External rotary valve problem

[stanley]

I am trying to get a Johnson S45 to start.I have good spark,compression and gas getting to the carb throat but none getting to the cylinders.All I can think of is a problem with the rotary valve. The rotary valve is properly timed.What issues might the valve have that could cause this?

[george-emmanuel]

Without being there and seeing it, it is hard to answer. Rotary valves sometimes had issues with moisture settling in the lower bearing and corroding he bearing. That led to the barrel, as I call it, in the valve moving and rubbing against the valve bore. That caused wear leading to excessive clearance. How does the surface of your barrel look?–Smooth with no lines?

Other than that the only thing I can think of is timing. What is the position of the piston when the "J" is visible in the inspection hole?–Did you time it before TDC or after TDC? Should be after TDC.

George

[dockbuster1]

the timing procedure is very well covered in the Johnson repair manual ed #2 and #4

[stanley]

I’ve timed it according to directions.The barrel is not smooth and does have lines.I think that must be the problem.Time to start looking for another,I guess.

[Randy in Tampa]

try shooting some gas mix in it with the rotary valve open,my P50 likes a lot of fuel to start 😎

[george-emmanuel]

Stanley,

Depending on the condition of the barrel it may be brought back to life. There is a trick!–It requires a lathe and a glass cutter, a good one. Set the barrel up in the lathe and get it running true. Improvise a device to hold the glass cutter in the tool holder. Cut a ring above and below the air passage. This will raise the outside edge of the barrel to increase its diameter just enough to "fill the gap" and aid in crankcase compression. Don’t go crazy with the cutting depth,—just enough to raise the edge to achieve the needed tolerance. Then reset the cutter to run left to right in the tool holder and make a left to right "cut" along the barrel near the air passage opening on both sides. Those raised edges fill the gaps created when the barrel wobbled and they will sort of self adjust to their surrounding and you should once again have an efficient valve……or you could look for a better barrel.

I assume you have rebuilt the valve and installed new bearings?–Don’t do the trick w/out having new bearings.

George

[stanley]

Have not replaced bearings yet.I assume there is a modern equivalent?If so do you have a supplier and part number you can suggest?I like your "fix" suggestion.I also thought about teflon coating the barrel.I figure good rotary valve barrels are not easy to come by.

[Author]

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