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Discussion Starter · #1 ·
Just stripped an ex race bikes bottom end and the crank is kaput. What options are there in going forward ?

Done some searches and nothing has come up. I do a lot of crank rebuilds but this one is quite different. Integrated bigend pin is rather unusual. Only other motor I worked on like this was a Konig 350 4 cylinder.
 

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The best option is to buy another crank. You cannot really rebuild them, other than replace the rods and bearings. I have never seen anyone replace the big end part but it is possible that someone has done it in the past. If you ask me, it is a bit of bad design. It was probably the cheapest option for Honda. These bikes were really not meant to last for 40+ years. There still are some NOS cranks for sale but they are pretty expensive. I went for that route and I have a spare one lying in the attic. It has been lying there for some years now so the ridiculous amount of money I spent on it has long been forgotten.
 

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Actually, the design's not all that bad, 350 crank failures aren't all that common unless they've been abused or run dry of oil. Pretty good piece of kit for a motorcycle that retailed for $850 brand new.
 

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Discussion Starter · #4 ·
I have a full CNC workshop here. I can probably to a retrofit the crank with rods from another Honda. I would bore out the webs to take a straight press fit like other bikes rather than the stepped splined pin they have now. The problem with the 'splined' pin is that it hard to swap bits from one crank to another. If I can do this, means that the CBs will get another lease on life. If anyone is interested, PM me.

Cant believe this is 9 years old already.
 

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Discussion Starter · #5 ·
It was probably the cheapest option for Honda.
Not really. The way it was made took big chunk of blank material and a lot of machining. I think this solution was because of the stoke, bigend pin diameter and center shaft diameter. The diameters overlap. One of the pins would have to have a bit cut out of it.

The Konig was done to get the crankshaft shorter. 12 mm web with a bigend on either side. hardening the complete item and grinding to finished size is a difficult exercise.

Crank.JPG
 

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Refurbishing old Honda cranks could probably be a good business for someone, someday. With used spares out there, we may not be there yet.
 

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It's a pretty easy gamble to make, 100 or so for a used one vs. 400+ labour, 2-300 in parts if you buy NOS rods/bearings etc.
 
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