TOPIC:

Can anyone help me narrow down my search as to the year of Block I might have? Thinking of getting it honed and using the std pistons with new rings to replace my current 903 block? Alternatively, rebore to accept a set of new, flycut 1035 pistons & rings I recently acquired from a guy in Australia?

What would you guys do?

Looks like a black factory finish Block with "1015" in raised #'s in a block in the lower right (?) front corner?

Thanks.

1977-1980 KZ1000 block

70mm bore is stock.

Can be bored comfortably out to 1075cc using the original sleeves, even to 1105cc if you want to push the envelope a little.

Fitting the KZ1000 block may cause you to get the cases machined to accept the larger sleeve size.

Normally 1015cc is the max over bore for a stock KZ900 block - that's taking it from 66m to 70mm.

Jeff, I just got home and miced the pistons, 2.752", look like std. Bores look real clean.

Should I re-ring and go back with std or should I rebore and use the new (Auzie) domed/flycut pistons which appear to be 2.760" and I'm told will produce 1035cc?

What do you think? Thanks.

same comment as jeff if you go big then the cases will need to be done as well

Is the case work required to "go large" a dremel job or a machine shop job?

BH... there are TWO 1015cc blocks. Both look the same outside, near as I can tell. The early ones 77/78 use the thin little o-rings that go around the cylinder liners on the bottom-side of the block. The later ones don't have grooves for the o-rings. I have found that the earlier blocks fit on 903cc cases easier. The later may need machining. That means a die grinder... a Dremmel clean up isn't really going to get the job done as much needs ground. Test fit whatever block you have on the cases prior to final fitting. Make sure the engine dowels line up and fit.

WG, Thanks for the input. Looks like I have the earlier version, with the "o" rings. I dug them out last night.

Currently got the original pistons soaking in Berrymans, to free-up a couple of the rings a free up the carbon/coke.

Dont know whether to invest in new rings for the original pistons or invest in a minor rebore, to 70.25mm (1035cc) to use the new flycut pistons I have on the shelf.

What do you think?

BH - This is what I think... you have the pistons in kit form which include wrist pins and rings? If you bore, you will spend $150-200 depending on local cost. If you re-ring, you will spend $15 on the hone BUT will have to pick up rings which will be nearly $150. As far as cost goes, it seems almost a wash. If you go with the new pistons and the machinist is trustworthy, you will have a good top end (if you take care of the other things at the same time) for sure.

Other things:
1. REPLACE CAM CHAIN, cam chain dampener rubbers, any worn cam chain bits like the idler assembly or sprocketed rollers AND DEFINETLY Replace the piece that is screwed into the front of your block! It is broken. Repeat... it is broken... they are ALMOST ALL BROKEN. You have to use a long impact driver phillips bit to get the screw out that holes it in place. When you get it out, flex it. It has a crack 95 percent of the time. MOST ARE READY TO FALL APART!
Loctite all cam chain related bolts and screws or they will fall out too!

2. cylinder head. Disassemble, and at minimum lap valves and replace valve stem oil seals. MEASURE THE VALVE STEM LENGTH using a digital caliper. If any of the stem lengths are too long and out of spec, you will soon be having problems. Measure the springs. This is a static measurement on your bike and if they are weak, replace them. If the stems are long, a valve job may be in order. After hearing horror stories on this forum, I would find a VERY TRUSTED local machinst OR I can recommend one. APE would be a good choice and while it costs a couple bucks for shipping a head, I wouldn't want Alfonzo from down at Fred's auto machine shop working on my bike's cylinder head. Car machinists will grind your valve seats to powder before they know what hit you!

3. (optional)If you really want to go nuts, you will inspect the gears in your transmission for rounding and the shift forks. This might not really be worthwhile if you aren't having shifting problems but I have lost 2nd gear in KZs before. AND ALSO, all new gaskets and seals are in order while you do this thing!

I believe there has always been only one 1015 sleeve. Don't know one would fit 903 cases any easier than another.

A 70.25 piston makes the motor 1023cc, not 1035.

Jay

Thanks everyone for all the great advice. I'll let you know how it all turns out.

Jay the 79/80 sleeve is actually about .15mm less diameter than the earlier ones but they just don't fit as well... possibly the locating dowel pins are slightly different or at least the ones I have dealt with. If you check the underside of the sleeves you will see the early castings have channels for an oring while the later do not.