4 valve head swap?

I think the old GS cams and head were the ticket back in the day - circa 1984... I am a died in the wool Kawasaki guy, but the first time I rode a GS1100/VF1000/5 valve Yamaha 750 - not sure of the name, but bloody fast ! I could not believe the power and acceleration of those machines - true there are a few on that list of 1 liter capacity, but damn those things were rockets !!! I think that 750 Yamaha was as fast as those 1000's... almost wheelied into a parked car - as peaky as a 750 tripple !!!
I thought about switching teams, but backed off due to the short shorts...

Larry, what you said is exactly what I am trying to do. The zx750 had the center cam chain until 1991.

I may very well pick up jugs from other center cam chain 750's to see if they are a closer fit.

My goal has always been 100hp at the rear wheel with a useable torque curve.

Be aware that any old 4 valve head you find is likely to be in poor condition valve wise. Don't be surprised if it needs valve seats. If you get one, pull it apart and blast the carbon out of the chambers. Often times the pitted seats are masked by carbon build up. Looks good until you blast it

Generally it's just the intake seats so you might be looking at 8 seats.

Hope something simple falls in place for you so you can actually make it happen cost effectively

Injected wrote:

I think the old GS cams and head were the ticket back in the day - circa 1984... I am a died in the wool Kawasaki guy, but the first time I rode a GS1100/VF1000/5 valve Yamaha 750 - not sure of the name, but bloody fast ! I could not believe the power and acceleration of those machines - true there are a few on that list of 1 liter capacity, but damn those things were rockets !!! I think that 750 Yamaha was as fast as those 1000's... almost wheelied into a parked car - as peaky as a 750 tripple !!!
I thought about switching teams, but backed off due to the short shorts...

Those early 5 Valve Yamaha's were strong runners. Way ahead of the rest of the pack in head technology and it showed in performance.....

I saw a KZ long ago with a GS1000 head grafted on. Waste of time and money IMO.

I hear you loud and clear! I figure with any of these older 4 valve heads it will probably need seats and valves. With the zx750 head I was looking around for stainless valves as the factory valves had a tendancy to eat themselves

The debate now is how cost effectivly can my guy make the head swap, I think I know what it will cost to get close 2 my goal with the 2 valve head. (figure 810 kit $600, head work $1,500, cams $400) but from all the dyno results I have seen that only gets me close not there.

Ok well I talked to my guy on the phone last night and we will be moving forward with the zx750 swap.

Spacing between 1 and 2 is correct
Spacing between 3 and 4 is correct

Spacing between 2 and 3 is off by 1/8 - 3/16

He will correct this by cutting 2 heads and 2 blocks then welding them together. Using 2 heads and 2 blocks means there will only be one weld.

The cam chain tensioner hole will be an oval, so he will make a custom manuel tensioner.

The studs will be close but off, he will make threaded alum rods to fill the holes then weld those in place. Then he will drill and tap the new holes for the bolts. We will use the zx750 bolts in the initial build for easy and upgrade to studs eventually.

The through block oil lines are way off so we will be using braded steel lines to the head.

The cams will be milled for a key way before they are cut, this way we can aling them perfectly later. Then he will machine up a collar to hold the key's and finally weld the collar onto the cams.

Water will flow via a electric water pump, this is something 'busa owners are doing because the electric pump will pump at full speed regardless of RPM.

The inital build will be on a sound, but cheap spare 650 bottom end, saving the high dollar parts I have been collecting for a later rebuild (so if it blows up badly I don't lose $2000 in parts!).

The head gasket we are split on, I want a cometic copper, he wants to cut and rtv a standard head gasket. He is not a fan of copper head gaskets on water cooled motors... I will probably go his route cause he knows his stuff.

He wants to do this... this is the kind of work that he enjoys so is encouraging me.

What does everyone think?

Pistons: we are not sure yet... the wrist pin holes on the pistons will be 2mm larger than the stock holes. We may bore out the stock kz650 rods on the test motor to fit the larger wrist pins, but I am not going to bore out the small end of my carrillo rods! And carrillo told me on the phone that, the rods I have cannot be borred to use any larger wrist pins.

The displacment will work out to 780cc's 68mm bore and 54mm stroke. With 1991 zx7 pistons fitted I will have 71mm bore for a displacement of 860cc's but that would be an upgrade that I deal with years after the inital build... there are so many things that can go wrong I don't need to tempt fate.


My buddy (Rob from RTR Enterprises of Palmyra NY) tells me people do stuff like this all the time on race sleds, but those are 2 strokes so quite a bit different.

Hey, if some LIMEY can a 2400cc v12 kz1300 and another can make a 210mph gpz750 then this is certainly worth a try!

I'm definitely paying attention...I don't know nearly enough to know whether it will work or not, but I can't wait to find out the results!

hardr0ck68 wrote:

Hey, if some LIMEY can a 2400cc v12 kz1300 and another can make a 210mph gpz750 then this is certainly worth a try!

:laugh:

I wondered when my name was going to come up

I bought a mid 90s ZX750 (GPX750 over here) gasket some years ago with the same idea but discounted it as too much work for too little gain.

Good luck with it though, I'll be watching.

Lorcan wrote:

hardr0ck68 wrote:

Hey, if some LIMEY can a 2400cc v12 kz1300 and another can make a 210mph gpz750 then this is certainly worth a try!

:laugh:

I wondered when my name was going to come up

I bought a mid 90s ZX750 (GPX750 over here) gasket some years ago with the same idea but discounted it as too much work for too little gain.

Good luck with it though, I'll be watching.

Now that's funny stuff there :laugh:

This thread ROCKS! This is going to be awesome when it's done. 100hp and BEYOND! And the desighn was simple: get off your ass and build it. The key all along was thinking it through. And then doing the work. And the benifits are yet to come. Wonder how good the head will actually be for flow. Quench and the port work, whatever has to be done to make the head rock is critical here. Lobe centers are going to be fun. You can dial up anything you want for power band. The size of the carbs alone and the engines ability to use them properly is key factor that allows the high hp gain. Just what your looking for.:woohoo:

I just ordered a second block.

I am trying to find out if there are differences in the heads from 1986-90 because many of the cheap ones on ebay don't list the exact year.

There will be no porting or expensive work done on the head this year... we just want to make it work. If we can make it work and be reliable then maybe it will be sent off for a light port and some valves (stainless) and valve seats.

The valves and seats in the zx750 motors were reported to be the weakness of the motor, so I would like to replace them.

Carbs will only be on this bike until I find the time/money to get a megasquirt kit... I HATE carbs of any kind, but for the time being they are a necessary evil. Carb spacing will have to be addressed along with what carb to run... whatever is easiest and cheapest will be used.

Still moving forward, I am currently looking for 2 heads and a set is 1990 cams.