MS660 wrist pin bearing failure

[jakekinney]

I picked this saw up used about a month ago. Meteor kit, muffler work, and whatever else the guy did, ran great when I got it and have been milling with it ever since and no issues, until the other day. Let off the throttle to put in some wedges and it died, went to start again and I could feel there was no compression.

Long story short when I got everything apart, the wrist pin was very hard to get out and the fell out in 40 pieces. Took out the top of the piston and cylinder. Checked the bottom end luckily nothing found its way down there. Plenty of oil and everything was lubed well.

I have a new meteor kit on the way. Should I use that bearing or go OEM? Anyone ever had this issue before?

 

[Czed]

I picked this saw up used about a month ago. Meteor kit, muffler work, and whatever else the guy did, ran great when I got it and have been milling with it ever since and no issues, until the other day. Let off the throttle to put in some wedges and it died, went to start again and I could feel there was no compression.

Long story short when I got everything apart, the wrist pin was very hard to get out and the fell out in 40 pieces. Took out the top of the piston and cylinder. Checked the bottom end luckily nothing found its way down there. Plenty of oil and everything was lubed well.View attachment 672386 View attachment 672387 View attachment 672388

I have a new meteor kit on the way. Should I use that bearing or go OEM? Anyone ever had this issue before?

Oem on the wrist pin bearings.
Your lucky it didn't get in the bottom end.

 

[jakekinney]

Oem on the wrist pin bearings.
Your lucky it didn't get in the bottom end.

I'll be stopping in the dealer first thing tomorrow morning for one. Certainly dont need anything like this happening again. Might not get so lucky next time.

 

[user 122190]

I don't see a broken wrist pin. Those fragments look more like needle bearings. And how do needle bearing at the wrist pin make their way above the piston?

 

[hotshot]

Believe those needles came out of the WP bearing at dissassembly, but the shadows from the picture lighting makes them look bigger.

The cage part carnage came around to the top through the transfer ports.

I’ve been wrong before, but that is the way I would write up the autopsy.

 

[user 122190]

When I did my project saw, I thought the wrist pin was protected on both sides for the full travel of the stroke. I remember looking at it, questioning the sage advise given here to ALWAYS use OEM circlips, else burn in hell, or something worse.

 

[Mad Professor]

Most piston kits don't come with wrist pin bearings.

Maybe prior builder cheapped out with Chi-Com bearing instead of OEM?

 

[jakekinney]

Believe those needles came out of the WP bearing at dissassembly, but the shadows from the picture lighting makes them look bigger.

The cage part carnage came around to the top through the transfer ports.

I’ve been wrong before, but that is the way I would write up the autopsy.

Yeah that was a typo....meant to say the bearing came out in 40 pieces. Absolutely no cage left, just needles came falling out once the pin was clear.

 

[67L36Driver]

On a side note:
The aftermarket wrist pins often are not identical to the original.

If you look close the end condition, squared or chamfered, is different. Retainer comparability comes into play.

 

[holeycow]

Dirt/debris. Destroys wrist pin bearings.

My guess is it wasn’t perfectly clean when it was reassembled.

Just a guess..

Perhaps he re-used a worn out assembly? Pins, clips, and bearings are cheap. If you keep the wrist pin tight it won’t hammer out the bottom..

You got lucky.

Be sure to flush the crankcase over and over. Gently rotate the crank and flush, flush, flush.

 

[Mad Professor]

Look over the top end and bottom ends of your connecting rod real good. Must have been flopping about a bit before it let loose.

 

[Deleted member 117362]

Is your oem piston and cylinder scored? Hard to tell from pictures, only see marks on piston top and squish band. If it's not scored and bottom end bearings are good, why not reuse them?

 

[jakekinney]

Is your oem piston and cylinder scored? Hard to tell from pictures, only see marks on piston top and squish band. If it's not scored and bottom end bearings are good, why not reuse them?

Yeah there is a good deal of scoring on the exhaust side. At least I'll have peace of mind knowing everything is new.

 

[holeycow]

Is the big end ok?

 

[jakekinney]

Is the big end ok?

Luckily. Took holeycow's advice and flushed out the crankcase today so its nice and clean.
USPS says i'll have the top end kit tomorrow so if everything is ok I should be back up and running shortly after I get home from work tomorrow.

 

[holeycow]

Is there any endplay in the rod at the big end, is what I meant. It is standard procedure to check that when it’s apart.

 

[holeycow]

And oil those bearings on reassembly so they don’t start dry.

 

[Mad Professor]

Luckily. Took holeycow's advice and flushed out the crankcase today so its nice and clean.
USPS says i'll have the top end kit tomorrow so if everything is ok I should be back up and running shortly after I get home from work tomorrow.

I good top kit with a bad bottom end. is like humping a Ho with cooties, good luck...............

 

[jakekinney]

Is there any endplay in the rod at the big end, is what I meant. It is standard procedure to check that when it’s apart.

Everything is solid and butter smooth. The two saw shops by me were closed today so if one of them has a new bearing on the shelf tomorrow and the mail doesn't have any issues she should be running soon. I'll have to let you guys know how it goes.

 

[holeycow]

I usually look at those big end needles and cages with a strong magnifying glass under good light. It’s a bit of a pita rotating and sliding back and forth and such, but you can see stress marks and/or cracks in the cage or marks in the needles this way.

Part of this is because I can’t fricken see any more!