E: Engine Comet Mongrel

[eglijim]

Meeyow!
Royal Enfield decompresor.........

We always removed the complete valve lifter assembly on any "quick" engines due to previous failures and you do not want extra broken bits floating around in the timing chest. While the engine is in bits, could be worth investigating the "Harley" pop off push button decompressor if you are prepared to machine an extra threaded hole into the combustion chamber.

 

[Cyborg]

The motor is complete now. All of the stock decompressor bits are new, so it should be ok. Also the ignition switch can be used to kill the engine. I hope that my twin plug conversion and programable ignition will allow me to start it without a bunch of drama. In other words, I'm praying the decompressor will outlive me.

My focus now is determining how to adequately brace the rear shock absorber rocker, so it doesn't launch itself into my nether regions.

 

[craig]

Thanks for posting photo.
Where did the special push rods come from please?
I am trying to avoid pulling the UFM.

Starting to look like it might be a product of North Korea.
View attachment 22418

 

[Cyborg]

I just modified a couple of long pan head JIS (like Philips) screws that I had in the junk bin. Rounded the ends to sit in the followers and dished out the other end, so the gauge would stay centred.

 

[craig]

Thank you, what was the length you have used? They are a little longer than stock .
Do you have a picture of the timing push rods please?

I just modified a couple of long pan head JIS (like Philips) screws that I had in the junk bin. Rounded the ends to sit in the followers and dished out the other end, so the gauge would stay centred.

 

[Cyborg]

Length doesn't matter much as long as they stick out through the rockers enough. The ones I used were different lengths, but if I was going to make a proper set, I'd make them about 6 3/4". For dial gauges, digital are preferable because one valve is opening and the other is closing. With analog gauges, this means they are spinning in opposite directions and counting the revolutions will make folks like me go a little bug eyed. Two magnetic bases stuck onto the UFM should work ok.

 

[Cyborg]

Can't believe I'm actually posting pictures of this... I used CAD to come up with brackets to support the rear shock rocker (progressive linkage), CAD stands for cardboard aided design. Had to locate the rocker relative to two crossmembers, so used several pieces of cardboard hot glued together in order to make a template for a template, so I could scribe it onto a piece of boiler plate. Drilled some holes to reduce the weight a bit... as previously mentioned, its in a critical area, so strength is more important than weight. This is turning out to be one strange looking motorcycle.

 

[BigEd]

Can't believe I'm actually posting pictures of this... I used CAD to come up with brackets to support the rear shock rocker (progressive linkage), CAD stands for cardboard aided design. .........

View attachment 23810View attachment 23811View attachment 23812

Cardboard prototyping makes a lot of sense. I often use a bit of discarded cereal packet or cardboard box to prove something will turn out as expected or even fit at all. Cardboard is quick and no cost so mistakes are not such a big deal. Purchasing potentially costly metal and spending lots of time cutting and forming complex items can lead to lots of bad language when you find it is wrong.
This is a very interesting project.

 

[chankly bore]

I've bought Vincent parts that were C.N.C.- CLOSE, NO CIGAR.

 

[Cyborg]

Sounds as though you have covered the bases which could cause build problems downstream. As i think i said previously, the reason for the built in adjustability with the bears chassis was a belt and braces approach to permit tinkering with the handling if required(or it was a dog). Don't know if you intend a frame rail from the headstock to swinging arm area but we tacked on an abutment here on the bears for the steering damper. The Egli's fixed abutment we have fixed to the front (milled aluminium) head bracket.

Just wondering if you or anyone else has any comments regarding swing arm angle. I haven't done the final calculation for rear wheel suspension travel, but loosely based on Ducati Monster geometry, it will be somewhere in the ballpark of 144mm. That may be reduced but better to explain that later. I am just about to tack together a rats nest of tubes and brackets that support the shock rocker, but I haven't made a mounting bracket that locates the bottom of the shock to the swing arm. Before I do that I need to have everything else tacked in place and sort out ride height etc etc. So my question is.... Do I take the centreline between the countershaft, swing arm pivot point, and rear axle... then split the difference? As in 72mm of travel above the centreline and 72mm below. I'm thinking I should subtract whatever the sag will be (say 30mm), so take the remainder and split that above and below the centreline. So I would end up with 57mm above and 87 (57mm + 30) below. That way the drive chain slack would be more consistent while under way.

The shock fork that connects the rocker to the swing arm has heim joints on either end, so a little more adjustability than the Ducati setup which only has the joints on one end. I may try and build in some more adjustment into the lower shock mount as well. Might come in handy if rake and trail differ much from the initial calculations.