noise in valve body of 99 b12

[chevsuz12]

Hi, my 99 B12 with 31,000 miles has a knocking sound coming from the right side valve body.  I noticed it when I repacked my exhaust.  It may have been there for quite some time; but I only heard it once the exhaust was silenced.

It definately is not a ticking sound, as would be expected from loose valves.  It only occurs when the motor is under load from about 5500RPM and higher.  If holding steady throttle in that rpm range the noise is not noticeable.  But when on the gas hard you definately hear it.  

Last weekend I adjusted the valves, as I do about every other year.  The intake of #3 and #4 cylinders were just slightly loose, just .oo1 out of spec.  Everything else seemed fine.  I didn't see any evidence of anything rubbing,  to the naked eye the cams look fine, as does the cam chain.  The chain did seem a little loose, but I am not sure what the tension should be like.  It had about 1/4" of play when measured between cams.  

After the adjustment the knock is still there.  The only mods I have are Holeshot stage 2 w/ pods 5°adv. D&D can and holeshot midpipe.  The engine is completely stock.  

Otherwise the bike runs perfectly.  Even when it is knocking, there is no noticeable loss in power.


Thanks.

[Red01]

Could it be a case of detonation? Is your gas old? If so, try fresh gas, if not, try the next octane grade up.

[ZenMan]

If you adjusted the valves and there was no change in the knock, and fresh gas doesn't do the trick, also check your ignition timng. Pull all your spark plugs and see if one is different than the rest. If all that is ok than you might have deeper problems.

The fact that it's only coming from the one side would make me suspicious of a problem in a cylinder. A broken piston skirt will knock under load and acceleration, and sometimes a loose wrist pin will, though it usually knocks during deceleration too.  A bad connecting rod bearing usually knocks during deceleration as you rev it sittng there, uness it's really spun, then it would rattle pretty good all the time.

If it's a broken ring than you'd probably have a little smoke and some loss of power. A compression test should determine if that's the problem.

If you don't have a stethescope, use a long socket extension or screwdriver against your ear-bone and touch it on the cylinder block and crankcase in different places while somebody blips the throttle. Cracking open the throttle quickly might bring out the knock for a second or two. Try to pinpoint where the sound is coming from more accurately. A mechanical knock can travel through the motor and make it hard to tell where it's coming from just with your naked ear.

With 31,000 miles you are just getting into the "wear zone" where it could be anything, especialy if you hammer it a lot. Good luck and keep us posted...

[Red01]

Well, Zen, the way the timing works on a standard production motorcycle inline 4 these days, timing is very unlikely to be an issue, and most every engine made it's nearly impossible to have only one cylinder to spark at a different degree of TDC advance or retard than the others.

The way today's electronic ignition I4's work is there's a crank trigger & pickup arrangement that sends a signal to the ignition computer. The computer then fires cyl 1 & 3's coil the first time the trigger passes the pickup, then 2 & 4's coil the next time and continues alternating this way. Yes, the spark plugs will spark every time the piston reaches the timing point near TDC, regardless of whether it's a compression or exhaust stroke. (Advance curves are handled by the computer.) Thus, the plate the pickup is mounted to is usually in a fixed and non-adjustable position unless someone has modified it after it left the factory (ie; poor-man's timing advancer mod).

[CWO4GUNNER]

Hearing a noise like that once in another air cooled engine I once owned with allot of miles, instead of just adjusting the valves I pulled the cams and rockers and re-torqued the head and to my surprise I had some lose head bolts which were causing valve adjustment problems (kept changing). After the re-torque I readjusted the valve clearance which was way off after the re-torque and synchronized the carbs which were also off. Just out of personal habit I added my usual 1 once of STP per quart and I never heard the slight knock again for 2 more years until my oil pump failed and one of my pistons dissolved due to the rod bearing that failed.
If you have never done so it might be a good idea to check/re-torque the head and also re-synchronize the carbs as one cylinder could be placing large loads on another if it is out of sync.

[chevsuz12]

All excellent comments...Thanks!

I have never synch'd the carbs.  As it runs just fine.  I figured why fix what ain't broke.  I did pull the plugs and cleaned them.  They were all evenly colored and a little black (BUt not bad).  I cleaned, regapped and put them back in.  

I do have the poor mans ignition mod.  I cnc'd the holes in it to give exactly 5° advance and no more.  So even if it did move it will only retard down to the stock setting.

[ZenMan]

Well, Zen, the way the timing works on a standard production motorcycle inline 4 these days, timing is very unlikely to be an issue, and most every engine made it's nearly impossible to have only one cylinder to spark at a different degree of TDC advance or retard than the others.

Red, I appreciate the input, but I'm well aware of how modern digital and electronic ignitions work... I'm sure your explanation will be helpful to those that don't, however.

My suggestion to check ignition timing is just part of the normal process of elimination, and certainly doesn't hurt anything. You yourself suggested "Could it be a case of detonation?" If it is the fuel, how could only one cylinder be affected? Yet suggesting fresh fuel is a good idea.

We haven't heard this motor run personally, so we can't be sure that it's only one cylinder that's knocking. Pinging under load is commonly caused by bad gas or advanced ignition timing. So without being there, it's common sense to suggest checking the timing, thus eliminating the possibility that it's the cause of the noise.

Now that we find that the timing has been advanced 5 degrees from stock, perhaps simply setting it back to stock and running it wouldn't be a bad idea... if the knock disappeared it sure would save a lot of trouble tearing into the engine.

Just trying to help Chevsuz12 out here, I didn't mean to cause any issues with you by making a few suggestions.  

[Bob Holland]

Check the exhaust header bolts, a loose header will make a noise that can sound like a knock.

[Bezzer]

seconded, almost guaranteed as it started after the exhaust was removed, a loose header causes a ticking sound.

[ZenMan]

Yep, definitely a good idea to check those header bolts/studs/nuts first... good call.  

[chevsuz12]

The exhaust header has never been touched.  Just the midpipe and can have.  But I will check the torque this weekend.  

Also this does not sound like a "TICK"  it is definately a "KNOCK KNOCK KNOCK" sound.

It has been cold here and I will be out of town next week.  I will try to work on it some this weekend.

Thanks again guys!