Prop problem - 3W 100
12-28-2004, 10:13 AM
#1
Prop problem - 3W 100
While testing the throttle settings on a 3W-100, the prop let go and sheared off all the bolts flush with the engine's thrust washer. Any suggestions on how to remove the studs from the engine? Maybe that Carbon Fiber prop WASN'T balanced after all! Good thing it was at idle when the prop decided to 'go forward'!
Just one more reason to stay BEHIND the engine when it is running!
Jerry
Just one more reason to stay BEHIND the engine when it is running!
Jerry
12-28-2004, 10:29 AM
#2
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RE: Prop problem - 3W 100
sounds like the prop bolts were not torqued properly to me
as far as getting the broken ones out you can use a left-hand drill bit
and you might get lucky to catch the bolt and it will spin right out
or you may have to drill a small hole in the exact center of the bolt
and use a tool called an easy-out
hope this helps
as far as getting the broken ones out you can use a left-hand drill bit
and you might get lucky to catch the bolt and it will spin right out
or you may have to drill a small hole in the exact center of the bolt
and use a tool called an easy-out
hope this helps
12-28-2004, 10:51 AM
#3
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RE: Prop problem - 3W 100
Your problem was likely the result of the prop bolts being a few MM to long. What happens is the bolt bottoms out on the hub when the threads run out. This is pretty common. Prop hubs vary in thickness. This can also be the result of improperly tightened and or torqued bolts.
Recommended torque range is 38-40in-lbs.
The bolts are generally no problem to remove. Typical screw extraction techniques work well.
3W offers new hubs for about $40.00 if needed.
Recommended torque range is 38-40in-lbs.
The bolts are generally no problem to remove. Typical screw extraction techniques work well.
3W offers new hubs for about $40.00 if needed.
12-28-2004, 11:45 AM
#4
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RE: Prop problem - 3W 100
Getting the screws out is easy - as was mentioned, use a small drill bit with lots of oil, drill a 3/32" hole in the center of the bolt, and use an extractor (get at ace hardware).
If the bolt is not easy to turn, use a torch to slightly heat the aluminum flange (Al expands faster than Steel) and it will come right out. Don't force it... if you break off the easy out you are done!!
When you had it running did it backfire or miss?? I have seen only two engines throw props like that .. both were caused by bad ignition modules / faulty spark or a low ignition battery. Tthe spark misses causing the cylinder to load up with fuel, then it catches on the next compression stroke, creating a large pop in opposing direction, which shears off the bolts. The rod bearings usually are damaged too.
You should be able to tell how much bolt is left in the hole when you remove them. If there is only a few mm of bolt, the prop was probably loose and bolts backed out or stress cracked from being loose. If the bolts are hard to remove, are broken clean, and there still is a lot of it left in the hole, chance are you had a misfire that sheared the bolts.
My guess is that the torque was off probably due to the bolt length as mentioned by Mglavin, but make sure you check all before firing up again... if you can't find anything you might want to send the engine back to 3W for a check just in case.. trust me you don't want that happening in flight. I watched a guy bury a new CompArf 2.6 when his prop sheared from a misfire. His battery pack was low....
DP
If the bolt is not easy to turn, use a torch to slightly heat the aluminum flange (Al expands faster than Steel) and it will come right out. Don't force it... if you break off the easy out you are done!!
When you had it running did it backfire or miss?? I have seen only two engines throw props like that .. both were caused by bad ignition modules / faulty spark or a low ignition battery. Tthe spark misses causing the cylinder to load up with fuel, then it catches on the next compression stroke, creating a large pop in opposing direction, which shears off the bolts. The rod bearings usually are damaged too.
You should be able to tell how much bolt is left in the hole when you remove them. If there is only a few mm of bolt, the prop was probably loose and bolts backed out or stress cracked from being loose. If the bolts are hard to remove, are broken clean, and there still is a lot of it left in the hole, chance are you had a misfire that sheared the bolts.
My guess is that the torque was off probably due to the bolt length as mentioned by Mglavin, but make sure you check all before firing up again... if you can't find anything you might want to send the engine back to 3W for a check just in case.. trust me you don't want that happening in flight. I watched a guy bury a new CompArf 2.6 when his prop sheared from a misfire. His battery pack was low....
DP
