cam sprockets spun out of place
Posted January 10, 2001 - 11:06 PM
I have low compression due to my bilitanium hydrolic clutch decompression (add on) lever pulling on the exauste valve enough to hit the intake slightly bending both.
and my exauste cam sprocket spun out of place by about a tooth and a half.
no wonder i could not get this thing up hills.
Was just wondering if any of you have had your cam sprockets spin on you.
Posted January 11, 2001 - 12:11 AM
Posted January 11, 2001 - 01:46 AM
I'll check that spinning thing during the next valve clearance check, though. I think that this kind of information is where these owners forums are at best. Official importers and dealers don't often announce about things like this, at least I've never heard. They propably rather have the bike for a repair after the damage is done and then give you a nice bill.
Posted January 11, 2001 - 02:32 AM
Ande: No, the compression release shaft puts downward pressure on the shim bucket only. It does not come in contact with the cam lobe or camshaft at all. It's postioned in such a way that it is beside the cam lobe. That bucket is pretty big in diameter...relatively speaking.
[This message has been edited by Boit (edited 01-11-2001).]
Posted January 11, 2001 - 03:31 AM
I believe that only serious mistiming affects could be transmitted to the cam, that is when the piston and the valve have a contact. I experienced that with FZR1000 (similar 5-valve head) resulting two bent valves, no other damage, rather tender touch, I think... Before I opened the head I just set the timing right. The engine did run but there was a considerable loss of power and it sounded as if it was running only on three cylinders. That taught me something about circumspection... One should never hurry while assembling engine!
Posted January 11, 2001 - 08:23 AM
I think I may actually UNDERSTAND what Boit is trying to say. Let me say it differently though (not that it will help, I flunked Physics. Twice.):
The cam, via the lobes, encounters resistance every revolution as it opens the valves. The steeper the ramp of the lobe the greater the acceleration of resistance. So if we hold one valve slightly open it misses the initial ramp up of resistance. By the time the lobe contacts the valve bucket it is at a much steeper angle, producing a much more abrupt force for the cam and gear to deal with.
I think what Boit is saying is that this abrupt resistance on the second exhaust valve (i.e. it offers zero resistance then suddenly applies a lot of resistance when the steep angle of the lobe finally whacks it) finally caused the cam gear to rotate out of position on the cam (WHACK-WHACK-WHACK-WHACK, 5k times/minute). It makes sense to me that the two are related (compression release stuck and cam gear slipped).
But the main reason to periodically check for play in your comp release lever is that the valve buckets, like lifters in my Chevy, rotate to distribute the wear and friction. If the comp. release is contacting the bucket at all it will not rotate and wear unevenly and fail prematurely. This happened to someone here when they got a small rock wedged in their lever and it even damaged the head a little in addition to ruining the cam and bucket.
But what do I know?
Posted January 11, 2001 - 04:58 PM
A lady I dated a few years ago kept driving her V6 Mustang at 60mph on the interstate long after the hot light came on. She drove it til it seized. I asked her why she didn't stop when the warning light first came on. She replied, "Well....it was still going..." Women's logic! God, help me!
Posted January 13, 2001 - 04:01 AM
Posted January 14, 2001 - 03:06 AM
Because it has been some two or three months since I checked the clearances, I don't quite remember the exact composition of cam and the sproket. I've been wondering that should one have a cam bearing failure, changing that ball bearing wouldn't propably be easy. In that sense bolts would have been better choice. They would also prevent the possible spinning.
Posted January 14, 2001 - 06:02 AM
rich wouldn't have been able to ride the bike without it stalling if the decomp was always open.
secondly, the cams first contact with the bucket would still be at the most acute of angles.
thirdly, we can sort all this tosh out when they go to refit rich's cams. they will have to re-time the wheel. are we all agreed? then we'll find out.
knowing most workshop mech's the shop will just order a new cam inc. the wheel costing rich a packet. all because they can't do the valve timing themselves.
rich, your problem is somewhere else.
if your workshop want the valve timing figures i will send them to you.
if you want to fit a falicon timing wheel & do it you can get my figures & have a power boost. i know you won't take the second option because when in doubt you will go back to standard. i can't blame you.
rich, couldn't you hear a loud 'ticking noise' while all this was happening?
didn't your bike stall on left handers?
sorry lads but i think you're wrong.
something to dt with the snarled up valves, probably. how did that happen?
get that & you've got your answer.
[This message has been edited by Taffy (edited 01-14-2001).]
Posted January 14, 2001 - 06:02 PM
Let me add that one of the RPM limiting factors of a 4-stroke is "valve float". This is when the valve springs can't close the valves fast enough to follow the cam profile. The rev limiter will protect this from happening as long as the valve springs haven't weakened beyond design. In a high performance 4-stroke such as the YZF, it's imperative that the engine is maintained in a high state of tune. With an engine that's capable of 11,200 RPM's(rev limited), any mistiming is magnified exponentially. I'm not saying that because the decompression lever was too tight and slightly held open one exhaust valve, that this was the definitive cause of the cam sprocket spinning. I'm simply suggesting it as a possibility if the engine was operated over time with this occuring. If may have been as simple as the sprocket fit wasn't tight enough to begin with. Quality control isn't 100% on anything. Maybe the engine assembler had a hangover and didn't feel like rejecting what he/she knew to be a loose fitting sprocket. Nobody can say for certain.
[This message has been edited by Boit (edited 01-14-2001).]