Valve adjustment

[Atabeach]

Gentleman, I own two K75 bikes. A 1990 and 94. Both have a strange rattle / slight stutter at or about 1,100- 1,800 rpm range. The rattle ends abruptly at 1,800 RPMS. Period. I  am thinking valves need adjustment. I can’t think of anything else. Thoughts? Also…any advice on adjusting valves would be appreciated

[Laitch]

A rattle differs from a stutter. A rattle is a noise; stutters consist of rapid, temporary gaps in engine performance. Bricks need revs—plenty of fuel in the take-off plus shifting and riding at higher revs. The engine will rattle at low revs.

Checking the valve clearances and balancing the throttle bodies always should be done if you don't know when they were done last, but this sounds like throttle input and shifting adjustments might correct this.

[Atabeach]

I’ll check the throttle bodies first and keep the fellas posted. Thanks!

[stokester]

Agree with Laitch, I checked the valve clearances in both my bricks after I purchased them to have a starting point.

If you do check the throttle bodies be sure to adjust them properly.  Check on this site for the proper way.

As far as adjusting the valves.  After the initial check and adjustment, frequently that is all that is needed but as I think FrankenDuck posted, if it takes longer to warm up that is a sign that another check is needed as I have found out.

If you need shims, do the math and figure out the proper thickness and check with your local Yamaha/Kawasaki dealer to see if they will swap them with you.  Mine did.

[The Mighty Gryphon]

The rattle between idle and 1800rpm is caused by slop in the dog that drives the balance shaft.  It seems to affect some engines and not others.  Probably because of a sloppy manufacturing tolerance.

There is essentially nothing you can do about it short of tearing down the engine and modifying the dog.  Fortunately, it won't harm your engine as far as I could tell.  The bike I had with that rattle was still running like a bear when I sold it at 100,000 miles.

Below is a photo of the dog and balance shaft from my bike.  What seems to happen is that the power pulses cause rotational speed changes in the output shaft that will cause the dog to move back and forth in the slot in the balance shaft making the clank noise your hear.  As engine speed increases, the power pulses come so quickly that the output shaft speed stabilizes and the dog's motion in the slot stops.


DSCN1759.JPG (44.66 kB . 768x576 - viewed 174 times)

[The Mighty Gryphon]

The bikes I owned with the Jetronic control had a a very slight stumble when snapping the throttle open.  After a lot of searching for the cause I decided that the cause was probably a lag in the response of the airflow meter's heavy "barn door" flapper. 

When the throttle is opened quickly there is a sudden rush of air from the plenum, but this air flow is not yet being sensed by the flapper because of inertia so there is no additional fuel being injected so for an instant the mixture goes lean.  When the throttle is rolled on, it is easier for the flapper to keep up with the airflow at the throttle bodies and the mixture stays in the correct range for proper ignition.

The Motronic engine controls on the 4 valve brick engines deleted the flapper in favor of sensing the butterfly position in the throttle body and as a result that slight stumble when the throttle is snapped open doesn't happen.

[Chaos]

checking the valves is dirt simple, adjusting them is simple compared to some bikes.  Tight valves should be addressed pronto, good way to burn one. 

[stokester]

The rattle between idle and 1800rpm is caused by slop in the dog that drives the balance shaft.  It seems to affect some engines and not others.  Probably because of a sloppy manufacturing tolerance.

Agree.
My 1993 is fairly quiet even at low RPMs while the 1994 sounds like there are ball bearings in the crankcase when cold.

[daveson]

There are a number of different problems that could cause a rattle, so any one particular problem would be unlikely to be the cause. Did this noise slowly get louder, or suddenly after a service, or something else?

A faulty alternator could cause a rattle, or an incompatible one, or worn alternator monkey nuts. If the noise goes away after the alternator is temporarily removed, one of those might be the problem. Could be something else, like an unbalanced clutch.

Another possibility is something related to the output shaft. Is the noise absent in neutral at those revs with the clutch pulled in, or when riding with the rattle, does the noise disappear with the clutch pulled in slightly? If pulled in slightly, it would still be under load, unlike if it were pulled in fully.

[Martin]

I had a problem with slow maneuvering as in being snatchy also with rapid throttle movements it had a slight hesitation. Both problems were eliminated by interconnecting the vacuum ports on the throttle bodies. See this post https://www.k100-forum.com/t15212-vacuum-modification#177755 This modification seems to benefit K75's more than K100's. We did a couple of bricks and ran tests.
Regards Martin.

[Kaos]

Coincidence has it that I have encountered an old man on an old k75 police model this weekend.
His k had nearly 500k (kilometers) on the clock and gave me a tour around his bike.
It was modded to run on gas (not gasoline) and then back to gasoline because of some expensive gastank laws.
He told me about the valves, weird rpm spikes and a rattle that came with the throttle body because the springs tended to give out after i dont remember how many kilometers. He eventually ended up mounting a counter spring to ensure good closure -and some extra rubber on his grip for the extra tension needed to open the throttle -
Anyway. Not from my own experience, but a wonderful story that might have some merrit.
Found it worth to share.

[daveson]

I'm not sure about this, but from the small sample I'm aware of, the problem seems more likely to be from the auxiliary shaft when the noise suddenly disappears at about 2,000 rpm, and more likely from the output shaft with the noise suddenly disappearing at about 4,000 rpm. Why does the noise suddenly disappear at 2,000 rpm you ask? Don't ask, but it reminds me about using spinning tops as kids, and their gyroscope affects.

Here is an output shaft noise thread, where the problem was actually at the auxiliary shaft, where the alternator was putting too much pressure on the shaft:

https://www.k100-forum.com/t15754p100-output-shaft-questions#198845

The problem was fixed by shimming the alternator out a bit.

Here is a thread, about a K75 with a noise that suddenly disappeared at 2,000 rpm. The problem was fixed, it was a loose alternator drive dog bolt which caused some other parts to get flogged out a bit:

https://www.motobrick.com/index.php?topic=13382.msg120397#msg120397

[daveson]

Some of the other examples, which were solved, that I thought might not be as relevant.

Hollister, k100-forum:
(K1100?) Clatter at 2000 rpm in first and second gear. When purchased, the oil level was overfull. Problem solved after an oil change and maintenance.

Rhodes rash, Motobrick:
A K75 with a rattle between 3500 to 3700 during gradual acceleration. The noise was gone with the alternator temporarily removed. The alternator bearing and the monkey nuts were replaced but the noise remained. Torquing the clutch nut solved the problem.

Tim Tyler, Motobrick:
K75. Started a thread about a knock at 3700 rpm. Pallum (K75) posted the same symptoms and that a loose spark plug wire was the problem. Chaos (K75) posted a similar problem and solution. Tim replaced the plugs and leads which solved the problem. K75 spark plug leads are supposed to have an air gap!

Kyle10, Motobrick:
K100. Replacing the backlash spring and output shaft dampers solved the problem.

MLR, K100-forum:
K75. Clatter at 3500 to 3700 when slightly uphill or  with slight acceleration. The noise was gone with the alternator temporarily removed. Lots of alternator and auxiliary shaft parts were replaced, but the noise remained. Went into the output shaft, found a worn shim and a worn bearing. Replaced those and other parts, which solved the problem. I'm thinking the worn bearing would result in output shaft end float, causing the noise. The clatter at those revs when going slightly uphill has been mentioned on a number of threads. I'll guess we could chalk that up to a symptom of output shaft endfloat.

Jetpoweredmonkey, Motobrick:
K100. A rattle from 4000 to 4800 rpm. Changing the alternator monkey nuts did not solve the problem. During a maintenance routine the output shaft thrust washer was found to be broken. I think it's pretty clear that output shaft end float was the problem here. The thrust washer was replaced and the noise was eliminated.

Beemer Wheeler, K100-forum:
K100. A rattle from 3700 to 4500 rpm. It was found to be coming from the exhaust heat shield. Placing cork spacers between the fixing points fixed the problem. Others chimed in on the thread and solved it by removing the heat shield.

[Laitch]

Did you enroll in a computer search course, daveson? You're on fire!    

[daveson]

A few days ago my son showed me how to add a link to a post. I said wow that was easy. So it's copy and paste, who'd of thunk.

I googled Motobrick 3700 and Motobrick 1800, came up with a lot of matches.

Posting a photo only takes me a few seconds, but the first photo I posted on Motobrick took me three hours. Strangely, that photo popped up on my previous post and all my posts on that thread, and even posts by other posters. Dunno how I done it, wouldn't be able to do it again if I tried.

https://www.motobrick.com/index.php?topic=11301.msg98578#msg98578

Soggz showed me a quicker way to post a photo, thanks Soggz.

Anyways, a small number of cases, yes, but I think there's a pattern that a rattle from the output shaft that suddenly disappears around 2000 points to the auxiliary shaft, around 4000 points to the output shaft. There's more examples, but don't want to thread jack too much. It's odd that a rattle from the output shaft disappears with the alternator removed, but if it does turn out to be a pattern, we can call it a symptom without knowing the reason. Maybe something to do with less drive or turning direction, dunno.

Anyways, I don't think we have to think about it too much, cause there's a BMW service bulletin about the problem. It says the minimum action to be taken is to install a new shim, and check the other items for wear. I guess the bearing would deserve the closest look. Since it takes so long to get to the output shaft, it would make sense to replace both bearings, and other wear items even if they look good. Let's say it's done 100, 000 km, you could say I'm not even going to measure them, I'll just replace with new.

[daveson]

Hey Laitch,
Do you remember the entertaining case of bgcameron? I do.
I didn't include it in the above posts because it wasn't solved, but it was partially solved by torquing the clutch nut.

Almost identical to MLR's case. A K75 with a clatter from 3500 to 4000 rpm when going slightly uphill. He looked under the cam cover and timing chain cover, but didn't look at the output shaft.

I'll guess if he ever does go into the engine, like MLR did, and replaces the shim, bearings, and whatnot, like MLR did, that would fix the problem, like MLR did.

I'll guess bgcameron's brick has a worn bearing, causing output shaft endfloat. A worn shim would allow a rattle with the backlash gear, which I think would be noisy at low revs.

Another pattern that I think has emerged with these K75 output shaft clatters is, why do they always seem to be late models? Dunno. Me thinks, I don't like shims there, if there's any wear, shims can't take up any slack, springs can. Maybe replacing the spring with a shim, causes more problems than it solves. The K100 has an extra diaphragm spring tucked away out of sight to help take up some slack. The K75 only has the circlip. How much slack can the circlip take up? Almost nix. Does anyone know which year the K75 had shims installed from new?

I won't add my new guess to his thread, as it's too old.

https://www.motobrick.com/index.php?topic=14231.msg127353#msg127353