Gpz 750 head is bowed slightly

Heads I could use oven and head straightening plate, but for the proper peice of steel better off finding a used head, and no one in the sw Minnesota are has one or willing to do it. It has about1/16 of and inch clearance on the out edges of valvee side, and a little to much clearance on center cams. Any way to go about this or useful information that would help me, or just bolt it back in motor and hope when I retorque it pulls straight enough? Please help. Or someone that is a professional at straightening I can ship it to? Thanks

Salvaging a head that far warped is pretty questionable. If you are measuring 1/16", I wouldn't bother trying to fix it. It will never "torque down" and seal like that either...

Is it actually warped that much or has some idiot sanded the mating surface at some point in a hacker attempt at raising compression or just cleaning the old gasket off? If the cam bearing bores are straight and the valve cover gasket surface is too, the latter is more likely. If that is the case, take it to a good automotive or better, bike machine shop and have it re-surfaced. Be sure to tell them they need to index ("dial") off of the flat valve cover surface and not the [strike]warped[/strike] wavy existing deck surface, or your head will sit on the engine tilted and crooked after being surfaced. Only cut as little as possible. If it is 1/16", you may be in trouble - that is milling at least 0.065" off! This will significantly increase the compression ratio, and you may also run into piston to head and valve to piston clearance issues, or might have to cut too close to the intake valve seats for comfort. Let the machine shop advise you on this. If you need to find a used replacement head, try Sport Wheels near Minni, or ebay "Mr Monkey Claw" (one of many ebay user names for a major bike wrecker near Appleton, WI). Both would likely have a usable head somewhere in the vastness of their operations....

Good luck...hope this helps.

-Scott

Cam bearing bores are a little off too. Pretty sure someone pryed to hard on each end of the head with center head bolts still in and that's what's bowed it. It's more like 1/32 off. A motorcycle machine shop I've got in contact with claims they should be able to straighten it out, and hopefully no machining.

I'm almost positive if someone had pried that much on the ends, there would be broken or at least cracked and bent cooling fins and all kinds of gouges and chips taken out by the pry bars. In any event, I'd still be shopping for a used head rather than trying to fix one that bad. Straightening it might end up as a big waste of effort, as the cam bearings can only be out a couple thousandths before that will cause severe problems. Steel can warp pretty good when machined and / or heated too, BTW. Cast iron is more dimensionally stable in most circumstances. Ever wonder why big machine tools aren't made of machined steel?

-Scott

Jay at APE has commented before about straightening heads. No idea how much they charge for that though.

Thanks for the good advice Scott. Wondering what heads would work for my motor the 1982 N1 gpz motor. Has electrical yacht, but nothing on the current head. I know these motors have bigger cams. This has definitely turned into a nightmare and a money pit. Bikes clean as clean can be with 27k on it, had to be one thing holding me up. And pretty sure my current head can be straightened without issues. It's been successfully done numerous times with straightening plates, get the cam journals in spec and machine as least at possible on the deck if any at all. I'm going to contact APE and possibly ship it to them and let them be the judge. Any decent used head is $300. Plenty for $200 but no matching cam journals caps if any.

Wondering what the exact cam journals tolerances are? Anyone know? Can't find it in the manual

I'm confused, actually. To my knowledge, the GPz750 was only an 82 and later model (no 81's). The early (82) GPz engine was never used in any model Kawasaki with shaft drive. None of the later (83 and up) GPz's had shaft, although the 84 - 86 ZN750LTD shaft drives used a similar head to the 83 - 85 GPz750, from what I have been told.

I'd bet your bike has a standard Spectre 750 engine, from the paint colors and shaft drive. The 80 - 83 "cruiser" cams are pretty mild, and any 80 - 83 750LTD or Spectre head should be a bolt on if you get the complete head with valves, springs, cams, and - definitely a must IMO - the original cam caps!

Who is charging that much for a standard 750 head? The GPz models I can understand asking a few hundred with cams, the later Hi - Perf. "bathtub" style combustion chamber heads even more, but a standard KZ750 4-cyl. head should be findable for about $125 - $150 in good usable condition. Might not be pretty, but it will work...

-Scott

jenningsjesse wrote: Wondering what the exact cam journals tolerances are? Anyone know? Can't find it in the manual

The 81 Kwak Manual states cam bearing clearance service limit (max.) is 0.19 mm (0.00748"), checking with Plasti-Gauge. The manual does not state a minimum, but other manuals recommend an absolute minimum of 0.0015" for anywhere along the entire camshaft (checking all bearings at once), preferred is 0.002 - 0.0035"...

Added - you can't check all the bearings at once using plasti-gauge with the valves / springs in the head. The head has to be disassembled for that. It is very difficult to get accurate measurements of running bearing clearances any other way, however. Checking each bearing individually does not necessarily tell if the cam bearing bores are aligned (straight) in the head!
First check your cams for run-out too, as bent cams would give false measurements here.

-Scott

Just checked evil - bay ... lots of KZ750 complete heads for less than $150. The cam drive fitting on some can be left in place with the gear removed and plugged with high temp epoxy or, as I have done with 1000 cc heads, plugged with aluminum plug made of rod turned on a lathe.
-Scott

I'd like see a pic of the bearing journals and caps.
Steve

My bad 82 just a mindless mistake