Can I use 77-80 KZ1000 Pistons on '82 J Engine?

I'm getting frustrated with my M2 project. It was burning a lot of oil when I got it. Took it apart, found three broken oil rings. Replaced them. Also bought a different head that looks in good condition. Replaced the head gasket and o-rings. Put back together, and still burns oil. Checked torque on head nuts. All correct.

Took apart again. Rings still in tact. Can't figure out where the oil is coming from.

Now I'm thinking about finding a set of low-miles cyls and pistons. But then I got to thinking.

Since my current pistons are 69.5mm, could I bore the cyls out and use 70mm pistons from a 77-80 1015 engine? Other than the piston diameter, are their any differences? I've had my '78 apart before, and from my memory, the piston tops look identical.

If they are interchangeable (with bore job), would this be better than trying my luck with a set of 998 jugs and pistons off EBay?

Post edited by: Skyman, at: 2007/12/03 16:49

www.aperaceparts.com/tech/techkz1000.html

Take a look at the link and it will answer some of your questions.

Later, Doug

The simple answer is no - not without making more changes than's worthwhile. The piston pin is at a different height - you'd end up with no compression due to the height of the piston in relattion to the deck height, AND the shape of the piston is sized for a 66mm hemi-shaped head versus 69.5mm on the J engine.

(the early KZ1000's are an over-bored 900 - so the shape of the combustion chamber is shaped for the 900's 66mm bore).

Could the bores be glazed and just need a good honing?

Actually YES, APE makes a cylinder spacer you can use under your cylinders to accommodate the difference in wrist pin position. The main thing beyond that is that is that your compression will be about two points less than advertised on the 73-80 piston instructions. I will be doing the same thing to mine, and using 12.5:1 pistons to get 10.5:1 actual.

Lorcan wrote:

Could the bores be glazed and just need a good honing?

Is this something you can tell just by looking at it?

I don't have it in front of me right now, but from what I remember, there did seem to be--uh, how do you say it--an "abrasion pattern" (there were fine lines in the cyls). How can I tell if it is good or glazed?

If you can still see the "cross hatch" pattern in the cylinder walls, I would not even touch the bore.This means that the cylinders are just barely broken in.

otakar wrote:

Actually YES, APE makes a cylinder spacer you can use under your cylinders to accommodate the difference in wrist pin position. The main thing beyond that is that is that your compression will be about two points less than advertised on the 73-80 piston instructions. I will be doing the same thing to mine, and using 12.5:1 pistons to get 10.5:1 actual.

Wrong way around... if you use the spacer with early KZ1000 pistons in a J motor, you'd end up with next to no compression. Using the early pistons in a J motor will drop the compression about 2 points due to the combustion chamber and another point due to the piston being below deck height. Add a spacer and that drops the compression even more....

The spacer is for an early engine (77-80) using later style pistons and a J head.

You are right Jeff, now that you mention it. They did shorten the rods, so the pins would also be lower on the new stile pistons. This means that the higher pins on the old stile pistons would drp them in the hole. OK so deck the Jugs. But I think thet it's a mute point at this stage, but I do admit my lack of thought.:whistle: :blush:

otakar wrote:

If you can still see the "cross hatch" pattern in the cylinder walls, I would not even touch the bore.This means that the cylinders are just barely broken in.

That makes sense. The guy I bought the bike from said the person HE got the bike from had just installed new rings. He even gave me a box of spare parts, and in there I found the old rings. So I'm not surprised that they still look freshly honed.

But I think when they reassembled the engine, they ended up overlapping the oil rings because three of them had broken end tabs. Since I had the old rings, I just replaced the three broken oil rings with the old ones. But it still smoked like crazy. So I'm trying to figure out why.

The old oil rings looked in decent shape. I thought I could get away with a cheap fix by using them. But maybe I need to bite the bullet and get new ring sets. Since my rings are supposedly newish, I hate to have to get whole new sets. But I assume that it isn't possible to just buy the oil rings, right?

Post edited by: Skyman, at: 2007/12/04 00:28

UPDATE:

I did all the measurements on my cylinders and found that they were all close to "out of spec" for bore. Manual says 69.50mm is the upper limit. All my cyls were from 69.46-69.50. I also checked the ring gaps, and they were also all above the specified 0.70mm limit. So perhaps that explains why I'm getting oil leakage, even with supposedly new rings.

SO, I went to EBay and found a set of 82 KZ1100-D cases, freshly bored and a set of Wiseco 74mm (1135cc) pistons. So they are on their way here now.

I called Z1E, and they set me up with the right size head gasket. And so that's on its way here too.

I spoke with Jeff at Z1E about any other changes he would recommend I make to carb jetting, ignition, etc. I'll start another thread in the Carb forum to ask more about that. So interested parties please rejoin me over there.