Marks on back of bearings

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Truckedup
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Marks on back of bearings

Post by Truckedup » Tue Oct 02, 2018 8:03 pm

I just removed these rod bearings from one of my old Triumph bikes...This is an original never taken apart 40 year apart engine .I had been riding the bike all summer..... are the dark stripes on the back of these bearings trying to tell me something? Are they fretting? The crank side of the bearing looks just fine...

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Re: Marks on back of bearings

Post by engineguyBill » Tue Oct 02, 2018 8:07 pm

Fretting caused by many years of heat cycles and possibly a very small amount of debris between the bearing shell and housing bore. Forty years is a long time . . . .

Evidently the bearings did their job though. Journal side of the bearings are in good shape and the crank pins are in relatively good condition too??
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Re: Marks on back of bearings

Post by Dave Koehler » Tue Oct 02, 2018 10:21 pm

OR
the big end when bored had some chatter
OR
The bearing tooling had some chatter
Either way...No biggie. It's more of an image than a measurable fault.

FWIW as most of us have witnessed honed rods that have run long enough will leave a crosshatch image on the bearing back.
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Re: Marks on back of bearings

Post by Truckedup » Wed Oct 03, 2018 7:04 am

Thanks guys....
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Re: Marks on back of bearings

Post by rebelrouser » Wed Oct 03, 2018 11:16 am

don't work on motorcycles, but the marks you show are normal with an aluminum rod. Does the triumph have an aluminum rod? First time I freshened my race motor with aluminum rods I called Mickey Thompson, and the guy chuckled a little and said don't worry about it. He was right.

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Re: Marks on back of bearings

Post by rebelrouser » Wed Oct 03, 2018 11:16 am

don't work on motorcycles, but the marks you show are normal with an aluminum rod. Does the triumph have an aluminum rod? First time I freshened my race motor with aluminum rods I called Mickey Thompson, and the guy chuckled a little and said don't worry about it. He was right.

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Re: Marks on back of bearings

Post by Truckedup » Wed Oct 03, 2018 12:14 pm

Yes, Triumphs originally had forged aluminum rods with a steel cap.If the rod big end is not round, they are junk, cannot be resized safely...I have never seen bearing shell marks like this before...On my race Triumphs I use forged steel rods ..
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Re: Marks on back of bearings

Post by modok » Fri Oct 05, 2018 7:35 pm

Looks normal to me. the pattern has something to do with how the bearings were made. They were not fretting.
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Re: Marks on back of bearings

Post by Truckedup » Thu Oct 11, 2018 12:26 pm

Update... I was busy on polishing other turds but I did find something interesting when I looked close...The connecting rod caps were installed 180 degrees off....The big end was not round...I flipped them around so the bearing tang notches are together like usual, big ends are round...I should have seen this before, but was distracted or just dumb
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Re: Marks on back of bearings

Post by Dave Koehler » Thu Oct 11, 2018 2:13 pm

Must have had some serious clearance to get away with that.
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Re: Marks on back of bearings

Post by grandsport51 » Thu Oct 11, 2018 6:50 pm

Must have been using Castrol R.

I miss the smell in my cousins old MGA Twin Cam but not the
sludge!!

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Re: Marks on back of bearings

Post by MadBill » Thu Oct 11, 2018 8:46 pm

Normally, good old bean oil fumes are instant nostalgia but I had a different experience with Castrol R at a garage I worked for in the mid-sixties. A much-modded Mini Minor came in on the hook: "Won't start". It reeked so bad we rolled it right out the back door and I wrenched on it in the yard, but the shop stunk for weeks anyway.

Turns out the guy got stuck in a snowbank and just lost it; revved the whee out of it until it stopped. It cranked like it had no compression so I pulled the rocker cover and found that the head fasteners were very loose, but torqued up strangely. Then I realized the springs were so cooked the valves were falling open from their own weight. I pulled the head and discovered that he'd gotten it so hot that the copper head gasket had melted; there were blobs of it everywhere. We had to scrap virtually everything but the intake and the valve cover...

I can't imagine any conventional oil of the era allowing the engine to survive long enough for such devastation to occur... :shock:
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