Topic: Looking to bump a CB750 K8 up to 836cc, looking for recommendations.

[Mr Freeze]

I recently got a CB750 K8 motor with 13k on it. I'm interested in taking it up to 836 with a camshaft and any other necessary items to make it sweet for city / highway riding and all that. I'm looking to mate it with a set of '74 Keihin 657A "roundtop" carbs with dual 4-2 exhaust from Cycle X.

I'm looking for recommendations on camshaft / piston kit combos and anything else you can think of while the motors apart.

[Jerry Rxman Griffin aka MuthaF'er]

Grab the cruzinimage 836 kit off ebay. $120. Mid-range cam better for the street unless you're twisting it at high rpms all the time. Megacycle 125-65 maybe? Less expensive would be APE 360 maybe? Webcam 41A?

[chewbacca5000]

Jerry is that mega the same one Hodaman recommends.

[tlbranth]

I recently got a CB750 K8 motor with 13k on it. I'm interested in taking it up to 836

Why?

[Jerry Rxman Griffin aka MuthaF'er]

Jerry is that mega the same one Hodaman recommends.

Not sure if that's Mark's favorite?? I'm staying away from the more radical ones here that are big HP at higher rpms.

[Retro Rocket]

I recently got a CB750 K8 motor with 13k on it. I'm interested in taking it up to 836

Why?

If that motor only has 13k miles on it i would invest in a port job {maybe bigger valves}, a 4into1 a bigger cam and some bigger jets, it's done no miles at all and would be a waste to start boring it now, this will be better than just throwing pistons and a cam in it and when its got some more wear in it, throw in the 10.5 to one weisco pistons and be done with it...there's more power locked up in the heads on these bikes than any other area, start there...

[Mr Freeze]

I recently got a CB750 K8 motor with 13k on it. I'm interested in taking it up to 836

Why?

If that motor only has 13k miles on it i would invest in a port job {maybe bigger valves}, a 4into1 a bigger cam and some bigger jets, it's done no miles at all and would be a waste to start boring it now, this will be better than just throwing pistons and a cam in it and when its got some more wear in it, throw in the 10.5 to one weisco pistons and be done with it...there's more power locked up in the heads on these bikes than any other area, start there...

Well the reason I was thinking all this is because the head gasket doesn't look that great. So I pulled the head first and figured I'd weigh my options about doing any other freshening up and maybe going up to some Wiseco's while I was in there. I've been doing research on the forum, but was mostly looking for advice on a combo kit with proven results.

I know 13k isn't a lot of miles at this point, I was thinking of APE HD studs and valve guides if needed as well.

RetroRocket, do you have a recommendation as far as valves and camshaft go? I'm looking into the Cycle X exhaust and I'm really digging their 4 into 2 systems.

[madScientist]

Bigger displacement is all well and good and i'm not knocking the desire...but...the head on these bikes seems to leave a lot on the floor. Having a good porting job done can really help wake these bikes up. Especially if you're going to be putting a cam in.

Also, if you go with a Megacycle 125-65 (i did), it'll likely be a hardwelded cam which means they're going to recommend hardwelding rockers.

Just some food for thought. And it's stuff you could do after the 836 increase. If you have a frame kit it can be done in the bike.

[Retro Rocket]

I recently got a CB750 K8 motor with 13k on it. I'm interested in taking it up to 836

Why?

If that motor only has 13k miles on it i would invest in a port job {maybe bigger valves}, a 4into1 a bigger cam and some bigger jets, it's done no miles at all and would be a waste to start boring it now, this will be better than just throwing pistons and a cam in it and when its got some more wear in it, throw in the 10.5 to one weisco pistons and be done with it...there's more power locked up in the heads on these bikes than any other area, start there...

Well the reason I was thinking all this is because the head gasket doesn't look that great. So I pulled the head first and figured I'd weigh my options about doing any other freshening up and maybe going up to some Wiseco's while I was in there. I've been doing research on the forum, but was mostly looking for advice on a combo kit with proven results.

I know 13k isn't a lot of miles at this point, I was thinking of APE HD studs and valve guides if needed as well.

RetroRocket, do you have a recommendation as far as valves and camshaft go? I'm looking into the Cycle X exhaust and I'm really digging their 4 into 2 systems.

Cam wise, You wouldn't want anything too big if you retain the stock bore and Kibblewhite valves are the ones i buy, but if i were you i would send  forum member MRieck a pm and speak to him, he is renowned internationally for his head work and is the resident expert here, his advice is the best...   As about cam valves springs and porting, you will be amazed at how well these bikes go in stock bore with the above mods, and like i said earlier, when it all gets a bit tired, stick in the 836 pistons and enjoy...

Mike Riecks contact details below..

http://forums.sohc4.net/index.php?action=profile;u=49

[Mr Freeze]

I PM'ed him. See what he has to say. Thanks again.

[Mr Freeze]

So I talked myself out of the 836CC hop up for the time being. Here's what I figured I'll do now instead.

APE Cylinder Studs
APE Valve Springs
APE Valve Guides
Engine Gasket Set (obviously)
Porting the head
Re-ring the pistons

Now I'm curious on the right camshaft....

[Grinnin]

I'll read the replies too.

Just took mine apart for rings, gaskets, and guides.  Neighbor says that instead of honing I should just have it bored for 836 and more fun/torque.  OK, why not?

(Welll, the rings are at the edge of the wear tolerance in Clymer but not out of spec.  The cylinders are tapered less than .001 to the best of my (rough) measuring ability.  That's why.  (If I lean toward not boring I can get better measurements of my cylinders.))

It had enough power for me for some 12,000 miles.  I didn't tear down to add power.  But with it torn down I might as well pep it up.

So I'll watch your advice to Mr. Freeze.

[Retro Rocket]

So I talked myself out of the 836CC hop up for the time being. Here's what I figured I'll do now instead.

APE Cylinder Studs
APE Valve Springs
APE Valve Guides
Engine Gasket Set (obviously)
Porting the head
Re-ring the pistons

Now I'm curious on the right camshaft....

See if you can get the MLS gaskets in stock sizes, simply the best ...