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Heyo! Just pulled apart my bottom end on a somewhat routine rebuild.
Found the main bearings and con rod bearings worn below limit.

What does one do in this position? Can you get NOS stock or used ones that aren’t worn? Checking around eBay I see plenty that aren’t measured for tolerance— gives me pause.


Thanks!

Found this thread for you to review. It answers most of the various questions you may have. And be sure to download a factory manual for your bike...

www.kzrider.com/forum/2-engine/609309-kz...aring-source?start=0

www.zedrider.co.uk/service--owners-manuals.html

What Year 650 ? Peanut chain or HIVO ? I Pretty sure I have a good crank and rods from a 750 Turbo but its a HIVO style Chain.

This is an 80 kz650 hyvo.
I measured the bearings on cam and got 36.96mm on my caliper. So that’s leading me to wear.

Looking at it.. is the hyvo chain the one going up to the cams or the one going to the transmission?

Do the 750 cams fit?

Hivo Cam Chain.

I thought the 1980 and earlier 650s used a roller cam chain and then switched to the HY-VO cam chain in 1981.

Measure journals with a micrometer, not a calipers

What makes you think the crank journals are worn? Are they scored, burn't or galled. If not your way over thinking this, get new bearings or used ones and plasti gauge them. I bet you'll find it's just worn bearings. I've rebuilt well over two dozen KZ650 / 750 engines and never found a worn out crankshaft even on abused ones. Most didn't even need new bearings. I simply plasti gauge the old bearings and if they ars in spec I reuse them.

Actually the KZ650 had a soft journal surface. When these motors were subjected to big power boost, the journals would die. Back in the day, when people raced these bikes we would offer a service where we hard chromed the journals not make them live. It is the only crank we have ever had this service for.