Z2 750 crank (Bossie the Kaw)

Put the 125's back in. Much crisper. Going for a short ride to see how it does. :woohoo:
Steve

A comp test at 500 and at thousand miles will tell you the real numbers. Mines at 165 last check so thinking its right at 10/1 or a hair under.

But remember CR and compression pressure is not exactly the same thing, the wilder GPz variants often have lower compression pressures despite higher CR due to the hotter cams.

What are the chances of that being a pre z1 750 crank?

Assuming the extra squish doesn't cause problems, you have a great candidate for a turbo bike with the modest CR and mild cams. And with all that clearance you can rag the nuts off it without piton/valve interference.

Don't close the thread, I think it is interesting. These jobs always take a long time of planning and accumulating parts beforehand, so nice to see it coming together and up and running with a few days.

Put about 50 miles on it. Sky valley, to 1000 Palms, to Desert Hot Springs and back to Sky Valley. Running about 10* hotter. A little blubbery just off idle. Pulls clean up to 6000 RPM. Good strong throttle response off the line and in fifth gear. A .5 step up on the pilots is a big jump. Over 100 now so I'll check the plugs in the evening.
Maybe I should put the 60's back in and raise the needles?
It came out of a wrecked Z2 750 engine. I don't plan on putting a Turbo on it, I don't want to be launched off a cliff. :lol:
I'm thinking on sending this thread to the original Poser thread. Lots of info there and combining the two just makes sense to me.
Comments?
Steve

Tyrell Corp wrote: A comp test at 500 and at thousand miles will tell you the real numbers. Mines at 165 last check so thinking its right at 10/1 or a hair under.

But remember CR and compression pressure is not exactly the same thing, the wilder GPz variants often have lower compression pressures despite higher CR due to the hotter cams.

What are the chances of that being a pre z1 750 crank?

Assuming the extra squish doesn't cause problems, you have a great candidate for a turbo bike with the modest CR and mild cams. And with all that clearance you can rag the nuts off it without piton/valve interference.

Don't close the thread, I think it is interesting. These jobs always take a long time of planning and accumulating parts beforehand, so nice to see it coming together and up and running with a few days.

Thanks Tyrell so your saying since I put in the slightly warmer 750 cams I am a "little" bit better off yet ? Maybe I'll get to that 101/4 to one after all. Only went with a min cut on the head APE said .004 got it and it looked perfect. Moving this to the original Poser thread sounds good to me.......I'm interested in following your build Steve.

KZB2, your head skim really is very minimal, a 'gnats willy' is the technical term i think. Your CR increase will be quite minimal on that, as a guess less than 0.25 points.

More duration and overlap onthe cams increases power and brings it up on the rpm range...think grunty z650 compared to screaming redline zx750 unitrack. A very nice compromise might be GPz750R1 cams, if you can find.

What i like about this thread is it is 'wrong' , just like my earlier'wrong' low compression GPz 550 build that worked really nice -until I trashed a piston 5k miles later. All the muppets laughing at Steve as he has a part he hasn't correctly identified - join the club, this is what happens when you hoard 30 year old motorcycle parts.

It was also said, "I haven't heard of this as being done before. Was it a combination of slightly shorter rods, wrist pin location and piston crown? I'd like to know. 12mm is a lot. I think I've accounted for 2.5mm, where did the other 9.5 go?
Steve

Is the 750 stroke the same but the 750 rods are shorter? Or is the pin boss lower in the skirt on the 750? I have no idea.

I've compared the pistons. What I didn't have were the stock 8.5/1 pistons to match against. Now I do. The stroke is supposed to be 58mm. The 903/1000 is 66mm. Even if the rods were 2.5mm shorter, the wrist pins are lower and the piston dome is 10mm. It still doesn't add up. Or does it? I used the 750 sleeves in my 903 barrels. Mine were bored off center buy a clown that had wrecking yard/.shop. I took them to Clupper racing and had them bore them out. He complained they were so thick and were spinning in the block he almost gave up. Would the block have something to do with it?
Bruce, when you went to your 1075 kit, were your 1015 pistons even with the deck? If so did your 10.5 pistons sit above the deck?
This is one of those things that will bother me until it's solved. :pinch:
Steve

The flat edge of the Wiseco pistons were just about. .010"over the bare cylinder/sleeve deck with the 1075 kit. I think the 1015 Pistons were right at or a very tiny bit below the deck. I originally was a bit worried that the 1075s were too far above the deck and could be a problem. Especially since my back up head had a .010" warp and had .012" milled off to flatten it.
So much so that I considered using two base gaskets but taking head gasket crush into consideration, they were still below the top of the metal ring made into the head gasket. So I let it go.
Also, keep in mind that the 8mm difference in stroke means 4mm up and 4mm down so if you have a 58mm stroke, the pistons would only be 4mm (or less then .16") below flush with the deck.

Good point. I measured the stock 1015 piston crown and the 10.25/1 cast piston to the top of the wrist pin bore. No difference. So I must have 2mm below the deck and didn't notice it. :dry:
Steve

Combining 1&2
Steve

I put my 4 ohm coils back in this morning. Had some corrsion at the coil H/T leads. It started misfiring on the way to my daughter's a few months ago. I can feel the difference. I have my spares under the seat, just in case. Almost 200 miles now. I feel like a kid waiting for XMAS. 500 miles and I can grab a hand full. :woohoo:
Steve