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Old 06-24-2021, 07:16 AM
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Baffled over DA-70

Hey all,
I've got something that's stumping me on my DA-70. It's got about 90 flights and 85-90hrs on it, and about halfway through I had sent it back due to some pinkish hue on the cylinders and there was some grease like stuff that had been pushed out the Prop Hub. They said the engine had gotten hot (and I know why/when, Cam Shaw if you see this you know when I'm talking about ).

So I got that back (this is late 2018) and tuned it correctly (again), and it's run PERFECT ever since. No signs of overheating etc. This is on a 94"MXS, motor is baffled, and has plenty of air exit (a series of diagonal holes on the cowl, and most of the holes for the can tunnel are cut out along with a twi-stock spoiler put in front of a few of them.
A week or so ago, I pulled the cowl to check a few things and fix the cowl mount tabs which came loose. When I did, I found MORE grease that had ejected out the front of the case. The cylinders are still pink, BUT they did not get replaced from DA (they replaced pistons, rings, and a bearing IIRC). Also, they have not gotten pinker since. Pulled spark plugs and checked them, you can see for yourself. Essentially perfect. Curiously though, the left plug lost all of its gap for some strange reason (any ideas???). Unsure on how long but it's still ran like a top. The blue ring in the case seems too be intact looking at it from the prop hub (I assume that's part of a sealed bearing?).

I'm baffled on this. It runs perfect, but this is the second time it's thrown grease out. Any ideas will be much appreciated. Thanks
Josh
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Old 06-24-2021, 08:58 AM
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Heat is causing the grease leaking.Plugs look ok , more air movement is needed for cooling.
Now I be thinking how much grease the bearing has.
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Old 06-24-2021, 09:14 AM
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Heat is causing the grease leaking.Plugs look ok , more air movement is needed for cooling.
Now I be thinking how much grease the bearing has.
Here's the odd part.......... Unless I completely REMOVE the can tunnel access hatch or cut the entire bottom of the cowling, there's nothing else I can do for air exit. It's AT LEAST 3 times the exit the inlet is...... I'm using GHoffman's Baffle design on it. What about modifying the baffle to direct some air to the front of the hub/crankcase??? I've never seen that done but. I have zero idea. No rpm sag in flight, and I fly it pretty hard, not quite dussia hard but close.
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Old 06-24-2021, 09:29 AM
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All of those signs point to the fact that it’s overheating. When I designed those baffles I was surprised to see telemetry that it was cutting the temperature by around 80įF. Do you have any temperature probes on the cylinders themselves?
On my DA120, even on a 90į day the engine runs around 230 to 240 Fahrenheit. I would be very curious to see what your 70s running like?
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Old 06-24-2021, 10:02 AM
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Originally Posted by ghoffman View Post
All of those signs point to the fact that itís overheating. When I designed those baffles I was surprised to see telemetry that it was cutting the temperature by around 80įF. Do you have any temperature probes on the cylinders themselves?
On my DA120, even on a 90į day the engine runs around 230 to 240 Fahrenheit. I would be very curious to see what your 70s running like?
I don't have any probes or way to check the temp on it currently.

Concerning the cooling, I've got about a 4x6" area on the cowl opened for air exit, along with ALL of the canister tunnel holes on the access hatch open, with a try stock spoiler on 2 of them. I don't know why it'd be overheating with the amount of air flowing through there...
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Old 06-24-2021, 11:15 AM
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I'm still trying to work out how you have about 90 flights and 85-90hrs on it. You fly almost an hour per flight? Mine last 12 to 15 minutes.
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Old 06-24-2021, 11:16 AM
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I had the same two hole cowl design in a Aeroplus Edge with a DA70 and I couldn't keep it cool.But this was with out ghoffman's baffles.I took it out and replace it with a 60 single.I just don't think the two holes catch enough air.
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Old 06-24-2021, 11:17 AM
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I'm still trying to work out how you have about 90 flights and 85-90hrs on it. You fly almost an hour per flight? Mine last 12 to 15 minutes.
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Old 06-24-2021, 11:31 AM
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I'm still trying to work out how you have about 90 flights and 85-90hrs on it. You fly almost an hour per flight? Mine last 12 to 15 minutes.
WHOOPS! Meant 15hrs lol. Had to re-look at my spreadsheet of flight logs on it.
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Old 06-24-2021, 11:35 AM
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Originally Posted by closetguy View Post
I had the same two hole cowl design in a Aeroplus Edge with a DA70 and I couldn't keep it cool.But this was with out ghoffman's baffles.I took it out and replace it with a 60 single.I just don't think the two holes catch enough air.
It just doesn't make any sense. I'll take some pics later of the air inlet and exit amount I have. All three holes on the front are open, and ALL of the can tunnel holes are open. Motor is tuned perfectly, and doesn't even seem to have the power loss in flight typical of a motor getting hot, even slightly. Only thing I could think of to do is build an air dam on the back of the cylinders but I don't think it'd help. Could it be no air to the hub is causing lots of heat buildup there? I'm at a loss. This is the second time it's thrown grease out the front before, first was in 2018 after the WC in Muncie. I think it got lean there on the one freestyle flight due to a massive atmosphere change, but it was sent in when we found the pink cylinders, and was given a clean bill of health after a few things were replaced..... 3 years later it's doing it again......
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Old 06-24-2021, 11:38 AM
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WHOOPS! Meant 15hrs lol. Had to re-look at my spreadsheet of flight logs on it.
Math is hard
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Old 06-24-2021, 12:40 PM
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Has that front bearing ever been changed or disturbed ? The grease appears to be clear and could possibly just be a bad seal on the front bearing. There should be one on each side of the bearing. If the engine is getting hot and forcing the grease out the front of the bearing itís usually dark in color . All of my DA engines ended up with fairly pink cylinders . If it runs good and consistent itís probably not running that hot. Might be a good idea to just pull it and send it in with a description of whatís going on . Eventually that bearing is going to go dry and fail. Hope you figure it out.
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Old 06-24-2021, 03:39 PM
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Has that front bearing ever been changed or disturbed ? The grease appears to be clear and could possibly just be a bad seal on the front bearing. There should be one on each side of the bearing. If the engine is getting hot and forcing the grease out the front of the bearing itís usually dark in color . All of my DA engines ended up with fairly pink cylinders . If it runs good and consistent itís probably not running that hot. Might be a good idea to just pull it and send it in with a description of whatís going on . Eventually that bearing is going to go dry and fail. Hope you figure it out.
Yeah it's a lighter color like fresh grease. The first time it happened It was slightly darker grease. They said it got hot, messed a ring up, burnt a piston etc. But I never noticed any power loss before that. Below is how it looked last time. I'd agree it got hot last time. It's now almost 3 years into that seal. It runs very consistent, it has a slightly rich stumble going to high RPM if not cleared out and waiting longer than 10-15 seconds, and coming back to idle it goes to a slightly LOWER idle than normal idle, indicating high is slightly rich. I agree I don't think it's overheating, as the "pinkness" in the cylinders hasn't changed. Below is a pic of the previous grease for comparison.

Josh
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Old 06-24-2021, 04:43 PM
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That is a bearing that more than likely got hot at some point for sure or one that had a lot of run time on it. Iím assuming that bearing was replaced in the first go round. Only way to know for sure is to remove the hub and see whatís going on behind it. Also if you still think you may be running hot take a look at both pistons thru the exhaust ports. If ran hot for any length of time the piston skirts should be discolored . If theyíre clean and relatively bright I would tend to believe you just have a bearing or seal problem . Out of balance propellers can really wreak havoc on that front bearing as well. Again hope this helps in some way.

Scott
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Old 06-24-2021, 04:51 PM
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I'm not sure grease color means much here. Different bearing companies use different colored grease .... some almost clear, some almost black. You'd almost have to know what the color of the grease was in the new bearing to know if that was an issue.

Let me throw this out there. The main cause of grease coming out of a front bearing is failed grease seals on the rear bearing. These allow crankcase pressure to the front bearing and the seals there are less capable of retaining the pressure than the two bearings (and 4 seals) working together. The pressure pushes grease out of that front bearing. Probably not a heat issue at all. Just bearings whose time have come for replacement due to use. Most of the time there are no symptoms of the seal failures until they get really bad then the engine tune will change, especially at the low end. Send it in and it'll be good to go for some time to come.
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