will these fit?

OK, so I was wnting to know if 1980 kz1000 pistons would fit and work with a 1983-2003 head? J motor

How much did these change over the years?

APE does a good job explaining the differences HERE

the j motor is a totally differant series of motor;)

steell wrote:

APE does a good job explaining the differences HERE

That was great info thanx!

Both the bore and stroke are different from the J motor to the 1015... this means that the pistons are a different width but the big killer is the different stroke. This means that at TDC, there is a different distance from the crank center to the top of the stroke making the piston pin bore in the wrong place. In other words, the piston either wouldn't come up far enough OR would bounce off the combustion chamber. Not sure which one it is, but the re-engineering would be too great to make it worth the effort.

Bore and stroke:

77-80 KZ1000 70mm x 66mm
81-2005 (?) J motor 69.4mm x 66mm

Specs from Zedder

Quote from the previous APE link:

Pistons... All pistons have 17 mm pin holes, but the J model/ '81-'82 GPZ1100 pistons have the pin hole lower in the piston to make up for the short connecting rod. All J model and early '81-'82 GPZ1100 pistons are the same ( '83-'84 GPZ has 18 mm pins ) Therefore any '81-'82 GPZ piston can be fitted to a J model engine to make a big bore engine. Pistons for the J model / '81-'82 GPZ1100 can not be used in a motor that has an early style long connecting rods unless a spacer plate is used under the cylinder block to compensate. If early style KZ pistons are used in an engine that has the short J model / '81-'82 GPZ1100 connecting rods, a special short cylinder block has to be used.

Post edited by: steell, at: 2007/04/14 19:25

Sorry, first sentence was somehow chopped...

KZ head has small chamber. J head has big Hemi chamber. Use J pistons.

The J head should be fine with the APE idler. Haven't tried but have one and plan to do the following as $ allow.

J 72.5mm(kz1100) pistons, and a spacer under the KZ block. APE sells the spacer too. Can't remember how thick but it's easy to measure and see what's needed. 0.040" maybe?

The 1070 pistons are 72mm, the 1105 are 73mm, and the (kz1100) are 72.5mm(1089CC). Folks on the list report that the 1105 kit works OK so the 1089's should be fine.

AFAIK your 1980 has a 16 tooth sprocket on the crank so you can replace the hyvo sprockets on the J camshafts with 32 tooth roller sprockets from APE. My main hold up has been finding 30 tooth to match the older 900's 15 tooth on the crank.

Let us know if you do this and how it works out.

Post edited by: Duck, at: 2007/04/14 23:30