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Offline 75 super sport

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copper base gasket question.
« on: March 04, 2015, 07:02:05 PM »
Having trouble choosing which copper base gasket to use on my 836 build. Motor is a '75 cb750f. I am just curious what size to use and thickness. Thanks in advance
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Offline chewbacca5000

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Re: copper base gasket question.
« Reply #1 on: March 04, 2015, 07:30:27 PM »
Quote from: 75 super sport on March 04, 2015, 07:02:05 PM
Having trouble choosing which copper base gasket to use on my 836 build. Motor is a '75 cb750f. I am just curious what size to use and thickness. Thanks in advance

Why spend the money on a copper base gasket when the stock gasket works just fine?  Base gaskets rarely ever leak.  Always the head gasket. 
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Offline 75 super sport

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Re: copper base gasket question.
« Reply #2 on: March 04, 2015, 07:35:35 PM »
I was told not to use a fiber base gasket...idk.
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Offline bwaller

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Re: copper base gasket question.
« Reply #3 on: March 04, 2015, 07:50:55 PM »
Another option is Viton coated steel, available in various thicknesses.
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Offline flybox1

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Re: copper base gasket question.
« Reply #4 on: March 05, 2015, 08:49:36 AM »
I used Vesrah w a few coats of copper spray.  No leaks here.
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

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Offline PeWe

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Re: copper base gasket question.
« Reply #5 on: March 05, 2015, 09:34:24 AM »
I have never had a leak from base gasket on my CB750-K6. Always std fiber.
I have lifted head several times without disturbing cylinder and old base gasket. Total rebuild opening cases 3 times + additional 2 lifting cylinders with new base gasket.
Metal gasket good as spacer for lowering compression, longer rods, higher pistons.... The racers opening the engine more frequent like metal gasket when it is reusable,right?
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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 lrutt

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Re: copper base gasket question.
« Reply #6 on: March 05, 2015, 10:02:49 AM »
Never seen a 750 leak at the base gasket. Head gasket maybe but not base.
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06 Harley Sporster 1200C, 06 Triumph Scrambler, 01 Ducati Chromo 900, 01 Honda XR650L, 94 Harley Heritage, 88 Honda Hawk GT, 84 Yamaha Virago 1000, 78 Honda 750K w/sidecar, 77 Moto Guzzi Lemans 850, 76 Honda CB750K, 73 Norton 850, 73 Honda Z50, 70 & 65 Honda Trail 90, 70 & 71 Triumph 650s, 65 Honda 305 Dream, 81 Honda 70 Passport, 70 Suzuki T250II, 71 Yamaha 360 RT1B, 77 BMW R75/7, 75 Honda CB550K, 70 Honda CT70

Offline 75 super sport

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Re: copper base gasket question.
« Reply #7 on: March 05, 2015, 11:28:58 AM »
Nice thanks, so when you use a thicker gasket it lowers compression? I was curious about that too
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Offline PeWe

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Re: copper base gasket question.
« Reply #8 on: March 06, 2015, 12:50:17 PM »
Quote from: lrutt on March 05, 2015, 10:02:49 AM
Never seen a 750 leak at the base gasket. Head gasket maybe but not base.

I have seen base leak with big bore, 900cc or more...
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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 chewbacca5000

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Re: copper base gasket question.
« Reply #9 on: March 06, 2015, 02:55:26 PM »
Quote from: 75 super sport on March 05, 2015, 11:28:58 AM
Nice thanks, so when you use a thicker gasket it lowers compression? I was curious about that too

Compression is how much you are squishing your air / fuel mixture.  Adding more heigh means less intense of a squish.  Think of it this way you and 10 of your friend are stuff into a 10x10 room.  Pretty right right?  Then someone adds on another 5 feet to make the room 10x15 not so bad.

Compression of 9 or 10 for street lower for turbo and higher for drag applications non turbo.
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