TOPIC:

I have read many places here about compatibility and interchangeability of heads. Most of the threads state a summary of what the APE site states on interchange. 

www.aperaceparts.com/tech/techkz1000.html

Most articles and threads don’t specifically speak to later police models after the civilian bikes were no longer produced. I believe they are ALL J engines from my research, after 81. 

So for my questions, specifically for the police bikes to the end of production-
Were there any changes in the J heads through the end of the production run that make them incompatible the the A engines? (Not including the regular mods mentioned in the link above) 
Are the chamber volumes, valve train specs, or cam grinds different than any other J?

thanks in advance everyone!!

 

By "A" engines i presume you mean the GPZ1100A/ZX1100A Unitrack.
These heads although identical externally to the J have twin swirl "bathtub" design combustion chamber , larger valves , a steeper angled exhaust valve and under bucket shims.
The same head is also used on the 1100R Lawson and some 1100 spectres but with shim over buckets.
The combustion chamber volume is the same 40cc as the J as opposed to 36cc of the early pre 1980 KZ900/1000.
Care must be taken if using an A head on the J to ensure piston to valve clearance and to account for the exhaust vavle angle etc.
The A cams are also a better spec than all the others with higher lift etc.
Al J heads are the same.

Thanks for the reply Zed! I'm glad to know that compatibility is the same.
I can clarify a bit more on this. 
I have a 78 kz1000a2 engine, fresh machine work on the cylinders at the stock 70mm bore. I have a head that is in horrible shape. It's probably going to cost me more to have this head repaired than I want to spend with broken fins, stripped threads, mismatched valves, damaged seats.
I have access to a few mid to late 90's police bikes for parts. 
 
Stock head compression with factory bore & stroke with 36cc chambers along with the same engine with a J head is below in the screenshots.

I'm not sure I'm willing to go from 8.7:1 to 7.9:1 (if the calcs are correct). 

I'm guessing that the head/ cylinders could be decked, but would I run into piston valve issues? according to my calculations I'd have to deck either the head or the cylinders by approximately 1mm to get back to 8.7:1.




 

One thing to ponder when switching to the “J” head is the tach. Very few years have the casting bored to accept the tach drive gear. Your ‘78 A2 has a cable driven tach. 

merf1a wrote:

Thanks for the reply Zed! I'm glad to know that compatibility is the same.

I'm guessing that the head/ cylinders could be decked, but would I run into piston valve issues? according to my calculations I'd have to deck either the head or the cylinders by approximately 1mm to get back to 8.7:1.






 

Stock J 40cc head drops the comp approx two points.
Total engine displacement is 1015cc and 1mm of 70cm stroke ( single cyl capacity of 253.75cc divided by 66 ) = 3.844cc approx so decking the head 1.3 mm approx ( minus 4cc approx allowing for curvature of the hemi combustion chamber to get back to 36cc ) will restore the compression.
There is plenty of clearance to deck the head over 1mm before you run into the seats.
The valves are also set into the head 1mm deeper ( they have 1mm shorter stems to match ) so piston to valve clearance will be fine.
I have done this many times..
 

I hadn’t considered this. This is a great point on the tach drive

I hadn’t taken into account the rounded hemispherical combustion chamber in decking requirements. I appreciate that. I may just continue looking for another head like I have now. They’re just so few and far between and very expensive when you do find them online somewhere. I haven’t posted here asking for one. I may do that in the classifieds. I appreciate all of your help.

What is wrong with your original head, most things can be repaired by a good shop (although it's not always cost effective)