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TOPIC: Z2 750 crank (Bossie the Kaw)

Z2 750 crank (Bossie the Kaw) 19 Sep 2015 04:59 #690805

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Tyrell Corp wrote: What's the deck height on that :laugh: Some of these marine deisel engines are the size of a block of flats, quite amazing really.


Yeah, 1015 and 10.25/1 pistons but with the 2.5mm drop, I'll bet it's more like 9-9.5/1. Good enough for me

I think about 1 point drop in CR for every 1mm, so down about 2.5 points? 10.25 - 2.50 = 7.75

Is it 8.5: 1 standard? If your head has been skimmed at all that will get some back. If the exhaust valve timing lines are just a bit higher than the gasket face it is one indication that the head has been skimmed.

About 3% power for every point of CR, so I guess you are down less than 10 percent. They do run nice and smooth though you have noticed.




Attachment Compression_Power.gif not found





www.daytona-sensors.com/tech_tuning.html


Looking at your chart makes me want to get a 903 crank. On the other hand, I shouldn't have any problems running regular gas. :whistle:
Steve
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 06:03 #690815

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I guess it's time to close this one out. If anyone has some info on the Z2 750 crank, rod markings, numbers on the crank throws etc. Please post them here. I am confident it is a 750 crank but little is available on identifying markings. I started the Poser thread in response to one members questioning my truthfulness. Rather than stoop down to his level, I did my best to prove what I claimed is true.
In the end, I satisfied the question if nothing more than to myself.
Steve
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 06:06 #690816

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swest wrote:

missionkz wrote: Steve and a few of his buddies trying to decide if this is the crank he's been looking for to eliminate any question about the 750 crank possibly
installed previously...




:woohoo: Now that's a crank. :lol:
Steve

I went out to the Bar at Lunch and burned a fatty :woohoo:
Livin in "CheektaVegas, NY
Still have a Kaw! 76 KZ900 Pro-Street.
Went thru 25 of these in 40 yrs.

And The Old Girl, Harley 75 FLH Electra Glide,
Old faithful! Points ign. Bendix Orig. carb.
Starts everytime!

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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 06:10 #690820

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That stuff makes me stupid. I don't do it anymore. :lol:
Steve
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 07:31 #690834

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Put the 125's back in. Much crisper. Going for a short ride to see how it does. :woohoo:
Steve
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 07:59 #690838

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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. ;)
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 09:49 #690850

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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
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 11:51 #690867

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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.
1978 KZ650 b-2
700cc Wiseco kit 10 to 1.
1980 KZ750 cam, ape springs, stock clutch/ Barnett springs.
Vance and Hines Header w/ comp baffle and Ape pods, Dyna S and green coils, copper wires.
29MM smooth bores W/ 17.5 pilots, 0-6s and 117.5 main
16/42 gearing X ring chain and alum rear JT sprocket....
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 12:17 #690872

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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.
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces

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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 13:17 #690882

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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? :unsure:
Steve
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 14:12 #690895

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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.
Bruce
1977 KZ1000A1
2016 Triumph T120 Bonneville
Far North East Metro Denver Colorado

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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 14:44 #690896

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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? :unsure:
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
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 15:39 #690898

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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.
Bruce
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Z2 750 crank (Bossie the Kaw) 19 Sep 2015 16:19 #690901

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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
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Z2 750 crank (Bossie the Kaw) 20 Sep 2015 18:25 #691092

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Combining 1&2
Steve
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Z2 750 crank (Bossie the Kaw) 20 Sep 2015 18:38 #691093

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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
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Z2 750 crank (Bossie the Kaw) 20 Sep 2015 19:15 #691100

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I'm curious so I started doing some maths... something still doesn't add up.

Stock K1000 is as follows
Bore: 70mm
Stoke: 66mm
Disp: 254cc
V(TDC): 33cc
CR = 8.7:1

Stock Bore with 10.25:1 Weiscos
Bore: 70mm
Stroke: 66mm
Disp:254cc
V(TDC):27.5cc
CR = 10.25:1

Now lets look at the 750 crank with the 2.5mm Deck height measured with stock pistons
Bore: 70mm
Stroke: 58mm
Disp: 223.2cc
V(TDC):42.6cc
CR = 6.2 : 1

Now again with 10.25:1 pistons
Bore: 70mm
Stroke: 58mm
Disp: 223.2cc
V(TDC):37.1cc
CR = 7.0 : 1

Did I miss something here?
If I knew what I was doing all the time life wouldn't be any fun.

'80 KZ650 E 700cc, dyna ignition and coils, frame up restoration, daily driver
'81 KZ1300 A3 full restoration, custom big bore pistons, 1400cc 6 cylinder super bike
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"74 Yamaha DT 400 Enduro...

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Z2 750 crank (Bossie the Kaw) 21 Sep 2015 02:59 #691121

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Nice analysis Tyler, I wanted to calculate it exactly but didn't have the combustion chamber volume V(tdc)
If you are right on the 33cc V(tdc) , and the Wiseco are definitely exactly 10.25 then the numbers look right to me.
I'm getting 1016cc on those bore and stroke numbers.

Just an extra base gasket 0.5mm makes a measurable difference, so 2.5mm on the stroke will be very noticeable.
Those forged pistons and low CR woud be a good turbo bike project I guess.

Running-in will leave the unworn top part of the cylinder rough and could be a problem if you change the crank later.
Not really sure.
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces

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Z2 750 crank (Bossie the Kaw) 21 Sep 2015 03:15 #691128

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That's what I said. It doesn't add up. If it weren't for the 2.5mm drop, I was ready to accept that I made a mistake and it was a 903 crank and admit it. After all it was 28 years ago.
www.kawasakiz1.com/Kawasaki-Z2.html
That's why I've been trying to identify the crank. It shouldn't be that difficult. I was on eBay yesterday looking at crank shafts. The markings were all letters, this one has the number 45 stamped on it. I don't know if that means anything. So the nagging question persists. It was suggested I mark a wire at BDC, then at TDC and measure the difference, this I will do.
By your chart it goes from 42.6cc to 37.1cc so wouldn't the overall displacement be effected too?
I'd like to put this issue to bed for good.
Steve
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Z2 750 crank (Bossie the Kaw) 21 Sep 2015 03:35 #691133

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Tyler, if your math is correct and it seems to be .that would make it 892.8 CC engine with a compression ratio of 7;1 if anybody can verify the combustion chamber volume and piston dome volume . that would help.
original owner of a 1984 gpz 750
1985 turbo 750 stock, being restored.
1984 gpz 750 with 810 cc wiesco's megacycle cams(471-10) 34 mm flatslides v&h pipe ported head dyna ignition. bottom end, crank case from turbo 750 and sprockets.

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