Re: Best way to lower the ports on an .049 cylinder.

Cox International Wed Dec 21, 2011 1:03 pm

Rusty,

On a TD it will be about the same. SPI makes little difference on a TD (perhaps 200 - 300 RPM); wheres the slit exhaust reduces the RPM by about the same, creating a wash.

On a reed-valve engine, however, the SPI slit-exhaust version should outperform the TD version.

Having said all this, there are so many tolerance variations with all of these cylinder/pistons that RPM's can easily vary 1,000 RPM between them. It's a matter of experimenting.

Our upcoming #1 cylinders should be the highest performing (for TD and reedies) for those of you willing to pay more to get last few 100 RPM's out of an engine tongue

Bernie
www.coxinternational.ca

**Cribbs74** Wed Dec 21, 2011 5:48 pm

Cox International wrote:The piston could be lightened but we would be creeping up towards the $20 retail mark by then.

I did some measurements on my stash of #1 cylinders and they will be perfect for the mod. Should then have real Tee Dee cylinders available in January. They will be identical (inside and out) to the # 4 ones that Cox made. The only differences will be a port opening 0.4mm bigger and silver colour showing there the metal was machined.

At the same time will also have Venom/Killer Bee drive-plates available.

Bernie
www.coxinternational.ca

Bernie,

Just a thought, would gun bluing solution return the cylinders to a black color?

Cox International Wed Dec 21, 2011 6:04 pm

Yes, gun blueing would but it is too much work. We did the first batch that way and then gave up on this.

At $20/hr for my staff it would have just added another $1.50 to $2.00 to the retail price of the product - and that for only a cosmetic change.

Bernie
www.coxengines.ca

Jaspur_x Wed Dec 21, 2011 6:36 pm

Thanks for the clarification;and thanks for taking the next step Bernie!
I know I will have to try the new cylinders out too, just for the giggles of it;it`s a need for speed thing......overkill isn`t always a bad thing.

I prefer the savings to the authentic look anyway.

**Cribbs74** Wed Dec 21, 2011 7:10 pm

Cox International wrote:Yes, gun blueing would but it is too much work. We did the first batch that way and then gave up on this.

At $20/hr for my staff it would have just added another $1.50 to $2.00 to the retail price of the product - and that for only a cosmetic change.

Bernie
www.coxengines.ca

Yep, your right. I just tried it on a pee wee that had a couple of tool marks. It's not a big deal, customers can do it on their own if it was an issue. I was just curious.

**RknRusty** Thu Dec 22, 2011 10:49 pm

I tore down both BWs tonight and compared parts. I swapped everything back and forth between the two engines and it was the piston that made the difference in the SPI gap. The one with the small gap from the slower engine had zero slop in the ball socket. The one with the wide gap had a slight amount of slop.

So, I figured I'd tighten up the ball socket a bit before reassembling. I took my tool and placed it on the Pontiac brake rotor I use as an anvil for this, sitting on the concrete floor. I gave it a few taps, checking the fit to make sure I wasn't mushrooming it. I finally got it to close until there was only a very slight movement. No mushroom, it slid through the bore smoothly. But, now this one has a small SPI gap. Maybe my resetting tool is misshapen. I probably did 25 taps with a medium rivet hammer. I don't think I'm ever going to try resetting the gap on a piston again. I've had some bad luck doing that.

I didn't put the cylinder and piston back on it, I used a new SPI set from Bernie that I've never used before other than breaking it in. It ran very well, maybe not faster, but certainly not slower. And get this; it was Much easier to needle and ran very smooth. I'm happy with that. It's true, the slit cylinder/short piston set is superior to the BW #1 cylinder. I say superior not because of RPM so much, but because it's so easy to needle. And another thing; it must be more efficient because my run times were 2:25 every time. In the video in my other thread I wrote that was getting 2:05 with the fastest engine. I wish I had a tach so I could give some more exacting information. I'll go over to the Run Time thread and mention that too.

But I'm going to be buying some new SPI sets in the near future.

Cox International Fri Dec 23, 2011 10:22 am

Thanks for posting the results, Rusty.

I find SPI setups more difficult to start initially but, once broken in, they run great. I am just guessing here but the lower fuel consumptin may be attributed to the lower mass of the (shortened and lightened) piston.

Bernie
www.coxinternational.ca

**RknRusty** Fri Dec 23, 2011 10:31 am

Cox International wrote:Thanks for posting the results, Rusty.

I find SPI setups more difficult to start initially but, once broken in, they run great. I am just guessing here but the lower fuel consumptin may be attributed to the lower mass of the (shortened and lightened) piston.

Bernie
www.coxinternational.ca

Maybe so, or the improved porting. That's above my realm of knowledge. I posted in my other thread about run time that I'll have to fly it to see if the light piston develops as much torque as the heavy one. I use a 6" prop for stunting, so that'll be the ultimate test.

Cox International Fri Dec 23, 2011 10:38 am

I would think that torque is less.

My tests have shown an aprx. 20% RPM increase with a 5" prop but only a 10% increase with a 6" prop. Part of that would be torque but most of it would be because SPI feeds on itself and is happiest at high RPM.

Bernie
www.coxinternational.ca

PV Pilot Fri Dec 23, 2011 1:20 pm

Cox International wrote:I did some measurements on my stash of #1 cylinders and they will be perfect for the mod. Should then have real Tee Dee cylinders available in January. They will be identical (inside and out) to the # 4 ones that Cox made. The only differences will be a port opening 0.4mm bigger and silver colour showing there the metal was machined.

Bernie
www.coxinternational.ca

Neat!!

Jaspur_x Thu Dec 29, 2011 4:01 am

PV Pilot wrote:
Cox International wrote:I did some measurements on my stash of #1 cylinders and they will be perfect for the mod. Should then have real Tee Dee cylinders available in January. They will be identical (inside and out) to the # 4 ones that Cox made. The only differences will be a port opening 0.4mm bigger and silver colour showing there the metal was machined.

Bernie
www.coxinternational.ca

Neat!!

Almost can`t wait,and I still have new "teedee" cylinders from bernie to run,I guess i will have reserves soon lol!

oh the horror of it. Not having parts available is what retired my now old,still retired(for sentimental reasons) ,teedee049 r/c (r/c conversion circa 1991) but the 2 replacements I have for it are back in play thanks to Bernie!!

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Best way to lower the ports on an .049 cylinder.