Yamahajoe292

08 yz450f

13 posts in this topic

Alright so my 08 has started making a terrible noise so I pulled the motor off the bike to tear it down thinking that it was a shot crank, only thing I've found is the clutch side main bearing had a very little, .02 play in it, and cam chain looks like it's shot, rod is tight, and stator side main bearing has zero play. ImageUploadedByThumper Talk1461159110.614845.jpg

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A stiff cam chain is a potentially very dangerous thing.

Could it make a noise that sounds like the bottom end is shot? It's getting a new one regardless I'm just trying to pinpoint my noise

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No, I doubt it could make that much noise. 

 

Checking rod clearance is done by seeing how much the rod can be rocked (NOT slid left/right, rocked) on the crank pin.  Set up a dial gauge and check this.  The limit is .020" at the small end.

 

Pistons can get noisy if they're loose.  Measure the clearance.  Also be sure the crank nut is tight over the drive gear, and that the whole set of gears in the primary case all rotate smoothly together.

rod.png

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No, I doubt it could make that much noise.

Checking rod clearance is done by seeing how much the rod can be rocked (NOT slid left/right, rocked) on the crank pin. Set up a dial gauge and check this. The limit is .020" at the small end.

Pistons can get noisy if they're loose. Measure the clearance. Also be sure the crank nut is tight over the drive gear, and that the whole set of gears in the primary case all rotate smoothly together.

Everything seems to be rotating smoothly, rod bearing at the crank has .005 play in it according to my dial indicator, stator side main bearing has no noticeable play and clutch side main had barely enough to feel, I'm planning to put a piston in it anyway while I have it tore down.

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You're measuring the .005" as in "F" in the clip from the manual?

measuring the bearing that's on the crank itself. Not where the wrist pin goes through

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Right, but the dial is supposed to be placed on one side of the small end of the rod, and then the rod is rocked to the left and right without sliding it either way on the crank pin, so as to determine the clearance between the rod, rod bearing, and crank. If you actually have .005" vertical play at the crank pin, it's way too loose.

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Right, but the dial is supposed to be placed on one side of the small end of the rod, and then the rod is rocked to the left and right without sliding it either way on the crank pin, so as to determine the clearance between the rod, rod bearing, and crank. If you actually have .005" vertical play at the crank pin, it's way too loose.

If the limit is .020 and I'm at .005, that's tighter than the limit...

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That's .020 at the small end, though, not at the big end.  And actually, .020 - .040" is the normal range measured as shown (specs are on the picture). The service limit is .080".  It's what I get for trying to do three things at once and remember shit all at the same time. :smirk:

 

Much tighter than the low standard limit might be an indication of a problem with the bearing cage.

 

Since the amount the rod will rock is dependent on the clearance in the big end, Yamaha set up the measurement this way because it's an easier method to use accurately, especially with the crank in place.

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That's .020 at the small end, though, not at the big end. And actually, .020 - .040" is the normal range measured as shown (specs are on the picture). The service limit is .080". It's what I get for trying to do three things at once and remember shit all at the same time. :smirk:

Much tighter than the low standard limit might be an indication of a problem with the bearing cage.

Since the amount the rod will rock is dependent on the clearance in the big end, Yamaha set up the measurement this way because it's an easier method to use accurately, especially with the crank in place.

Ok well that's the measurement I got with a dial indicator, but when I try and feel movement with just my hand I can't feel any what so ever. So I'm at a loss. I know I need to get a service manual but I'm trying to figure this out, I've had a lot of bikes with a lot more play than this rod and mains that never made a peep.

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Ok so I took the engine to my mechanic and had him look it over and the source of my noise seems to be from a week cam chain tensioner, and cam chain. Planning to change both of them and the cam chain guides, piston checked good but probably going to replace it as well.

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