HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Feb 18, 2011, 06:10 PM
Registered User
Joined Apr 2007
16 Posts
Help!
OS GT55 Gas engine issue

Hey group,
We have two of these on 50 CC extras.
My son was flying and when he landed heard a pop and realized the prop was spinning freely.
Turns out only thing holding the wooden prop on was the spinner.
Must have happened close to the end of the flight.

We busted all four bolts and are having a hard time getting them out of the prop hub.
I drilled a small hole and used a knife thinking they would be loose but wont budge.
How do you get the prop hub off?? anyone know?
I see that its bolted from the front pilot shaft but looks like you need a special tool to get to it inside the hub.
Help would be appreciated.
Doug
pilotdoug is offline Find More Posts by pilotdoug
Reply With Quote
Sign up now
to remove ads between posts
Old Feb 18, 2011, 10:12 PM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
11,833 Posts
wow I am impressed, I didn't think one could shear off all four of those bolts at one time. That is something new to me.

In looking at the instruction sheet that comes with the engine, and the review of the engine, where they disassembled it here http://downloads.hobbico.com/reviews/osmg1555-rcsf.pdf
I would say that the drive spacer is a very light press fit onto the crankshaft. They have what looks like a drive key near the rear maybe a screw like pin. Then there is a woodruff key on a slot on the inside, next there is a tapered collet at the rear to help keep the drive spacer centered.

So anyway, it looks like the drive key pin is unscrewed, next unscrew and remove the ignition timing sensor, so it isn't damaged by the heat or something, and then you heat up the drive spacer some, then holding it carefully in a leather gloved hand, gingerly tap on the crankshaft tip, or the pilot shaft tip, with a brass hammer, and the drive spacer should pop loose. You want to have something like your lap or someone else ready to catch the engine when the drive spacer comes loose.
what I cannot tell is if you unbolt the pilot shaft from the crankshaft before or after you get the drive spacer loose. sometimes you have to hit them harder, but always start off easy and work your way up to more force. What likely has the drive spacer stuck is the tapered collet at the rear of the spacer.

Using a brass hammer minimizes the shock effect that might cause a hardened steel shaft or hardened steel bearing races to crack or break off. Sometimes a steel hammer will cause the hardened steel bearing races to crack or a crankshaft to break apart.

I have had to occasionally break out my antique BFBH before on recalcitrant motorcycle bearings that didn't want to come out easily. But I have several different weight brass hammers I can use situations like this. Unless a engine or wheel bearing begins to get me upset, I seldom need to resort to this sucker.
earlwb is offline Find More Posts by earlwb
RCG Plus Member
Last edited by earlwb; Feb 18, 2011 at 10:27 PM.
Reply With Quote
Old Feb 18, 2011, 11:07 PM
Registered User
Joined Apr 2007
16 Posts
pilot shaft

I thought the pilot shaft was holding the prop hub on??
so if i can get a correct elongated socket and took the pilot shaft off it would be able to slide off??
pilotdoug is offline Find More Posts by pilotdoug
Reply With Quote
Old Feb 19, 2011, 03:00 PM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
11,833 Posts
I reviewed it and yes you are correct in that you'll need a special super extra deep socket to fit the pilot shaft nut. Sorry my mistake.
I doubt OS will sell it to anyone either. I think you could make one by welding another socket onto the one that fits. If you can find a socket that has the hex head on it to fit a box end wrench, that might be a better way to go.
The extra deep sockets I saw on the internet didn't look quite long enough, but maybe I missed some.
earlwb is offline Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My Low Wing plane
Reply With Quote
Old Feb 19, 2011, 04:42 PM
Registered User
Joined Apr 2007
16 Posts
Os gt55

Yep,
Kind of a crappy way to sell an engine..
We were running a wood prop and sure that it got just a little loose..
They should supply the tool if they are going to sell something that takes special tools to fix ..
I have two of these engines and will make sure the other plane prop stays very tight.
I am in touch with them and will see what they say,
Thanks
Doug
pilotdoug is offline Find More Posts by pilotdoug
Reply With Quote
Old Feb 19, 2011, 08:37 PM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
11,833 Posts
Well, I can sort of agree with you too, but I do not know of any car company or motorcycle company that sold any of their special tools to the public either. I had to look long and hard to find some special tools for my Harley. So it is about par for the course. I think they consider the engine a non-user serviceable item just as many other companies do. One is supposed to send it in for repair and pay them for it. So they aren't obligated to make it easier for someone to DIY it. Now considering how much those extra deep sockets cost as I don't see them being sold individually (unless Snap On or Mac tools does off their truck dealers) so it would be expensive to have to buy a set. So maybe there is a small market for someone to fabricate a socket tool for this purpose and sell it.
earlwb is offline Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My Low Wing plane
Reply With Quote
Old Feb 19, 2011, 09:59 PM
Registered User
Joined Apr 2007
16 Posts
tools

I suppose that we should be counting our blessings that the prop did not fall apart with the stress against the spinner while in a 3D situation.. that would have been no fun..
Doug
pilotdoug is offline Find More Posts by pilotdoug
Reply With Quote
Old Feb 20, 2011, 07:20 AM
Registered User
earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
11,833 Posts
Yeah I think so.
I am still back there thinking it might be a defect with the bolts being overly case hardened and made brittle. I would have likely sent the engine back to see if they fixed it under warranty or not.
earlwb is offline Find More Posts by earlwb
RCG Plus Member
Latest blog entry: My Low Wing plane
Reply With Quote
Old Feb 20, 2011, 12:39 PM
Gas Only
Fokker DII's Avatar
USA So. Cal.
Joined Sep 2010
979 Posts
Quote:
Originally Posted by earlwb View Post
Yeah I think so.
I am still back there thinking it might be a defect with the bolts being overly case hardened and made brittle. I would have likely sent the engine back to see if they fixed it under warranty or not.
There was a major recall of hardware where I worked a few years ago. Seems that some of Chineese hardware was fraudelently marked as to material type and was failing in high stress aplicatins due to (as I recall) hydrogen imbrittlement. Could be more of same??
Fokker DII is offline Find More Posts by Fokker DII
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion OS GT55 Gas engine issue pilotdoug Engines 0 Feb 18, 2011 05:25 PM
Help! OS GT55 Repair Bristlebasher Engines 8 Jan 29, 2011 10:03 PM
Sold O.S. GT55 Gasoline Engine For Sale Dynomike Aircraft - Fuel - Engines and Accessories (FS/W) 10 Sep 11, 2010 08:08 AM
Discussion OS GT55 Gas Engines g_mkoch Engines 26 Aug 17, 2010 07:38 AM
Discussion OS .40 engine issue shamrock1990 Engines 12 May 10, 2008 08:23 PM