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Engine boring CB750 to 823 question

shadowmoses42

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Hi Guys,

I'm bring my 1980 CB750C from 62mm to 65mm for the Wiseco 823cc piston kit. I'm curious though, what's the most the stock cylinders can be bored out? Will the cylinders become unstable sooner now because I am widening them each by 3mm?

thanks!
 
That's pretty much it. You will have maybe a sixteenth inch (.060") thick liner thickness left. They seem to last in stock bike use but you wouldn't really care to race on that, Race thickness better at .100".

Bigger issue would be who does the borejob, it's getting quite hard to find people competent enough to do the work correctly. The final finish has to be right or oil consumption and ring sealing issues.
 
Thanks for the response! I have a place somewhat near me who was recommended by another mechanic (originally recommended to me and who bores cylinders but typically only cars). I spoke to the guy and he seemed to know what he was talking about, and they specialize in automotive machining. I was just a bit worried that the cylinders would be thinner while making the engine more powerful by using wider pistons. I plan on using this bike as a commuter or for trips under 100 miles. No interest in racing. I'm only boring out because I heard the Wiseco 823cc kit is good and a common upgrade for the CB750s. After sitting around for 20 years I didn't want to attempt to use the original pistons.
 
The kit is jam up but I've had my fill of hi-perf shops that talk the talk and then turn your parts into junk.

Be leery of a car shop, they will not have the honing tools in small enough boresize for your stuff, I'd press for that. Handboring with boring bar is out, too hard to find competent people to do it and even worse the hand honing to finish it out perfectly. I STRONGLY suggest packing the parts up and sending to a bike specialty place that can do it right on a Sunnen machine and even the honing. Like APE Engineering, you pay but what you get back is ultra primo work.

Last time I bored at a local hot rod BIKE shop I went there and talked to them myself, they knew all the bullshit talk and were known for fine hi-perf work, the cylinder I got back had pistons not even going into holes but they had handforced them in and new pistons scarred up. The bore job itself was so rough the hone did not remove the cutting marks and the whole thing was junk. Quite a row over that one, that's when I quit using any local talent, they just can't do it right.

Boring and honing are fast approaching being a lost art, nobody seems to know how to do it right any more. The element of 'time is money' is too rushed to do it competently. Many shops know it and have given up doing it, rather using the most American of all screwjobs in replacement.............the THIRD PARTY supplier. You appear to be there.

We (Dad and us boys) used to drag race cars a lot and we went through national known shops that did fine work on their own stuff but commonly put out utter crap for work for the public. Ever hear of Blue Max Performance (nationally known funny car winner) or Reher/Morrison Racing Engines? I could tell you you such stories..............beware, most of the best-of-the-best will give you garbage back and still be telling you how damn good they are. We were forced to learn to do it ourselves as no one else could do it and here in the huge DFW Metroplex back in the '70s. That has not gotten any better, in my view anyway.
 
Really appreciate the help. Any preference you have, one over the other? I'm in PA so I'd have to ship it to either option. APE looks a little more expensive than my local automotive machining shop but if the job is done better I am ok with it.
 
I use both APE and Cycex, both do good work. I would call both and see who can do the work for you in the time you need it.
 
Called both, and both are reasonable pricing (actually better than my local). Both seemed to know what they were talking about too and had good reviews. Think i'll go with Cycle X as it's physically closer and Ken stated he could have a quick turnaround once I send it to him. Thanks for the help, both of you.
 
Luck..............so much of that work depends on how the worker got up that day...........you should be good there though.
 
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