questions on 836 kit

[Truck]

So I'm looking at this 72 cb750. Will be a complete strip down bobber mod if I get it. Unfortunatlly I'm a Graduate of the Tim Allen school of Engineering and I want more power!

I've been looking online at some big bore kits and just wondering if its really worth all the work. I understand you have to get the the bores expanded, but what other work is involved? I'm guessing a larger cam is required, possibily upgraded coils?

Any advice would be helpful. I have the 900 so this will be a long term project and I can get the bike for a few $100's.

[TOOLS1]

You do not NEED to do any other modifications to run an 836 kit. You will have a nice increase in power with just the oversized pistons. However a camshaft change will really wake an engine up.
TOOLS

[Truck]

Hmmm, interesting. Although if I'm going through the trouble of tearing apart the engine might as well throw in a hot cam    

Any recomendations on which big bore kit to go with? I've read some good things on the Weisco kits.

[Re-run]

I know people who have used this and had good results.
http://www.ebay.com/itm/69-77-HONDA-CB750K-836cc-BIGBORE-PISTON-KIT-W-GASKET-/141395412927?pt=Motorcycles_Parts_Accessories&hash=item20ebd2c7bf&vxp=mtr

This seller has been selling cb750 pistons for years.

There are 4 things for hotter engines.

Big bore pistons, obviously.

Hotter cam

BUT you will want to add this to the list. A good head port. These heads flow poorly and while you will get some increase with a cam and pistons, porting the head is required if you want a serious boost.

Now, if you DO decide to get a serious boost, the stock rods must be shot peened, at minimum. Otherwise they will bend. Especially since they are over 40 years old now.

Better yet, new rods. Now, rods can be expensive. Carillos run $1000 for a set. Falicons were somewhat cheaper but not anymore, but unless you are seriously wanting to put through some power, the cyclex rods are 600.

As I hate spending money if I don't have to, I would just find new stock rods and shot peen them.

There are also forged aluminum connecting rods. Some use them, some don't. Some say they stretch too much, hard to say. I suppose it depends on the power bump you want.

Or you could always go apeshit and stroke the motor. http://www.satanicmechanic.org/bigbore.shtml

IF you decide to stick with your rods, at minimum, replace the bearings and the con rod bolts, they must be replaced no matter what.

If you are just planning a small increase, 836 with just a mild cam, then the stock rods will be fine, though you should still replace the con rod bolts.

[TOOLS1]

I just did an engine with one of those piston kits. I just had the cylinders bored, and installed a WEB Cams 63A grind cam with an adjustable cam sprocket, so I could degree the cam. The only other mods were heavy duty head studs, and heavy duty clutch springs. I did not do any of that other stuff. How is this engine running? Is it going to blow up? Should I take it apart, and do all those modifications? And yes I am being sarcastic. All those modifications are only necessary if you plan on making some serious HP for racing.
TOOLS

[Re-run]

"Unfortunatlly I'm a Graduate of the Tim Allen school of Engineering and I want more power! "
Miss that part? That's why I listed what I did. otherwise, read my last sentence.

[TOOLS1]

Oh. I was having a flash back to when I used to follow another forum.
TOOLS

[Truck]

Naaa, not looking to build a drag bike, just something fun to run around town own a run from light to light. I'll wait till I get my hands on a 'busa engine for the race bike. Like I said planning on a bobber, forward controls, might have rear springs, might not... I have learned the hard way that +200 hp and a hardtail do not go well together for you butt bone

Tools, you would nt have any HP numbers from before and after would you?

[Re-run]

Another forum huh, the forum that shall not be named! yeah, there is a reason why I left that one.


Truck, Your 72, stock, would rate about 58+ hp, at the rear, give or take. Most specs you find are crank specs and rear wheel usually drops about 10 hp.
A bore and cam would bump you up about 15ish, say 70 or so. Obviously, this all depends on the overall condition of your engine. Now 15 might not sound like much, but look at it in a percentage and the number is more impressive. Heck, maybe even a 20 hp increase but that might be pushing it a bit.

I have seen cb750s, sohc mind you, push over 100 hp at the rear. Obviously that will cost and I think either of us would just get a different bike if we wanted that power.

So, while a bore and cam will hop things up, I would do a port, but that is just me and is certainly NOT required!

You know, you COULD always get your hands on a 1080 kit! Of course, most are not comfortable milling their engines so much that they need to weld holes closed!

[Truck]

Yeah I looked at the 1000+ kits and although they sound cool I don't like the idea of carving that much out of the motor.

Doesn't matter, guy wanted to much for the bike. Guess I'll just have to continue to make my 900 badd ass. Next step new seat and forward controls!

[Re-run]

Yeah 1080 isnt for the faint of heart. Unless done right, lots of these mods leak oil and have poor cooling.

Still, it would be cool.

[Truck]

I don't want to drop any names, but I do know a dude who's skills are up to the challenge of such a feat...

[rich]

I'm so old. A stock SOHC 750, in third gear, at redline, damn near scares the pi$$ outta me. I don't need any more speed.