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Treadmill Dyno
taylorp035:
--- Quote ---Are you still working on the valve port geometry?
--- End quote ---
The new inserts should be the final answer. It's now down to adjusting the advance of the valves relative to the crankshaft and ECU tuning.
Some photos of the new inserts. We did lap the inserts into the half pipe shape. Then we thermally fit them into each of the floating seals with a very, very aggressive 0.003" interference + some green Permatex locking compound.
Here's the valve for scale. The ports are 1.2" wide and 2" long. This was when we had to replace the muffler bearing (yup....). On the intake side, it's usually possible to replace them without removing the valve. The exhaust has a harder life because we often pound the valve through with a hammer and it's exposed to hot temperatures when the cooling loop isn't working and still elevated temps when it is.
SparWeb:
I don't remember everything you came up with to make a solid seal (this is a LOOONNNG thread, now!) but I know you tried a lot of things.
Do you have any estimate how much power this sucks from the engine, compared to a cam/valve system you took off?
(not that it really matters - the whole idea more than makes up for nit-picky stuff like mechanical efficiency)
Have you worked on any methods to advance/retard valve timing?
How much does brass like being a cylinder head?
taylorp035:
--- Quote ---"I don't remember everything you came up with to make a solid seal "
--- End quote ---
- There's 4 parts to sealing this. Two rotary shaft seals. The half-pipe floating seal is pushed up during the combustion event for increased contact pressure. And a spring loaded top seal so the vacuum from the intake manifold isn't lost when the intake port on a particular valve is up above the half-pipe shape. In addition, we also made some silicone pieces to cover the whole head to help reduce the smoke that escapes from all the joints.
--- Quote ---Do you have any estimate how much power this sucks from the engine, compared to a cam/valve system you took off?
--- End quote ---
- Not on this engine, but the one we did in college on a Briggs and Stratton, yes. There has been other people who have estimated that the rotary valve system takes less to drive than a camshaft, but I think that's probably if everything is working well. It's not too bad, so I would say the savings or penalty isn't large.
--- Quote ---Have you worked on any methods to advance/retard valve timing?
--- End quote ---
- Yes, there is a taper fit #40 chain sprocket coming out of the bevel gear box that is adjustable within ~2 minutes. This is an important part of the design since you can really tell the difference depending on where you have it set or if it slips.
If you really want to scratch your head, we built another Briggs and Stratton rotary valve head that allows you to change the rotating velocity of the valve at different parts of the 4-stroke cycle while it's running. This effectively allows you to change the duration of the intake and exhaust events. I have a video of it running and it actually works quite well. We are upgrading it right now to a 5 hp engine for a go-kart and making it more robust. There is a lever you can pull to change the timing.
//www.youtube.com/watch?v=0yKQTxA56CM
--- Quote ---How much does brass like being a cylinder head?
--- End quote ---
- Haven't had any issues yet with the brass. It holds up well to the rotating surfaces. I've had the engine fairly hot with no coolant flow and also I've driven it ~ 8 miles straight without stopping. So far it has about 105 miles on it over the last 5 years. Hopefully that number goes up here now that we have it back together and it's stopped snowing.
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