Upshur's twin opposed cyl. engine

[Vixen]

Brian has built a number of engines which do not run. At model scale, both flat flank and curved flank cams should still allow the engine to at least run, that is assuming the cams are at the correct angular position relative to the camshaft and crankshaft. Brian tends to use individual cams located on the camshaft by grub-screws. He appears to set each cam angular position with respect to the angle where the valve opens.

I believe Brian may achieve better results if he were to set each cam's angular position with respect to the angle of maximum lift of each cam i.e. the 235 and 125 degree angles; as shown in the diagram of the right (a typical Edgar Westbury camshaft) rather than the valve opening events. Using the angle of maximum lift removes all the uncertainties associated with play in the pushrod/ rocker mechanism, tappet clearance etc. etc.




Just a thought.     

Mike

[Charles Lamont]

With the flat being shorter than the diameter of the tappet then it is only running on the flat for a split second so really running on a curved surface just about all the time.

So?

[Allan Ostling]

With the flat being shorter than the diameter of the tappet then it is only running on the flat for a split second so really running on a curved surface just about all the time.

I see what you mean. Kinematically this cam would have the tappet face contacting one or the other of the small and large radii, never pausing on a flat face after the instantaneous (split second) contact there. Dynamically, something's gotta give.

Exactly what Charles was saying in reply #163. If the cam is soft enough, and if the engine ever starts maybe all those hammering forces can beat the cam into a more suitable profile. 

[Jasonb]

Agree with you Mike and I have said as much on HMEM. With the 5thou lash Brian sets his engine up with the duration that the Valve is actually open will be a lot less so if timed from when it starts to open then god knows how early it will close.

It is also worth remembering that back in the day Hamilton designed this as an engine that could be built quite easily by the average model engineer who may only have had a lathe to do the turning AND MILLING so a flat flank cam was a lot easier to produce. I've built other flat cam designs where you were expected to file the profile so again easier to file a flat flank. Hamilton may even have expected them to be filed as there is a note on the drawngs "make sure flanks are reasonably straight. His engines were not really about performance, just something to run in various configurations and then the running would tend to be a quick one to show it off rather than hours on end so unlikely to see much wear. Certainly not expected to work like the old Fairbanks Sheffield engines that it is loosly based on. Too easy to overthink what these engines are about.

Interestingly the filed flank design suggests that the second lobe is positioned by extablishing where it's peak is on the part assembled engine. No rotary tables etc here.

[gbritnell]

Having studied and worked with full size and model cams I fully understand what the acceleration and deceleration ramp is for. I bought a Yamaha 750 V-twin motorcycle back in the late 70's. I rode it several hundred miles and it began to have a noticeable click. I took it back to the dealer and they adjusted the valves. All was good for several hundred miles and the click came back. This time the dealership said there was a recall on the cams. Apparently the cams weren't hardened properly and the acceleration ramp was wearing down. There's more to these ramps than just a curve. Let's say you have a flat sided lobe with certain angular characteristics. (Timing) now say you have .005  valve clearance. The ramp curve has to be created so that it doesn't affect the timing. If the curve radius is larger than .005 then the valve will start to open or close at the wrong timing point. For model engine cams with a base circle of say. 50 diameter (which would be a pretty good sized cam) the acceleration ramp curve would be so small as to almost negate the time put in to machine it. On a full size cam lobe with a base diameter of 1-2 inches the ramp curve could be more defined.  I have always made my lobes with flat flanks and some of the engines have many hours of run time on them with no issues.

[Jasonb]

It's tempting to build a version of the Upshur that is a bit closer to the Fairbanks Sheffield. Carve a crankcase and top cover from Aluminium, more finer fins to the cylinders, move the distributor to the top and hide it inside a dummy Mag and a bit more detail to the heads.

https://www.oldmarineengine.com/history/Fairbanks/aircooled.html

I have started to draw up an engine based on the old Springfield opposed twin but could be tempted to change track

[Allan Ostling]

Brian, I have just returned from a 3-week drive to Santa Rosa CA and back to Phoenix. I hoped for some progress on your engine. Are you OK?

[Brian Rupnow]

Yes Allen, I'm okay. I have been bitten by the "powder paint bug" and have been devoting my time to a powder paint booth and a sandblasting cabinet. By the time I have that sorted out, I will be quite happy to return to my unfinished engine, and attempt to get my other non running engines sorted out.---Brian

[Allan Ostling]

Are you going to paint your engines that run, and sandblast those that don't?

[Brian Rupnow]

Something like that.

[wjh308]

Powder coating is so much better than wet paint I think, just need a big enough oven for your parts to hang easily.