Upshur's opposed twin engine

Jasonb · Oct 10, 2024

minh-thanh said:
An other way : Fix the 2 lobes on the shaft at an angle of 102 degrees, then adjust the position of the gear.

You need to have the correct cam leading.

Brian why not Loctite the two cams in place, if you get it wrong pull the shaft out, heat to break the Loctite and then reposition the other way round. Saves making a new cam with screw boss.

As I and others have said forget about the 2nd cylinder, just turn the engine over by hand and get the first set up as you have done with previous singles which will soon show which way the two camsneed to be set. The second cylinder will take care of itself apart from a bit of lash adjustment.

Brian Rupnow · Oct 10, 2024

Not a lot got done at the Rupnow house today. We did make one cam with a hub and set screws. I thought a lot about loctiting the cams in place and trying to see if I got it right, but its a major job to do that and then find out I got it wrong. My powder paint is at my front door and I haven't had a chance to go and get it yet. That's all my machining today.--I haven't even given the new cam a bath yet. I just photographed it straight from heat threat.

Vietti · Oct 10, 2024

Just a thought. I superglue the lobes in position till I'm sure I like them and then pin them. Comes apart easy if need be and they don't seem to slip.

Brian Rupnow · Oct 11, 2024

So here we are, one cam J.B. Welded to the shaft, other cam with set screws wiped with greasy q-tip inside so it won't stick to the J.B. weld, and the gear wiped inside with grease so it doesn't stick to the J. B. Weld. This seems like such a simple thing, but it took me two hours to do this. Now it's time for some lunch!!!

Brian Rupnow · Oct 11, 2024

Today I'm figuring out how far powder paint goes. I paid $26 per pound. With my trusty teaspoon I put 10 tea-spoonful's into my powder paint gun bottle. I painted everything multiple coats---the reason being that I can only spray what faces the opening in the spray booth. I turned the aluminum sheet everything was setting on about 6 times to ensure that I got full coverage on everything. (the ground was hooked to the aluminum sheet) Then with my trusty teaspoon, I put 9 teaspoons of powder from the gun bottle back into the bag of powder paint. That's right---one teaspoonfull of powder to paint everything at least six times. That included the flywheel, the coned front of the flywheel, the top plate, the cam gear cover, the air breather that sets on top of the top plate, and the large base/gastank and the threaded cap that screws onto the gas tank spout. Everything is now setting in the curing oven, where, if I have lived right the powder is melting and flowing out into a gloss finish.

Brian Rupnow · Oct 11, 2024

This is the green paint glossed out after the oven had cooled down. My main concern was "Would a powder paint from Emerald Coatings flow and gloss out using an oven from Eastwood?" The question has been answered in a most satisfactory manner. Tomorrow I will start putting everything back together and see if this thing will run.---Brian

olf20 · Oct 11, 2024

Nice job. Your new toys are paying off. LOL
olf20 / Bob

Ghosty · Oct 11, 2024

Brian,
It looks good, can't wait and see what else will be done
Cheers
Andrew

Brian Rupnow · Oct 12, 2024

I have the engine reassembled, and it looks really good. Looks like a John Deere tractor!!! I am puzzled by the notes regarding the valve timing on this engine. The note says "Viewed from the flywheel end of the engine, set the left (1 piston) on top dead center. Loosen the distributor rotor. Slide it back to allow the camshaft to be slid forward just enough to disengage the gears. Re-engage the gears where the left cylinder cam followers rise approximately an equal amount for the same crank angle on either side of top dead center. If the rise is not equal, slide, engage the tooth which favors early intake follower rise with ccw flywheel rotation." ---I don't have the faintest damned idea what this really means. Normally on these small engines I set the intake valve to begin opening about 15 degrees before the piston reaches top dead center. The shape of the cam determines when the valve closes--(I followed the drawings to make my cams). Can somebody set me straight on whatever I'm supposed to do here please.----Brian

Basil · Oct 12, 2024

The way I would do it is to set the pistons at TDC and get one cylinder with the lifters rocking, that is exhaust closing and intake opening. Once this is confirmed rotate the engine crankshaft one revolution and look at the other cylinder. This cylinder should now have the valves rocking, ie Exhaust closing, Intake opening. Make sure you rotate the engine crankshaft in the direction you want the engine to run. Hope this helps.

Brian Rupnow · Oct 12, 2024

This is what I thought it meant, but this is very fishy. Using models created from the Upshur drawings, I placed one side of the cam right up to touching the cam follower, but not yet lifting it. Then I placed an overlay of the same cam on the other side of the cam follower, but with the cam follower just touching it, as it would be when the cam follower was fully "not lifted". 48.3 degrees is a long way from the 15 degrees I have used on all my other engines.

Sparky_SC · Oct 12, 2024

Is that drawing to scale? The cam lobe is dwarfed by the size of the lifter.

Brian Rupnow · Oct 12, 2024

Yes, the drawing is to scale. Perspective is weird sometimes.

Sparky_SC · Oct 12, 2024

Brian Rupnow said:
Yes, the drawing is to scale. Perspective is weird sometimes.

Ok. Proportionally the head on the lifter is huge compared to the lift lobe on the cam. That will have a big effect on valve timing, greatly increasing the duration. I am sure you made them to the drawing dimensions. The ratio of the lifter head do the cam lobe just seems much much different than the norm by eye.

Brian Rupnow · Oct 12, 2024

As shown in post 351, the cam duration is 96.3 degrees. On other engines I have built, the cam begins to influence the intake valve 15 degrees before the piston reaches top dead center and stops influencing the intake valve when the piston is 45 degrees past bottom dead center.---This is of course, assuming 0 valve lash. So, the cam duration on those engines is 15 + 180 +45 =240 degrees. It's quite possible that I am not understanding the Upshur instruction sheet. if I take that 96.3 degrees and add 180 degrees to it, then I have 276.3 degrees, which gets me a lot closer to the 240 degrees that I generally use.

Jasonb · Oct 13, 2024

You have got to do two things with this engine.

1. Set the cam timing, we have covered this in many posts

2. As you have a 2 cylinder engine and a distributor you ALSO need to set the rotor in the distributor so that the correct cylinder fires at the correct time in relation to what the cam is doing to the valves..

What is being said is to first set rotor by engaging the gears in the right position. As you have deviated from the original design you are unlikely to be able to slide the gears out of mesh. But you have a grub screw on the large cam gear so can make adjustments that way.

The description is for an engine built as per drawings with both the cams and the cam gear all fixed to the camshaft with loctite so the only way to make adjustment is but meshing different teeth. All the description is saying is how to set the rotor equal to the two valves opening and making any slight adjustments if something is slightly out. As the setting is done at TDC it will ensure you get your spark at TDC.

You will also need to ensure the ignition points fire at the same time that the rotor makes the two contacts as you won't get a complete circuit otherwise. So and changes to the points will also need a change to the rotor position. That is why I said early on to mount the distributor on curved slots so you can rotate it either way to make adjustment easier, much like you rotate the distributor on an old hot rod.

TonyM · Oct 13, 2024

What Jason said. I was posting a slightly different response at same time.

Jasonb · Oct 13, 2024

Brian Rupnow said:
As shown in post 351, the cam duration is 96.3 degrees. On other engines I have built, the cam begins to influence the intake valve 15 degrees before the piston reaches top dead center and stops influencing the intake valve when the piston is 45 degrees past bottom dead center.---This is of course, assuming 0 valve lash. So, the cam duration on those engines is 15 + 180 +45 =240 degrees. It's quite possible that I am not understanding the Upshur instruction sheet. if I take that 96.3 degrees and add 180 degrees to it, then I have 276.3 degrees, which gets me a lot closer to the 240 degrees that I generally use.

You are mixing cam rotation (96.3 deg) and crank rotation 15+180+45

So as the cam rotates at half the crank rotation your cam duration of 96.3 will equate to 192.6deg of crank rotation.

Therefore with 192.6deg to play with I would set the engine up so that the intake starts to open at 4deg OF CRANK rotation before TDC and it will close 8.6deg After BDC or a bit less allowing for lash which wants to be about 1 thou not 5 thou.

minh-thanh · Oct 13, 2024

Brian Rupnow said:
On other engines I have built, the cam begins to influence the intake valve 15 degrees before the piston reaches top dead center

That is when the exhaust pressure in the cylinder is still quite large and it will affect the intake stroke.

Brian Rupnow said:
and stops influencing the intake valve when the piston is 45 degrees past bottom dead center.---

When you build an engine with a compression ratio of 4-1, 5-1 or 6-1 the entire cylinder volume is calculated and when you give it 45 degrees after BDC, what will be the remaining compression ratio of the engine !?

Jasonb said:
I would set the engine up so that the intake starts to open at 4deg OF CRANK rotation before TDC and it will close 8.6deg After BDC or a bit less allowing for lash which wants to be about 1 thou not 5 thou.

I usually tune the engine this way, maybe a little more but never 45 degrees after BDC

Brian Rupnow · Oct 13, 2024

Okay, I'm almost ready to rock and roll!!! I still have to source some very small hose clamps to go on my flexible intake lines and still have to receive a pair of sparkplug wires from an outside supplier. As far as my cam/valve timing is concerned, I'm going to set things up so that the intake cams just begin to affect the intake valve at 15 degrees before the piston reaches top dead center on the compression stroke.---this will be set the same for both cylinders. The position of the rotor for the distributor will be set to deliver a spark to the correct cylinder when that cylinder has the piston at top dead center on compression. (The rotor is fixed to the camshaft by a set screw, no keyway, so I can set it wherever I have to). Its Thanksgiving Sunday here today, so I am expecting an invasion of sons, daughters, their and various grandchildren in about half an hour.

Upshur's opposed twin engine

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