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Author Topic: 1982 CB750F... The resto-not  (Read 33065 times)

Offline doc_rot

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Re: 1982 CB750F... The resto-not
« Reply #350 on: Feb 26, 2019, 12:21:56 »
make sure you clean the piston ring grooves really well. Carbon is highly abrasive and if there are loose bits in there it will break your rings down quickly. Nice work.

Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #351 on: Feb 26, 2019, 12:33:10 »
Cheers Doc - I've been cramming a q-tip with some carb cleaner into the grooves to clean them up as much as possible.  Any other methods I'm ears - the pistons won't be coming off the con rods though I don't think.
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Offline advCo

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Re: 1982 CB750F... The resto-not
« Reply #352 on: Feb 26, 2019, 12:35:21 »
Cheers Doc - I've been cramming a q-tip with some carb cleaner into the grooves to clean them up as much as possible.  Any other methods I'm ears - the pistons won't be coming off the con rods though I don't think.

What I do when I'm re-ringing is take an old ring (one from each groove) and break it into a small 1-2" piece, file the end down so its not going to gouge the piston and run that along the groove to clean out any carbon.

Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #353 on: Feb 26, 2019, 12:42:52 »
That would do it, but I'm hoping the rings are in good shape and that I can reuse them.  Bad idea?
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Offline advCo

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Re: 1982 CB750F... The resto-not
« Reply #354 on: Feb 26, 2019, 12:59:46 »
That would do it, but I'm hoping the rings are in good shape and that I can reuse them.  Bad idea?

Not necessarily, the end gap needs to be checked and if they're out of spec you'll need to replace them. Really all the piston and cylinder clearances should be measured while you have the whole thing apart.  I pull a cylinder off I will usually re-ring and hone.

Offline Maritime

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Re: 1982 CB750F... The resto-not
« Reply #355 on: Feb 26, 2019, 13:04:31 »
Only need to re-ring if they measure out of spec on any one of the dimensions. Gap, thickness etc. and those have ranges so if your close to the good side of the range, keep em, if you are close to the almost worn side but still good, consider changing em. And of course if out of spec all together new is a must.
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Offline doc_rot

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Re: 1982 CB750F... The resto-not
« Reply #356 on: Feb 27, 2019, 05:17:07 »
all sound advice.

I had to rebuild a top end twice last year because I assumed the pistons rings would be good to reuse because it had decent compression before tear down. It smoked a bit after the rebuild, despite having great compression and it was leaking less than 1% on all cylinders.

My point is; you don't know its good unless you check. Its not much more effort once you're in there.  If you don't want to buy the tool to measure the cylinder bore properly, get cozy with your local machine shop. My experience has been if you go in chat it up a bit and ask some informed questions they will typically go out of their way to give you a hand with your project as so few people work on their own engines in this fashion anymore.
« Last Edit: Feb 27, 2019, 05:18:54 by doc_rot »

Offline farmer92

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Re: 1982 CB750F... The resto-not
« Reply #357 on: Feb 27, 2019, 07:05:11 »
Rings are cheap vs the time and disappointment it takes to tear it all down a second time.

Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #358 on: Feb 27, 2019, 09:51:28 »
Don’t get me wrong guys - I’m absolutely going to be checking the rings, pistons and cylinders. And if anything is out of spec then it’ll be getting replaced/machined for sure.

I’ll see if I can borrow the required tools, and Doc you’re right - I get a lot of help from a few local shops for exactly that reason it seems. I ask a ton of questions, and the pros I know don’t seem to mind taking the time to help me out.

Viton valve seals showed up yesterday - now that they’re here I’ll give the head a good clean again, reinstall the valves, check the shim clearances and get everything ready for paint.


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Offline Jimbonaut

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Re: 1982 CB750F... The resto-not
« Reply #359 on: Mar 01, 2019, 12:58:20 »
By a rather circuitous and very fortunate manner I scored a set of cams from a 900F yesterday - I've read that they are a straight swap into the head and give some pretty noticeable power gains (while at the same time a bit of a drop off in the low end).  I'm trying to understand how that happens however.  Is it because the lobes are machined differently to keep the valves open/closed for longer/shorter?  Or are the lobes angled differently to each other on the cam so the valves open and close at different times?  Interested to find out.

Also borrowed a tool for measuring the inside of the cylinders, and a valve spring compressor -



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