Kevin Horton
Well Known Member
Well, today didn't turn out as I had hoped.
I went to the hangar mid-day, to pull the cowlings and do a good inspection ahead of the firewall before going flying to do some more engine break-in. But, I discovered two significant issues that needed dealing with ASAP, and another issue that will need correcting eventually.
1. The alternator pulley had been touching the lower cowling, and put a pretty good gouge into it.
2. The throttle cable showed signs of heat stress where it passed close to the exhaust system. I had thought that there was enough clearance, but obviously not. The damage doesn't look too bad after 20 minutes of running. I think the cable would have been trashed with an hour of high power running time.
3. There were signs of a bit of rubbing on the upper cowl from part of the oil cooler mount. Also, four of the screw heads that hold the plenum chamber cover on showed signs of rubbing on the cowling - three of these were very minor rubs, but one was more significant.
Tomorrow, I'll pull the prop and change the alternator belt for a shorter one. I'll put a piece of tape over the gouge in the cowl to act as a witness for future clearance issues. If I still have a clearance problem with the 7355 belt, I'll have to fabricate some sort of pad on an arm to prevent the lower cowl from being pushed closer to the engine by the ram air pressure. Once I am sure the clearance problem is resolved, I'll fill in the gouge.
I'll put a heat shield on the exhaust where the throttle cable passes by. That'll be a quick, easy fix.
As for the oil cooler mount, today I removed a bit of metal from the mount in the affected area. I'll put a piece of UHMW tape on the cowling, and see how it does. I can remove more metal if needed. As for the screws that touched, eventually I'll replace those four with flush head screws. For now, I'll remove those screws, as there should be enough other ones to hold the cover in place. I'll put some UHMW tape on the cowling to act as a rub guard. In the end, it may be necessary to rework the contours of the plenum chamber cover to move the outer edges closer to the engine. This would be a big job, so I am hoping to avoid it, if possible.
I'll do another 20 minute flight to see how things are doing. Maybe late tomorrow, or maybe some other day if the work takes too long.
Originally, I had planned to fly for an hour on the first flight, in order to minimize the low power running time. But, Ron MacEwen, the local Aircraft Maintenance Engineer and EAA Flight Advisor suggested that it would be better to only fly for 20 minutes or so, and then do a big firewall forward inspection before flying again. I am very glad I took his advice - I believe that the alternator pulley would have completely worn through the lower cowling if I had flown for an hour, which would have necessitated a lot of fibreglas work to fix. As it is, I only need to mix some resin and fibre to fill the gouge - that'll be a quick fix, and it can wait for a few flights.
Moral of the story - keep those first flights short, to minimize the risk of undetected small problems quickly becoming big problems. A lot can happen in the course of an hour.
I went to the hangar mid-day, to pull the cowlings and do a good inspection ahead of the firewall before going flying to do some more engine break-in. But, I discovered two significant issues that needed dealing with ASAP, and another issue that will need correcting eventually.
1. The alternator pulley had been touching the lower cowling, and put a pretty good gouge into it.
2. The throttle cable showed signs of heat stress where it passed close to the exhaust system. I had thought that there was enough clearance, but obviously not. The damage doesn't look too bad after 20 minutes of running. I think the cable would have been trashed with an hour of high power running time.
3. There were signs of a bit of rubbing on the upper cowl from part of the oil cooler mount. Also, four of the screw heads that hold the plenum chamber cover on showed signs of rubbing on the cowling - three of these were very minor rubs, but one was more significant.
Tomorrow, I'll pull the prop and change the alternator belt for a shorter one. I'll put a piece of tape over the gouge in the cowl to act as a witness for future clearance issues. If I still have a clearance problem with the 7355 belt, I'll have to fabricate some sort of pad on an arm to prevent the lower cowl from being pushed closer to the engine by the ram air pressure. Once I am sure the clearance problem is resolved, I'll fill in the gouge.
I'll put a heat shield on the exhaust where the throttle cable passes by. That'll be a quick, easy fix.
As for the oil cooler mount, today I removed a bit of metal from the mount in the affected area. I'll put a piece of UHMW tape on the cowling, and see how it does. I can remove more metal if needed. As for the screws that touched, eventually I'll replace those four with flush head screws. For now, I'll remove those screws, as there should be enough other ones to hold the cover in place. I'll put some UHMW tape on the cowling to act as a rub guard. In the end, it may be necessary to rework the contours of the plenum chamber cover to move the outer edges closer to the engine. This would be a big job, so I am hoping to avoid it, if possible.
I'll do another 20 minute flight to see how things are doing. Maybe late tomorrow, or maybe some other day if the work takes too long.
Originally, I had planned to fly for an hour on the first flight, in order to minimize the low power running time. But, Ron MacEwen, the local Aircraft Maintenance Engineer and EAA Flight Advisor suggested that it would be better to only fly for 20 minutes or so, and then do a big firewall forward inspection before flying again. I am very glad I took his advice - I believe that the alternator pulley would have completely worn through the lower cowling if I had flown for an hour, which would have necessitated a lot of fibreglas work to fix. As it is, I only need to mix some resin and fibre to fill the gouge - that'll be a quick fix, and it can wait for a few flights.
Moral of the story - keep those first flights short, to minimize the risk of undetected small problems quickly becoming big problems. A lot can happen in the course of an hour.