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· Premium Member
3,178 Posts
Discussion Starter · #1 ·
so i set out to attempt to destroy... er ... repair my m900 engine from the chain throwing incident suffered by a previous owner.

it started with pulling the engine and humping it onto the mill:

what is left out is how i previously talked about the posts the engine is resting on. there are two cylidners that thread to the table in which the motor mounts thread into. and then there's a block that a third motor mount threads into which is then clamped to the table.

then i set up a test indicator to survey things. first off, i checked how "level" the engine is. it was actually pretty dang level, but the sealing surface did vary .010" around the whole area. the only trend i could detect was that one "corner" seemed to be the low point. since it didn't correspond to the X or Y plane of the mill, i can only surmise that the "precision" grinding of the outer plane of the case was not perfect.

here's an animated GIF of the gouge area:

basically, i'm rotating the test gauge via the mill's spindle about 45 degrees and the gauge reads about a .010" dip right there! sorry, i must have bumped the camera, as the image jumps a little. that gauge reads in tenths of a thousandth of an inch. each whole number is .001 of an inch and there are 10 graduations between the numbers. what i did was after seeing that the alternator cover was broken and filled with JB Weld, i got a used cover then tried to "feather" the area around the gouge in the engine case with a soft scotch brite pad on a die grinder. at least it leaked LESS than when i got pongo...

here's a 2 meg quick time movie of actual machining. (pretty boring, really) please right click and Save As to download to your computer:

that's a 3/4" carbide end mill. i really should have removed the flywheel and all that other stuff. instead, i covered it all. i used the 3/4" mill so i could be somewhat sloppy and not have to make multiple passes over the bolt hole areas. i milled in a single pass 600 rpm, .015" depth cut, with slow feed rate, and using kerosene as a cutting fluid. the depth of the engine is greater than the Y span of my mill, so i had to loosen the turret and move it forward at one point. even though i verified repeatability, i was still worried that when i completed the circle of machining that there would be a step. nope. was perfect. no vibration and the setup was rigid and didn't sway or oscillate at all. the area where the gouge was is now flat for about 1/2 the width of the mating surface, so it should seal up fine.

here is a pic showing the reflections of the tooling marks left in the surface:

in the foreground is the shift shaft. that was loads of fun... i basically drove the spindle right up against the shift shaft. really should have removed all that crap in the middle... :)

this was a fun experiment / lesson and i'm glad that so far, my engine is still not scrap metal, and i thought maybe some of y'all might enjoy. :) just in case this went to hell, i've got a line on a set of cases. but it looks like me and pongo are going to be ok.

tomorrow, i'll clean up then test fit the alternator cover to make sure the .015" of extra depth do not cause problem. then it all gets to sit until i reassemble my aprilia RS250 race bike for next weekend's big races.

:) chris

· Premium Member
2,773 Posts
Good job!. Liked the pics and movie. Hopefully you won't run into problems with end clearances on shafts when you put the cover back on. (If so, I vote with a previous poster who suggested fabbing a spacer similar to a gasket of the required thickness - seems simpler than some of the alternatives)
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