J Head

I know im bringing up an issue that has already been gone over, but i need to know what is necessary to put a J model cylinder head on a 1979 kz mkII. I already have the APE top chain guide and the drill jig. but im not sure what else i need to do, i already have new cylinder head gasket from a 79, or will i need a j model head gasket?

do i need to worry about cam chain length?

do the 79 cams work in a j head, or are the j cams better?

im using stock pistons with new rings.
was planning on using stock carbs and re jetting. can i do that?.

need some expert opinions.

IN BRIEF
Once you've got the head machined to fit the idler the head just bolts straight on.
Use std mk11 head gasket or a Cometic which would be better.
Use the std length mk11 camchain.
Any Z9/1000 cams will fit as long as you use the correct sprockets,Although the J cams would need adaptor sprockets as they have a two bolt mount as opposed to the earlier engines three.
You will lose compression by about 2 points (i.e. 9 to 1 will become 7 to 1 etc )with the J head as it has got bigger combustion chambers so you ought to get it skimmed by 1.5 to 2 mm or get higher comp pistons to compensate.
It will run ok with stock carbs etc,
All depends on your reasons for doing the conversion and what you plan to use the motor for.

Brad D wrote:

dont mean to jump in but do you have ur motor tore down or you just have the head off? i have a crank issue regarding the oil pump,need to know if the gear on the crank that runs the oil pump spins freely.theres a lil resistance but mines spins.

You might want to start a new thread Brad. You'll get ALOT more responses that way.

In regards to the J head... J heads are not power/flow makers that most people seem to think/very little increase at all for the work, UNLESS you plan on really porting it out! :laugh:

A later model GPZ head would make a MUCH bigger improvement, but you need different pistons/work to correct the compression for real usability.

Anyway... do waht you like of course. Either way is a bunch of work, and LOTS of jetting :silly:

The J cams are better I believe, then the standard LTD cams from 79.

Good luck!

Brad D wrote:

dont mean to jump in but do you have ur motor tore down or you just have the head off? i have a crank issue regarding the oil pump,need to know if the gear on the crank that runs the oil pump spins freely.theres a lil resistance but mines spins.

The gear on the crank is pressed on and should not under any circumstance turn without the crank turning too.
If it is spinning independently of the crank then do not run the motor or you run the risk of wrecking it.
Time for another crank or a repair.

what exactly would be required to use a gpz head instead exactly?

It will flow a lot better than your KZ head, ( Larry can chime in with numbers ) but you are not going to like the compression drop. You should run J pistons with a .040 spacer.

Captaingamez wrote:

what exactly would be required to use a gpz head instead exactly?

Fitment is the same and early GPZ and J heads are the same. Later GEEP heads have different 'Bath tub' style combustion chambers.

i figured i wouldnt like 7:1 unless i put some un-natural aspiration behind it!!!!!!!!

but im trying to maintain the 9:1 compression ratio that i have with the stock head so if i mill it about 1.5 to 2 millimeters how close will it get to 9:1.

i also have easy access to a flow bench so doing some flow improvements to the runners wouldnt be too difficult (just time consuming)
i think i may put shim under buckets in the j head that i get. any comments suggestions here?

j cams intake 36.910 ex 37.090. - ltd K/M int 36.006 ex 36.186 - z1 int 36.260 ex 35.760

Captaingamez wrote:

i figured i wouldnt like 7:1 unless i put some un-natural aspiration behind it!!!!!!!!

but im trying to maintain the 9:1 compression ratio that i have with the stock head so if i mill it about 1.5 to 2 millimeters how close will it get to 9:1.

I don't know if anyone could give a real answer to that? There are so many things that come into play.

Base gasket thickness.
Has the cylinder ever been surfaced or milled.
Head gasket thickness.
Has the head ever been surfaced or milled.

If you want a true 9:1 compression ratio, you will need to check it for yourself. You will need a Pipet or Buret tube, so you can CC it for yourself. It will involve labor on your part, no two motors are the same. Anything less is just guessing.