Kawasaki Motorcycle Forums banner

1 - 20 of 21 Posts

·
Registered
Joined
·
58 Posts
Discussion Starter #1
Hi, I´m currently in the process of rebuilding the engine in my Gpz750 -83.
I need a new headgasket, cylinder base gasket, valve cover gasket and new valve seals.
I got a few questions:
I have been told that the gpz750 turbo headgasket will fit my engine, the main reason for choosing this is that it is half the price.
But I´m wondering if the thickness are the same? If not the camshaft timing will be upset. Correct?

Second question: Since I need a few different gaskets it might be good idea to buy a gasket kit. Preferable with the valve seals included. Any recommendations on a cheap and good gasket kit?

The reason for the thread is that I searched the whole internet and I didn´t find any answers on the turbo gasket question.

Regards,

Karl
 

·
Registered
Joined
·
10 Posts
Hi, I´m currently in the process of rebuilding the engine in my Gpz750 -83.
I need a new headgasket, cylinder base gasket, valve cover gasket and new valve seals.
I got a few questions:
I have been told that the gpz750 turbo headgasket will fit my engine, the main reason for choosing this is that it is half the price.
But I´m wondering if the thickness are the same? If not the camshaft timing will be upset. Correct?

Second question: Since I need a few different gaskets it might be good idea to buy a gasket kit. Preferable with the valve seals included. Any recommendations on a cheap and good gasket kit?

The reason for the thread is that I searched the whole internet and I didn´t find any answers on the turbo gasket question.

Regards,

Karl
Hi Karl,
Have you posted this question on here?

750turbo.com

Gary
 

·
This space for rent
Joined
·
687 Posts
For those of you with the Kz/GPz 750 that are replacing the stock "bore" Kaw head gasket I recommend that you use a Cometic "graphite" head gasket. These gaskets "won't" weep oil like the stock Kaw head gasket, and have proven themselves in many racing applications. These are what come standard with the 810 piston kit from Wiseco. I've used these for years and swear by them. Even Harley Davidson uses the same material in their stock head gaskets for all their motors today. And they don't leak ! Cometic can be reached at 216-974-1077 in Mentor,Ohio. The gasket model you want to order is H0126044G and cut to 66mm Bore size. The price is $38.95 plus $4 for shipping and they take major credit cards. This is cheaper than the stock Kaw gasket.
The GPz750 Modification FAQ



The stock 750 Turbo head gasket is well thought of, many Turbo owners with 810 kits use the stock head gasket, the Cometic gasket apparently doesn't work well with the Turbo.

As far as throwing the valve timing off, few if any of the bikes left the factory with perfect timing (production tolerances), so your cam timing is likely not perfect now. Cutting .75mm from the head surface, and slotting the cam sprockets to time the cams correctly would probably pick up a couple of HP or so.
 

·
itching to ride
Joined
·
2,233 Posts
How are you going to upset cam timing by going with a different head gasket thickness? The difference in thickness is miniscule anyway.
 

·
Registered
Joined
·
58 Posts
Discussion Starter #5
How are you going to upset cam timing by going with a different head gasket thickness? The difference in thickness is miniscule anyway.
If I have a different headgasket thickness the camshaft will at a different distance from the crank shaft, because we can only move the camchain a cog or more on the camsprocket the cam timing might be of by a few degrees. And the camchain stretches when it is worn, therefore you might not get the ideal setting if you don´t slot the camsprocket so you can move them forward and backwards.
Also when we install the camshaft cover a rubber cushion pushes down on the camchain and this upsets the timing of the intake cam with a few degrees. All those things might add upp and loose us several hp.

But I might get my sprockets slotted and then it won´t be a problem.

I don´t know how big the difference is between the turbo and the non-turbo gasket, is it used to lower the compression on the turbo engines?

/Karl
 

·
itching to ride
Joined
·
2,233 Posts
Seriously, no. Like I said earlier it is not enough to matter. You will get more variance from chain stretch and whip than from a difference in gasket thickness. People shave heads and do not worry about such matters. A slight advance or retarding of the cam timing will shift torque peak but changing a gasket is not enough to do so.

Now if you are trying to squeeze the maximum HP from a stock engine then attention to detail can work wonders. To borrow a line from cycle world test 1984 ...
It seems that adding five or six teeth to a GPz750's rear sprocket, a good valve job, second-oversize Kawasaki pistons and strict attention to minimum factory specifications for cylinder deck height all work wonders for a Kawasaki.
 

·
Registered
Joined
·
58 Posts
Discussion Starter #8
Seriously, no. Like I said earlier it is not enough to matter. You will get more variance from chain stretch and whip than from a difference in gasket thickness. People shave heads and do not worry about such matters. A slight advance or retarding of the cam timing will shift torque peak but changing a gasket is not enough to do so.

Now if you are trying to squeeze the maximum HP from a stock engine then attention to detail can work wonders. To borrow a line from cycle world test 1984 ...
Well I trust your experience and judgement if you say that the diffence between the different headgasket is to small to make a difference.
But shaving the head and not worry enough to check the impact on the valve timing seems lika a waste of horsepower.

It made a difference on our track car but then we shave of almost 0.1 inch.

/Karl
 

·
itching to ride
Joined
·
2,233 Posts
But shaving the head and not worry enough to check the impact on the valve timing seems lika a waste of horsepower.
You would of necessity re-time after such a task. But would'nt this slack in the chain be taken up with the tensioner? I fail to see how it will alter cam timing.
 

·
Registered
Joined
·
58 Posts
Discussion Starter #10
You would of necessity re-time after such a task. But would'nt this slack in the chain be taken up with the tensioner? I fail to see how it will alter cam timing.
Yes, you are right I didn´t use my brain properly. The problem there was that moving the chain a full tooth on the sprocket changed the cam timing to much.

Moving the chain a full tooth on the cam sprocket on the gpz 750 alters the valve opening with 8 degrees. 45 teeths on the sprocket and 360 degrees. In the worst case the timing is half a tooth off which is 4 degrees advance or retard on the cam timing, I think 4 degrees is quite a lot.
 

·
This space for rent
Joined
·
687 Posts
You would of necessity re-time after such a task. But would'nt this slack in the chain be taken up with the tensioner? I fail to see how it will alter cam timing.
You're right, all the chain slack is taken up by the tensioner, as a matter of fact the chain slack on "both" sides of the cams is taken up by the tensioner, which is on one side of the cams. So, when you shave a head .030" you put an extra .030" of slack in "both" sides, and the slack in front of the cams gets pulled across the cams, to the tensioner, causing the cams to rotate by that amount.

Make sense now?

If you're going to the trouble of shaving a 750 four head, you're doing it for performance. And if you're building for performance, then you don't ignore cheap hp (the cost of slotting the cam sprockets),
 

·
itching to ride
Joined
·
2,233 Posts
There is something to be said for advancing one cam and retarding the other whereby you increase or decrease lobe centers. In this case slotted cam sprokets are the way to pull it off. And with the shaving of the head for performance one would use them. However they also shave heads to true them when they get slightly warped.

I used to rack my brain when it came to these half tooth off things but realized that I was not building a racing engine and I could push the half to either advance or retard depending on where I wanted that powerband shifted to. I never was able to discern any notable difference by seat of the pants either way. But I guess there are some who feel they are sensitive enough to be able to. I would venture that with a stop watch one might see a fraction of time difference. But if you are into racing then build the engine with that in mind to begin with.

Oh and steell, it always made sense. It is just that anyone who is that particular about a couple degrees should realize that the timing changes as the chain stretches anyway.
 

·
This space for rent
Joined
·
687 Posts
Yep, and the timing will be checked and the cams readjusted when it does stretch.
Check out the GPZ750 Faq I linked above. hp is all in the details, and there are those who want every single tenth of an hp available. A tenth here, and a tenth there, and pretty soon you're looking at serious power :)
 

·
Registered
Joined
·
58 Posts
Discussion Starter #14
Yep, and the timing will be checked and the cams readjusted when it does stretch.
Check out the GPZ750 Faq I linked above. hp is all in the details, and there are those who want every single tenth of an hp available. A tenth here, and a tenth there, and pretty soon you're looking at serious power :)
Yes, I don´t like to cut corners. If I end up with an engine that doesn´t run as good as I hoped and I know that I didn´t do everything I could, within reasonable limits, I would be annoyed.
I don´t build a race-engine but it is four months to riding season here in Sweden so I have time to care about the details.

I think I will order a gasket set from Yamaha Parts, Honda Parts, Kawasaki Parts, Sea-Doo Parts, Ski Doo Parts, Motorcycle, ATV Parts, 80 $ for all the gaskets I need and I will also order the piston rings from them. Does anyone have any experience from dealing with powersedge?

/Karl
 

·
itching to ride
Joined
·
2,233 Posts
Yep, and the timing will be checked and the cams readjusted when it does stretch.
Check out the GPZ750 Faq I linked above. hp is all in the details, and there are those who want every single tenth of an hp available. A tenth here, and a tenth there, and pretty soon you're looking at serious power :)
I've read that before. He spent a lot of money to shave a bit over a second off his quarter mile time. The OP did not indicate he was building a drag motor and only wondered if using a turbo gasket would affect cam timing enough to avoid using one. That question was never answered by anyone. I did state it would not matter enough to worry about which I stand by. The push slack from the head cover bumper is worth 4 degrees according to that link. So using a gasket that is maybe a few thousandths difference would maybe change cam timing less than one degree. Not enough for anyone to fret over that is not building an engine for racing.

If the OP is really wanting to get the most bang for his buck then I would suggest he PM kopcicle. He knows his stuff on these old bikes and it would be worthwhile to pick his brain.
 

·
Registered
Joined
·
58 Posts
Discussion Starter #16
I've read that before. He spent a lot of money to shave a bit over a second off his quarter mile time. The OP did not indicate he was building a drag motor and only wondered if using a turbo gasket would affect cam timing enough to avoid using one. That question was never answered by anyone. I did state it would not matter enough to worry about which I stand by. The push slack from the head cover bumper is worth 4 degrees according to that link. So using a gasket that is maybe a few thousandths difference would maybe change cam timing less than one degree. Not enough for anyone to fret over that is not building an engine for racing.

If the OP is really wanting to get the most bang for his buck then I would suggest he PM kopcicle. He knows his stuff on these old bikes and it would be worthwhile to pick his brain.
If the difference between the gaskets are no more than a few thousands of an inch you are absolutely right, then it doesn´t matter. My main concern when I started this thread was that the headgasket would be much thicker in order to lower the compression on the turbo bikes in order to run higher boost pressures. The big price difference I have seen, turbo gasket almost half the price compared to the regular, suggested that there were bigger differences between the two headgaskets.

I do appreciate the information you are sharing, youre points are very valied. I also appreciate the input from Steell his points are valied too and depending on the time and money available, it might be worth spending some extra on the details.

Regards

/Karl
 

·
Registered
Joined
·
124 Posts
On car engines advancing the timing 4 degrees will give you more low end grunt and retarding will give more on the top end. I guess the same would be for the motorcycle engines also.
 

·
Registered
Joined
·
58 Posts
Discussion Starter #18
On car engines advancing the timing 4 degrees will give you more low end grunt and retarding will give more on the top end. I guess the same would be for the motorcycle engines also.
I just been to the gym and I´m low on energy so please help me work out if the push of the rubber cushion in the valve cover will advance or retard the intake cam. Am I right if I think it will advance the intake cam?
 

·
This space for rent
Joined
·
687 Posts
kawpaul, to you and probably most others it makes no difference if the cams are out by a tiny bit. To me it does make a difference, on a motor that I expect max power from. On a daily rider no one would notice, but my daily rider is a 750 twin, the 750 four is for "fun" :)
 

·
itching to ride
Joined
·
2,233 Posts
Steell, so how often do you go back in and check cam timing since with chain stretch you get different timing? I do not know how long it takes for the chain to stretch enough to matter but I do know racers tear down their engines frequently to keep everything on edge so to speak.
 
1 - 20 of 21 Posts
Top