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Author Topic: Pistons  (Read 1386 times)

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Offline Dan.T

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Pistons
« on: May 01, 2021, 02:28:21 PM »
Anyone recognize these?
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Offline Dan.T

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Re: Pistons
« Reply #1 on: May 01, 2021, 02:30:14 PM »
Helping a friend with a 76 750f. Was planning to do an 836, but I beleive these are 836 already. A stock piston from a 77 750k slides in with about 2mm on each side by my calibrated eyeball. Just curious if we should throw em away or try to find rings
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Offline Dan.T

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Re: Pistons
« Reply #2 on: May 01, 2021, 02:30:53 PM »
Another
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Offline Alan F.

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Re: Pistons
« Reply #3 on: May 01, 2021, 03:24:57 PM »
I'd go for some rings.

Got a dial caliper?
https://www.harborfreight.com/6-in-dial-caliper-63730.html
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Offline Dan.T

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Re: Pistons
« Reply #4 on: May 01, 2021, 03:57:27 PM »
Borrowed a cheap one and I'm getting 64mm on the piston and bore. Will need to verify with a known good one, but this was easily accessed.
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Pistons
« Reply #5 on: May 01, 2021, 07:02:45 PM »
64 = 812

If the ring lands are 2.5mm, 1.5mm, 1.5mm then the stock Honda CB350 twin rings will work. From '68 until the 360's came out
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline 754

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Re: Pistons
« Reply #6 on: May 01, 2021, 09:41:20 PM »
I got a set like those, 65mm i think. I too started a thread, no info though..
 They are mentioned at least 3 times in different threads... over the years...
« Last Edit: May 01, 2021, 09:45:57 PM by 754 »
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Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline PeWe

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Re: Pistons
« Reply #7 on: May 01, 2021, 11:31:11 PM »
64mm bore rings are tricky to find. There was a seller 5-6 years ago selling Yoshimura 64 mm rings.
Check if rings have big clearance up-down in grooves.

If they have, pistons are too worn. See Honda CB750 shop manual that specify this clearance.

Better to find new pistons.
836 (65mm) is next step after 64mm.

Bores that need a corrective hone are probably too wide for Dynomans 811 pistons, 64mm.
Correct clearance a must.
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CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline teebee67

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Re: Pistons
« Reply #8 on: May 02, 2021, 01:49:37 AM »
They look very much like standard Honda 350 (325)K4 pistons which are 64mm.
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Offline MRieck

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Re: Pistons
« Reply #9 on: May 02, 2021, 05:04:32 AM »
Quote from: PeWe on May 01, 2021, 11:31:11 PM

Better to find new pistons.
836 (65mm) is next step after 64mm.

I agree....those are past their prime
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Offline valt

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Re: Pistons
« Reply #10 on: May 02, 2021, 06:15:50 PM »
Yeah I just looked on the hastings website and they don't even have 64mm rings. If that is indeed what those are, but its easy enough to measure with digital calipers. Also those oil control rings look pretty weird, I would bet that they are pretty old.
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Offline 754

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Re: Pistons
« Reply #11 on: May 02, 2021, 08:04:48 PM »
 They are one piece oil rings, should be a Honda part.., i got them for my 65mm pistons .. 4th over CB 350.
 Check your ring widths.
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Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Pistons
« Reply #12 on: May 02, 2021, 08:15:14 PM »
« Last Edit: May 02, 2021, 08:20:24 PM by Jerry Rxman Griffin aka MuthaF'er »
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Pistons
« Reply #13 on: May 02, 2021, 08:19:40 PM »
Quote from: 754 on May 02, 2021, 08:04:48 PM
They are one piece oil rings, should be a Honda part.., i got them for my 65mm pistons .. 4th over CB 350.
 Check your ring widths.

Frank he is looking for 64mm
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline 754

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Re: Pistons
« Reply #14 on: May 02, 2021, 09:32:10 PM »
Okayyyyy
. That would be CB 350 std size rings......far as I know..
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Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline valt

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Re: Pistons
« Reply #15 on: May 03, 2021, 02:39:14 AM »
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