Bipe Flyer

I was playing around with the lathe and made an exhaust throttle for an .020.

I didn't lap it or anything fancy like that. I just kept opening the inside until it would just barely slide onto the cylinder.

If I was smart I would have left a flange to attach a throttle cable.

I'll let you know how it works.

DICKEYBIRD

Hey, now THAT'S what I call a worthwhile lathe project. Good work there Andrew! Just grind down a parting tool and cut a shallow groove in the top of the cyl. and slide on a external retaining ring clip like the original. I think that's the best way so's you have an easy adjustment.

Bipe Flyer

I wrapped a piece of piano wire around it and gave it a test run.

The throttle sounds like it is really doing something, but after taching it I found that the top end was 16K and the bottom was 12.5K. Ok, so making an exaust throttle may not be that easy, but making a muffler is a piece of cake. It really runs quiet!

I wonder if being made from a thin piece of aluminum is part of the problem. It probably expands a little as it heats up.

The good news is that my starter works great!

EDIT: Typo

DICKEYBIRD

My experience with aluminum throttle sleeves has been that they don't slow the engine down enough to suit me. Like you say, the expansion rate of aluminum has to affect the clearance. Can you make one out of mild steel? It probably also needs a honed or lapped fit to really do well.

BMatthews

This may be why the Cox OEM ones are steel. The sleeves on the Medallion engines I have are a pretty nice fit but I still think the idle could go lower than it does. Apparently the fit has to be very close and the exhaust ports in the sleeve MUST cut off the cylinder ports entirely so the openings are surprisingly small. I also notice that the cylinders on the original RC versions are lapped or ground and not finished. I suspect this is part of the fitting aspect.

If you can bore the inside a little on the tight side you can then either gring the final size and finish with a Dremel in a tool post holder or make up a little brass or aluminium lap. It may not hurt to make an exterior lap for the cylinder as well and size that first.

Bipe Flyer

The ports get completely closed, but the exhaust escapes under the bottom of the ring where the cyl meets the crankcase. It'll have to be a tight fitting steel sleeve to be able to shut the engine off.

rrragmanliam

My Feedback: (1)

Nice try Bipe, It's not somthing I could do.

It's amazing to me the miniscule amount of open exhaust that's required for a good idle. When I built my DB .049's, essentially the port was closed at idle. Tighter, less expacsive steel seems to be the ticket.

Darren

mclintock

My Feedback: (3)

Remember the 'Muffler' that came with those plastic testors c/l planes sold in the '70s? It was a steel band that looked just like yer aluminum throttle cept it didn't have any holes in it. The exaust managed to squirm out between the last fin and the edge of the band which had small serrations in it. the poor zero I had was weak enough without the muffler, but it still flew with it.
Could get all the way up to eye level if I pulled it along.
It was really quiet tho.