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Author Topic: 1975 cb750f pitting in cylinders.  (Read 591 times)

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Offline mechanic3

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1975 cb750f pitting in cylinders.
« on: March 06, 2020, 08:46:00 AM »
After approximately 2 years have had a chance to get back to my cb750f project. It sat in a building for about 18 years not touched. Shows 7000 miles? Changed the oil and filter,points cleaned carbs (a real mess.)new plugs and set static ignition timing. It fired right up and runs. After a few times running did a compression test. All cylinders around 140 psi. I then pulled plugs and bore scoped cylinders. Found quit a lot of pitting. Does not look good. Do you guys think its worth putting on road in this condition or am i into an overhaul? Any help would be appreciated.
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Offline danyo

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Re: 1975 cb750f pitting in cylinders.
« Reply #1 on: March 06, 2020, 09:29:52 AM »
Run it without worries now. Compression looks good so why to worry now.

Sent from my SM-N920T using Tapatalk

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Offline PeWe

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Re: 1975 cb750f pitting in cylinders.
« Reply #2 on: March 06, 2020, 10:01:54 AM »
140 PSI is not bad for a stock CB750.
If all 4 have same value = good.

Cruzinimage.net has cheap piston kit for future upgrade like +0.5 mm pistons.
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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 carnivorous chicken

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Re: 1975 cb750f pitting in cylinders.
« Reply #3 on: March 06, 2020, 11:25:21 AM »
If it ain't broke...
Run it.
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Offline PeWe

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Re: 1975 cb750f pitting in cylinders.
« Reply #4 on: March 06, 2020, 11:59:56 AM »
Not smoking oil is another factor. Valves + seats with  guides and seals affect compression readings and eventual oil smoke.

Smoke from rear wheel when twisting the throttle is good too!
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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 mechanic3

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Re: 1975 cb750f pitting in cylinders.
« Reply #5 on: March 06, 2020, 02:43:59 PM »
Thanks guys. Just wanted your opinion before spending money on tires. I think i will give it a go the way it is. Very much appreciate your help
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