JettPilot

My Feedback: (6)

My airplane with a G-26 engine and APC prop was at idle and rolled into a metal pole, when the prop hit the pole it instantly stopped it without breaking the prop [:@] But it did break the spinner since the prop twisted on the shaft ever so slightly [X(]

I know the crankshaft pins on the G-26 is pressed in to the crank, and the weight of the flywheel is on the back of the engine. My question is will a sudden stop at idle be enough to twist the crank where its pressed together ? How could I tell for sure if the crank did twist ? then engine seems to run OK, no excessive vibration, but thats just my impression from eyeballing it... Any of you have info or thoughts on this ?

Thanks,

JettPilot

Tired Old Man

My Feedback: (1)

Hi JettPilot,

Funny thing about prop strikes. Sometimes they are a disaster and sometimes nothing becomes evident until after a few of them. Eventually it's pretty much a sure thing the the front bearing or the rod bearing will go bye-bye, and depending on the type of crankshaft construction it can become damaged. No prop strike is a good thing.

Best bet for the moment is to look at the prop shaft and see if there is any twisting evident. Remove the spark plug and rotate the crank several times through full rotations, both forward and backward. Listen for any clicking sounds. If you hear anything that does not belong, send it in for repair. Next mount the prop in place and spin the engine, again without the plug, to see if the prop is still tracking true or wobbling. Check it from the side and the front, Next check the end play in the crank. Does it seem the same or does it appear that there is more play than it used to have. If in doubt, send it out for a check up.

JettPilot

My Feedback: (6)

Thanks Silver Surfer,

Not great news, but I will try what you said... Never thought of taking the plug out to get a better reading on how things feel.

JettPilot

jkhorvath

My Feedback: (1)

Check your engine manual to find out if you have roller bearings on your crank pin. The crank pin is the part of the crankshaft that is connected to the connecting rod. If you do have roller bearing there, then most prop strikes will break the cage of that roller bearing. If this happens, then you would be able to hear quite a new and different noise from your engine if you continue to run it.

Note that some engines have bushings instead of roller bearings on the crank pin. Bushings on the crank pin will typically survive a prop strike better than roller bearings, but roller bearings will give you more RPMs.

Turd

you probably closed the trunk lid of your HONDA on it and bent it you dummy

Kweasel

My Feedback: (29)

You should check the crank after a prop strike. Its very easy if you have access to a lathe but can be done well enough by solidly supporting the case and using a dial indicator at each end. Running a twisted crank will usually kill bearings, how quickly depends on the severity of twist.

JettPilot

My Feedback: (6)

I have no lathe or Dial indicator [sm=cry_smile.gif] The closest thing I have to a dial indicator are my eyeballs, I was hoping idle power would not have been fast enough to do any damage, but most seem to think that a strike from idle is enough to damage bearings or twist the crank [:@]

JettPilot

Tired Old Man

My Feedback: (1)

If the crank was damaged then the bearings were as well. That's why I mentioned listening for new sounds, that would be a roller/needle bearing. Bottom line is that if it's damaged, then it's damaged and repair is required. Turning it over at this point will not have an impact one way or another. However, running it without checking may have a severe impact. Checking the prop for visual wobble is the easiest way to look at a crank, although nowhere near as accurate as it needs to be.

Give her a few spins, and if you have a machine shop up there close then have them mount it up so they can run a dial indicator on the prop shaft. If there is nothing audible or rough feeling now, then you won't know about bearing damage until it cuts loose if there is any hidden damage. How well I know this to be true. Sometimes it only takes once, sometimes it takes a lot more hits to be a problem. any prop strike that stops the engine should be considered a hard one. Ya never know.

Antique

My Feedback: (4)

Facts
All gassers have roller bearings on the big end of the con rod..
A prop strike will not in any way damage the roller bearing on the big end of the con rod..
A prop strike will sometimes bend the front shaft..
A prop strike will sometimes put the long hub on the G26 off center on the taper...
A prop strike will sometimes result twist the 2 halves of the crank out of concentricity..
A simple prop strike will not damage the front bearing on the crankshaft...
These facts come from 20 years of looking at and straightening all brands of gasoline engines in model airplanes....
There are many well meaning people on here who wish to help but don't have the knowledge..
Hearsay is rampant........

tkg

My Feedback: (1)

Even a Maloney??

Antique

My Feedback: (4)

On the big end, even a Maloney

thevirginian

Hey Ralph,
I love the way you come across with your expertise and tell people how wrong they areOn the other hand, most folks mean it honest when they try to help here in this forum. As an mechanical engineer I couldn't agree with you more on your "facts" about gassers and prop strikes.

Antique

My Feedback: (4)

All in fun

Kweasel

My Feedback: (29)

I have seen the ball bearings in a G62 turn blue after running with a twisted crank.