4 valve head swap?

hardr0ck68, if you are going to use the entire top end on a air cooled bottom end, seems like you'd be money and time ahead to use the complete motor?

Might check Wiseco's site for piston pin diameter for both motors to compare.

Without a doubt, liquids cooled motors make more power and last longer, but IMHO, if a KZ 750 is not air cooled it ceases to be a KZ750.


Dave Sloan's KZ650/810 has a problem, since it is only getting 80 hp to the rear, and I'm pretty sure Dave knows this, I'm also pretty sure he's working on it. So don't take that 80 hp number as a limit. Especially since I think Reborn650 would seriously disagree with you

Speaking of, where is he anyway? Fall in love with the Ferrari and dump the KZ or something?

Last time I messaged Dave he said he seemed pretty happy with the tune of the bike but I could be wrong, I thought he had told me he was at 82hp and expected to pick up 2 or so more with some more dyno time to iron out the map.

I have serious doubts that some of the z1's out there have more than 10% of the origional parts on them but folks still say they are z1's. And anyways I don't care what people call it I know what I started with.

It very likly may not be possiable... but so what; what is $50 these days? A 24 of beer and a large pizza?

I didn't mention Nitrous because I am not a fan...

Also the numbers you put up for those 750's ridden by fat guys pulling high nines don't seem to jive...
If your bike is say 350lbs and rider is 250lbs then with that kind of weight it will require about 130HP to achieve that sort of ET... maybe those guys are spraying?

My drag bike weights 340lbs and suited up I am 190lbs... my 831cc 15:1 F.I. motor on alcohol has a best performance of 10.2 @ 132 (against a headwind) motor makes 122HP so I believe it is capable of at least 9.5-9.7 @ +140 MPH on a perfect pass.

Still working on the tune up and that elusive best past.

I have heard all kinds of stories about fast 650/750's because it seems like everybody has one... sort of like fishing stories.

Dave is fixing his clutch with the rubber I sent him a while back, but I don't think that will affect his power level. Hopefully he does have a bit more in it as I would like to see another motor running near it's limits.

hardr0ck68 - Where are you gonna put the water pump?
If you need a rad my buddy was in the small engine rad/oil cooler business and still has a lot of samples kicking around... I believe he still has a new never used Benelli rad off a Tornado 1130 - Its a full sized curved unit - could get you a sweet deal on it.

I tend to agree with the idea the high HP KZ650's are often fish tales. I am not saying they all are, or that a 100+ hp kz650/750/810 street motor isn't possiable with a traditional top end. Just that the seat of the pants dyno is the most often cited in measuring these big numbers.

Thanks for the offer, I will keep it in mind;
let's see how the jugs sit first... this may still be completely unfesaable for many reasons. But man that would be a bitchin rad

On the plus side.... even if it will take a crazy amount of machine work; the cat that helps me is both a total perfectionist and an insomniac and cause we have been riding buddies for years and friends since HS he is very reasonable.

Steell I am glad to see you around the forum again. There are few people with your knowledge of the 650/750 platform. I may sound dismissive, but I am listening to what you say... and thanks for taking the time to say it.

Hey, I like a good argument, it's fun and I often learn something new.

What;s the guy's name that built the V8, V5, etc Kawasaki's? Alan Milyard? Or something like that? He's got my respect, that's some serious modification!

I'm not suggesting you don't use the four valve head, I'm just saying that if you're using the entire top end, then it might be a lot easier to use the entire motor. Take it or leave it, it's just a suggestion

Keep in mind that I have over $3000 invested in a slow KZ750 twin, and I love it

And just how much sense does that make :laugh:

I lot of people thought I was nuts to spend a ton of time and dollars trying to get a 650 based drag bike to run fuel injected... but I made it happen anyways.

I always wondered what a 4 valve head would run like on a 650 bottom end... that head looks like it does not run any water in it - does it?

If you can get your hands on a used stock Honda CB750 piston (4V from 78-82) which is 62mm (stock 650) and has a 15mm wrist pin, you could see if the deck height and skirt were correct to run with that head/barrel/crank. Wiseco makes a forged big bore kit of that piston which would take you to 720cc - max for the stock liners.

Run that air cooled with a set of 34mm RS Mikunis and I bet it would flow lots of air stock.

Only downside would be that closed up rocker cover... will hold a lot of heat without the water keeping those pistons cool.

If your set on running the water cooled setup then maybe look at bushing the pistons and using the stock wrist pins - 3mm difference gives enough for a 1.5mm wall steel bushing which would be perfectly OK for a non race motor. That would get you around the custom rods.

You can probably run the water pump under the clutch cover off the secondary shaft with a rod sticking thru the plug cover with a cog and toothed belt at half engine speed.

Injected, are you the one that runs the KZ650 drag bike with the magneto that I think the pic is posted at cyclemadness?

Still not as bad as the guy that invested over 10 years and $10,000 into the KZ750 twin motor in his road race bike, and he was putting 95 hp to the ground (and still breaking parts)

But close (need a thumbs up emoticon here).

Yes... there's probably only one like that on the planet and that would be mine - I have over 15 years into the fuel injection part of that bike and I lost count on the dollar figure... it's all homemade anyways so it's not like somebody built it for me - I guess I did it on the cheap!

I have been playing with that same bike since '85.

I also have a buddy who like to fabricate...

The zx head does have water running through it. I thought about that at first (running it air cooled or running it with oil through the water jackets) and have not ruled anything out yet, but if I can get the entire water cooled set up to work I can crank up the compression

great idea about the honda piston though I will definatly keep that in mind.

you say it is alright to bush piston pin holes? I have heard that was a no-no before (my connecting rods have brass bushings in them so I wondered what the difference is....). Any info on the process or common uses of symiliarly bushed pistons?

Steell it definatly would be cheaper and easier to use the whole zx motor... but where is the fun in that? I dunno I just want to try this the hard way i guess.

Fun's where it's at, three guys here building small displacement bikes :laugh:

I'm not sure about using a steel bushing in an aluminum piston, seems like the different expansion rates may leave the steel bushing loose when it warms up. Wouldn't an aluminum bushing work better? Probably wouldn't want to bore the rod end 3mm, might weaken it past the failure point.

I lot of the early CB750 SOHC over bores were done that way as well as some smaller CB series motors (450-500) - there is some info out there on it... those Honda guys even raced those motors with bushed pistons - just start Googling...

The bushings have to be made to exacting tolerances... they have to have a light press fit on the piston hole bore pressed in from either end and the ID should have the same fit as the original pin did in the piston... make the bushings out of tool steel - the finish has to be the same as what is on the stock pin.

If you can't make them as described then don't attempt it!

You can also hone the small ends of those rods - maybe 1mm at best... there seems to be some info on that out there also... in the middle of the rod end there would be 3.7mm of wall stock and on the outer edge 2.7mm of wall stock after opening up the middle to 16mm diameter.
You will have to make a fixture up to do this machining to keep everything square and straight. Those rods are forged and extremely strong... at the same time you might want to swap those rod bolts for larger ones...
If in doubt ask around and get some measurements from other different rod ends to compare dimensions.

Again, if you don't have the equipment to do this then don't attempt it!

Hell, if Burt Munroe cast his own pistons and made con rods from pieces of truck axle, then I think bushing a piston is within reason...

That would open up your piston choices... my local engine builder uses all kinds of weird piston combos for different applications - he has even used a lot of jet ski pistons for singles and twins...

If this motorcycle is your main transportation I would not suggest these modifications... but if your trying to R&D that motor, then these would be ideas to look at - but make sure you investigate before diving in too deep.

Weather you make the piston pin bushing out of steel or aluminum I don't think would matter as far as expansion rates go... I could be wrong but that would be one of the key questions to investigate... I think the most important part of it is the fits involved - you want to be sure that the bushing does not move or twist within the piston pin hole.

I did see some info about bushing pistons on a Honda CB forum recently when I was investigating using Honda CB450 pistons in a KZ900 motor - with some work they swap over to yield 1025cc motor.