DOHC Big Bore -- What do I need?

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DOHC Big Bore -- What do I need?

jwaltmire
Hey friends,

Some background: I have a 79' 750K which has a hole in the cylinder block (sawed through by the cam chain). Otherwise, the bike is in good shape and runs surprisingly well aside from the oil leak and cam chain rattle.

I've ordered a new block on eBay, and am considering boring it out and using a Wiesco kit to get more power/better compression while I have the top end apart anyway.

Can anyone give me a definitive list of parts that I would need to swap/upgrade to make a big bore kit work on my K? I already plan on replacing the gaskets, pistons and rings (obviously), and cam chain. Do I need a different or modded cylinder head? Different cams?

I've already done some searching through the forums and haven't been able to find out what has actually worked. Any help would be great!!
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Re: DOHC Big Bore -- What do I need?

TOOLS1
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These are the piston kits I use when I overbore engines. Excellent quality, and a lot cheaper then Wisco.

http://www.ebay.com/itm/79-82-HONDA-CB750F-823cc-BIGBORE-PISTONS-KIT-65mm-PISTON-10-CB750FBB-/162355320744?vxp=mtr&hash=item25cd2197a8

As for the engine needing anything else, nothing else is necessary, but a CB 900 cam is a direct swap, and does improve performance.
TOOLS
BTW. I bore and hone cylinders, and do valve jobs.
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."

1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: DOHC Big Bore -- What do I need?

jwaltmire
Thanks, Tools! This is awesome news. I've ordered those pistons-- $150 is much more manageable than $500 with the money that's already going into boring, new gaskets, cam chains, and anything else I'm liable to find in there once I open the engine up.

I've also managed to get my hands on some CB900 camshafts. Any best practices when I drop them in? This is going to be my first foray into engine rebuilding-- using my Clymer manual as a bible.

We've got several machine shops here in Portland that should be able to do the engine boring for me, but I appreciate the offer. I have no idea what state my valves are going to be in.
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Re: DOHC Big Bore -- What do I need?

TOOLS1
Administrator
Portland, my friend Becca just moved there. I would recommend you down load the factory service manual from our manuals thread here. It is a lot better then the Clymer/Haynes manuals.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.
"That is awesome shit there" Re-Run
"Fear nothing, attack everything" Eric Berry
" Oh, you read that on the internet? Clearly it IS a massive problem. Of course it CAN’t be normal operation."

1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: DOHC Big Bore -- What do I need?

Truck
DAAAMN....wonder how much it costs to send an engine to KC???
It's only illegal if you get caught.

If at first you don't succeed, use more lighter fluid

95% of Harley Davidsons ever made are still on the road... The other 5% made it home.

New Baltimore, Va '82 CB900c, 1980 CB985F/K 'Mutt"
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Re: DOHC Big Bore -- What do I need?

deskinthewoods
"I have no idea what state my valves are going to be in." I would imagine they would be in Oregon...Sorry, couldn't resist...
1981 CB750K
Wakefield, Québec, CANADA
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Re: DOHC Big Bore -- What do I need?

jwaltmire
Hah! You got me there.

Thanks for the heads up about the factory manuals. I'll definitely use them. If there's any interest, I'll keep posting through the rebuild process and share the final result.
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