Engine Noise on Deceleration

I was out riding today and noticed that the engine sounded fine. But when I throttle off the engine as in going down hill, or approaching an intersection, it has an unusual sound to it. A bit hard to describe but I will try - Kind of like the sound of old cars with straight cut reverse gears but not as loud or high pitched and a bit like a car clutch thrust bearing that needs attention. Perhaps it is the straight cut gears from crank to clutch taking the different loading?

Any ideas?

Edit: The sound is very much like that from the engine of a farm tractor when you hit a bump and the tractor starts to rock forward and back - Hope that helps.

Hey, Paul. This sounds like one of those 'monitoring' situations.

Change and inspect the oil, magnetic drainplugs, and screens for hints.

Closely monitor/listen the situation while riding and experimenting with acceleration/deceleration. See if it's independent of gear selection, and localized to the primary drive. Feather the clutch and see if any changes.

Visualizing the right side of the engine, primary gears area:

During acceleration, the crank, rotating clockwise, will be trying to 'lift' the clutch basket gear (which rotates CCW). This puts downward pressure on the crank bearing, and upward pressure on the double-row mainshaft bearing (behind the clutch). Similar reactive thrust on the countershaft bearings, pushing them down.

During deceleration, those forces are reversed, bearings get loads on their opposite side.

There have been some incidents where the clutch basket gear rubs on the case, just behind the crank's ball-bearing.

A mechanics stethoscope may help, but they're funky to use while riding...

Thank you very much. I will start monitoring closely and try to pin point the area. It is definitely the right-side but must narrow this down more.

Update: TwoManyXS1Bs - I have researched this issue on other sites based on your ideas and the common explanation is the chain being too loose. I have put the bike in first and pushed it forward until compression comes on and them examined the chain. It looks as if the chain may be just touching the top of the swing arm above the bush. I have made adjustments a now await fine weather to test. You mentioned the clutch basket possibly rubbing and I found this very interesting. There is an excellent video about this on Youtube - to do with washers fitted in wrong sequence:


Will keep you all updated - Thank you.

Second Update: Bad weather slowing progress. Just went out to test ride and another winter thunderstorm arrived so must wait now for another day.

I found a gap in the clouds so went for a spin. I have done the following checks based on the advice given:

1. When riding the noise always exists in the back ground but seems very soft - probably masked by the exhaust sound.
2. On deceleration the noise is quite noticeable but goes away when clutch lever is pulled in.
3. When stationary and in neutral the noise is not noticeable, even when revving up.
4. When stationary and in 1st with clutch pulled fully in no noise is heard. When the clutch starts to release the noise then starts up and is quite noticeable.
5. When 4 above is repeated but with the foot brake hard no so the bike does not move the noise is again quite noticeable when releasing the clutch.

I suspect I will need to remove the side cover to dismantle and inspect the full clutch assembly. Bear in mind that this bike has only done about 20 - 30 miles after been stored since the late 90s. Total mileage is recorded as 13800. The only work done by me on the engine has been a top end decoke, all seals replaced, replaced front cam chain guide, new filters/strainers, transmission chain and both sprockets replaced, new spring on gear star selector, new head gasket and new washers for the head studs. The gears all select nicely and neutral is quite easy to select. I assume the thrust bearing in ok because there is no noise when clutch lever is pulled in i.e. full load on thrust bearing. Inspection of the oil and magnets did not show up any concerns apart from cam chain guide rubber. Oil was perfectly clean.

I will remove the side cover and inspect the full clutch assembly. Is there anything in particular that I should focus on e.g. do the clutch plates delaminate after 36 years?

Thank you for any thoughts on this - Much appreciated.

Note: Forgot to say, very hard to pinpoint the exact location of the noise.Seems fairly even both sides of engine but will work on that one.

Well done Paul. Your tests seem to have isolated the issue to strictly the primary drive. Check the gears, their alignment, backlash, and scraping on the case. FYI, that axial-thrust roller bearing behind the clutch hub doesn't handle any "throwout" loads. Those loads are handled by the mainshaft's double-row bearing and the clutch pushrod & balls.

There's also the crank's rightside ball bearing. If you enjoy punishment, check this thread:

http://www.xs650.com/threads/high-pitched-mystery-sound.23162/

Thank you for that TwoMany, I will attack the beast and come back with my findings in a couple of days.

I have made the following observations with the side cover off:

1. 1 mm feeler gauge fits easily between the clutch gear and both the casing and the main crank bearing outer race.
2. If I grip the clutch gear and move it there is only the slightest bit of free movement between it and the primary gear on the crank.
3. There is no obvious damage to any gear teeth.
4. Some of the clutch gear teeth have minor scratches running width ways on the backlash side.
5. Both gears appear to be aligned i.e. outer most edges lining up but the gear on the crank seems to be slightly wider on the inside.

I will dig deeper into the clutch tonight.

Question: What is the purpose of the thrust gear in the XS clutch - the one sitting deep inside behind the clutch plates and the big washer? Does it just take the load of the clutch basket when the clutch activates?

I used a very bright light and rechecked the gear positions and teeth and everything looks good. However, I think I am onto the problem.With the clutch still assembled I grabbed the clutch basket with one hand at 12 o'clock and the the other at 6 o'clock. When I applied some force the whole assembly including the gear could be rocked back and forth. Clearly something behind the clutch plates is loose. I know there is a spline and lock nut in there or perhaps a damaged thrust/needle bearing pack. Hopefully I will find out tomorrow after a bit of shopping for a new impact driver.

All suggestions very welcome!

Paul Sutton said:

Question: What is the purpose of the thrust gear in the XS clutch - the one sitting deep inside behind the clutch plates and the big washer? Does it just take the load of the clutch basket when the clutch activates?

Click to expand...

During clutch disengagement, the pressure plate moves outward. If the clutchpack is sticking to the pressure plate, the friction fingers may try to pull the basket outward as well. So, that roller/thrust bearing simply handles that 'outward' pull on the basket.

Paul Sutton said:

...I think I am onto the problem.With the clutch still assembled I grabbed the clutch basket with one hand at 12 o'clock and the the other at 6 o'clock. When I applied some force the whole assembly including the gear could be rocked back and forth. Clearly something behind the clutch plates is loose.

...perhaps a damaged thrust/needle bearing pack...

Click to expand...

Sounds like you're getting closer, Paul. The basket and roller/thrust bearing (with its thin washer) are sandwiched between 2 thick washers.


Those 2 thick washers are spaced apart by 30mm by the basket's inner bushing. The basket's running clearances, both axial and radial, should be about 0.002" (0.050mm). Check the surface condition of those 2 thick washers, especially where they contact the bushing, and put the better sides facing the basket.

Here's the 'basket spin test':

With the primary drive gear removed, you can spin the clutch basket.
The hub and all related washers need to be installed and tightened.
You'll want to check for:
Free spinning, no interference with things behind it.
Clearance to the raised portion of the case just to the left of the crank ball-bearing. Would like at least 1/2 mm here.
Wobbling. It must run true. No runout, no wobble.
Looseness. Don't want it flopping around in there. Should have little to no perceptable side-side, up-down, in-out slack. About 0.002" (0.050mm) running clearances.

If all is OK, then reinstall primary drive gear. Ensure that primary drive gear teeth are at same level/elevation as clutch basket gear teeth...

Thank you for the diagram TwoMany and the the instructions - Much Appreciated. I will not get the Impact Driver until Wednesday, the one in stock locally was not particularly well made. Instead I will retorque the head and check out the turn indicator switch, it is a bit stiff and difficult to push to cancel.

Good News - The clutch nut is 27 mm and I have one of these sockets.

I have dismantled the clutch and everything is in the correct order. However, the nut came of very easy for 58ftlb. There is no sign of the basket rubbing against the case and bearing but I didn't expect that because there was approx.1 mm clearance when tested earlier. I can feel no movement at all in the center shaft but will have another check tomorrow. The friction plates meet specification and are close to 2.9 mm. The metal plates still need to be tested for warp but look good. The size springs are all testing at approx 41.6 mm but this does not match the 36.4 mm in my manual. My clutch has the 6 friction plates but manual says 7.

With the plates removed I spun the inner clutch and there is a noise from the needle bearing. If I remove the bearing and spin the noise is not present. Visually I can see no damage to the needles and it is the original Yamaha part. Tomorrow I expect to receive a new needle bearing so will put this in and test again. I will also remove the primary gear and do the spin tests as outlined above.

When does the needle bearing see maximum load? If it is faulty then max load must be when the clutch lever is released if this is my problem.

Is the clutch basket bronze bearing still available and how can I test this for wear?

Til tomorrow - Thank you.

Paul Sutton said:

...The size springs are all testing at approx 41.6 mm but this does not match the 36.4 mm in my manual. My clutch has the 6 friction plates but manual says 7.

Click to expand...

Sounds like you have a later '80-up clutch. I'm not real familiar with those. 6 friction plates. A retained spring plate at the base of the unique hub. Longer clutch springs.

Paul Sutton said:

...When does the needle bearing see maximum load? If it is faulty then max load must be when the clutch lever is released if this is my problem.

Click to expand...

The needle bearing sees loads when the basket is pulled outward. The only time this can happen is when the clutch is disengaging and the frictionplates' tabs want to move outboard. But, there's nothing pushing those friction plates outboard, so it's a minimal load.
Edit: Except for the '80-up clutches, which have the spring plate at the hub base.

Paul Sutton said:

...Is the clutch basket bronze bearing still available and how can I test this for wear?

Click to expand...

It's part of the basket. Haven't seen it available separately...

Thank you TwoMany. My bike is an 81 SH but the manual does not match the clutch so thank you for the pictures. I shall continue my search tomorrow when the bearing arrives.

Update:

• New needle bearing fitted and this has removed the play in the basket.
• Clutch area is much quieter now when riding.
• The only noise I hear when riding is what is probably just the primary gears.

Now I know the clutch is all within specification and there are no issues with the bearings. Unfortunately disturbing the clutch has released the accumulated friction dust so an oil flush will follow soon. I will continue to monitor the situation but I am confident all is well now.

Just checked the plugs and they are identical in colour - light grey. I expect this for around town but will have to do some harder riding to check on richness. At least all my carburetor repairs and work have resulted in balance caburetors. When I got the bike one side was very rich which turned out to be manly due to a broken support post for the float.

Thank you for all the great advice and diagrams.

I appreciate this thread, having the identical problem on the identical bike. My noise sounds like a seizing needle bearing but only on hard deceleration or braking with oil level just below middle of sight glass. Looks like a clutch inspection is in order!

If inspecting the clutch check to see if the crankshaft is slightly out of true. I think the maximum runout is 2/1000", but best to check a manual for the specification - memories change with time.

I'll set up the dial indicator but am hoping that's not an issue or this project might be toast, thanks.