GS450 engine knocking

[daspirate]

I've got an 82 GS450 that has developed a serious sounding knock over the last season. It seemed to vary based on rpm and engine load, getting really bad during engine braking. Oddly, though, the sound would come and go but it got more frequent as the season went on.

Fearing rod knock, I've torn the motor down and removed the crankshaft but all of the bearings look pretty good. I wasn't able to get the flywheel off to inspect the starter clutch, but it seems to function fine by rotating it by hand. Does anyone have any ideas of what might be wrong?

 

[tom203]

This is likely a plain bearing motor, so maybe your oil pump is clogged/not working- this would cause knocking. The bearings could survive a little torture before things got nasty.

 

[Guest]

It is a plain bearing motor and needs 75Psi oil pressure IIRC.

And how does the balance shaft bearings look?

One bad left or right gasket and you end up starving those balance shaft bearings.

 

[daspirate]

This is likely a plain bearing motor, so maybe your oil pump is clogged/not working- this would cause knocking. The bearings could survive a little torture before things got nasty.

I pulled the oil pump and it looks very good. No scoring, very clean, very flat.

It is a plain bearing motor and needs 75Psi oil pressure IIRC.

And how does the balance shaft bearings look?

One bad left or right gasket and you end up starving those balance shaft bearings.

I don't know much about bike engines, but every car engine I've worked on had journal bearings and they generally ran around 45psi oil pressure.

Balance shaft bearings look pretty good as well. I've got some pictures below.

All bearing clearances (crank main journal, crank rod journal, and balance shaft) measured between .002 and .0015.

 

[Guest]

Runout ?

What about the two thrust bearings?

How loud was the knock and where was it coming from ??
Could it have been piston slap or cam walk ?

 

[tom203]

I pulled the oil pump and it looks very good. No scoring, very clean, very flat.

If you still got pump out,open it up, and check the impeller clearance , but I doubt this would be your problem.

 

[daspirate]

If you still got pump out,open it up, and check the impeller clearance , but I doubt this would be your problem.

Clearance is tight. ~.0015

Runout ?

What about the two thrust bearings?

How loud was the knock and where was it coming from ??
Could it have been piston slap or cam walk ?

I have no way of measuring runout. Unless someone local cares to lend me a dial indicator. In any case, with the case halves back together, the crank turns very smoothly.

The thrust bearings look okay. One has a small gouge in it, but nothing sticks up proud of the surface. Crank end play measures .007"

I suppose it could be piston slap. I pulled the head and cylinders just now and there's no scuff marks on the pistons except for light ones on the skirts. I presume that's normal. Rings look good. Cylinders look okay. Light on the crosshatch, maybe, but the finish is consistent and there's no scratches.

I also tried feeling for play in the wrist pins. While I didn't take the pistons off to measure, there is no discernible play in any direction except for axial.

The knocking occurred only when the engine was under load (that is, in gear and moving). Under those circumstances, I actually considered borrowing the wife's stethoscope and riding down the block trying to pinpoint the location. I ultimately decided discretion was the better part of valor and resigned myself to pulling the engine apart instead.

The only questionable thing I've seen so far in this motor is a bunch of coarse, sandy grit at the bottom of the inner studs after I pulled the cylinders off. Of course, some of this garbage found its way down into the case so now I've got some careful cleaning to do. Other than that, it all appears and measures well.

Should I just button it up and ride until she blows? I'm completely out of ideas.

 

[blowerbike]

just wanted to add..
my neighbor has one of these and his sounds fine at idle.
when you bring it up off of idle it knocks..reminds me of the 80-82 750 when they spin a bearing and the piston hits the head creating the knock.
he called today and said his oil filter was full of aluminum shavings/chips.
i may help him tomorrow look around for the culprit.

 

[Guest]

Put the case halves in the dishwasher if the wife is ok with it

Having too much oil can slosh up and hit the piston and cause it to rock under load. That causes a knock or rattle when you lug the engine but goes away if load is lightened.


What about piston to wall clearance at different level's in the bore.

I'm just throwing ideas out there but it sounds like the bottom end is good.

 

[Flyboy]

Obviously i don't know how bad the knock is, but you did mention in your first post that it only happens when you come off the throttle under engine braking.

It seemed to vary based on rpm and engine load, getting really bad during engine braking

Just a curve ball to spice things up a bit
How do your cam chain guides look, and how is the tensioner, sounds like the chain might be slapping as the load comes off it or is reversed.....just a thought, seen it before.

 

[daspirate]

just wanted to add..
my neighbor has one of these and his sounds fine at idle.
when you bring it up off of idle it knocks..reminds me of the 80-82 750 when they spin a bearing and the piston hits the head creating the knock.
he called today and said his oil filter was full of aluminum shavings/chips.
i may help him tomorrow look around for the culprit.

I'd definitely be curious to know what you find. I haven't cut my filter apart yet, but I'll probably do it after work tonight.

Put the case halves in the dishwasher if the wife is ok with it

Having too much oil can slosh up and hit the piston and cause it to rock under load. That causes a knock or rattle when you lug the engine but goes away if load is lightened.


What about piston to wall clearance at different level's in the bore.

I'm just throwing ideas out there but it sounds like the bottom end is good.

I wish my wife were THAT supportive of my habbi, I mean, hobby. She's already letting me take up the whole garage (single bay at a townhouse).

Regarding oil level, I tried to always keep it at the top of the dipstick when the bike was on the center stand. Is that too high? Too low?

I'll try to borrow a transfer mic and measure the cylinder up. We'll see what it tells me.

Obviously i don't know how bad the knock is, but you did mention in your first post that it only happens when you come off the throttle under engine braking.

Just a curve ball to spice things up a bit
How do your cam chain guides look, and how is the tensioner, sounds like the chain might be slapping as the load comes off it or is reversed.....just a thought, seen it before.

It's entirely possible. The tensioner seemed to be putting load on the chain, but I haven't really inspected it at all. As a clarification, it would happen if you pinned the throttle as well, but it was always worse off-throttle. I'll look at that also tonight.

I do want to thank you guys for throwing the oddball stuff out there. It's all good stuff I wouldn't have thought to check, and it at least gives me something to do while I wait for way to much money worth of gaskets to arrive at my door.

 

[Nessism]

Regarding oil level, I tried to always keep it at the top of the dipstick when the bike was on the center stand. Is that too high? Too low?

The Suzuki service manual calls for cold engine, start engine for about one min, shut down engine and wait one more min, with bike on center stand, clean dipstick then stick down into engine cover until threads touch, then pull out dipstick and check oil level. Note: dipstick should not be threaded back into the engine case when checking oil level. If you do so the oil level will be too low.

 

[daspirate]

The Suzuki service manual calls for cold engine, start engine for about one min, shut down engine and wait one more min, with bike on center stand, clean dipstick then stick down into engine cover until threads touch, then pull out dipstick and check oil level. Note: dipstick should not be threaded back into the engine case when checking oil level. If you do so the oil level will be too low.

Looks like I've been running it a bit low then. Good to know.

I did cut apart the filter and it's completely devoid of any metal whatsoever. By the looks of things, the next thing I should look at is finding a good psychiatrist.

No transfer mics, btw, so I won't be checking the cylinders. At this point, I'm about ready to just button the thing back together and run it until it blows. Only thing I'm waiting on is gaskets to ship. Thanks to everyone for your support and ideas.