E: Engine Comet Mongrel

[davidd]

That sounds like a reasonable plan. I would note from observation that the Comet tends to run the RFM at more of an angle than the twin. When a single is loaded, the RFM remains pointing downward to the axle. This seems to make some sense because the single and twin use the same parts (springboxes) and yet the Comet RFM pivot is an inch higher and 1/2" more forward than the twin. I think this has the effect of pushing the RFM down at the axle.

You can do the same thing to the twin using Reg Bolton's mod that moves the spring boxes back a few inches. It puts the RFM at more of an angle (the Girdraulic as well.)

These observations lead me to believe that you have some decent wiggle room with your selection. You might want to measure the distance from the CS to the axle to see if there is a travel range you can use that will keep the chain adjustment best. This might cause you to use a slightly different split than the center of the suspension travel range. You might be able to bias the selection to the best chain adjustment range and find that it works well in the suspension travel range also.

David

 

[Cyborg]

Thinking I will set the rear axle, swing arm pivot and c/s in a straight line (longest distance between axle and c/s) and then set chain slack at that point. Then with the bike sitting normally under it's own weight, I can remeasure the chain slack and then use that number for future adjustments. Factoring in the sag should keep the suspension travel close to the centre point, so the least amount of chain slack while riding. I may be over thinking it, but with a swing arm slightly longer than I would like and the required distance between the c/s sprocket and swing arm pivot, I'm assuming the least amount of slack the better. I do have a selection chain rub strips ( complements of the man with the dumpster full of motorcycle frames) just in case.

 

[Cyborg]

My avatar would suggest I have a decent collection of shims, however... somewhere it is written that no matter how many you have, none will be the required size and thickness.

This trick seems to work quite well. Tried it with .020" and .025" stock.

 

[Bill Thomas]

There is another one on youtube, Where he puts thin sheets steel, clamped between thick steel plates,
And drills through the lot, Works well. Cheers Bill

 

[Cyborg]

Finished all of the gearbox spacers and made one up to move the rear sprocket into alignment. If I had used thinner material for the engine plates, I could have done without the sprocket spacer,but the rear wheel wouldn't have been right on centre. Sprocket still sits completely on the carrier, wheels are aligned, rear wheel spacers are done and drive chain is happy.
I'm assuming it would be best to run the primary drive belt all the way to the inside so it is more or less over top of the bearing in the clutch hub.... or do we worry about such things?

 

[davidd]

I don't think I had a choice! The clutch ends up where it is when the box is mounted and the guides for the belt were on the crank sprocket. I adjusted the crank sprocket with shims behind it to center the belt on the clutch.

David

 

[Cyborg]

Thanks, I'm able to do the same as you (shim the drive pulley out) , but was wondering if it is better to have the belt further inward so there is less leverage on that clutch hub bearing. Maybe I'm overthinking it again....

 

[Cyborg]

So the plan with this abominable creation was to assemble the engine using parts that I already had under the bench and focus on getting the bike rolling under its own steam. Assuming it turns out to be reasonably well behaved and has acceptable road manners, then at that point I could justify a proper crank assembly, head and the other 600cc bits. This brings me to the subject of a carburetor. The intake port on the head is currently about 28mm, so don't see the point in installing anything larger. I ordered a Mikuni TM28 flat slide and I'm wondering if anyone has any experience setting one of these up on a Vincent. It comes with a 15 pilot and a 180 main.
Even jetting information about 28 mm Mikuni round slides would help, although I'm assuming the flat slide will be happier with a slightly smaller pilot jet than the round slide (although much larger than the 15 that is in there now).

 

[BigEd]

So the plan with this abominable creation was to assemble the engine using parts that I already had under the bench and focus on getting the bike rolling under its own steam. Assuming it turns out to be reasonably well behaved and has acceptable road manners, then at that point I could justify a proper crank assembly, head and the other 600cc bits. This brings me to the subject of a carburetor. The intake port on the head is currently about 28mm, so don't see the point in installing anything larger. I ordered a Mikuni TM28 flat slide and I'm wondering if anyone has any experience setting one of these up on a Vincent. It comes with a 15 pilot and a 180 main.
Even jetting information about 28 mm Mikuni round slides would help, although I'm assuming the flat slide will be happier with a slightly smaller pilot jet than the round slide (although much larger than the 15 that is in there now).

Several people with Vincent twins are using #30 pilot jets in the 28mm round slide Mikunis so that might be a good starting point. (No pun intended.)

 

[Cyborg]

Thanks, Before I order any jets, I'll drill out the primary in stages to get a basic idea of what it wants. Based on your comment, maybe I'll start with 25 and see how the idle mixture screw likes that. With the 180 main, I'm assuming that will get me on the edge of the ballpark... even though it does seem a little small.