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Discussion Starter · #1 ·
Hi! I'm totally new to this world of motorcycle building/restoring. This last summer I picked up a '78 Hawk with the intent of fixing it up over the winter - alas, winter is almost over and I'm still working on the engine rebuild. Anyway, a buddy and I (both in college) intend to finish the engine over spring break, and to do that we need to solve a few problems. I figure that this a good place to search for knowledge, so any wisdom ya'll have to throw at me would be much appreciated .

Anyway, here is the first question: How do I determine the con-rod bearing sizes? Unfortunately, I don't have the original bearing inserts (as I had to order in a new crank/con-rods), and so I assume that plastigage is out of the question. In my shop manual it says that you can determine the bearing sizes based on the con-rod I.D. code number and the corresponding crankpin O.D. code number - that being said, I have recorded the crankpin numbers, but it appears that the con-rod I.D. code has worn off (or, at least, I can't see it, and I don't believe my eyes have failed me yet).

Secondly question: fortunately, when my friend and I measured the main-journal bearing clearances with plastigage (I DO have those bearing inserts), it read that everything was in-spec. Still, I wonder if it would be worth ordering new ones main-journal bearings while we are at it? (We are doing a full-engine rebuild, after all). What recommendations do you all have?

I'll include pictures of the crank, con-rods, and case codes, in case you can find something that has slipped by me (more than likely).

Thanks in advance for the help! Again, any other advice for a first-time builder is greatly appreciated! IMG_1874.JPG IMG_1875.JPG IMG_1879.JPG IMG_1880.JPG IMG_1881.JPG
 

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Do you have the factory service manual? Sent you a PM just in case...................

There's a pretty good explanation of how to determine the answers to your questions starting on page 10-9.

It's uncommon for these engines to require bottom end work, but then, "as long as you're in there..............."
 

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Discussion Starter · #4 ·
J-T, thanks for the PM and advice! I already had the manual, but I appreciate access to the treasure trove of manuals!

You're looking in the wrong place for the rod numbers, they're on the sides by the rod bolts. Sometimes very faint
longdistancerider, I also appreciate your suggestion to look on the sides of the rods! Unfortunately, it appears that the numbers have totally worn off. Any other ideas? Or should I just start taking measurements? IMG_1887.JPG IMG_1888.JPG
 

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Discussion Starter · #6 · (Edited)
So, after a little bit of work, I was able to get some bearings and measure the crankpin/conrod oil clearance with plastiguage. The bearings are color-coded blue, and appear to still be in spec: oil clearance measured at right about 0.001". Does anyone know if that is enough of a clearance? The factory manual says that the service limit for these bearings is 0.003" (so obviously I'm below that), but I'd like to make sure that they aren't too tight. If it turns out that they are fine, I'll just order in a new set of blue ones in the am.

***edit***
Just found in the factory manual that the standard is 0.0008-0.0017", so I guess that I'm in the clear :D. If I am incorrect, though, please, someone correct me!
 
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