Hello everyone. I have a DA-50 on an Aeroworks Extra 300. When I'm flying at about mid-throttle, I hear what sounds like 'knocking' or pre-ignition from the engine (it actually sounds like a clicking). It's not the airframe or anything loose as I've previously had this engine on a different plane (Aeroworks Yak) with a different exhaust system and could hear the exact same thing. Others at the field notice it too and are always asking me what it is. I run regular unleaded pump gas with Belray H1R synthetic 32:1. I'm about 2-3 gallons into using synthetic oil but even during break-in when I was still on Lawnboy ashless, I could hear the same thing.

Any suggestions ? Timing perhaps ? Can the timing be checked or set ? Anything else ?

Any feedback would be very much appreciated !

Thank you !

needle bearings?

If it's tuned right, try a higher grade of gas. If it does not go away take advantage of some customer service and send it in. Could be a wrist pin bearing, may be nothing at all.

Piston slap?? Is there any difference in the sound between hot and cold?

AV8TOR

There was a DA50 at the field a couple weeks ago that had this noise

After everyone felt of the slack in the crankshaft, we decided it was the needle bearings in the rod or the crank pin.

it went back to DA

I have a DL50 with this noise. It runs very well but the noise is irriating.  Sometimes I have the feeling that it is weather dependant. It would be nice to know what was replaced in the DA.

Sounds like rattling an old plastic pop bottle with a little pea size gravel in it.

Which is also what detonation and pre-ignition sound like. Piston slap in our engines is a generally non issue.

All of our engines should have a metallic "tic" sound when the crank passes through top and bottom dead center. I would be concerned about one that did not. Typically that sound will not be heard when the engine is running. If an engine has a distinct mechanical clanking sound when running it should go in for a check up. The problem is, so many people do not understand how to at least reasonably tune an engine they don't know how to differentiate sounds that tell them what they need to know. Tuned too lean with a low grade gas on a hot day and they get detonation. Running a carbon dirty engine permits accumulated carbon on the spark plug and combustion chamber to become hot enough to ignite the fuel charge before the normal ignition point (pre-ignition) and they have a similar sound. Both can and will severely damage or destroy an engine if left uncorrected.

If you've had a couple of prop strikes and mechanical sounds are more than they used to be, send it in for an inspection. The engines were not designed to handle the severe stresses of prop strikes. Bearings fail and cranks bend. At the level one should be at by the time they get to gas engines their ability level should be high enough that prop strikes were left behind with .40 size glow engines. Bearings cannot take the abuse that bushings did.

And only at mid-throttle. Not at idle and not at full. At full-throttle noise from the propeller takes over. I have a canister on mine. I had the same noise from a ZDZ40 that I run several years ago. In fact I had the same canister on the ZDZ. But I have never heard that canisters give this noise. And the noise has come with age.
How to find out if it is piston slap? The bearings seem good.

off to DA and that baby will be like new[8D]