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TOPIC: Z2 750 crank (Bossie the Kaw)

Z2 750 crank (Bossie the Kaw) 15 Sep 2015 15:38 #690231

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I still have my spring loaded tensioner. I'm tempted to put it back on. If my chain had broken, it would have made for one FK'ED UP DAY. :ohmy: It's ironic I was warning about them and here is the perfect example.
You can see the number 45 stamped on the crank. Before I button it up I'll measure the rods. 2.5mm is a lot. No wonder I had low compression. If I lose cc's, so FKing what. That would mean it IS a 750 crank and should spin faster as planned. I'll take more pics tomorrow.
Steve
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Z2 750 crank (Bossie the Kaw) 15 Sep 2015 16:20 #690244

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i was right you had a low compresion POS
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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Z2 750 crank (Bossie the Kaw) 15 Sep 2015 17:08 #690247

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I expected that. :lol:
Steve
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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 01:13 #690281

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looks like you need a valve job i would send it out and have new viton seals put in .one of the cylinders looks pretty scored up time for a rebore.take some more pics so we can see how bad the cylinder is do you have a dial bore gauge to measure the tapper ? and take a valve out so we can see how bad the seats are.
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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Last edit: by kawi810.

Z2 750 crank (Bossie the Kaw) 16 Sep 2015 03:21 #690289

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I have no interest in YOUR opinion or anything you can dig out of a book. :lol: Valves done last year. For everyone else.
Kibblewhite valve springs, new valve guide seals, new Dorimi valves. More pics to come. B)
kzrider.com/forum/2-engine/596420-valves#653678
Steve
















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Last edit: by SWest.

Z2 750 crank (Bossie the Kaw) 16 Sep 2015 04:49 #690300

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Bruce, you're right. I'll need to drop the pan and clean out all the junk on the strainer. When I did my oil change a small piece of plastic came out. It was from the cam chain sprocket. 40 years old so I wasn't alarmed, now I am'. Everything is cleaned up and I will put it back together today. Still have to take pics of the rings and if they migrated or not :whistle: , more of the crank, the hone job, etc. There always has to be a snag and I was prepared for it. B)
Steve
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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 09:07 #690319

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I took some pics of the rings. They migrated quite a bit. Not close to where they were set.






Head cleaned up, painted and ready to go.


Some pics of the crank and rods. The only place you can see where it was welded is the center pin. I'll also jot down the markings on the rods. You can barely see them.










Steve
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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 09:18 #690321

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Interesting looking below the rings where the oil has been burning, and how it differs slightly between pistons. Looks to me like they were past their best.

I'm thinking now the most critical thing for good ring seating is the cross hatch hone, I have a honing tool taht I've used in the past but In future I'll leave it to a pro..
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces

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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 09:48 #690327

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It was a used set I got on eBay. Great shape, wasn't planning on using the pistons, that's when I found I lunched one of my good ones. I put them in used rings and all with a light hone. The bores have light scratches in them now. I honed them and they will work. I see a 1075 or 1105 in my future.
Steve
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Last edit: by SWest.

Z2 750 crank (Bossie the Kaw) 16 Sep 2015 12:05 #690343

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These are used pistons and rings going into a different block? Done that myself too. Just hope your rings bed in.

I cant find nos old design wiseco rings for my GPz615 so I'm going to have to risk it and use 'quick seat' lube from total seal and some running-in oil.

Maybe check your installed ring gap to match the pistons to the bores as best you can, there is often a measureable difference - 4 thou on my last used set.
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces

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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 12:30 #690346

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swest wrote: It was a used set I got on eBay. Great shape, wasn't planning on using the pistons, that's when I found I lunched one of my good ones. I put it one used rings and all with a light hone. The bores have light scratches in them now. I honed them and they will work. I see a 1075 or 1105 in my future.
Steve

Go big!
My curiosity : what kind of oil do you use?

thank you

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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 13:01 #690348

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Those were the stock pistons for a KZ 1000. I just fitted the new rings to the bores. Didn't have to shave any of them. New piston clearance is .002 so I can hone more to get the marks out or at least most of them. Got some room to play with. These are Wiseco 10.25/1 pistons. Taking my time and they should be fine. :whistle:
I'm using Rotilla oil.
I didn't want to use the old rings that came with the stock pistons but had no choice. The oil on the pistons is after two years of running. The bike ran like a scalded cat even tho it did have low compression. I figure with the 2.5mm drop, I was running at 7/7.5/1 compression. With these new pistons, I should be at around 9/9.5. Good enough for now. B)
Steve
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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 15:27 #690375

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Got the bores looking pretty good. My stones were loaded up so I sanded them and kept going. Still a tight .002. The block and pistons were brand new. It had two chips out of the fins so I got them for $100 delivered. I'll do a little more when I'm fresh in the morning. I'm not getting the 45* cross hatch I'm looking for. I knew I should've picked up some course stones. My old bottle brush is useless. :angry: I'm making up some better ring compressors this evening. B)
Steve





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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 15:33 #690378

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Similar story here, I bought an unseen 'gpz550' motor that turned out to be a kz550 on the inside, but the lower compression pistons (9 instead of 10 to one) ran really nice..

Good squish and combustion chamber design is worth a point in compression ratio all day imo. I think flatter top pistons have some advantages in an old- school design.
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces

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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 15:56 #690381

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It was in 87 when I had the crank welded and put it in. :unsure: Being I didn't have stock pistons, I didn't notice the deck height. When I was accused of lying about it really being a 750 crank and I'd have low compression, I started wondering if it was or not. I'm not in the habit of lying about things and if it was a 903 crank, it would be stronger off the line. No reason to lie. I'm confident now it is a 750 and whatever compression I've lost will be made up by revs. It does want to bury the red line. :woohoo:
We'll see what it looks like tomorrow. B)
Steve
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Z2 750 crank (Bossie the Kaw) 16 Sep 2015 17:02 #690396

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Worked up some ring compressors. Used metal tape to keep them together. We'll see how well they work or not. :unsure:
Steve



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Z2 750 crank (Bossie the Kaw) 17 Sep 2015 04:46 #690449

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Have you ever had problems using that much RTV silicone?
1980B4 1000
1978 Z1R
1978 B3 750

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Z2 750 crank (Bossie the Kaw) 17 Sep 2015 04:55 #690452

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I never use that much. Going one piece head gasket you have to fill the groove where the O ring sits. I will never use a two piece gasket with a O ring that WILL leak ever again. :whistle:
Steve

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Z2 750 crank (Bossie the Kaw) 17 Sep 2015 05:28 #690456

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I'm confident now it is a 750 and whatever compression I've lost will be made up by revs.

And when you get around to boring it out, the motor will become even more 'undersquare' .
What you lose in bottom end tourque I guess you could pick up more pm power.

Seems like with all that deck height you won't have any issues with valve/piston contact. Not sure if there are any other problems with the extra deck height. Valve to valve clearance seems very generous on mine. You could even get some slotted cam sprockets and tweak the valve timing for more overlap and some more retard for rpm power, or find hotter cams.



Attachment Advance_graph.jpg not found



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Z2 750 crank (Bossie the Kaw) 17 Sep 2015 05:36 #690458

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Thanks Tyrell. I may get some more aggressive cams but only looking to the future. I wish I had invested in some used 1075 or 1105 kits when I had the money. Didn't think of eBay. The crank, if it is a 750 is wasted on a normal build. $100 or so will buy me a 903 crank and I could sell the 750 to someone restoring a Z2 or building a turbo whatever. Live and learn. :whistle:
Steve
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