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Weird Wrist Pin Bearing Issue

21 Oct 2019 18:41
Isaac
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Weird Wrist Pin Bearing Issue #1
Hey Guys!

I've really enjoyed all the help I've gotten here for my Yamaha's. Thanks for that!

I am working on my 1977 Suzuki PE250 and have replaced the main bearing and gaskets. When I pulled the top end apart I checked the piston and head and they were in great shape. I followed the Manual and removed the wrist pin, bearing and piston before splitting the cases. Some light tapping with a socket and hammer was needed to remove the pin.

I am finished with the low end and when I put the wrist in back in it was really tight. When I finally got it back in the bearing felt like it was binding. It was perfectly smooth when I removed it. I ordered a new bearing and when I installed it, it was also binding.

What is going on here? I have researched this and have not found any answers as to why this would happen.

Any ideas?

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21 Oct 2019 18:50
Isaac
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Weird Wrist Pin Bearing Issue #2
Here is some eye candy of my friends '79 PE and my 7'79 XT500. Hoping to have my PE next to his soon.
Attachments:

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21 Oct 2019 19:20
DEET
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Weird Wrist Pin Bearing Issue #3
Did you replace the connecting rod?
Did you drop the connecting rod?

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Where the Yamaha Enduro is still a current model...

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22 Oct 2019 00:01
liferbiker
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Weird Wrist Pin Bearing Issue #4
How is the wrist pin all by itself (w/needle bearing in rod)? It should slide in w/no resistance. If not, try your old needle brg assembly, or new one, if still binding, like Deet said you may have damaged small end of rod making it out of round & non-usable. I usually heat pistons on a hot plate & chill pins if they offer much resistance during assembly. This only applies to piston boss, it needs to slide into needle bearing with zero effort.

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22 Oct 2019 10:06
RT360Fan
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Weird Wrist Pin Bearing Issue #5
Check the fit of the pin and bearing outside of the piston, there should be no binding at all, even slightly 'loose'. If not, you need a new pin and/or bearing. Then check that assembly installed in the rod. Should be the same, slightly loose. If not, your rod may be damaged.

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22 Oct 2019 12:50
Isaac
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Weird Wrist Pin Bearing Issue #6

DEET wrote: Did you replace the connecting rod?
Did you drop the connecting rod?



It's the same connecting rod and no, I didn't drop it. It never left the bench. Do you think it is out of round? Should I put a micro meter on it and measure?

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22 Oct 2019 12:52
Isaac
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Weird Wrist Pin Bearing Issue #7

liferbiker wrote: How is the wrist pin all by itself (w/needle bearing in rod)? It should slide in w/no resistance. If not, try your old needle brg assembly, or new one, if still binding, like Deet said you may have damaged small end of rod making it out of round & non-usable. I usually heat pistons on a hot plate & chill pins if they offer much resistance during assembly. This only applies to piston boss, it needs to slide into needle bearing with zero effort.


Yes it's all by its self. It doesn't slide in with no resistance, but some. When the bearing is in the piston there is a lot more resistance. I just bought a new bearing and there was no change as compared to the old fit.

I heated the small end of the rod and the piston and it slid in fine, but then it binds after it cools.

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22 Oct 2019 14:03
RT325
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Weird Wrist Pin Bearing Issue #8
I'm worried as to why you're heating the little end eye of the rod but assuming your doing it to see if it expands & makes the bearing looser. The pin in the piston should idealy be a sliding fit but the dags left against the circlip grooves catch the pin & make it bind in sliding. I recall kawasaki having different little end bearings with incremental differences of fit if you felt the original was a little loose but don't think suzuk did that. Sorry--no help without being there, but sounds like damage to the eye. does it roll evenly but tight or does it roll in lumps like the eye is out of shape. Do PE250's have thrust washers between piston & bearing & side of rod. I thought they did as the rod is thrusted against the piston & not at the crank, so with cylinder off you'll have lots of side movement at the big end. Not that that has anything to do with your problem but are the top thrust washers stepped to sit one way only over the end of the bearing. I give up & sorry for confusing things.

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22 Oct 2019 14:13
RT325
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Weird Wrist Pin Bearing Issue #9
ok ignore most of that above as cant find any record of thrust washers up top but still think its thrusted there so must be the piston sits close to the rod to keep it central to thrust it, but that's not helping is it. How hot did you heat the gudgeon eye of the rod.

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22 Oct 2019 14:29 22 Oct 2019 14:31 by RT360Fan.
RT360Fan
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Weird Wrist Pin Bearing Issue #10
Hammering, heating, neither are good on pistons/rods. I'm assuming since the bottom end was all together you used a torch?

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