Engine Swap Questions:

I have a bunch of question going into this, this is my first engine rebuild. So if any would be so kind as answer one or two of the questions, I would appreciate that.

I may be buying a 750 maxim to take the engine and put it in my 750 Seca so I can rebuild the engine (no 2nd gear). So,

1) Rereading past posts has shown me that the two models have a different mounting system. How hard will it be to get a maxim engine on a Seca frame?

2) I also read that they have different final drives. What is different? I just want it to hook up long enough for me to rebuild and reinstall the original, how much of an issue is this?

3) Are they electrically identical?

4) Are the carbs interchangeable. My Seca carbs are adjusted great, the donor maxim is not running, so can I just put my Seca carbs on the Maxim engine?

5) Are their any issues I am missing?

6) Like I said, I am doing this so I can rebuild the original at my leisure and still ride my bike this summer, so what should I check/replace while I am in there?

7) Is the fork that would cause *major* 2nd gear slipping the one circled in the attached picture?

Thanks for all the help guys.

Stephen.

 

not sure as I've not done that exact swap but I can tell you that I have used both engines in my 650 seca turbo chassis without problems.

Sean

 

I just did this last weekend. Not a smooth job.

The mounts on the Maxim engine I bought on ebay (which ended up having a bad 2nd gear BTW) were vibration dampened by rubber inserts into the engine lobes. The diameter of the holes in the maxim engine are larger to accommodate these. The Seca, on the other hand, has a rigid mounting system which also translates into some frame tabs that that the lobes on the front and rear of the engine fit snugly into which the maxim did not have. The maxim mounting hardware must be obtained (at least for the front) and altered or the frame tabs need to be altered to accomodate the added thickness of the large stabilizing washer on the Maxim mounting hardware.

I decided that I would just cut the large stabilizing washer off the mounting hardware tube that they are welded to (and in turn dipped in a mold to accommodate the rubber insert.), insert the remaining mount into the lobe holes on the engine, and mount them snugly in between the Seca's front lower mounting tabs. (Tight fit!!)

The top front mounts work fine with the maxim hardware and do not need to be altered in any way.

The rear mounts from the Seca engine have inserts to fill the large diameter holes (the only translation to the Maxim large hole mount system of the 6 lobes) and they can be knocked out easily and re-used in the maxim engine.

The biggest stumbling block I ran into was the rear mount alignment. The Maxim uses one long through chassis bolt and the frame does not have the inner mounting tabs that the Seca does. The Seca uses 2 individual bolts through the foot pegs, the main tube on the frame mount, the engine mount lobe, steel tab welded to the frame, and then the nut for a tight fit. The Maxim rear mounts must be slightly offset to the left side of the frame by 1/16" as I could not get the left lobe to slide in between the steel tabs on the seca frame due to the fact that it was setting on top of the tube mount! The spacing was correct, but because the right side of the frame lined up ok in the sleeves, I had to cut 1/16" off the left side tube mount on the frame. to get it all into place.

Also...the shifter linkage...I had to swap the shifter linkage engine cover from my old seca engine to the maxim as the linkage system uses a forward axis that is mounted on the cover for the pedal whereas the Maxim uses a rear axis mounted on a frame system.

Quite the unexpected chain of modifications. I was hot the whole time as I was doing this in 50 degree weather in the parking lot of my apartment complex, but If you have a garage, it'll pan out.

 

Wow, thanks for the tips, I will keep that in mind. Especially the experience, odic.

I am hoping not modify anything on the seca side, as I intend to return to the motor I am taking out.

 

My advise would be to get yourself an extra rear mount spacer to grind and then you shouldn't have to modify the frame mounts at all. I just don't have a grinder or workbench for that matter, so it was easier to user the dremel with a fiberglass cut-off wheel on the frame mount instead. If you can find a maxim engine that was rigid mounted, you should have no problems, but I'm not sure if they were all rubber mounted or not. This is where, hopefully, someone else could chime in as a Maxim owner to clarify.

I should add that the electrical and fuel systems were 100% interchangeable for me, so those can be marked off your mystery list.

Best of luck!