So much engine confusion j/mkII/?!;&48;&

Gentlemen, first post here, this post will be hopefully the beginning to an end for me to get a complete grip of exactly what engine parts I have. Avidly have came to this sight to find some very detailed answers to questions ever since I got my first kaw(440 bobber in 2018) I have since purchased a 1981 kz1000 LTD (title states this) now I know this is the j engine due to the bottom case stamp of KZTOOJ***** but I have accumulated one and a half trannys, a hair line fractured bottom case, a engine collision top end with broke guide and torch'd then bent back in place valve.. holds 120psi 😂. I want to take the Frankenstein old broke sheit and make good sheit (big bore nothing crazy) Now we know I have j bottom case, but my key says GPZ? Is this common? My valve cover has bolts dead center both at front and back, I have no idler pulley, my cam chain I have to count 44pins for timing, is this a standard j engine? And if so what's the difference in mk11? Can a j engine simotaneously be a J and MKII? I know this has been ran into the ground but I have countless hours of read time, I due my due diligence but after 7 years of wrenching I can't find my answer
(she looks nothing like this now lol)   

This isn't a full answer but is a good starting point.

From the Ape Racing site: www.aperaceparts.com/tech/techkz1000.html   (edited to remove hyperlinks).
There are two different KZ1000 engines. The first is the Z1 type which was built between 1976 and 1980. The second is the 1000J, or "J model" as it is called, and was built from 1981 until present (currently only available in police motorcycles). These engines are different, but some of the parts can be interchanged, and this has caused much confusion. We hope this makes everything clearer.

The first example is simply a big bore Z1 900. This engine came with a kick starter and electric starter. The cam chain tensioner hole in the cylinder block is a rectangle. The ccs cast on the cylinder is 1015. The later "J model" has no kick starter, and the cam chain tensioner hole in the cylinder block is round. The cc's cast on the cylinder is 998. This engine also became the GPZ1100 in 1981 and '82, and virtually everything between them is the same. (The '83-'84 GPZ1100 was changed).  Cylinder blocks and lower engine cases are NOT interchangeable. You can not put a J model cylinder on an older style lower end, and vise versa.

Cylinder blocks.. Not interchangeable. If you have a J model block/GPZ1100 block you must use a J model or GPZ1100 cases.

Crankshafts... Early KZ1000 used a roller type cam chain and the crank has that style center sprocket. J model used Hy-vo style chain. J model cranks can be used in early lower end if the center crank pin is changed to one with a roller chain sprocket. The J model connecting rods are approx 1.2 mm shorter than early style rods.

Cylinder head.. J model head has larger valves and ports. This head can be used on earlier style cylinder and lower end by installing APE #CCIA cam chain sprocket adapter in head. How to tell which head you have..  Early style heads have four factory drilled and tapped 6mm holes in the center to bolt in cam chain idler gear. Z1 900 heads have 6 mm exhaust studs, KZ1000 8 mm. On the J model head, the four  cam plugs  at the ends of the camshaft areas are bolted in, on the early style head, they just push in and the valve cover holds them in. The J model / '81-'82 GPZ1100 cylinder head has a larger combustion chamber than the early style head. When these heads are used on the early style motor, a compression ratio drop of about 2 full points can be expected.

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.

We have tried to make this as clear as possible. When ordering your parts from APE, let us know which engine you have, or if you are mixing early style and late style parts, let our tech/order department know and we will see to it that you get the correct parts combination. Ape Racing END.

The MKII was a development of the earlier Z/KZ 900 and 1000. All of them use a roller cam chain. The later J series head can be modified to fit the earlier cam chain system, but based on your picture that is not what you have.

The J series engines, used from 1981 to 2005, used a Hy-Vo, or silent, cam chain that is incompatible with the earlier chain and sprocket setup. I am not sure it is even possible to convert an earlier head to use that chain, as I do not think there is a way to install the upper rubbing block.


The bike in your pictures appears to have a J model engine.

The GPZ uses the "J" series motor which doesn't have a top idler on the cam-chain, instead it has a guide mounted inside the cam cover so chain tension can only be set with the cover in place

Ok cool. So can you maybe enlighten me a little on what mkII is? Can bike simotanously be j and mk11? Cause when looking threw big bores it seems to be very vaugue to me at least, I know what I work on that's it and I ain't even sure what "it" is hahaha     

YoungBuckOldKaw wrote:

Can a j engine simotaneously be a J and MKII?

 

Simple answer is NO!.
MK2 engine is the last of the kickstart enabled engines with roller camchain.
The J/GPZ is the last incarnation of the 1000/1100cc aircooled fours, has no provision for a kickstart and has a hyvo style camchain.

The MKII is the last incarnation of the earlier engine, as per Martin CSR's post some parts are interchangeable but the MKII is not the same motor as a "J"
PS: the later GPZ has different sized wrist pins and the piston/cyl head set up is different so these parts aren't directly transferrable with the rest of the "J" family

Mmmkay mmmmkay, only one more I hope, do both the gpz1100 and kz1000j have the .998 stamp on jugs..?

YoungBuckOldKaw wrote:

Mmmkay mmmmkay, only one more I hope, do both the gpz1100 and kz1000j have the .998 stamp on jugs..?

998 is the capacity 998cc - the GPZ is either 1086 or 1088 (can't remember)

YoungBuckOldKaw wrote:

Mmmkay mmmmkay, only one more I hope, do both the gpz1100 and kz1000j have the .998 stamp on jugs..?

No! The 1000 has 998  and the 1100 has 1089.
Both of which denotes the actual cubic capacity of the stock motors.

To totally confusing you, my engine is a Z1 low end engine (roller cam chain) and a Z1000J (HYVO cam chain) top end cyl. head.
See the CCIA (cam chain idler adapter) between the IN and EX cam shafts.

 
 

This picture shows a GPZ 1100 UT (ZX1100A) cyl. head and cam shaft (HYVO chain) to Z1/KZ1000 roller chain low end conversion kit parts.

 
 
 

zed1015 wrote:

YoungBuckOldKaw wrote:

Can a j engine simotaneously be a J and MKII?


 

Simple answer is NO!.
MK2 engine is the last of the kickstart enabled engines with roller camchain.
The J/GPZ is the last incarnation of the 1000/1100cc aircooled fours, has no provision for a kickstart and has a hyvo style camchain.

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The last?

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