason
Hope you get it sorted anyway - you sound like a good source of knowledge!
Jason
