Zenoah g62 operating advice.
10-28-2016, 08:10 AM
#1
Thread Starter
Join Date: Mar 2006
Location: West KirbyWirral, UNITED KINGDOM
Posts: 545
Likes: 0
Received 0 Likes
on
0 Posts
Zenoah g62 operating advice.
Hi all, I have just completed a Ziroli mustang. I have fitted the recommended engine, a Zenoah g62. Prior to installing in the Mustang the engine has had very little running, probably 20 flights and a half hour break in. The engine was involved in a crash on soft ground immediately after take off (reversed ailerons) and has not run until I fitted it in the Mustang.
The test flight went fine but quite a lot of vibration was present. I was advised that the impact from the earlier crash had probably displaced the rear crank web. A stripdown confirmed this and a friend found that, although the crankshaft wasn't bent, it was out of true by 26 thou''. He managed to re-position the shafts and re-align them but could not get them closer than 6 thou'' out of true. I re-assembled the engine and gave it a test run. I used the recommended spinner and backplate and found that although the vibration was reduced, it was still unacceptable. I fly turbines and have access to an electronic balancer and had established a very good balance on the backplate which is a substantial piece of aluminium. Although this was perfectly balanced when it was removed and the engine re-run, the vibration was reduced.. The conclusion was that the out of true crank shaft was causing the problem. The engine was once again stripped and trued to half a thou'' accuracy. I was told to tig weld the big end shaft which I did but although it was a small weld, it distorted the shaft which although remaining parallel, returned to 6 thou out of true rotationally.
Now for the advice please. I have ground off the weld and a friend with a good quality lathe and dial gauge has returned the shaft to true.
Lots of early experience trying to start the engine (magneto) persuaded me to invest in a coil spring recoil starter which quite honestly is fantastic. Since the big end shaft is a press fit in the crank webs/journals the recoil starter imposes a torsional load on the rear crank web which could possibly induce the big end pin to rotate in the crank web unless it is re-welded and the merry go round starts again.. In other words the coil spring assembly could induce a torsional load which can overcome the grip of the press fit and return the shafts to an out of true situation. Any thoughts please before I give up and go back to turbines.
Apologies for the British venacular and terminology.
The test flight went fine but quite a lot of vibration was present. I was advised that the impact from the earlier crash had probably displaced the rear crank web. A stripdown confirmed this and a friend found that, although the crankshaft wasn't bent, it was out of true by 26 thou''. He managed to re-position the shafts and re-align them but could not get them closer than 6 thou'' out of true. I re-assembled the engine and gave it a test run. I used the recommended spinner and backplate and found that although the vibration was reduced, it was still unacceptable. I fly turbines and have access to an electronic balancer and had established a very good balance on the backplate which is a substantial piece of aluminium. Although this was perfectly balanced when it was removed and the engine re-run, the vibration was reduced.. The conclusion was that the out of true crank shaft was causing the problem. The engine was once again stripped and trued to half a thou'' accuracy. I was told to tig weld the big end shaft which I did but although it was a small weld, it distorted the shaft which although remaining parallel, returned to 6 thou out of true rotationally.
Now for the advice please. I have ground off the weld and a friend with a good quality lathe and dial gauge has returned the shaft to true.
Lots of early experience trying to start the engine (magneto) persuaded me to invest in a coil spring recoil starter which quite honestly is fantastic. Since the big end shaft is a press fit in the crank webs/journals the recoil starter imposes a torsional load on the rear crank web which could possibly induce the big end pin to rotate in the crank web unless it is re-welded and the merry go round starts again.. In other words the coil spring assembly could induce a torsional load which can overcome the grip of the press fit and return the shafts to an out of true situation. Any thoughts please before I give up and go back to turbines.
Apologies for the British venacular and terminology.
