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#1
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Flight test report and intake leak question
My Lyc. O320-D2C idles rough on the right mag, with the
#3 cyl showing an EGT drop. The roughness clears up above 1200 RPM or so, still on one mag. It's also noticably smoother on just the left mag, and everything's smooth on both mags. In flight #3 CHT runs 50 degF hotter than the rest, as well as higher EGT, which is not unusual in RVs (I'm told)...dunno if this is also related in my case. General consensus around here is it's either because the engine isn't broken in yet (10 hours STOH, all at high power so far) or an intake leak on #3. Has anyone got any suggestions on how to find an intake leak that don't involve standing close to a turning propellor? Any other troubleshooting advice? Timing checks good for both mags, BTW. Chrome cylinders, bayonet CHT probes. In other news, with the engine throttled back a bit for temps and the airpseed up for cooling, flight tests are going well. Adapted from an e-mail one of you might recognize: 165 KIAS tops so far, and that's without wheel pants and throttled back a little to keep the CHT under control. Stall points are done. I think I've got the only -4 with stall warning. With the flaps down the stick shakes like mad (+/- 1", 3-4 Hz) prior to stall and airplane shudders hard about 1/2 knot before. The shudder isn't usable as warning, but the stick sure is. 4g turns are awesome. My g-tolerance has faded completely, so I'm pulling up to 4 as often as I can to get some tolerance back before going out to 6. I've already got the gloc box checked (not in this airplane!). Haven't had the nerve (or a plan) to roll it yet, but I've been to about 135 deg doing pitchbacks to keep the speed and g up. Snuffed the engine when I pushed over to stop it ballooning after rolling out from an overbank yesterday. It started right up again, it was just a little unexpected at the time. I found the seat cushion sometime after landing. Today was more of the same...without the unload. Landings are much easier, but I still tend to drop it in. The RV-4 seems really good-natured on the ground, thank goodness. Supposed to rain tomorrow. Maintenance day! Dave 'testy' Hyde |
#2
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"nauga" wrote in message ink.net... Has anyone got any suggestions on how to find an intake leak that don't involve standing close to a turning propellor? Any other troubleshooting advice? Timing checks good for both mags, BTW. Chrome cylinders, bayonet CHT probes. Dave 'testy' Hyde I use the blow side of a VERY CLEAN shop vac to pressurize the intake. Use cardboard and a lot of duct tape to seal off the air box and fit the vacuum hose. You have to plug the exhaust too since a cylinder may have both intake and exhaust valves open. Then spray soap solution on the intake pipes and watch for bubbles. Same trick works for finding exhaust leaks. Works on cars too. I pressurized the intake of a Jeep V8 and found a couple of pretty good vacuum leaks. Bill Daniels |
#3
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I use the blow side of a VERY CLEAN shop vac to pressurize the intake. Use
cardboard and a lot good idea.......buttttt.... One thing to worry about here.... Some (most) shop vacs rely on the air flowing through the motor to keep the motor cool... If you run a shop vac to provide a low air pressure source and youve got it all plugged up so that very little air is actually FLOWING...I imagine you could destroy it pretty quickly... If you are gonna do this, you need to alternate short periods of time where the vac is providing pressure but no real air flow with significantly longer periods of time where you allow the air to flow freely to cool the engine back down.... Note that just running a short period of time with it plugged, then shutting it off wont really help in the cooling department....unless you wait on the order of hours before you crank it up again Maybe Im being paranoid and/or shop vacs today are built like brick ****houses.....but I m cheap enough to not risk a couple cases of beer money to find out the hard way.... Oh yeah...NEVER ever use a shop vac to clean out a charcoal grill or fireplace even if its been days since the fire...and as if you need to be told this....never use a shop vac to clean up a gasoline spill (yes I know someone who did this) good luck! Blll |
#4
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"Bill Daniels" wrote in message news:mSJdc.103965$gA5.1394034@attbi_s03...
"nauga" wrote in message ink.net... Has anyone got any suggestions on how to find an intake leak that don't involve standing close to a turning propellor? Any other troubleshooting advice? Timing checks good for both mags, BTW. Chrome cylinders, bayonet CHT probes. Dave 'testy' Hyde I use the blow side of a VERY CLEAN shop vac to pressurize the intake. Use cardboard and a lot of duct tape to seal off the air box and fit the vacuum hose. You have to plug the exhaust too since a cylinder may have both intake and exhaust valves open. We use the shop vac thing to pressurize the exhaust system to check for monoxide leaks in the cabin heat system, as per the Canadian AD that applies to all Canadian aircraft, and also required by Cessna on their airplanes in the latest maintenance schedules. The intake and exhaust valves have so little overlap that they present no problem, and if there is any, a slight turn of the prop stops it. And we find leaks in those exhaust systems, too, before they get dangerous. Leaks you'd never spot with your eyeballs alone. Another respondent was concerned about vacuum motor life, and he's right. Got to avoid running the vac for too long with so little airflow through it. We use an old household canister vacuum, reserved just for this sort of thing, thoroughly cleaned out, no bag or anything, and labelled clearly. Dan |
#5
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In . net nauga wrote:
My Lyc. O320-D2C idles rough on the right mag, with the #3 cyl showing an EGT drop. The roughness clears up above 1200 RPM or so, still on one mag. It's also noticably smoother on just the left mag, and everything's smooth on both mags. Fouled plug? Bad lead to plug? ---------------------------------------------------- Del Rawlins- Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website: http://www.rawlinsbrothers.org/bhfaq/ |
#6
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#7
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In et nauga wrote:
Del Rawlins wrote: Fouled plug? Bad lead to plug? I forgot to mention: New mags, plugs, and harness. Swapped plugs across the engine, same problem. Harness checks good. Did you try swapping the mags? A long shot for sure, but you never know. ---------------------------------------------------- Del Rawlins- Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website: http://www.rawlinsbrothers.org/bhfaq/ |
#8
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Del Rawlins wrote:
In et nauga wrote: Del Rawlins wrote: Fouled plug? Bad lead to plug? I forgot to mention: New mags, plugs, and harness. Swapped plugs across the engine, same problem. Harness checks good. Did you try swapping the mags? A long shot for sure, but you never know. ---------------------------------------------------- Del Rawlins- Remove _kills_spammers_ to reply via email. Unofficial Bearhawk FAQ website: http://www.rawlinsbrothers.org/bhfaq/ Before swapping the mags, I'd pull the cigarette plugs out and take a close look at the contacts. We had a weak mag on the Taylorcraft last summer that we chased for months. Finally checked these guys and fount the problem. Our cigarette plugs were probably origional equipment on this engine (A-65 built in -=1939=-). Sure, it's a long shot, but an easy one to eliminate. best of luck. Richard |
#9
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I have seen auto mechanics use an unlit propane torch at a very low setting.
Directing it around the gaskets of a running engine, causes a very noticealbe RPM increase, should a leaking intake system be present. One has to be aware to keep the propane away from the normal fuel air intake. I don't know if this system of testing would be proper in an aviation instance, where the prop wash may interfere. Maybe, feeding the propane very close to the area to be checked, in small plastic tubing may help. |
#10
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"Charles S" wrote in message nk.net... I have seen auto mechanics use an unlit propane torch at a very low setting. Directing it around the gaskets of a running engine, causes a very noticealbe RPM increase, should a leaking intake system be present. One has to be aware to keep the propane away from the normal fuel air intake. I don't know if this system of testing would be proper in an aviation instance, where the prop wash may interfere. Maybe, feeding the propane very close to the area to be checked, in small plastic tubing may help. That big fan on the front of the aircraft engine keeps blowing the propane away. Anyway this works best with a lean burn engines where the additional fuel seeping in through the intake leak moves the mixture toward best power. Bill Daniels |
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