Another (unsure) Upshur twin (lots of beginner questions?)

I am not really confident, that this will not become a never finished item. I decided to start anyway. I also took the decision to start a parallel thread, because I do not want to clutter up Brian Rupnows thread.

I am following video series by Andrew whale and since April Brian Rupnow. (never made an engine and did not plan on the materials).

Studying the plans there is a Part1 "adapter" I am unsure what the function of this part is? Is it just to register the plastic cap of the distributor on the housing?

More of those "stupid questions" will come.

I might go just ahead and blindly follow the long parts list from top to bottom.

part 1

Already at part one the second big question. Would it harm to alter the crank shaft diameter from 1/4" to 6 mm? 6 mm will be easier, because most of my tools and parts are metric.

Greetings Timo

Change the crankshaft to 8mm 6mm would be a bit too small. Look at the assembly drawing of the distributor on page 10 of 13 . you do need that adapter.---Brian

I can't really see what the "adapror plate" does but if it were my engine I would fit the adaptor as it is shown on the drawing. But I would alter the distributor cap to have curved slots rather than just the two screw fixings. My reasoning is that you could then loosen the screws ( or have spring washers under them) and rotate the distributor cap which would allow you to advance and retard the timing. Te adaptor would help locate the distributor cap though not really needed.

My drawing shows the crankshaft as 5/16" and I would be quite happy increasing that to 8mm. Same with the camshaft if that is what you mean, it could be reduced that from 1/4" down to 6mm.

I have a few thoughts on cylinder/fin construction to avoid the problems Brian and Andrew have had, let me know if you want to hear them. I also have a vie son running the steel camshaft in the steel crankcase without any form of bearing surface

Jasonb said:

I can't really see what the "adapror plate" does but if it were my engine I would fit the adaptor as it is shown on the drawing. But I would alter the distributor cap to have curved slots rather than just the two screw fixings. My reasoning is that you could then loosen the screws ( or have spring washers under them) and rotate the distributor cap which would allow you to advance and retard the timing. Te adaptor would help locate the distributor cap though not really needed.

My drawing shows the crankshaft as 5/16" and I would be quite happy increasing that to 8mm. Same with the camshaft if that is what you mean, it could be reduced that from 1/4" down to 6mm.

I have a few thoughts on cylinder/fin construction to avoid the problems Brian and Andrew have had, let me know if you want to hear them. I also have a vie son running the steel camshaft in the steel crankcase without any form of bearing surface

Click to expand...

You are correct the crank shaft is not 0.25" (do not know how I came to this)
So far crank shaft change to 8 mm. (that makes the adapter plate "useless" )


I made two new adapters, (one is lost forever in the chip tray of the lathe, or under the lathe or somewhere) the other is on the foto.
8 mm hole for the crank shaft.


Yes want to hear! (read) what your comment to the cylinder fins is.

I noticed that the slot for the gear on the top plate is not centered. (wrong!) the slot is, but the screw holes to mount the gear cover are not symmetrical. (Trying to figure out if that is a mistake or on purpose) .

Thanks for replies.

No, adaptor goes around the end of the 6mm camshaft

Will come back to you in a while about the cylinder.

Jasonb said:

No, adaptor goes around the end of the 6mm camshaft

Will come back to you in a while about the cylinder.

Click to expand...

maybe I should go sleep and look into that another day, mixing up the camshaft and crankshaft all the time. (maybe because I have no clue about it ).

Part2 breather cap. Cancel the breather tube and will thread the top plate for it. if it does look too much like a steam dome (because of size) I have to see.

Cylinder Liner and Fin Modifications

Since Brian started his build thread I have become aware of a few issues with these parts.

The Issues

1. Shrink Fit. Some who have omitted the lip on the top of the liner have found the fins move when the engine gets hot though I don't know what sort of shrink fit they went for.
2. People using 0.002" and 0.003" shrink fits to overcome the above have not been able to get the fins to expand enough when heated to allow them to slide into place. They have had to resort to brute force which has damaged the parts.
3. Concerns that these tight fits will mark the liner when the fins are forced on.
4. Poor flow of solder when liner soldered to side plate. The jig shown acts as a heat sink and makes it harder to heat the joint. Heating for too long exhausts the flux and then the solder does not flow easily or neatly around the joint.

My Suggestions.

1 & 2. Use the 0.001" shrink fit shown on the drawings as it should be possible to get the fins to expand sufficiently. Also reduce the depth of the recess in the top of the fins by 0.005". This will allow the lip of the liner to stand proud so that when the head is bolted into place it will clamp around the lip and prevent the head/fins from rotating if they become loose due to expansion when running. This lip standing proud also helps give a good seal to the head therefore reducing leaks and loss of compression. Just make sure you work around the bolts snugging them down otherwise you can tilt the head and get a poor seal.

3. Reduce the diameter of the liner below the bottom of the fins by 0.010". This will not only stop it being marked as the fins are put into place but also help line things up before they possibly become tight and you only have half the distance to cover before the fins cool too much.

4. If the bottom of the liner is further reduced to 0.906" for a length of 0.156" and the holes in the side plates reduced to match the liner will not drop through the side plate when being soldered so does not need the jig. This means a lot less material to heat up so soldering will be faster and should not exhaust the flux.

5. Add chamfers where shown to further ease assembly, the 0.010" under the liners lip will allow it to clear any small internal radius left in the fin's recess by the tip radius of an insert.

On the subject of fins, I noticed that Andrew in his video was making hard work of cutting the grooves, Brian says it was butt clenching and from the looks of his parts the sides of the fins are quite rough and torn. Get your grooving/parting cuts sorted on some scrap before you tackle the actual engine. This is how the swarf should come off and leave a bright cleanly cut edge and bottom to the groove.

Also set your topslide parallel to the lathe axis and use that to space the grooves some of what I'm seeing is not evenly spaced.

Distributor Cap

As I mentioned above if the two mounting holes are slotted then that will give you the ability to advance and retard the ignition timing by approx 20deg each way. Far easier than having to take the distributor off, loosen rotor's grub screw, move it's position and then put it all back together again.

CAMshaft Bush

As I said not keen on the crankshaft running in the steel endplate so if it were me making it I would add some bronze flanged bushes. I've not done the full assembly check but if the flange were 20thou or 0.5mm thick and placed on the INSIDE of the crankcase that would make sure the timing gear did not rub the crankcase. Bore to suit the CAMshaft which could actually come down to 5mm if that suits the metrically minded even more or 6mm is OK. Hole in the endplates needs to be Reamed 8mm and flange dia 10mm, retail with Loctite.

Jasonb said:

Distributor Cap

As I mentioned above if the two mounting holes are slotted then that will give you the ability to advance and retard the ignition timing by approx 20deg each way. Far easier than having to take the distributor off, loosen rotor's grub screw, move it's position and then put it all back together again.

View attachment 155260

Click to expand...

This is probably some feature that would not have made it into the original plan, because it is supposed to be doable wiht a lathe and drill press only.
Making those slots would be difficult. But my cap will probalby milled anyway, so slot design is likely happening.
I cam across a small omron encoder a while ago, they use smal L-shaped sheet metal brackets that clamp into a ring groove. (would be easy to use as alternative, saving the mounting ears)

The comments on the cylinder liners make very much sense, it is on the list as well.

Next question do to lack of understanding at this point. In the explosion drawing the cams look like 180°

In the article it is 90°.

There is no "assembly" drawing of the cam shaft as far as I saw.

Greetings Timo

p.s. from the section drawings of complete assembly I think the 90° must be it.

Have a look at drawing 13 if you are using the MEB plans. "Cam Shaft Layout" 102deg

timo_gross said:

This is probably some feature that would not have made it into the original plan, because it is supposed to be doable wiht a lathe and drill press only.
Making those slots would be difficult. But my cap will probalby milled anyway, so slot design is likely happening.
I cam across a small omron encoder a while ago, they use smal L-shaped sheet metal brackets that clamp into a ring groove. (would be easy to use as alternative, saving the mounting ears)
View attachment 155267
The comments on the cylinder liners make very much sense, it is on the list as well.

Next question do to lack of understanding at this point. In the explosion drawing the cams look like 180°
View attachment 155269
In the article it is 90°View attachment 155270.

There is no "assembly" drawing of the cam shaft as far as I saw.

Greetings Timo

p.s. from the section drawings of complete assembly I think the 90° must be it.

Click to expand...

it's 102 degrees, referenced on page 13 of 13

raspii and Jasonb you saved me a lot of head scratching.

Brian Rupnow said:

you do need that adapter.---Brian

Click to expand...

Brian, can you enlighten us as to why the adaptor is needed?

I can't see it serves any special purpose and just making the rotor hub a bit longer so it runs against the crankcase would fill the gap if it were not fitted.

I would expect that the material used for the distributor is somewhat weak compared to the other components. I believe that the adapter is simply there to help the distributor cap hold it's round shape. The o.d. of the adapter is the same as the i.d. of the distributor cap.

Really? From the parts I have made from Delrin I would not have thought there was a problem with distortion due to being weak or flexible. Given the overall size and wall thickness there should be plenty of strength there to resist abuse let alone normal use..

Have a read about Delrin

The High-Performance Acetal Resin​

Leading companies across the globe specify Delrin® acetal homopolymer for high-load mechanical applications such as gears, safety restraints, door systems, conveyor belts, healthcare delivery devices, and other demanding products and parts. Delrin® acetal homopolymer (Polyoxymethylene POM) is the ideal material in parts designed to replace metal. It combines low-friction and high-wear resistance with the high strength and stiffness such applications require. It provides a wide operating temperature range (-40 °C to 90 °C) and good colorability. Delrin® also mates well with metals and other polymers and offers excellent dimensional stability in high precision molding.

I'm not going to trash another mans design. Obviously, Upshur thought it was a good idea when he designed the engine. I will be using the adapter plate.---Brian

I necked down some Endmill to cut the lower cam lobe. Chatter was not good, made some big marks on the part and during the 2nd approach broke off the DIY cutter.






I ended up with something that looks like a cam shaft, but might not be one. ( I will see)


p.s. it is make from cold rolled steel and not hardened. (I hope I can get away with that.)

Greetings Timo

Brian Rupnow said:

I'm not going to trash another mans design. Obviously, Upshur thought it was a good idea when he designed the engine. I will be using the adapter plate.---Brian

Click to expand...

A few minor changes I am taking the feedom to do. e.g. using my existing metric tooling. (the adapter will stay).
POM machines quite nice, it will stay probably round enough.
Will use a bar of black POM to make the cap.