Starter springs...

roddie Mon Feb 10, 2014 1:28 pm

Hey all, some recent discussion in the "Tach Race" thread got me curious. Apparently, running one "may" adversely affect engine performance. I don't have any Cox .020 engines... that were discussed in that thread. My engines are all .049 reed-valve type. I have both the "zero-drag" and the 2 piece "cam" styles that fit the hex drive-plates.

I would imagine that running the "cam" style will cause a slight drop in rpm's because the back of the cam's lobe contacts the spring on every revolution. Has anyone "tach'd" an engine with/without the cam style installed, to see just how much difference there is?

I do not have clearance to run the "zero-drag" style in the cowl of my speed model... and I'd prefer not to use the drag-inducing cam style, if the drag is significant.

Roddie

Mark Boesen Mon Feb 10, 2014 1:44 pm

I'd like to see the numbers as well, I think the 'cam' style would loose some rpm for sure.

Funny, as a kid that spring was always the first thing to go, even though I might of ended up spending a lot of time flipping the prop....just think if the weight savings!

**Cribbs74** Mon Feb 10, 2014 2:23 pm

I think Travis did a little run up with the cam vs no-drag. He said that the cam did not make a big difference in RPM drop.

Now in a tach race the difference between a winner and a loser might only be 50 RPM's. Are you willing to risk that?

Cast that little hexie-demon away!!! Devil

Ron

Edit: after reading your post again I see that you were concerned about the speed contest not the tach race. So forget the part in the middle, but my last statement still stands.

**RknRusty** Mon Feb 10, 2014 3:17 pm

If the engine harmonic set up an oscillation in the zero drag spring, the two could conceivably combine to cause enough vibration to affect the RPMs. Every time I have seen a spring vibrate, I attributed it to an unbalanced prop.

I have a long Black Widow thread where this is addressed in a small part of it.

https://www.coxengineforum.com/t1695-rebuilding-a-black-widow-mouse-racer-style

Look on the next to last page or so, depends on your browser and settings.
Rusty

WingingIt74 Mon Feb 10, 2014 8:31 pm

Cribbs74 wrote:I think Travis did a little run up with the cam vs no-drag. He said that the cam did not make a big difference in RPM drop.

Now in a tach race the difference between a winner and a loser might only be 50 RPM's. Are you willing to risk that?

Cast that little hexie-demon away!!!

Ron

Edit: after reading your post again I see that you were concerned about the speed contest not the tach race. So forget the part in the middle, but my last statement still stands.

**Cribbs74** Mon Feb 10, 2014 9:43 pm

Yeah I am not a snap starter fan. They do work though. Just seems like a poor design the way it bumps the spring while running.

To be honest I think the no drags are unsightly as well, especially when used on the old thin taper cases. It detracts from the smooth flowing look of the engine.

I only use them because I have played the backward start game one too many times. Don't even get me started on how they tear up the finish!

Ron

Surfer_kris Tue Feb 11, 2014 4:30 am

The pressure from the spring on the disc is, or should be, minimal. I have actually made a few similar ones for cowled Norvel engines, at it works very well. You only need one hook on the cam, and with only a very small pressure on the cam there is no loss of power or even wear on the cam, as it is lubricated by the oil that comes out of the crankshaft.

Here is a Norvel .074 fully cowled and DIY built in springstarter;

Starter springs... Img_1211

roddie Tue Feb 11, 2014 6:40 am

Surfer_kris wrote:The pressure from the spring on the disc is, or should be, minimal. I have actually made a few similar ones for cowled Norvel engines, at it works very well. You only need one hook on the cam, and with only a very small pressure on the cam there is no loss of power or even wear on the cam, as it is lubricated by the oil that comes out of the crankshaft.

Here is a Norvel .074 fully cowled and DIY built in springstarter;

That's a nice set-up Kris. (nice model too) I am not too familiar with Norvel engines. Did you make/machine that drive-plate?

Roddie

Surfer_kris Tue Feb 11, 2014 12:25 pm

The stock starter spring is a non-friction style that grabs the prop. I've cut of the "loop" that usually grabs the prop and made a drive plate that grabs the spring instead. I'm very pleased with the solution, one can turn the drive plate (before tightening the prop) in such a way that the spring grabs before TDC. One can easily feel the grab an pull back about half a turn and then let go, it will easily pull through TDC and gives a faster snap than I can manage with my fingers...

Paulgibeault Fri Feb 28, 2014 12:56 am

Hi Guys,

Last time I did an actual Tach Test many years ago the difference was a surprisingly low 200 rpm loss with the snap starter. I had to investigate after being beat in a mouse race final by Bob Boling from El Cerito whose model had a snap starter equipped L/H propped motor... (4.5D X 4P ). I deduced the loss was essentially insignificant for the extra reliability gained. (i.e. the engine would never start backwards). Plus his L/H prop was unusually fast.
Not a concern for a Tach race motor though...

Cheers, Paul

John Goddard Fri Feb 28, 2014 11:29 am

IME
300 difference RPM on my suretdstartee. 17,950 before 18250 after removal.

Very Happy

**Cribbs74** Fri Feb 28, 2014 11:38 am

John Goddard wrote:IME
300 difference RPM on my suretdstartee. 17,950 before 18250 after removal.

No drag? Or the the crappy one?

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