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TOPIC: Cam chain idler gear, wear and tear. Service limit pistons?

Cam chain idler gear, wear and tear. Service limit pistons? 3 months 2 weeks ago #24347

  • Kawboy
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Hard to tell from the pics. The polished indications on the third pic? are diagonally opposite. Interesting. Not seen that before. It suggests that the bearing insert was cocked in the casing or machined after the babbitt was applied out of round to the outer diameter of the bearing.

Only way to know for sure is to plastigage them and measure the clearances. The pitting on the first pic- I've seen guys replace the bearings because of the imperfection but in the world of babbitt bearings, it wouldn't be a problem that needed fixing. Babbitt bearings, (plain bearings) are not meant to bear load through metal to metal contact. An oil wedge must be built up and maintained between the loaded parts. I've had to rebuild babbitt bearings for electrical power generators and after pouring new babbitt and machining the bearings, we had to hand scrape the bearings with carbide scrapers. The goal was to mate the surface with 80% contact. So the minor pitting I see would not add up to 20% of the bearing surface.

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Last edit: by Kawboy.

Cam chain idler gear, wear and tear. Service limit pistons? 3 months 2 weeks ago #24349

  • Frank833
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I agree with Kawboy. The bearings don't need to be perfect. The burnishing I see is fine if they measure in spec.

Do make sure the oil pump gears look good and side clearances are correct. GENERALLY, if the oil pressure is good and the bearings look reasonable, you are in good shape.

I too have seen Babbitt bearings hand scrapped. Even have seen the "wrong" bearings used in old equipment after being hand massaged by a master.
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