Mixing used Cox reedie parts? Need help from the Gurus. :)
11-27-2004, 01:47 PM
#1
Mixing used Cox reedie parts? Need help from the Gurus. :)
Any mechanic/tinkerer knows you shouldn't mix used parts (pistons, rods, valves etc) on a full size plane/car engine if you're taking it apart because of the wear patterns and if engine is taken apart for some work parts must be put back in their original locations. NOW, how true is that when it comes to Cox reedies or any other 2 stroke glow engines for that matter? I have a collection of used cylinders, cranks, cases, pistons and will try to assemble a few complete reedies from them.
Anyways, bottom line, is mixing up used parts critical with engines this small? Anyone have some data (or opinions) on any adverse effects (poor running, longevity, etc)? I'm planning to assemble 5 identical reedies for a 5 cylinder radial that I want to tackle to it's important that after I've put a lot of work into it one or two engines don't develop low compression or a sloppy crankshaft after a few spins on the test stand.
Anyways, bottom line, is mixing up used parts critical with engines this small? Anyone have some data (or opinions) on any adverse effects (poor running, longevity, etc)? I'm planning to assemble 5 identical reedies for a 5 cylinder radial that I want to tackle to it's important that after I've put a lot of work into it one or two engines don't develop low compression or a sloppy crankshaft after a few spins on the test stand.
11-27-2004, 02:02 PM
#2
Senior Member
Join Date: Apr 2002
Location: Collierville,
TN
Posts: 2,749
Likes: 0
Received 0 Likes
on
0 Posts
RE: Mixing used Cox reedie parts? Need help from the Gurus. :)
Crankshaft and crankcase matches generally aren't a problem as long as you use common sense ie: swap around until none are too tight or are wobbly loose.
Piston/cyls. are another matter. Obviously the galled & scored stuff is junk. I check each piston for size and roundness, yes they will wear or warp out of round! I just use a dial caliper and set it to .405" and a bit. The piston should then slide between the jaws a little ways before dragging to a stop using a light touch. Slide it in from 3 or 4 positions to check for roundness, set the lumpy ones aside to sell to your competitors. Try each good piston in various cyls and look for a fit that has light drag just as the piston gets to the top (or a little looser for high nitro.) Don't let cyls. with a slightly burred exhaust port fool you into thinking it's a tight fit that will break in and give great compression....not!
Now that I've told you this stuff, I'll have to kill ya!
Piston/cyls. are another matter. Obviously the galled & scored stuff is junk. I check each piston for size and roundness, yes they will wear or warp out of round! I just use a dial caliper and set it to .405" and a bit. The piston should then slide between the jaws a little ways before dragging to a stop using a light touch. Slide it in from 3 or 4 positions to check for roundness, set the lumpy ones aside to sell to your competitors. Try each good piston in various cyls and look for a fit that has light drag just as the piston gets to the top (or a little looser for high nitro.) Don't let cyls. with a slightly burred exhaust port fool you into thinking it's a tight fit that will break in and give great compression....not!
Now that I've told you this stuff, I'll have to kill ya!
11-27-2004, 02:32 PM
#3
RE: Mixing used Cox reedie parts? Need help from the Gurus. :)
Thanks dickey. So basically for the most part the same rules apply to these little engines as to the large ones...and you can "do the best you can" by measuring and careful matching.
12-20-2004, 03:33 AM
#4
Senior Member
Join Date: Dec 2004
Location: Corvallis,
OR
Posts: 456
Likes: 0
Received 0 Likes
on
0 Posts
RE: Mixing used Cox reedie parts? Need help from the Gurus. :)
I swap parts all the time - yes I'm an animal. When I buy a bag of Cox RV's at a swap meet, they geranally get torn down and the parts dropped in a box. I assemble an engine for it's intended purpose, Sport/RC, Free Flight etc. If I'm sport flying I may (yea right like almost always) lap the piston and cylinder with 1200/2000 grit compound. This is done until the piston will go at least a 1/16" past the bottom of the glow head threads in the cylinder. This almost always necessatates using a start spring - starter springs are our friends.
Degrease everything, when rummaging about for a crankcase I look at the fit between the trust washer and crankcase, I like these to be tight. if they're not you've got and engine somebody trashed with an electric starter. Bite the bullet and throw this one away. I prefer the old trust washers as opposed to the hex drivers but thats me. I prefer a crank/crankcase combo thats worn in the bore. I wanna mount a prop, flip it and watch the prob turn and turn and turn around - alot. For sport flying this dosn't matter. For competition it's a big deal.
Then I put everything together, new gaskets, tank/back plate "o-ring" new mylar reed valve and run the engine on the bench until it no longer hic-cups.
My RV and rotory valve engines are running 18.5k +. Use decent fuel, with exceptions (ie you know what your doing) 25-35% nitro is what you want to use. I haven't used Tee Dee's for years but when I did they were KK jobs with chrome cranks etc. - nice but AME's really rule.
HTH - Steve B.
PS Cox never made any scared parts, they all come from a parts bin (flame away).
Degrease everything, when rummaging about for a crankcase I look at the fit between the trust washer and crankcase, I like these to be tight. if they're not you've got and engine somebody trashed with an electric starter. Bite the bullet and throw this one away. I prefer the old trust washers as opposed to the hex drivers but thats me. I prefer a crank/crankcase combo thats worn in the bore. I wanna mount a prop, flip it and watch the prob turn and turn and turn around - alot. For sport flying this dosn't matter. For competition it's a big deal.
Then I put everything together, new gaskets, tank/back plate "o-ring" new mylar reed valve and run the engine on the bench until it no longer hic-cups.
My RV and rotory valve engines are running 18.5k +. Use decent fuel, with exceptions (ie you know what your doing) 25-35% nitro is what you want to use. I haven't used Tee Dee's for years but when I did they were KK jobs with chrome cranks etc. - nice but AME's really rule.
HTH - Steve B.
PS Cox never made any scared parts, they all come from a parts bin (flame away).
12-25-2004, 09:10 PM
#5
RE: Mixing used Cox reedie parts? Need help from the Gurus. :)
Burtcs, what do you mean by "I prefer a crank/crankcase combo thats worn in the bore. I wanna mount a prop, flip it and watch the prob turn and turn and turn around - alot. For sport flying this dosn't matter. For competition it's a big deal. " So what you're saying is that so long as the crank/thrisywasher is nice and tight you don't mind some bore wear and an engine with less than great compression? I know that in nitro cars some guys actually prefer a well-worn engine where the compression is somewhat on the lower side since that apparently allows the engine to turn a few extra rpms.
12-26-2004, 09:33 PM
#6
Senior Member
Join Date: Dec 2004
Location: Corvallis,
OR
Posts: 456
Likes: 0
Received 0 Likes
on
0 Posts
RE: Mixing used Cox reedie parts? Need help from the Gurus. :)
Listen to the car guys - I'm with them. I ordered three KK Tee Dee's back in the early 90's, these were brand new engines. If I took one of these engines and walked twenty feet away and shook it, you could hear it rattle - there was that much clearance. Those engines needed a starter spring (Davis Diesel) to start but they definitely sang a song when you needled them. This is also true of RV engines.
When I lap the piston and cylinder I'm lowering the compression abit as well as removing snug fit the piston must overcome while running. I figure every Cox engine (all others as well) is issued a FINITE amount of power it can produce. Stuff like compression, oil drag etc steals some of that power. I want it back so the engine can use it. I've noted that tight cranks and snug pistons steal 1000-1500 RPM from my engines. I costs very little to recover it - it's free horsepower. 60% nitro will give me another 1000 RPM or so but I gotta pay for that. One more thing if you ever reset the ball/socket joint in the piston, plan on lapping the piston back in - they swell just abit.
Now be carefull here, I'm using my engines for free flight where are engines only run for 5 to 15 seconds - launch to shut off. I'm not worried about overheating, vaperlocking, riching or leaning - only the run. The engine will cool back down, the glow plug will be just fine. I recover that model and do it all over again - kewl. By the way, I using 7cc brass shim stock tanks that are pressure plumbed (I hate bladders but that me).
For sport flying you probably don't want to do some of this. 60% is not necessary. Loose cranks and bore won't hurt you but you probably will need a starter spring. I have trashed too many Cox engines on electric 1/2 starters to trust them, I use springs. 1/2A RC Texaco is competion but it low key and very gentile on man and machine. I wind one spring turn on the 8-4 prop turn loose and the engine will spin that prop 10 or 12 times - thats what I talking about. My engine is turning about 6400-6500 RPM, the model will fly under power at this RPM, I burn all my fuel and I got bugs in my teeth. Have fun., pull some RV apart and play.
HTH - Steve B.
When I lap the piston and cylinder I'm lowering the compression abit as well as removing snug fit the piston must overcome while running. I figure every Cox engine (all others as well) is issued a FINITE amount of power it can produce. Stuff like compression, oil drag etc steals some of that power. I want it back so the engine can use it. I've noted that tight cranks and snug pistons steal 1000-1500 RPM from my engines. I costs very little to recover it - it's free horsepower. 60% nitro will give me another 1000 RPM or so but I gotta pay for that. One more thing if you ever reset the ball/socket joint in the piston, plan on lapping the piston back in - they swell just abit.
Now be carefull here, I'm using my engines for free flight where are engines only run for 5 to 15 seconds - launch to shut off. I'm not worried about overheating, vaperlocking, riching or leaning - only the run. The engine will cool back down, the glow plug will be just fine. I recover that model and do it all over again - kewl. By the way, I using 7cc brass shim stock tanks that are pressure plumbed (I hate bladders but that me).
For sport flying you probably don't want to do some of this. 60% is not necessary. Loose cranks and bore won't hurt you but you probably will need a starter spring. I have trashed too many Cox engines on electric 1/2 starters to trust them, I use springs. 1/2A RC Texaco is competion but it low key and very gentile on man and machine. I wind one spring turn on the 8-4 prop turn loose and the engine will spin that prop 10 or 12 times - thats what I talking about. My engine is turning about 6400-6500 RPM, the model will fly under power at this RPM, I burn all my fuel and I got bugs in my teeth. Have fun., pull some RV apart and play.
HTH - Steve B.
