saving a 1980 KZ750 twin

MotorbikeBruno said:
Doc, where did you find the new ones? I've had the same nagging issue on mine...too rich one day, too lean after the next change...made me so nuts I put her away for a while....

I pulled some out of a set of 29 smoothbores I had sitting around, exact same. Z1 enterprises sells new ones.
 
The forks were pretty soft, so i decided to rebuild them with new springs and try out the emulators. I dropped the fork lowers off to be powder-coated and despite my CLEAR INSTRUCTIONS they did not mask off the top of the fork tube. I'm pretty pissed about this because I literally wrote "NO" where I wanted them to mask. They only masked for powder not the sand blasting. It doesn't seem like the sand blasting got into the tube too far, but it did peel a bunch of Teflon off the bushing at the top of the tube where the inner tube rubs. There is now quite a bit of play between the fork inner and outer at this location. This coated bushing is not shown in the parts diagram, nor is it mentioned in the service manual. It looks like Racetech has a bushing that has the correct dimensions that may work (36x12x2) I have another pair of forks that I could use but the caliper mounts have been machined on these for my caliper conversion; something I would rather not do again.

how do I get this bushing out? there is very little lip on the backside, probably about 1mm. Also its in there pretty deep, my seal puller won't reach it.
 

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through some fugly butchery I was able to extract the bushing. I first turned a 37mm washer that was 1/4" thick. Drilled and tapped that and flatted two edges so it could be passed though and reoriented to catch the bushing. it pulled out easy. The small bolt is to keep the washer from spinning. just waiting on new bushings and the forks can go back together.
 

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I got the new bushing from Race Tech. They fit pretty good. I made a nylon plug to push them in because I thought I was going to have to use my press, but i was able to push them in by hand. This made me a little wary because there is nothing holding in the bushing but friction and it went in pretty easy. I have a set of later model forks that have a spring clip to retain the bushing for this reason. I decided to use a spring loaded center punch to "stake" the lip around the top of the bushing to make it harder to back out. I feel better about this. I finished assembling them with new Race Tech springs and gold valve emulators.
 

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So much for my quick top end swap.... no wonder it seemed low on power. The right piston pin was seized in the piston and took a puller to remove. Not sure how it started; further inspection required. the small end of the rod is trashed. Luckily i can remove the rods through the oil pan. but since I have to go this deep I'm wondering if i should pull the motor and go through the whole engine? that's a bunch more work i'd rather not do. There didn't seem to be any big chunks in the oil pan, just a little dirt that fell down when i removed the jugs. I just can't seem to get an easy one on the projects lately....
 

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Oh man.. That's ugly. Maybe it's time for the bigger bore and pistons we've been talking about for a few years?
 
I have 10.5/1 Venolia forged pistons (stock bore), matching cylinder, and a fresh head with a light port and polish, valve job and deck. I was hoping to just swap the top end but it looks like i'm going to have to go deeper.
 
Decided to go all in on the engine rebuild. got some cool mods in mind as well. stay tuned.
 

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In a way, I kinda love being forced into a rebuild and bigger bore. Excuses make it go down easier, and supping a motor up is never a letdown.
 
doc_rot said:
Decided to go all in on the engine rebuild. got some cool mods in mind as well. stay tuned.

Right on!. There's a strong chance I'll have to do the same when I get back into mine. I look forward to the details of your build.
 
Finally got the easy win I was looking for. New EBC single disk setup. Shaved 4 pounds off rotational mass and an additional 2.5 unsprung with the removal of the extra caliper. I bought a 12mm brembo MC to match. The fitment is super tight. less than 1mm on spoke/caliper and disk/fork leg. I'm digging the new look. Very interested to see how it feels.
 

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Venolia pistons - how much ?

My exhaust cam is off to be modded [ remove gear ] and will come back as an inlet !!!

Just waiting to get my new HD compressor and blast cabinet installed - then it's into engine mod mode ! ;D First job is to strip the new twin plug head down and get some blueprinting done. What do you guys use for valve springs ?

There WILL be two donkeys - one will be the Weber / NOS version and the second more long term [ money ! ] will be the blown version. Probably Turbo as the Eaton conversion will rely totally on the good grace of others for machining fab etc.
 
beachcomber said:
Venolia pistons - how much ?

I got them used from a member over at KZR for $150

beachcomber said:
What do you guys use for valve springs ?

stock springs. if I had a higher lift cam I would get some custom springs made by Kibblewhite.
 
Love the new set up. Looks great. That's about what I want on the 350F. The stock rotor on it is heavy.
 
1fasgsxr said:
Love the new set up. Looks great. That's about what I want on the 350F. The stock rotor on it is heavy.
this rotor is about 2.5lbs lighter than the stock single.
 
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