Head warping from overheating

I have a 1980 KZ750 E-1 (4-cyl)fully restored with new pistons, rings and exhaust valves. Since the rebuild I have had to replace the head gasket 3 times! I don't drive my bike often but take long (1000-1500 mile) rides every summer. The trips usually take me into hot conditions so I have fitted a large oil-cooler from a Zephyr 750 with no positive results. I think this latest over-heat may render the head DOA since I had to mill it down the last time. Is this a common problem? One note: When I bought this bike 20 years ago, the previous owner had overheated it and rebuilt the engine. He fried the head and replaced it with one from an LTD model. This was all done by a Kawi dealer so I assume kosher.

jimi

This is very not common. No way you should warp a head on a stock motor unless perhaps you are driving through death valley (even then I'd be suspect).

What high temps are your riding through? My built 650 street motor makes close to twice the stock horsepower and I don't run an oilcooler on it in the metro Atlanta Georgia area where temps are often at 100 degrees. I also ride the he** out of the bike using the motor very hard.

Have you checked jetting? Lean jetting can cause high cylinder temps and might result in your problem. Beyond that I'm at a loss to explain this one...

I agree this is odd, I wonder about the cyl side, if it is flat, or maybe the studs / bolts are giving up

Never heard of such a thing. How in the world can a 50lb piece of aluminum solidly bolted down with 10-12 studs possibly warp? Very strange. Are you getting oil leaks or loss of compression when this happens or what is the symtom? I assume you're replacing the rubber orings when you change the gasket, as these will leak up a storm.

I suggest replacing the head studs and nuts with a set ordered from APE. My guess is the current ones have been torqued past the yield point and they will just continue stretching until they finally snap.

I have ridden my 78 KZ650 through Death Valley in the middle of August, 120 degrees and never had a problem.
You have other issues you need to find before replacing another head gasket.
Was the head bolts retorqued the last time the gasket was replaced? They have to be retorqued after the engine cooled down from the first ride. I have gotten as much as a 1/2 turn from the head bolts after it was ridden the first time from a rebuild.

I think replacing the studs is the next best move. I'm only assuming that the head is warped beyond spec this time. There's oil leaking from the center front side of the head gasket and of coarse I replace the o-rings. And yes, I definitely torqued and re-torqued the bolts as specified but if the studs are stretching when hot then that could explain it. The last head gasket was done by the dealer and they checked the carb mix as well. At that time we thought the culprit was the Vesrah gasket so we went with the OEM one this last time. It did go 2-seasons but ultimately burst just the same. Aluminum heads warp all the time on cars despite a plethora of high-strength bolts holding them down. The forces of material expansion are much greater than a dozen bolts can handle under extreme conditions.

Thanks for the help!

when you pull the head and barrel off first check the bottem of the head to make sure its flat also check the barrel to make sure it its flat and the sleeves are all seated properly if you cant see anything take a look at the gasket,and follow it back to the spot on the head or barrel.it seems strange that you would have problems with studs on a mild motor,thats usually a problem with hi-compression motors but i guess it could happen.hope this helps!goodluck,happy wrenching!

The reason most aluminum heads warp on cars is because they are attached to a cast iron block. The two different metals expand and contract at different rates causing the aluminum head to warp.
The aluminum heads on these bikes are attached to an aluminum case so that problem is not there. It takes a lot of work to warp an aluminum head on a motorcycle.
I would check to make sure the case is not warped. I don't think the case studs are the problem unless they are stripped at the bottom.
I have rebuilt dozens of these engines over the years and never came across a warped heaad or overly streatched studs. The studs will stretch but usually this occurs on highly modified engines with lots of compression.
Are you doing this work or is a shop? If a shop is doing the work, who knows if it's being done correctly and you have to take their word for what is wrong.

I agree. It seems to me if you can use a torque wrench and torque the nuts to the correct setting without stripping or breaking than the studs are not the problem. I've never seen a warped head on any motorcycle and never owned an aluminum head car, so I'm no expert to say the least. What you are saying is the center of the head is warping high, the 2 outer ends low? On the new gaskets I've used in the past, the center section had a kind of sealer like coating on them to make 100% sure it will not leak where yours is. Do these new gaskets have this? If not I'd run some Yamabond #4 or equiv around the area to get a good seal.
baldy110 wrote:

The reason most aluminum heads warp on cars is because they are attached to a cast iron block. The two different metals expand and contract at different rates causing the aluminum head to warp.
The aluminum heads on these bikes are attached to an aluminum case so that problem is not there. It takes a lot of work to warp an aluminum head on a motorcycle.
I would check to make sure the case is not warped. I don't think the case studs are the problem unless they are stripped at the bottom.
I have rebuilt dozens of these engines over the years and never came across a warped heaad or overly streatched studs. The studs will stretch but usually this occurs on highly modified engines with lots of compression.
Are you doing this work or is a shop? If a shop is doing the work, who knows if it's being done correctly and you have to take their word for what is wrong.

Do not use any sealer on the head gasket. I would start with checking everything for being straight, head, bottom and top of the barrels, the top end of the case where the barrels sits.
There is something wrong and you just have stick with it until you find it. Sometimes it can be as simple as not scraping all the old gasket off. Good luck

Thanks for all the help everyone.

To answer a few questions...I did the initial rebuild myself and was damn-careful to clean all the mating surfaces prior to reassembly. I used a Vesrah gasket set and obeyed the factory Kawasaki procedure to the letter. The bike went about 1400 miles with no problem then on a short ride it started oozing out pretty good. The second gasket was a factory one installed by a reputable dealer and overseen by a friend of mine who's the service manager. I was really hoping to not have to remove the cylinder barrels this time and just deal with the head. But I can check the top-side of the barrels for flatness. The base gasket is fine. What is the best head gasket to use? Do I follow the factory procedure or not?

Coinciding with this problem was the installation of my oil cooler. I would assume that any oil starvation of the head would result in cam and valve breakdown long before overheating was an issue.