Author Topic: Engine rebuild and modification questions  (Read 1252 times)

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Offline pickingupdimes

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Engine rebuild and modification questions
« on: July 23, 2015, 05:44:20 pm »
So ive finally got to the point where I can begin rebuilding my 750K engine. I dont want to get too crazy, but I do want to build a solid machine thats light and quick and durable. This is my shopping list so far:

836cc cast piston kit
Webcam
Stainless intake and exhaust valves
Heavy Duty springs
Heavy Duty engine studs
Complete gasket set and engine oil seals
14 tooth front sprocket
Hone cylinders
Heavy duty cam chain and tensioner
530 drive chain

Is there anything else I could or should reasonably do to reach my goals? The motor was locked when I got it - the number four piston was frozen. Iv err taken a few pictures of my progress for your consideration. The only thing thats broken so far is the stem that holds the central bolt for the points mechanism. Is that a big job to fix? I know I couldvprobably get away with a valve lapping and a set of piston rings if I just want it to run again, but I want to make people drool over the engine.
1978 CB750K8
1981 GS550L

Offline calj737

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Re: Engine rebuild and modification questions
« Reply #1 on: July 23, 2015, 05:52:18 pm »
Send the head to Mike Rieck for a top notch Serdi valve job and his Stage II or III porting. New KW valves and seals too.

By the way, with an 836 kit, you'll be boring, not honing your cylinders.
'74 550 Build http://forums.sohc4.net/index.php?topic=126401.0
'73 500 Build http://forums.sohc4.net/index.php?topic=132935.0

"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Engine rebuild and modification questions
« Reply #2 on: July 23, 2015, 05:59:46 pm »
Not sure what K model you have but forget the 14T 530 sprocket. 17 minimum. Adjust further (+) at the rear sprocket and get a 530 long enough to fit 3 extra teeth or more on your rear sprocket (48 or 48+)
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline pickingupdimes

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Re: Engine rebuild and modification questions
« Reply #3 on: July 23, 2015, 07:36:08 pm »
Not sure what K model you have but forget the 14T 530 sprocket. 17 minimum. Adjust further (+) at the rear sprocket and get a 530 long enough to fit 3 extra teeth or more on your rear sprocket (48 or 48+)

The stock sprocket only has 15 teeth. Is it better to leave it alone and increase the rear sprocket?
1978 CB750K8
1981 GS550L

Online scottly

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Re: Engine rebuild and modification questions
« Reply #4 on: July 23, 2015, 08:23:25 pm »
The K8 has a 15 tooth 630 front sprocket. If you want to switch to 530 chain, a 17 tooth front with a 48 tooth rear is a good combo.
Don't fix it if it ain't broke!
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: Engine rebuild and modification questions
« Reply #5 on: July 23, 2015, 08:24:50 pm »
So we'll speculate it is a 77/78 K or F? If so you're counting teeth on a 630 sprocket.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Online scottly

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Re: Engine rebuild and modification questions
« Reply #6 on: July 23, 2015, 08:29:31 pm »
He has K8 in his sig, bro. ;)
Don't fix it if it ain't broke!
Helmets save brains. Always wear one and ride like everyone is trying to kill you....

Offline Phinn

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Re: Engine rebuild and modification questions
« Reply #7 on: July 23, 2015, 08:53:43 pm »
Both Webcam and Dynoman recommend giving the rocker arms the hardweld treatment, especially for an 836 with a more aggressive cam profile and HD valve springs.  I'm sure other posters can offer more reliable opinions on the subject than I can, though.

The APE valve guides are also a popular upgrade option.
« Last Edit: July 23, 2015, 09:00:09 pm by Phinn »
1978 CB750K -- "Mouse," a former basket case, resurrected

Offline Garage_guy_chris

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Re: Engine rebuild and modification questions
« Reply #8 on: July 23, 2015, 09:44:11 pm »
the piston pictured and the 14T sprocket discussed suggests that the engine is a late 77/78 K or F engine. I would run the engines serial number and figure out what you have.

One of the more popular choices for a cast 836 is the cruzin image kit available for $130 on ebay. Here is the main discussion thread for it. If your set on cast pistons this is likely your only choice.

http://forums.sohc4.net/index.php?topic=89779.3

Your build plans are in the right direction but you have to decide what you want the end result to be cost wise reliability wise and performance wise.

your talking about putting an inexpensive bottom end together and an expensive fancy top end together. In my opinion i would either go for a wiseco 836 or back off the cylinder head a bit. Also consider your connecting rods 836cc is generally regarded as the stock rods limit. if your gonna go budget cruzin image cast i would just go with the F2 rod bolt mod. if your gonna go wiseco i might suggest a set of cycle X super rods. I just built a very similar engine so ive just been through all this
1971 Cb450 Cafe  (on the road)
1974 Cb750 Restomod (on the road)