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Crank Bearing

C

Creid00

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Hi,

New here. Names Chris. From Northern California, West Sonoma County.

I have about 4, K's in different states of needing repair.
In the midst of getting the café style one back on the road. It's a 1973 frame, 1970 motor. Pics to come.


Pulled the crank bearing during a bottom end tear down. Looking to replace. How crucial is this? Should I get an engineer to look at?

They are all stamped:

AP20
DOI A
STD

Does the Lone "A" indicate "A" is the type of bearing across the cranks?
All places I'm seeing crank bearings for sale has them listed at different locations, with different letter codes. Did I make a mistake taking these out without cataloging where each one came from?
 
The lettering on the back does not indicate anything for the user. The bearings are color coded, on the edge there will be a green, yellow, brown, or black color...unless they are original in which case the color is probably long gone. The shop manual details how to determine bearing size. There are letters stamped on the case and letters engraved on one of the crank weights, you take these and look on the bearing chart to determine what bearing size is needed. This gets you close unless the crankshaft journals are worn. The same process is used for the connecting rod bearings except the they use a number system. Unless the bearings are worn or scored you can reuse them. You can either use a micrometer to measure crank journal sizes or get some plastigage and determine if you are out of spec. It would have been easier to mark where they came from so you could have checked the old bearing clearance now it would be a trial and error process to get your correct bearing spec. Now you will have to measure the crank and determine if it is worn and how much. Then go by the color coding and install new bearings assuming crank is at the spec that is stamped on it. Then plastigage them and see if the bearing clearance is correct and if not select the next smaller or larger bearing depending on the clearance you currently have. This is all in a good shop manual for the bike.

I would first look on the bottom of the top case and get your letter codes. Then get the letter codes engraved on the crank and look up what the chart says to use for bearings. Take a look on your current bearings and hope you can see some color marks. Post pictures back here and I can try to help you determine what you need. If this bearing selection is confusing I highly suggest you find someone that has worked on these motors before...bearing clearance is critical!
 
Thank you and many others.

I have a bearing and engineering shop to help with getting the right bearings in the correct spot.

I'm working with a friend, who's and old timer, and even though we usually mark things, it wouldn't have mattered in this instance. Both shops have determined I need new bearings, based on their wear.

I have not found markings in the crank weights. I di however find letters on the bottom part of the casing. Trying to figure out how to read them. They seem jumbled.
 
The letters go in the same order as the bearing journals in the case read from left to right. There are marks on the crankshaft unless its been machined, keep looking.
 
Will do. Actually, looking at the picture I'm trying to send it's the alphabet, in order????
e167d6cee5bb8b0eca2e5bdeda815cf8.jpg


 
Those are not the right letters. They are on the outside of the bottom case next to a frame mounting bolt. It will be a sequence of 5 letters. Only a combination of A b or C will be present, no other letters.
 
dirtdigger said:
Those are not the right letters. They are on the outside of the bottom case next to a frame mounting bolt. It will be a sequence of 5 letters. Only a combination of A b or C will be present, no other letters.
Click to expand...
Hummm. that is the bottom of the crank case. That red dot is mounting bolt hole. The red dot is the work bench.

Hopefully the engineer can get the right specs for me.

 
I miss spoke previously, I apologize. It is on the bottom of the front motor mount on the TOP case, you will flip the case upside down and will be able to see the letters. Dont know what I was thinking, other then I meant to say bottom of top case. Its been a long day.
 
Creid00 said:
Hummm. that is the bottom of the crank case. That red dot is mounting bolt hole. The red dot is the work bench.

Hopefully the engineer can get the right specs for me.
Click to expand...

That red dot is actually where the neutral switch/detent goes through the case, its directly under the gear shift drum.:thumbsup:
 
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