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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Motorhobo on October 31, 2022, 07:09:46 AM
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I need to replace my +130k engine with the rebuilt one sitting in the corner of the garage.
When I bought Gary Weaver's K75, it had a rebuilt engine with only maybe 40k on the rebuild. My original K75 had frame damage from a front-ender, but the engine only had 105k on it, so I decided to put the 105k engine on Gary's frame and ride it out till it was done. That moment has arrived, I think. Plus, the oil pump on my summer bike is toast, so I want to have option to use the oil pump from the 130k engine on it, which if I remember was replaced at some point, or at least to use whichever one looks like its in the best shape.
So the question is -- last time I swapped engines, I had a hell of a time getting the frame bolts on. I couldn't get them to line up and tried all kinds of kooky s**t to get them in line. I finally got it done but I think it was a combination of the sequence with which the bolts are installed and some creative leveraging of something or other... I can't remember. All I know is I don't want to go through that again.
I searched but couldn't find a combination of search terms that got me to a post that had this info. Any help greatly appreciated.
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From the folks who brought us the venerable K75:
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Which frame bolts were the problem? I guess you have to do the swap and let us know where you're having trouble.
I use the procedure Laitch posted, and have done several engine installations without any issues. The bolts just slid into the frame. If it takes a lot of persuading to get the bolts in, I suspect that the frame is tweaked.
Are you doing the swap with a fully dressed frame(tank, battery, forks, seat etc)? I have done all but one of my swaps with as much as possible removed. The less there is on the frame, the easier the engine seems to go in.
First and hardest was my first go around on my K75RT where I left almost the whole bike intact and raised the engine into the frame. That one took a bit of wiggling and fussing to get all the engine imounts n the right spots. Later jobs involved a bare or minimally equipped frames being put onto a stationary engine. Those went a lot easier.
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From the folks who brought us the venerable K75:
Thanks Laitch -- wish I'd asked last time. I just assumed, 'hey they're bolts, you screw them in, what could go wrong'?
Where'd you source that? I didn't see it in the aftermarket manuals, but that might be because I didn't look too hard.
Are you doing the swap with a fully dressed frame(tank, battery, forks, seat etc)? I have done all but one of my swaps with as much as possible removed. The less there is on the frame, the easier the engine seems to go in.
First and hardest was my first go around on my K75RT where I left almost the whole bike intact and raised the engine into the frame. That one took a bit of wiggling and fussing to get all the engine imounts n the right spots. Later jobs involved a bare or minimally equipped frames being put onto a stationary engine. Those went a lot easier.

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I'll leave the front end and wheel on, put the front wheel in a chock, then remove tank and battery and everything behind the engine, then winch up the tail from a hook in the ceiling and drop the frame down on the engine, which I put on a rollable plate with casters. That will allow me to adjust the engine position, keeping the frame basically stationary and floating. It worked pretty well last time, except I didn't know about the bolt sequence, so I hope it goes on as easily as it did for you :-)
I'm also going to try this method of aligning throttle bodies, since I screwed them up a while go trying to adjust them without knowing wtf I was doing.
https://www.youtube.com/watch?v=0xuKZNY-Ioo&t=5s
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Instead of washers, use small ball bearings. About 1/16" diameter works pretty well. They will be more uniform in size and roll easily to the lowest point of the butterfly where the opening will be.
Use the idle adjust screw on the throttle cable quadrant to slowly open the butterflies open until the bearing closest to the quadrant drops. Then, using the forbidden blue paint screws, adjust the other butterflies so their bearings drop.
https://www.youtube.com/watch?v=4sEotUU9EQw
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Where'd you source that? I didn't see it in the aftermarket manuals, but that might be because I didn't look too hard.
Page 46-67 of the factory repair manual.