Frozen CB750 Engine

[wscarter]

Hey everyone. So I have a '76 CB750F project that I am working on. Got the thing for dirt cheap, but I have a problem, the engine is seized. Wont turn over at all, nor will it kick. I was just wondering what the best course of action on this would be. I was already planning on doing a full rebuild, but having to rebore the engine is a big undertaking. Thoughts?

 

[VonYinzer]

Pull the motor and open the top end to inspect the cylindders. Are the pistons seized or are there bigger issues internally? At the end of the day you won't know anything without some disassembly and thorough inspection.

 

[Grazz256]

With my seized dohc cb750 I was able to see into the cylinders and see one had rust in it, I removed the plugs and sprayed in pb blaster every day for a week. After that I was able to turn it over with a ratchet.

Cheers

 

[focusinprogress]

if you're planning a full rebuild just pull the motor and break it open. A normal rebuild would require the cylinders be honed anyways, so you'd likely be visiting a machine shop regardless. Once you have the cylinders out take them to a machine shop that does engine work and ask them to inspect it and advise whether it needs an overbore or just a cleaning and honing.

if it needs bored, either buy the 836cc kit from cruzin_image on ebay, or let the shop bore it until the damage is gone and let you know what size pistons you'll need for them.

 

[coyote13]

If you can peek down in the cylinders and verify that it's just gummed/rusted up, you may have luck with Marvel Mystery Oil.