'00 M750 Motor Making Most Unpleasant Noises

[Raziel]

After successfully dealing with fuel delivery probs and finally riding for a few days, something worse rears its head...

Today on the way to work the bike began making a very difficult to describe noise... like an oscillating "supersound" above the engine, higher pitched, not a squeal, more like an unlubricated sewing machine running at high speed layered over the top of the engine. It came and went with no discernible relationship to clutching, throttle or anything that I could determine. 

For better or worse I decided to risk making the trip home. There was more of the same "oscillating sewing machine" and then worse... tink...clak...tunk... not too loud but exactly how you'd imagine a small piece of something flying around the inside of the motor to sound. The location was traveling as I could tell from the vibrations I felt through the frame and the variations in sound. I crawled home on it safely... perhaps not the wisest thing to do but I was quite close by then.

I don't have the means ATM for a service visit at the nearest shop 100 miles away.

I am interested in learning what I can possibly troubleshoot myself. I have never done a valve clearance check but planned to do so before long (the bike only has 3,000 miles on it) but I have no trouble rolling up my sleeves and poring through shop & Haynes manuals, tutorials, and sound advice from the board. I've plenty of good tools and success so far with rejetting and rebuilding the carbs and pulling the alt cover for a "shift claw" repair. And yes, that nut was torqued properly!

What's the first step, a compression test? Opening the valve covers and taking a look? I've considered getting a sound clip to post and using the "screwdriver stethoscope" technique but I fear damaging the motor further by running it, that seems to happen quite a bit.

[ducpainter]

I'd check the belt pulleys.

Loosen/Remove the belts and rotate them.

They should turn smoothly with no notchiness.

[vossy]

+1 on this.

Take the plugs out first to make it easier to turn

[Raziel]

Bad news for me, with what may be one of the most expensive mistakes I've ever made.

Before pulling the belts to check freeplay on the cam pulleys I took a good look at their positions. They line up just fine with their marks, unfortunately, not at TDC.

Below are some pics that show the actually pulley positions when the window shows the motor at TDC. Yeah, they're nowhere near close. When the cam/case marks are properly aligned, the window shows the TDC mark having just moved counterclockwise out of view. I don't know whether this means they are advanced, or retarded, but I'm guessing the clinky clank sound I've heard is part of one or more valves that have struck a piston. I'd like to think that the belts slipped or something, but I checked the tension and of course it can only have been my make the beast with two backs up when replacing the belts. I'm going to check the pulley play and see if I can tell which (hopefully not both) cylinders have been affected.

I'm sure I'll be back for more advice before long. For those who can read the marks, what do you guess would happen with this kind of bad timing?

[ducpainter]

Yeah...

you messed up.

The valves are definitely bent...probably both cylinders as they are both out about the same amount.

There is a possibility the guides are cracked too.

Are you going to do the work yourself?

[Raziel]

That depends on whether someone's willing to walk me through it  Half joking. It remains to be seen, this is pretty new to me but there are a lot of resources available and I do have the time over Winter. Admittedly, my track record isn't looking the best, but my budget is stretched unbelievably tight and I may have no choice. I think would like to assess the damage and while doing so determine whether or no it is outside my capabilities to do on my own.

I checked the pulley play... vertical cylinder meets resistance, rolls over and sticks a bit, then rotates and rolls over again. Same each rotation...resistance, roll, slight stick, roll... repeat

Horizontal cylinder pulley, rotates 60 degrees or so and comes to full stop.

[Raziel]

FAIL.

I totally dropped the ball on this diagnosis. I got to wondering how I could possibly have turned the crankshaft while changing the belts without some effort and it just didn't make sense, I'm pretty anal retentive about such things. So I put the belts back on (the crank hadn't turned since) and aligned them precisely according to  the pics I snapped as reference, and then turned it over until the cam pulley marks hit the case targets. Then I rechecked the TDC mark in the view window. Spot on!

I had misread what I thought was TDC through the window.

Which leads to the next thing, because the reason I misread the mark is that the edge of the flywheel which has the two TDC marks cut into it, is abraded in several places. This is why I read it wrongly.

I'm reminded of the loose flywheel nut issue I joked about above, I'm wondering if its come loose and is banging around in the case. This would explain why the bike didn't seem to lose any power on the ride home after it started making this gawdawful noise. I'm thinking that the easiest check I could do would be to pull the case and check. What else could abrade that lip on the flywheel apart from it coming loose and grinding on the inside of the case or having a loose part hit it?

Also, it occurred to me that the reason the horizontal cylinder pulley wouldn't spin is because the valves were hitting the cylinder head at TDC? Duh... Bear with me, it gets better!

[2 Wheel Wanderer]

Did you just change your belts? If they are too tight they can make that noise. After replacing mine and tensioning them correctly the engine was making a sewing machine sound. I rechecked the tension to make sure I did it right but the noise was still there(was using the 5mm method).  I loosened them a bit and they were fine.

Just a thought...

[ducpainter]

That depends on whether someone's willing to walk me through it  Half joking. It remains to be seen, this is pretty new to me but there are a lot of resources available and I do have the time over Winter. Admittedly, my track record isn't looking the best, but my budget is stretched unbelievably tight and I may have no choice. I think would like to assess the damage and while doing so determine whether or no it is outside my capabilities to do on my own.

I checked the pulley play... vertical cylinder meets resistance, rolls over and sticks a bit, then rotates and rolls over again. Same each rotation...resistance, roll, slight stick, roll... repeat

Horizontal cylinder pulley, rotates 60 degrees or so and comes to full stop.

You'll need machine shop services to cut the seats and do any other necessary work, but there are plenty of people here to help with the dis/reassembly.

First step is to decide if you want to take it on, and then start tearing it down.

The symptoms on that horizontal pulley kind of affirm bent valve/s.

[greenmonster]

Horizontal cylinder pulley, rotates 60 degrees or so and comes to full stop.

Is that the same now?
And it wont rotate, even w some force?

[2 Wheel Wanderer]

Is that the same now?
And it wont rotate, even w some force?

I think he is sayin that after he set the horizontal cylinder at TDC he took off the belts and tried to rotate the horizontal pulley. He can only rotate it so far by hand until a valve hits the cylinder.

[Raziel]

I *think* that's right... at TDC the horizontal cyl pulley won't move outside of an arc that is 90 degrees from either side of the tick mark at the top. So... 180 degrees total

When the vert cyl is at TDC the horiz pulley won't move much at all, maybe 20 degrees or so.

When the tick on the horiz. pulley is between the two TDCs, then I can spin the horizontal pulley all the way around. It resists, then spins on its own, stops, and I can spin it again. I guess I'd have to know how it is supposed to feel.. I can definitely feel several distinct positions: free spin, resistance, spins on its own, slightly less free spin, resistance, spins on its own. repeat. Does that make sense?

[ducpainter]

I *think* that's right... at TDC the horizontal cyl pulley won't move outside of an arc that is 90 degrees from either side of the tick mark at the top. So... 180 degrees total

When the vert cyl is at TDC the horiz pulley won't move much at all, maybe 20 degrees or so.

When the tick on the horiz. pulley is between the two TDCs, then I can spin the horizontal pulley all the way around. It resists, then spins on its own, stops, and I can spin it again. I guess I'd have to know how it is supposed to feel.. I can definitely feel several distinct positions: free spin, resistance, spins on its own, slightly less free spin, resistance, spins on its own. repeat. Does that make sense?

Yes...

When you spin the pulleys you are overcoming the assist spring. That is the resistance you feel. When it spins by itself the assist spring is closing the valve.

The fact that the horizontal pulley won't spin all the way around (dependent on piston position) is a problem.

[mitt]

You didn't fail - like you said you picked the wrong mark in the sight glass.  I could tell that from the first photos.  The drive pulley was off, but the others were off the same amount - so it looked good to me.

mitt

[mitt]

Also, I think you are not finding horizontal TDC correctly.  The tick mark on the crank is for TDC vertical if my memory is correct.  Then rotate the crank 270 degrees - that will get you to TDC for the other cylinder.  The cylinders are 90 deg apart, not 180.

mitt