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Tired ZDZ50

Old 10-21-2011, 03:52 AM
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rgoldy
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Default Tired ZDZ50

I have an older ZDZ 50 that has hardly any compression left. Will a set of rings "fix" it or is it time to retire it? Don't really want to put much more than that into it when new is so inexpensive nowdays.
Old 10-21-2011, 05:05 AM
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Default RE: Tired ZDZ50

For new rings Frank Bowman is the man.
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Old 10-21-2011, 05:38 AM
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Tired Old Man
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Default RE: Tired ZDZ50

Generally, when compression is lost the ring has become stuck in the groove due to an accumulation of carbon on the ring and in the groove. A new ring, combined with cleaning out the carbon build up, will bring the engine back to life. Often the old ring will still be good but need freed from the ring grovve if not run too long in a stuck condition.
Old 10-21-2011, 05:10 PM
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Diablo-RCU
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Default RE: Tired ZDZ50

Pull the cylinder off before you buy any parts. Inspect the piston and cylinder for gouges and any signs of damage. If the piston wasn't seized and the cylinder isn't scored, then the ring is likely just stuck in the piston groove with carbon. A little careful cleaning should fix it up. Don't break the ring, it's typically brittle.
Old 10-21-2011, 07:10 PM
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Tired Old Man
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Default RE: Tired ZDZ50

I'm doing one of those jobs in an "old" 3w right now.
Old 10-22-2011, 05:31 PM
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Default RE: Tired ZDZ50

I have an old ZDZ 40 that has little compression as well. It's been like that since I bought it used 5 or 6 years ago. It still runs good although sometimes (most times) it's hard to start the first run of the day. It also has a habit of shooting flames through the muffler during these tough to start conditions. I wonder if my ring may be stuck or partially stuck as well? Sure is loose compression wise but still spins up an NX 20/8 prop @ 7200/7300 rpm.
Old 10-23-2011, 04:48 AM
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rgoldy
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Default RE: Tired ZDZ50

Same thing that I am seeing-not sure if the flames out the muffler are a symptom or not. Absolutely howls on the ground, ripping a 23-8 prop like nobody's business. Get it in the air and it is an absolute dog. Was told this is typical of a low compression engine. I pulled out an old CRRC engine I had and there is no comparison to the compression. You almost have to work to flip it over and the ZDZ has nothing. Now just to get the time....
Old 11-23-2011, 05:32 AM
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Default RE: Tired ZDZ50

Many engines only show true compression when they're running. Some rings need enough pressure gradient to seal.
If your ZDZ is still powerfull, I would do nothing however, inspection of it's interior never harms.
Also if it did have compression in it's young days it's an indication of something needing to be checked.
The typical "hard to start" behaviour of ZDZ is due to the rotating valve that also needs some degree of pressure gradiant to close properly. My "trick" to start a ZDZ was flipping it real quick (2 flips/ second) and within a few seconds it ran. Those who did this normally (say 1 flip per 2 seconds) virtually never got it going.
Old 11-23-2011, 09:30 AM
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Default RE: Tired ZDZ50

My ZDZ 80 Supers had low compression after break-in when flipping in the normal direction but had plenty when flipped in reverse. Someone here on RCU suggested that this was due to connecting rod angle and pistion position in bore, makes sense. They both ran wellwith lowprecieved compression.
Old 11-23-2011, 09:41 AM
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rgoldy
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Default RE: Tired ZDZ50

This thing is a dog but actually starts pretty easy. I put it up against a CRRC 45 and the CRRC 45 has a ton more snort and that just should not be. I will tear it down over the winter.

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