Cox 049 timing

I know what NeedNitro is talking about but I havent seen anything as far as anyone putting a degree wheel on one before. It would be neat to see the numbers even though I'm a rookie at interpreting them.

There are shims in existence that fit under the barrel of .049's cylinder to allow raising the timing of the intake and exhaust.

My only experience with a degree wheel is with timing gears and cams in the SBC which, of course, is a four-stroke motor. Coxes are two-strokers. Two very different critters.

SD

I replaced the timing belt in my Mazda a couple of months ago. It was a PITA.
All I know about Cox timing, as stated above, is to raise and lower the cylinder height with shims. That just moves the exhaust ports up or down. As well as changing the compression.

RknRusty wrote:I replaced the timing belt in my Mazda a couple of months ago. It was a PITA.
All I know about Cox timing, as stated above, is to raise and lower the cylinder height with shims. That just moves the exhaust ports up or down. As well as changing the compression.

Rusty:

Didn't you read the Mazda manual first? I like the automotive manuals by Haynes; inexpensive and very helpful. Timing belts are EZ.

Raising or lowering the cylinder of a Cox also raises or lowers the compression ratio. Not usually a good thing to do.

SD

SD

I think the idea behind the shims is to get the SPI working proper which overweighs the problem of it, but yeah your right...raising what is there for exhaust isnt good. Compression ratio I think you can squeeze a bit out of a head by sanding it but you can only sand down to the first fin until it says it has to stop, but then you start shaving the lip on the top of the cylinder to keep increasing it if I'm thinking back right.

That would all be way extreme though. I think just sinking the combustion shape down a bit by sanding the plug might help with the loss. The shims are very thin, all in a range below .010" I think so about the same on the plug I would imagine or even less.

There's also what kind of glow head you have.

My experiences with cyl shims is to use them to get the Transfer ports to properly align with the Con rod trough in the crankcase for a direct fuel flow up the transfers. Someone neglected to index his Cyls to his Crankases.
Timings on TD's are actually very conservative.. surprisingly so.
IMO You couldn't fit enough shims to achieve a radical/performance timings setup . North American approach seemed to be to add lotsa Nitro to compensate for inadequate/ancient design .. unquestionably so in the 50's.
Only a fresh Cyl Design would make significant difference. That! certainly ..Never.. happened.
Ever wonder Why? there are 2 ex ports on a COX?? Me too ! NO other engine has... or... needs those.
Clearly two transfer ports is 'not enough' either. Goofy 'after the fact' Flutes aside.
What was Leroy thinking? He could have easily eliminated one ex port and added another transfer.. cheaply.
Only a fresh Cyl Design would have make significant difference. That! certainly ..Never.. happened.
In fairness the design was cast in stone very early on, immutably apparently, long before CZ advanced 2 stroke design dramatically in mid 50's. COX was ALL about mass production, Not 2 stroke design advances.
My Old Yama TZ350 Racers have a higher HP outut (when size extrapolated) than ANY cox ever built, by at least twice and arguably 3X and that's on Gasoline, Not nitro/ methanol fuel.. but then it has carefully designed squish and 7 transfer ports also the ex duration is 207 degrees .. It also runs, not too problematically, on the street.

Good point on using the shims to properly index the cylinder. If you are familiar Cox had the TD .15 single exhaust port engine which were timed threads. About the two exhaust ports having to do with performance I am not sure either way. You would think it would have an affect on the swirl patterns and there are swirl patterns. I've had them on my pistons before so thats all way past where I can think. I've often wondered about heat distortion between the two.

Theres a white and red TZ rolled out at the dealer I have to pass to go to the grocery store here in town. I've lived without a bike for awhile and grew up on them and this one keeps staring at me. I keep trying to convince myself I'm only going down there for pictures.

Some good comments there fred.

There was a time when you could get "blank" Tee Dee 049 cylinders. I'm not sure how people obtained them but they were used by competition guys like "Combat Albert" who used to grind their own schnerle ported single exhaust port Tee Dee cylinders like the Tee Dee 15 MKII Special which btw did have the thread indexed properly to align the exhaust to one side.

From all reports they definitely performed better than the dual exhaust cylinders.

They must have. I have a used one right here thats all rapped out.

fred wrote:
Ever wonder Why? there are 2 ex ports on a COX?? Me too ! NO other engine has... or... needs those.

AC Gilbert engines have 2 exhaust ports


http://www.rcgroups.com/forums/showpost.php?p=19357621&postcount=59

nitroairplane wrote:Port timing?
Ignition timing?
Intake timing?
I am sorry I don't know but I know the diesel ones have variable ignition timing.

Like your Quarterhorse!!

As you mention, adjusting compression on a diesel allows you to optimize firing timing for the particular fuel, prop, and atmospheric conditions.

To do this with a glow engine, you can adjust this by adding or removing head shims.

Additionally, from my understanding, if you alter port timing by varying shims under the cylinder...GENERALLY, raising the ports makes the engine achieve best running at higher RPM, removing them lowers the running RPM. If you adjust shims, remember that you must adjust head shims also.

Bear in mind that Cox has already optimized these for us and are probably better off left alone. If one feels they need a gazillion RPM, better off getting one of those very expensive engines that will handle it.

Of course these are only opinions, individual results may vary.

George

[quote="Cz10AC Gilbert engines have 2 exhaust ports

http://www.rcgroups.com/forums/showpost.php?p=19357621&postcount=59

[/quote]

OK Cub, Testors, McCoy, and many others had three.

George

[quote="gcb"]

nitroairplane wrote:

Bear in mind that Cox has already optimized these for us and are probably better off left alone. If one feels they need a gazillion RPM, better off getting one of those very expensive engines that will handle it.


George

Geo says it well.

The "need for speed" is GREATLY over-played, IMO.

Personally I prefer just perfecting my pilot skills; a never ending process even after all my years in model aviation where many horizons I've yet to explored; EDF's for one.

SD

RknRusty wrote:I replaced the timing belt in my Mazda a couple of months ago. It was a PITA.
All I know about Cox timing, as stated above, is to raise and lower the cylinder height with shims. That just moves the exhaust ports up or down. As well as changing the compression.

wait, doesn't adding or taking away head gaskets also move the ignition timing from a little slow (3 gaskets) to
very quick (1)?

[quote="GermanBeez] ...wait, doesn't adding or taking away head gaskets also move the ignition timing from a little slow (3 gaskets) to very quick (1)?[/quote]

Things that affect firing timing for a glow are fuel and compression. If I understand correctly, more nitro SLOWS firing timing a bit (remember it's the alcohol that has the catalytic reaction with the glow plug), then the nitro speeds up the burn rate. That is why the engine needles better with 15%-25% nitro than it does with 0%-5%.

To bring the firing timing back to the needed level, we adjust head shims.

Optimizing firing timing this way is only for a specific prop size. For a large prop, as in Texaco, we need to slow the burn rate and retard the timing a bit.

The best way to adjust timing is to start with someone elses results, then optimize for YOUR SPECIFIC SITUATION...experiment.

I hope I got this stuff right...please check it over.

George

gcb wrote:[quote="GermanBeez] ...wait, doesn't adding or taking away head gaskets also move the ignition timing from a little slow (3 gaskets) to very quick (1)?

Things that affect firing timing for a glow are fuel and compression. If I understand correctly, more nitro SLOWS firing timing a bit (remember it's the alcohol that has the catalytic reaction with the glow plug), then the nitro speeds up the burn rate. That is why the engine needles better with 15%-25% nitro than it does with 0%-5%.

To bring the firing timing back to the needed level, we adjust head shims.

Optimizing firing timing this way is only for a specific prop size. For a large prop, as in Texaco, we need to slow the burn rate and retard the timing a bit.

The best way to adjust timing is to start with someone elses results, then optimize for YOUR SPECIFIC SITUATION...experiment.

I hope I got this stuff right...please check it over.

George[/quote]

from what i know that is correct imagine variable ignition timing on glow engines maybe a glow head that has the same action as a contra piston not sure how one would achieve this but it would be interesting.

[quote="nitroairplane...from what i know that is correct imagine variable ignition timing on glow engines maybe a glow head that has the same action as a contra piston not sure how one would achieve this but it would be interesting.[/quote]

You could achieve that somewhat on an engine that uses a standard plug by switching between short, long, and medium plugs. This would extend the coil into the combustion chamber or recessing it into the head...considering norm is to have the coil even with the top of the combustion chamber.

If anyone does this, make sure you have good clearance between the plug and the piston.

George

Is anyone here going to, or, participating in this event? They have Mouse I (cox engine ) races. Do you think they'll be using stock engines??

Sponsor: SCAR (Southern California Air Racing)
Event Name: 24th Annual Virgil Wilbur Memorial
Location: Whittier Narrows
Details: Saturday Racing: Mouse I (Cox engine), B/Team Race, Cal 15 and Orange Crate
Sunday Racing: NCLRA S/S Rat, NCLRA Clown, SCAR GY, Q Rat

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Thanks, Mod Team]