GStwin.com GS500 Message Forum

what kind of bad things can happen to your bike if the valves are loose


Milhouse

Besides loss of power, you could have shims float out of their buckets and get ejected, damaging the bucket and cam. $$$$

It will clack like hell and be noisy. In extreme cases it will accelerate wear on the cams, and wear the shims (replaceable so who cares). But funny thing is the excess clearance will collect more oil and that in turn reduces the wear to an extent.
Cool.
Srinath.

Quote from: seshadri_srinathIt will clack like hell and be noisy. In extreme cases it will accelerate wear on the cams, and wear the shims (replaceable so who cares). But funny thing is the excess clearance will collect more oil and that in turn reduces the wear to an extent.
Cool.
Srinath.

Thanks James and Srinath for the 411.  Yeah it is very noisy and I don't like it.  Going to have to go back to the mechanic to have it readjusted.

House

I take it you mean the valve clarance is too large?

It depends how much too large, but large clearances will reduce the power the engine makes, and can cause anormal cam, valve face, and shim wear.

The cams are designed to pick up and release the valves on a certain part of the profile. The valve velocity and accleration in these areas are tailored to reduce wear on the valve faces and cams. If the clearance gets too large, the cam will be picking up and closing the valves on the wrong part of the profile. This alos makes the valve train noisier than it should be.

Power wise, the valves will not open as far as they should, and the duration of valve opening will be too short. Both these reduce the power output.

Quote from: KevinCI take it you mean the valve clarance is too large?

It depends how much too large, but large clearances will reduce the power the engine makes, and can cause anormal cam, valve face, and shim wear.

The cams are designed to pick up and release the valves on a certain part of the profile. The valve velocity and accleration in these areas are tailored to reduce wear on the valve faces and cams. If the clearance gets too large, the cam will be picking up and closing the valves on the wrong part of the profile. This alos makes the valve train noisier than it should be.

Power wise, the valves will not open as far as they should, and the duration of valve opening will be too short. Both these reduce the power output.

Thank you Kevin - you have much knowledge.  As do James and srinath.  Will get it taken care of.

House

OK I should have asked...How much loose...1 thou to 3 thousandths of an inch is what the range is...are we talking say 3-5 thousandths or 30-40 thou...30-40 thou will be much worse...Pretty much. 3-5 is not too bad. On a side note..I saw this guy who had a bunch of small holes drilled in his cam lobes all along its contact face. I also believe he did that with the rollers in the lifters on that motor. He said the holes have to be smooth and chamfered and deburred so they are very smooth and dont catch the lifter etc but they were for trapping and holding oil and he claimed that it reduced the wear quite a bit. Is that possible or was he farting.
Cool.
Srinath.

I think he's experimenting. Even pressure spread over a large surface will not wear as quickly as one with holes in it like a cheese grater. With the exception of brake discs, those holes are for reduced unsprung weight. The holes in the cams allow the oil to escape out from under the cam surface. Same thing with bearing surfaces, one little hole to let the oil in, under pressure, to keep the bearing surfaces from rubbin' together; but then what about when you start the motor in the morning, when there's little to no oil in the head? Answer: this is when oil viscosity and hydroplaning come into play, the cam bearing surface is hopefully not resting on the bottom of the bearing, but resting on oil that is thicker when it's cold, so that when it starts to rotate it builds up speed and begins hydroplaning until pressure builds up.

And regarding the valves, I thought the valves would begin to 'dish' when they're really loose. Not allowing compression pressure out, the pressure would 'push' the valve into the seat, distorting the valve and becoming even looser.

Possibly OffTopic:  When the valves aren't quite allowed to open properly, can't this cause the calves to 'burn'?"

Definitely OffTopic:  You don't want those valves to get too loose, I mean, what happens when they fall off, you don't want to pick up one of those in a D205 do ya?   :mrgreen:

This happens when the vavles are too loose or you flog too hard.  :cry:

(http://www.knology.net/~ARS/images/spitshim.jpg)

Ok, so were do you get replacement shims if you need them, would Bike Bandit have them?

QuoteWith the exception of brake discs, those holes are for reduced unsprung weight

those holes are to help disapate heat as there is more surface area exposed, not to mention helps scrape water from an otherwise flat surface, this aids in better braking during adverse weather conditions, the unsprung weight is a byproduct.

Quote from: JamesGThis happens when the vavles are too loose or you flog too hard.  :cry:

WTF?!  :?  Did the shim exit through that hole?

I noticed that the valvetrain of the GS is extremely noisy even when the clearances are ok.  Especially when hot and idling for some time (lower oilpressure?) the noise becomes louder.

Yeah, the shim floated off the bucket at about 12K rpm and the cam caught it and ejected it thru the front of the cam gallery.  :o

Now I was using a Megacycle high lift cam, which is a few mm longer than a stock cam, but this could concevably happen to a stock motor too.

Live, learn, and put shim UNDER buckets on your race bikes... :oops:

I hate doin' shim-under-bucket valve adjustments! Oops, dropped a shim, now how am I going to get that shim out of the engine cases... :lol:

go fishing with a magnet.

Quote from: SportbillyPossibly OffTopic:  When the valves aren't quite allowed to open properly, can't this cause the calves to 'burn'?"

Definitely OffTopic:  You don't want those valves to get too loose, I mean, what happens when they fall off, you don't want to pick up one of those in a D205 do ya?   :mrgreen:

Valves 'burn' when there's not enough clearance between shim and cam, not allowing the valve to seat properly or completely. One of the ways a valve dissapates heat is through the valve seat, when there's is not enough contact for a long enough time, it'll warp, the 'burn' comes from combution deposits on the contact side of the valve (the face) because it cannot close completely.

Quote from: scratchI think he's experimenting. Even pressure spread over a large surface will not wear as quickly as one with holes in it like a cheese grater. With the exception of brake discs, those holes are for reduced unsprung weight. The holes in the cams allow the oil to escape out from under the cam surface. Same thing with bearing surfaces, one little hole to let the oil in, under pressure, to keep the bearing surfaces from rubbin' together; but then what about when you start the motor in the morning, when there's little to no oil in the head? Answer: this is when oil viscosity and hydroplaning come into play, the cam bearing surface is hopefully not resting on the bottom of the bearing, but resting on oil that is thicker when it's cold, so that when it starts to rotate it builds up speed and begins hydroplaning until pressure builds up.

And regarding the valves, I thought the valves would begin to 'dish' when they're really loose. Not allowing compression pressure out, the pressure would 'push' the valve into the seat, distorting the valve and becoming even looser.

Actually pushing the valve into the seat will cause the clearance to go down not up. Yes it will dish with extremely high clearance cos the valve face retains more heat cos its holding in the hot high pressure mix longer and hence gets hotter...but the bike will run like its strangled  long before that happens.
Cool.
Srinath.

Quote from: scratchthe 'burn' comes from combution deposits on the contact side of the valve (the face) because it cannot close completely.

Aaaahhhh, thank you sir  :D

Quote from: seshadri_srinath
Actually pushing the valve into the seat will cause the clearance to go down not up. Yes it will dish with extremely high clearance cos the valve face retains more heat cos its holding in the hot high pressure mix longer and hence gets hotter...but the bike will run like its strangled  long before that happens.
Cool.
Srinath.

True, true. I stand corrected.

Quote from: Blueknyt

QuoteWith the exception of brake discs, those holes are for reduced unsprung weight

those holes are to help disapate heat as there is more surface area exposed, not to mention helps scrape water from an otherwise flat surface, this aids in better braking during adverse weather conditions, the unsprung weight is a byproduct.

Not only to scrape water from the discs but to release the gases that build up between the pad and the rotor which can cause the pad to "gasdroplane" across the face of the rotor after the pads have heated up and started to gas. Brake fade will be caused.

Wow, I've never heard of gasdroplaning, where did you read or hear that? What magazine? Can you give the month of the article?

Hey I gasdroplane many times a day....
Cool.
Srinath.