Hangar Flying => Hangar Flying => Topic started by: strake99 on July 11, 2005, 01:09:01 PM
Title: Engine maintenance story
Post by: strake99 on July 11, 2005, 01:09:01 PM
Just a quick note to explain how I swapped a vibration box for a watch in the back of my Long-EZ. While flying to Rough River last September, I had to climb over clouds in the Memphis area. When I levelled at 9500, I found that the engine was running roughly above 2450 rpm. It was not misfiring, but was not very smooth and there was more noise and vibration than normal. No carb icing symptoms - this was an unwelcome change. I adjusted my route for the rest of the journey to fly directly over airfields, but no further issues occurred. I experienced the same roughness on the return trip, but it only appeared after a while. Since then, I would encounter rough running and vibration most of the time above 2450 rpm. On a recent trip to Hondo, I ran at 2560 for a while and backed off because I could feel the vibration through the headrest, to the point that my eyesight was blurring. Not good. I had my A&P conduct an engine inspection (including internal cylinder bore inspection) as part of my ACI. He found no evidence of mechanical problems with the engine. However, with 430 hours on the magneto, which had been on the plane 10 years, and with an intermittent clicking sound coming from this Slick magneto (which is a non-impulse type) when the engine was turned over by hand, he recommended a magneto overhaul. I pulled the magneto and had it overhauled locally for $170. The magneto gear assembly was loose, and the contact points were worn. I re-installed the magneto on the plane, re-timed it and went flight testing yesterday. Instead of a vibrating rattletrap above 2460 rpm I now have a watch in the back. I ran at 2740 rpm for 5 minutes. There is actually less vibration at that rpm than at 2440 due to 2440 being in the zone of vibration resonance for a flat-4. Lessons learned:
1. If the engine starts running more roughly, even if it stablizes, something is not right, and needs to be remedied. I did modify my operational mode to protect myself - I probably ran for 25 hours at reduced rpm while carrying the problem, and I avoided long flights or areas away from airfields or major roads. 2. Magneto issues do not always show up as a misfire - in this case the engine simply ran roughly, which could have been mistaken for several other maladies (fuel system, carb icing, beginnings of valve sticking etc.) 3. Magnetos need to be overhauled to yellow-tag standards in accordance with manufacturer's recommendations, especially if they have been on a plane for a long time (in my case, 10 years). Do not skimp on this maintenance item.
Now I can go floor it!
Graham Shevlin N131JF Designed by Burt, built by Jesse Huerta