Saving a '81 KZ750-E

Thanks for the prod on the clutch hub, Nessism. And all the other advice. Everyone on this forum has been a tremendous help!!

I got the new clutch hub dampers today. They are an improvement, and reduced the amount of free play. They did not eliminate it, though. I was expecting a snug fit I guess. It went from almost a full gear tooth, to about one third of a gear tooth.


I will weld the rivet ends after I clean up and prep the parts a little better. I went ahead and ordered new friction plates. but don't have an estimated arrival yet. So the clutch won't be completed for another week or so. I did receive the new clutch spring bolts. The new torque wrench is due to arrive early next week as well.

Getting ready to start the top end.

Getting all of the parts accounted for. The comparison between the stock pistons and the 10.5:1 pistons is interesting. They are relieved for not only the valves, but the spark plugs as well.

The cylinder head studs went in much easier than coming out, since I bought the installation tool from APE. Wish I would have known about that tool when I was taking them out! I bought two sets of nuts to remove them, and ended up ruining both by the time all twelve studs were out. Nice addition to the tool box! The shop I had rebuild the head also numbered the pistons to match the bores. He also gapped all of the rings for me. The pistons I purchased from MTC Engineering. They were the last set of KZ750 pistons they had. He had to scrounge for them in the obsolete stock room since they no longer make them. Since they were the last ones he gave me a discount. The wrist pins were a little shorter than stock, so he made some custom sized teflon buttons instead of using clips. The oil ring groove was also too narrow. Apparently the oil ring sets available these days are taller. He machined the grooves on the pistons to fit the current oil ring sets. MTC Engineering has some outstanding customer service!

Those pistons look sweet! What size are they?

Regarding welding the clutch, my welder friend said he did 1/2 each stud at a time, to keep the heat down. Considering the dampers are rubber, I think this was a good call on his part. He also used silicon bronze which is lower heat.

67 mm. We had to go 1 mm over due to rust in the cylinder block.

Skidmark wrote: 67 mm. We had to go 1 mm over due to rust in the cylinder block.

Perfect! I like that more than going 3mm over which thins out the liners so much.

On the clutch hub - I only have MIG capability in my shop. I was planning on going over to my TIG guy that did my fuel tank to help keep the heat down. Since I was managing a metal fab shop for 24+ years, and certifying aerospace welders, I have a bit of weld knowledge. Your insight is always welcome, too!

Our shop made the fuel tanks for the 2014 factory Yamaha Superbike team. They were racing the R1's. I should dig through my hard drive and post some pics of some of the things we made. We were welding on Patriot missile parts for Raytheon, making parts for Dan Gurney's All American Racers, North American Porsche, and various other industries. I was lucky enough to absolutely love my job!

Small world. My welder friend worked in Porsche's US race shop before coming to work for us. We are an aerospace shop but don't weld on production hardware, just R&D stuff. We don't make missile's though, we make toilets (and related hardware.):side:

The first fit check on our first article.



Here is the fit check on the bike at the factory. Also a pic from the the first rider test. Apparently he didn't care for the width at his thighs and we had to narrow it up a little bit.