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Author Topic: 812CC CB750 kit and piston rings  (Read 3577 times)

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Offline PPG9944

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812CC CB750 kit and piston rings
« on: September 17, 2014, 06:49:06 PM »
Hey guys, could anyone shed any light on a few questions I have.  I got this 812cc kit with 64mm pistons.  I managed to snap 2 oil rings.  The pistons are stamped with ART on the sides which I've been told are OEM honda pistons or ART was an OEM honda supplier.  The honda cb350 pistons were 64mm as well.  Would those piston rings fit on my pistons?

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Offline seanbarney41

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Re: 812CC CB750 kit and piston rings
« Reply #1 on: September 17, 2014, 07:12:29 PM »
I believe I have the same exact pistons, and yes the cb350 rings will fit, but you have to find the correct
 oversize for them to be 64mm (I think it's 3rd oversize, iirc)
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Offline PPG9944

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Re: 812CC CB750 kit and piston rings
« Reply #2 on: September 17, 2014, 07:16:48 PM »
Why would an oversize be necessary if they're 64mm stock?  Sorry I'm very green to rebuilding an engine.
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Offline seanbarney41

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Re: 812CC CB750 kit and piston rings
« Reply #3 on: September 17, 2014, 07:22:29 PM »
Sorry, I don't remember the specifics, and I may be wrong, but I don't think cb350 pistons are quite 64mm stock, that's why you have to get oversize.  Do some searching here.  The correct info is here somewhere.
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Offline grcamna2

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Re: 812CC CB750 kit and piston rings
« Reply #4 on: September 17, 2014, 08:22:38 PM »
CB350 twin pistons are 64mm stock
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Offline PPG9944

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Re: 812CC CB750 kit and piston rings
« Reply #5 on: September 17, 2014, 08:29:04 PM »
Quote from: grcamna2 on September 17, 2014, 08:22:38 PM
CB350 twin pistons are 64mm stock


the rings from those should then fit my 64mm pistons in theory then correct?
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 812CC CB750 kit and piston rings
« Reply #6 on: September 17, 2014, 08:56:15 PM »
Yes, as long as ART ring land is 1.5mm, 1.5mm, and 2.5mm thick from top to the oil ring.
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Re: 812CC CB750 kit and piston rings
« Reply #7 on: September 18, 2014, 03:25:56 AM »
CB350 1mm oversize is 65mm pistons. Action Fours used them with 836.
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Offline PPG9944

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Re: 812CC CB750 kit and piston rings
« Reply #8 on: September 18, 2014, 04:14:16 PM »
Quote from: Jerry Rxman Griffin aka MuthaF'er on September 17, 2014, 08:56:15 PM
Yes, as long as ART ring land is 1.5mm, 1.5mm, and 2.5mm thick from top to the oil ring.


That's about the measurement I got.  I am going to order up some standard bore cb350 piston rings in that case. 
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 812CC CB750 kit and piston rings
« Reply #9 on: September 18, 2014, 05:40:09 PM »
That's what I've used on my Yoshimura 812 kit over the years.
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Offline seanbarney41

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Re: 812CC CB750 kit and piston rings
« Reply #10 on: September 18, 2014, 06:41:05 PM »
sorry PPG9944, not sure where I got that 3rd oversize baloney...now thats all straigtened out, maybe I can find rings for my pistons :)  I would appreciate updates on how your engine comes out. 
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Offline PPG9944

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Re: 812CC CB750 kit and piston rings
« Reply #11 on: September 18, 2014, 06:45:19 PM »
Quote from: seanbarney41 on September 18, 2014, 06:41:05 PM
sorry PPG9944, not sure where I got that 3rd oversize baloney...now thats all straigtened out, maybe I can find rings for my pistons :)  I would appreciate updates on how your engine comes out.

No worries.  I got some rings coming from Japan.  I'm pretty pumped on it though.  I've never rebuilt an engine before so I'm sure I'll be asking the help of the community when things arise. 
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Offline BradM

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Re: 812CC CB750 kit and piston rings
« Reply #12 on: January 14, 2019, 02:58:13 AM »
Quote from: PPG9944 on September 18, 2014, 06:45:19 PM
Quote from: seanbarney41 on September 18, 2014, 06:41:05 PM
sorry PPG9944, not sure where I got that 3rd oversize baloney...now thats all straigtened out, maybe I can find rings for my pistons :)  I would appreciate updates on how your engine comes out.

No worries.  I got some rings coming from Japan.  I'm pretty pumped on it though.  I've never rebuilt an engine before so I'm sure I'll be asking the help of the community when things arise. 

Hi, just curious if the standard CB350 rings worked. I just opened up a ‘72 750 and found RC 812 pistons. Maybe you could send me the link to where you bought yours if you liked the fit?
Thanks.
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 812CC CB750 kit and piston rings
« Reply #13 on: January 14, 2019, 05:40:42 AM »
They WILL work if they are 1.5mm, 1.5mm, 2.5mm
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Offline BradM

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Re: 812CC CB750 kit and piston rings
« Reply #14 on: January 17, 2019, 05:40:48 PM »
I just figured out that the old RC pistons have deeper grooves than standard 1.5 x 3 mm is what I need for this motor. Any ideas?
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Offline HondaMan

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Re: 812CC CB750 kit and piston rings
« Reply #15 on: January 17, 2019, 06:39:45 PM »
Quote from: Jerry Rxman Griffin aka MuthaF'er on January 14, 2019, 05:40:42 AM
They WILL work if they are 1.5mm, 1.5mm, 2.5mm

Thanks, Jerry! I had forgotten about this: I have some nice, lightly used 812cc pistons (Yosh) that need new rings before I can put them into an engine. Better get some of those rings!
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Offline PPG9944

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Re: 812CC CB750 kit and piston rings
« Reply #16 on: January 20, 2019, 07:09:36 PM »
They did work!   They were the CB350 piston rings if I remember correctly.  I wound up getting them on ebay.  Searched directly for those part numbers.
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