need pistons and rings kz750 twin 1978

Hi all I am new to this forum and new to my kz750 twin 1978. I've had it just two months- the previous onwer must have let it sit up awhile and rust formed in the cylinders. it overheated,seized and now i've taken the top end off.

head componests are fine and the crank rods are tight. The local bike shop owner says he can bore the cylinders over (honing is not an option) but he can't find a supplier for oversized pistons and rings.

So I need a source for oversize pistons and rings or I suppose new cylinders. The cylinders are stock at present and I don't know how much boring he wanted to do- I assume the next size up...

any ideas? thanks for your help in advance!
Jim in Atlanta 1978 kz750 twin

i have what you need on ebay right now.

jammor wrote:

Hi all I am new to this forum and new to my kz750 twin 1978. I've had it just two months- the previous onwer must have let it sit up awhile and rust formed in the cylinders. it overheated,seized and now i've taken the top end off.

head componests are fine and the crank rods are tight. The local bike shop owner says he can bore the cylinders over (honing is not an option) but he can't find a supplier for oversized pistons and rings.

So I need a source for oversize pistons and rings or I suppose new cylinders. The cylinders are stock at present and I don't know how much boring he wanted to do- I assume the next size up...

any ideas? thanks for your help in advance!
Jim in Atlanta 1978 kz750 twin

I have two brand new sets of NOS piston/ring sets (+1 over size) for the 750 twin. This is an extra pair I bought for the two that I put in my 750 twin.

2 new pistons, +0.50mm over (that's .020" over)
all new rings
new wrist pins
new wrist pin retaining clips

These are brand new, still in box, still wrapped in original paper.

I'll sell them for $75 plus $10 shipping for BOTH sets complete. Send me a PM if you want them, I can ship them out immediately since I am no longer employed...

I also have a full set of NOS valve guides if you want those I will sell them cheap.

Hi smith. I will take them but i have to figure out how to purchase them through ebay. I don't have a paypal account. I need to figure out how to work ebay better.

Just so you know the mechanic siad i would need plus 1 mm because my cylinders are so bad--so yours look great.. let me see if i can figure ebay out to get you paid
thanks
jim

bounty hunter
i will try to get smith's setup that he offered in his recent post. Mechanic says I need +1 mm pistons if I want to use my old cylinders. If I can't get Smith's I'll post again soon to let you know.

The head looks good but has lots of carbon. To i just have someone clean that up or would you do a valve job if I go with new cyl/pistons?

thanks

jim

jammor wrote:

bounty hunter
Mechanic says I need +1 mm pistons if I want to use my old cylinders.

Wow, that sleeve must really be messed up if he thinks the rust goes .040" deep. That's more than a spark plug gap.

I checked ebay and didn't see any +1mm piston/ring sets, but maybe I didn't know where to look?

BTW: be careful about piston sizing. It is common for pistons to be called "+1" meaning "first oversize".... but that is definitely NOT a 1 mm oversize piston. With kawi factory pistons listed for the 750 twin, first over is +0.50 mm. It can be kind of confusing, especially since some piston manufacturers make +0.25 mm oversize as the "first over", +0.50 is second over, etc.

The OEM style pistons should have the size stamped on top in mm: if it says "+0.50", that's the 0.5mm oversize piston. The "+1.00" stamp denotes the 1 mm oversize.

Anyway, if you decide you want the +0.50mm (.020" ) over set, let me know.

Good luck.

jammor wrote:

bounty hunter
i will try to get smith's setup that he offered in his recent post. Mechanic says I need +1 mm pistons if I want to use my old cylinders. If I can't get Smith's I'll post again soon to let you know.

The head looks good but has lots of carbon. To i just have someone clean that up or would you do a valve job if I go with new cyl/pistons?

thanks

jim

I would absolutely get a valve job because the valve guide oil seals are notorious for failing and screwing everything up. Old Bike Barn sells the oil seals, they are quite rare.

my mechanic put it ike this: He said the first bore over is .02 which is also called 1/2 millimeter---the second overbore is .04 which is the same as 1 mm...?

I think I will purchase smith's cylinders and pistons complete- I guess I can reuse the rings he sends with the set becuase they only have 900 miles on them.

Smith: I am jammor0 on ebay and am the one who has bid on your cylinders. I figured out how to get my paypal to work. If you like email me privately with your phone number (or just email me at jammor@bellsouth.net) and tell me how much you want for that started clutch you have.

Thanks to all I love this forum

jammor wrote:

my mechanic put it ike this: He said the first bore over is .02 which is also called 1/2 millimeter---the second overbore is .04 which is the same as 1 mm...?

That's what I was warning you about: the kawi OEM pistons are only listed in two over sizes, 0.5mm and 1.0mm. So, first over is 0.5mm in their minds. But, I know for a fact that the stock pistons do come in 0.25mm increments which means first over would be 0.25mm in those. I know that coincidentally because I have a set of the +0.25mm in my engine. I bought a set of +0.50 as a spare in case I ever need to bore it again. The point is to be careful if somebody only lists "first over" or "second over", because it could be two different sizes depending on who made the pistons.

jammor wrote:

I think I will purchase smith's cylinders and pistons complete- I guess I can reuse the rings he sends with the set becuase they only have 900 miles on them.

If you decide to have that one bored for new pistons/rings, let me know.

Good luck.

Hey Smith
I just sent you payment through paypal for the pistons rings and head! I can't wait to bolt them on....

once i get that covered i guess i can worry about getting a starter clutch.....

thx
jim

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