The "2-Bits" V-Twin

[RReid]

This is a little story about Dum A. Reidskenderian, hot shot cam maker.

Contracted to make a one piece exhaust cam for a little 50 degree V-twin, he first thought about what the angle between the lobes should be. One eighty degrees to account for the 4-stroke cycle, minus a 25 degree offset for the cylinder separation. So 155 degrees, done. He proceed to mill the cam profiles, finishing them off with some ECF work (Eye Controlled Filing).

Putting the new cam pair in place along with the pushrods, it quickly became obvious that Dum A. had overlooked something. With that lobe separation the exhaust valves would open within just a few degrees of each other. Dum A. went to bed that night still trying to figure out what he was missing. Eventually, laying there in bed, his head cleared enough for the screamingly obvious to become obvious.

The pushrods that the cams act upon are not inline with the cylinders, the way he was thinking about it in his simplified mental diagram, but are on opposite sides of the engine on a horizontal plane, 180 degrees apart. And that means the lobe separation should not be 180 – 25 degrees, but simply 25 degrees, the 180 is built into the mechanics.

Dum A. confessed his sin to me and I forgave him, while smugly thinking that I would never make a Silly A. mistake like that...

Luckily there was enough extra thickness in the lobes that I was able to use a parting tool to separate the pair. Then I repositioned them, and soft soldered them and the camshaft all together.

The machining of the cams actually went well, even though the design was flawed. Here are a few process shots.

The cam blank was set-up on the diving head so the part could be rotated to the various angles to mill flats defining the lobe flanks first.




Then the base circle diameter was milled in, up to the lobe flanks.


After blending the profile in with files and wet/dry paper, the part looked pretty good. The cam profile is borrowed/copied from the Upshur Farm Engine. Too bad the separation is wrong!


Here it is after repositioning the lobes and soldering the whole mess together; and in place between the pushrods.




The cam gear will be counterbored to fit over that shoulder left outside the cam pair, and will be screwed to it.

[crueby]

We've all had Homer Simpson moments,  , key is to realize them before getting too far down that road. Sounds like you did in time!


 

[Kim]

Seems like a pretty good save to me, Ron! 

Kim

[Admiral_dk]

Nice save - my only concern is if the soft solder would be strong enough to withstand the pounding forces of opening the valve .... 

Still following and enjoying your journey 

Per

[RReid]

Chris, Kim, Per - Thank you, guys!

my only concern is if the soft solder would be strong enough to withstand the pounding forces of opening the valve ....

I think it will be strong enough, but if I'm wrong it will be little more than an inconvenience to redo. One cam and the shoulder are a solid piece which is a press fit onto the camshaft. The other cam is more of a running fit, but the solder is applied to the interface area between the cams as well as down to the shaft, so a good area of coverage. If proved necessary it could be re-soldered with hard, or a locking pin could be easily added, or it could be completely remade as the one piece unit originally planned.

A big part of this project for me is the education I get from figuring things out for myself, in addition to tapping into the knowledge and experience of others. In that respect, mistakes add to knowledge, and experimenting with methods when the consequences are not overly critical or expensive (in time or $$), then I'm happy add to my personal database of what does work or does not.

It also must be remembered that this is not an F1 engine. The rated horsepower of the originals was listed at a mere 1500 rpm. 

[crueby]

Hi ron,
If the soft solder doesn't hold up, then the pin would be the easiest fix I think - the soft solder would have to be completely removed to redo it with hard solder, they dont like each other much. If its not hard to do now, just adding a pin should lock it all in place. Either a taper pin or a loctited in straight one would add a lot of strength to the joint.
Parts are looking great! How much more is left to make?

Chris

[RReid]

- the soft solder would have to be completely removed to redo it with hard solder, they don't like each other much.

Good to know, Chris. Thanks for that. I wondered about compatibility, but hadn't looked into it.

I agree that the pin would be the easiest option, but I still don't really think it will be needed. One option offered for making the cam in the Upshur Engine plans is to make the lobe and base circle parts separately and soft solder them together. I did mine that way and it has worked fine. That would have to be less strong than what I've done here, but the cam outline, valve size, and valve spring strength are the same for both. Also, in Randall Cox's MEB build article for the Hoglet V-Twin which is slightly larger, he simply loctites the cams onto a drill rod shaft. In any case, if I pinned mine now, I would never know the answer for sure.

How much more is left to make?

All four valves. One or two flywheels. Cam gear. The gear cover/breaker plate was made today (pic below). Probably some other little stuff I not thinking of right now. And the ancillary stuff like the breaker points assembly, a fuel tank, etc. 80% done, only 80% left to do.

[Roger B]

I think that the area of soldering and the likely forces will not be a problem for your modified cam. I am awaiting the first pops     

[RReid]

Thanks Roger. I appreciate the input.

I got some stand-offs made for mounting the gear cover shown in the last post. Since the cover also carries the bushing that supports the outboard end of the camshaft, I was able to assemble the assembly, including the gear blank, and verify that the pushrods push and the rockers rock when the camshaft is spun by hand.

You'll just have to take my word for it though, no photographic evidence today!

[RReid]

One of the stand-offs mentioned in the last post can be seen in the photo below. Originally these were to be soldered to the top of the pushrod guide/bushings, with a shallow counterbore to locate them. But I wasn't happy with the attachment of the guide shown, using a screw into it from behind. Because that pushrod is very close to the bottom of the guide, there is very little meat left for the screw threads.


So I redesigned the stand-offs to have a base that tightly drapes over the guide/bushings. Those then got two 2-56 screws from the back of the plate which fix both the stand-offs and guides. The original screw holes are no longer needed and won't be used.






And finally, a couple of pics show the completed assembly, and a short video of the valve train being exercised with a hand crank. (Yes, the rocker shafts do still need to be trimmed to length).



<a href="https://www.youtube.com/watch?v=51u9JIRcUxw" target="_blank">http://www.youtube.com/watch?v=51u9JIRcUxw</a>

[crueby]

 

[Kim]

Very cool, Ron! 

Kim

[Admiral_dk]

Always nice to see that all work as intended     

Per

[RReid]

Thank you, Chris. Thank you, Kim. Thank you, Per. 

[RReid]

Return of the Fly (wheel).

Back in Reply #160 I discussed making a flywheel from a discarded cast iron dolly wheel that I wasn't too satisfied with. Having ordered and received a couple of mild steel "hockey pucks", I made a new, improved flywheel today. The 1st try weighed in at 111 grams, this one is 187 grams, better than a 68% improvement.

The first picture shows the starting point of each. The second shows the finished parts. Not only is steel heavier than cast iron of the same size (higher density), you can see that the steel version has much more material out towards the rim, where it does the most good. The step in the OD is needed to clear the bottom of the pistons at BDC. It took a little while to figure out why it was locking up solid at that point! It wasn't much contact, and it wasn't easy to see, but at least it was easy to fix.