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Author Topic: saving a 1980 KZ750 twin  (Read 62691 times)

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #310 on: Apr 24, 2017, 14:20:40 »
Sure does! nothing says 70's performance like a megaphone to me.

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #311 on: May 03, 2017, 04:01:18 »
I have run into an issue with the upper engine mount and Im hoping to get some insight here. For some reason the mounts that bolt to the valve cover or don't even come close to lining up with the mounting holes. The same thing happened to me on my KZ400 when I rebuilt the top end. I ended up having to hog out 7mm on the mount plate holes on that to get it to bolt up.

I need to remake the head mounts on this 750 anyway because this is where the coil mounts and my aftermarket coil does not fit with the stock engine mounts. No problem, I can make a motor mount easy enough, but then I realize that the mating surface on the valve cover is not perpendicular to the bolt hole on the valve cover. The valve cover has about 5 degrees of draft on it so it can be cast but the mounting points were never machined flat. This causes me to believe that the reason the original mounts no longer fit is when they are torqued down they bend out of shape so once you remove them they no longer fit.  The original mounts also have a ton of slop in them.

 I was going to make some trick mounts out of aluminum plate, but now I don't know what to do. The original ones are stamped steel with this cheesy bend in them that probably helps deal with the fit issues. right now i see two routes of action. take the valve cover off, mill the mounting points flat and make the aluminum plates, or file out the existing motor mounts and mod them to accept the new coil, maybe weld in a washer to help take out the slop. Thoughts?
« Last Edit: May 03, 2017, 04:50:39 by doc_rot »

Offline Maritime

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Re: saving a 1980 KZ750 twin
« Reply #312 on: May 03, 2017, 08:44:24 »
my CM had similar head mounts and to get them to line up you put them on lose, then get the bolts in, then torque everything down and yes they deform or conform to fit. also you need to put them back on the same side and way they came off.
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Offline jpmobius

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Re: saving a 1980 KZ750 twin
« Reply #313 on: May 03, 2017, 11:22:35 »
I'd guess that if you loose all the other engine mounts, you will be able to assemble the uppers.  Presuming you can, you likely will be better served to use them if you can alter them to fit your coil setup.  You could fab them up from aluminum, but this sort of part often suffers from fatigue cracking unless carefully designed. 
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Offline canyoncarver

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Re: saving a 1980 KZ750 twin
« Reply #314 on: May 03, 2017, 12:01:04 »
Interesting hangup Doc.  They sure came out easy eh?    I haven't tried bolting mine back in lately but I remember the top mounts were side specific.   I had presumed first off, last on but maybe I'll have to check the fit up in mine for this same issue.
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YZF750/1000R The Fly
KZ 750 Twin
ZRX 1100
KZ400 The Rabbit
KLR650, 65 Norton, my never finished shovelhead chopper, an 86' FXR, and an F9 Bighorn
more YZF750R's, more KZ's, a Zephyr750...and the ever unfinished 75' CB550 cafe.
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Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #315 on: May 03, 2017, 13:34:03 »
Because I oversized the engine mount bolts there is very little slop there, so loosening the mounts wouldn't do anything  because some of the holes are a good 5-7mm off. Logically it would seem that this mount would put a lot of strain on the motor if it was assembled loose and then tightened as JP suggested. I wonder if this is a contributing factor as to why these motors so frequently have headgasket leaks.
I didn't even remove the motor on my kz400 and same thing happened. The mounts are sided but it is very obvious which side is which because the mounts have nuts welded to them, and its been so long since i pulled the motor I don't remember if the bolts were tough to get out. I was thinking about the fatigue cracking as well, the steel is probably pretty forgiving here. I guess I will try modifying what I have instead.
« Last Edit: May 03, 2017, 13:40:21 by doc_rot »

Offline Maritime

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Re: saving a 1980 KZ750 twin
« Reply #316 on: May 03, 2017, 13:41:49 »
Because I oversized the engine mount bolts there is very little slop, so loosening the mounts wouldn't do any thing particularly because some of the holes are a good 5-7mm off. I didn't even remove the motor on my kz400 and same thing happened. The mounts are sided but it is very obvious which side is which because the mounts have nuts welded to them. I was thinking about the fatigue cracking as well, the steel is probably pretty forgiving here. I guess I will try modifying what I have instead.

There's the reason, on the engine the bolts usually have some open space in the holes that allow the motor to move when they are lose, then when you get everything attached you torque them down to stay in place. did you put never seize etc. on the shafts of the bolts? if not being oversized even a little corrosion will make them a bitch to get out if you need to down the road.
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Offline irk miller

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Re: saving a 1980 KZ750 twin
« Reply #317 on: May 03, 2017, 15:01:45 »
Is there room to run dampeners/isolators, either between brackets and frame, or have them through bolt?

Offline doc_rot

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Re: saving a 1980 KZ750 twin
« Reply #318 on: May 04, 2017, 05:33:57 »
Is there room to run dampeners/isolators, either between brackets and frame, or have them through bolt?
I was thinking about something like this. I have seen some British bikes do this (commandos?) I wonder if it is worth the effort though.


There's the reason, on the engine the bolts usually have some open space in the holes that allow the motor to move when they are lose, then when you get everything attached you torque them down to stay in place. did you put never seize etc. on the shafts of the bolts? if not being oversized even a little corrosion will make them a bitch to get out if you need to down the road.

Most of the holes maybe had .5-1mm of slop; nowhere near the 5-7mm i'm seeing up top, but i don't deny that that very well could contribute to the problem. I did put a bit of anti sieze on the bolts, but i'm not concerned. Guys have been over-sizing the mounting bolts on their KZ1000s for years and the only story I have heard of the bolts getting stuck from corrosion was a guy that lived right on the ocean and parked his bike outside, thing looked like boat anchor but still ran.

Offline john15511

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Re: saving a 1980 KZ750 twin
« Reply #319 on: May 04, 2017, 17:01:57 »
I have been reading your thread for the past 2 days and just caught up.  AMAZING BUILD!


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