Best year for the GPZ 1100?

Jeff.Saunders wrote: The J motor is a mix of evolutionary improvements over the earlier engines, coupled with a few cost-cutting measures. In some ways it's a far better engine, in others not as good. Overall the J is a very good motor (except for the crank twisting issue with some of the first year models).

Kawasaki beat it to death in the police bikes - and ran that J engine from 1981 all the way to 2005... not a bad run for sure.

Drag racers have often blended the two together - preferring the earlier bottom ends, bundled with the later J cylinder head.

larrycavan wrote: RonKZ650 wrote:

I'm sure there are a hundred different views on the subject, but my personal one is by 1980 the KZ1000 was nowhere near as fast as the competition, but still a better engine, but "better" is not the big sales point. So 1981 they build the J engine which is a few less CCs. I think, but could have memory fade, that AMA superbike of the time limited CCs to 1000 so rather than building a new 1015CC engine they opted for 998. The J was lighter and much,much better running engine than the previous 1015cc. Had some teething problems though and reliability was not great.

Not a bad assesment

When Zuki introduced their GS1000, the fact of the matter is, it was faster than the KZ. 2mm larger intake valve certainly helped.

J motors, IMO are great motors but they weren't the solid motor the predecessor was.

Kawasaki redesigned a clutch basket that was previously problem free for any street application and made removable without splitting the engine case. In the process, the clutch basket was not as strong.

Their tooling at the factory was worn out and they didn't know it at the time. That led to crankshafts that slipped on the presss pins.

Crankshaft thrust bearings were prone to failure. Even on bone stock motors.

Oil leaks were common.

The cylinder had was redesigned with 1mm larger valves on both sides. Larger port runners that reall didn't flow much more air than a KZ head.

At the time, the factories were all about CV carburetors as the solution to increasing HP & meeting emissions standards. Using those carbs was behind the port redesign.

A J motor is a good motor. The thing of it is though, when you decide to push some HP out of one, the smart bet is to tear the complet engine apart and go from the bottom up addressing each weakness.

Kawasaki said the cranks were all fixed in the 82 model but that was hogwash. They were still failing in the 83 GPz11 motors.

In 83, Suzuki got smart and started welding their cranks! Kaw should have done the same. It would have saved them piles of money in warranty coverage. In 1983, we put cranks in over 20 GPz 1100s. That's not to even mention the rest of the J models we did back then. Falicon was pretty busy doing supercranks for us at the time.

Customers had it made in one respect. They rode the bike for a season and got a free rebuild for the next one! Plus the bonus of only paying a portion of a Falicon Supercrank treatment.

Jeff Saunders has a good analysis of another perspective on these motors...JMO

Larry C

Jeff.Saunders wrote: Depending how you view the Z1/KZ900/KZ1000 engine there are 4 main variants of the engines (and a few additional variants).

Z1/KZ900 - The 900 engines rev very quickly due to their lighter crankshaft. The crank has 'pork-chop' flywheels, and is considerably lighter than any of the 1000 cranks.

KZ1000 (77-78) - very heavy crank - full circle flywheels across the crank. Kawasaki beefed up the cases, and made minor improvements to transmission. Kawasaki retained the same stroke, just increased the bore from 66mm to 70mm. The same head design was used, so there was a 4mm 'squish' zone on the combustion chamber.

KZ1000 (79-80) - aka Mk II - beefed up center section on the crank using 16 teeth on the center section. intermediate weight crank - roughly halfway between the Z1 and early KZ1000 cranks. The cases were beefed up again in 80. 1980 is generally considered the strongest of the engines - and the most sought after for racing / high-performance engines. In the USA, the 79 was the first year of the engines to have smog ports on the head. The stator design changed.

KZ1000 (81 and up) - AKA J Motor - composite guides replaced cam idler sprockets. Transmission changed, clutch changed, head changed. Clutch basket removeable without splitting the cases. The head was reworked to match the new 69.5mm bore. The valves increased in size to compete with the GS1000's. The transmission change is a strange one - the early transmissions seem better to me - less clunky.

There are some interesting differences within these 4 main version. The 79 1000 LTD engine is a little odd with a variant of the crank that's unique to that bike. 1973 Z1 engines have a considerable number of difference as refinements hit the bike during the production run. Vacuum take-offs directly in the cylinder head, no center o-ring around the cam chain tunnel, hollow cams and more.