HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 27, 2012, 03:48 AM
Registered Misuser
Vince77's Avatar
Italy, Friuli-Venezia Giulia, Aviano
Joined Jan 2004
338 Posts
Many of my smaller motors feel like they have low compression, but do fine once they're up past 16,000 rpm. Seems reasonable that castor would help you there, but the actual physics is a bit more complicated. I'm sure you'd feel better if you had a broken-in Cox to compare it to.

Your's will likely run just fine, unless you're hopping to win some races.
Vince77 is offline Find More Posts by Vince77
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 27, 2012, 06:00 AM
Registered User
boingk's Avatar
NSW, Australia
Joined Feb 2011
2,120 Posts
Drop some oil or fuel into the cylinder. Compression will bump right back up.

- boingk
boingk is offline Find More Posts by boingk
Reply With Quote
Old Nov 27, 2012, 07:27 AM
Registered User
PyroMan's Avatar
United States, KY, Paducah
Joined Mar 2011
590 Posts
Yup, that was it. I put a drop of 3-in-1 oil in the cylinder and the compression is much better. Now it's just waiting on fuel! My dad is going out of town this week so I may have him pick up some fuel at the hobby shop there if they have it.
PyroMan is offline Find More Posts by PyroMan
Reply With Quote
Old Nov 27, 2012, 09:48 AM
Team Compass/KBDD Team Pilot
Ah Clem's Avatar
Joined Mar 2005
3,335 Posts
"Thanks! Just out of curiosity, are any of your Rotomatic springs still functional? My spring was broke when I got it and I read online that most of the springs these days are broke because of the age of the engines."

I have been purchasing quite a few Wen Mac engines from EBay, plus restoring my old ones. The springs for the Rotomatic starter are almost always in good shape. They only broke if used excessively or abused.

In good shape, and with the right fuel, the Wen Macs start in a few tries, so the starter spring should not get exercised that much.

It is the clutch that is usually locked up after sitting with castor oil in it for decades (soaking the clutch in acetone works nicely).

There are two types of springs:

The early ones which appear on all Wen Mac engines which had the Rotomatic starter, and early to mid-production Testors engines, use rivets to retain the spring to the center sleeve and the outside of the clutch housing.

The later ones, which are on late production front rotary, reed, and Fly'em motors which use a "Z" bend at one end and a "J" bend at the other. They were designed to be installed with the clutch still in place (the old spring was pulled out through the slot in the spring housing, the new one slipped in-"Z" bend end first, into the larger of the two holes in the center sleeve. The propeller would then be wound in the normal direction for winding the starter until the entire spring is wound in. The "J" bend would then catch/hook on the slot in the spring housing. This was tricky to do, at best.

The later springs can be used in the earlier motors. But you may need to remove the clutch to remove the old spring due to the rivets.

You may be able to bend the ends of your spring to use it like the later version.

I looked at your engine overhaul thread again, but could not see the end of the spring, so cannot tell which it had. The engine is fairly late production Testors, but not the last production version. It still has the Wen Mac type cylinder, which is not clocked so that the exhaust port face the sides, but still has the short venturi intake. Originally, these engines (both Wen Mac and Testors) had the cylinders clocked to face the sides, to that the exhaust would not flow down into the venturi. The version after yours had a slightly longer venturi, to prevent this, as it was determined that the exhaust in the venturi degraded performance (we had a few of these when I flew for Testors and the extended venturi was a very positive improvement).

The last versions had the Fly'em type cylinder (they fins around the exhaust port were removed so that a muffler ring could be fitted, although I only ever saw the muffler on the Fly'em motors, never on the front rotary motors). The longer venturi was retained until the end of production, as far as I know.
Ah Clem is offline Find More Posts by Ah Clem
Last edited by Ah Clem; Nov 27, 2012 at 10:02 AM.
Reply With Quote
Old Nov 27, 2012, 12:25 PM
Closed Account
Joined Feb 2006
433 Posts
Quote:
Originally Posted by JKinTX View Post
Crank rock is a character trait of these it seems, at least on the ones I have seen.
Thanks.

Quote:
If you run any Cox or other similar .049s (which is what this thread was about to start) these are all shaft in case bearing engines with no bushing and they need the castor, otherwise you will have crank rock out the wazoo real soon...
Actually, thread started out about McCoy .049's:

Quote:
Originally Posted by PyroMan View Post
I have a Testor's McCoy .049 that I restored back in the spring [...] What kind of fuel do I need and where can I buy it?
Ref. Post #37, "For my steel lapped cylinder engines and the Coxes, I'll be running the Wildcat fuel with Castor oil content." Already clarified use of Castor fuels. Thread is about small engines and fuel, related in topic.
OkiThumper is offline Find More Posts by OkiThumper
Reply With Quote
Old Nov 27, 2012, 02:08 PM
Registered User
PyroMan's Avatar
United States, KY, Paducah
Joined Mar 2011
590 Posts
Clem, are you calling those round disks on the front of the engine that house the starting spring the clutch? If so it appears to me that the spring is attached to the clutch by a rivet like you mentioned. I've attached a few pics so you can see. I would like to remove the broken spring and replace it with a new one. How do I go about doing that? If possible I would like to remove the clutch to have access to the spring so maybe I can just relate the current spring. I can't figure out how do that either. I'm thinking the front disk might be pressed on and I didnt want to damage anything while trying to get it off so I didn't mess with it too much.

About the fuel…I called the hobby shop that I'm going to have my dad go to and they do have one thing of 1/2A fuel. It is the same kind that tower hobbies sell. I think I'm going to get that because I just want to see if I can get the engine running, and if so then I will eventually buy a gallon of fuel. Another reason is I don't have have close to $30 right now for fuel, but I do have $12. I know it's 'cheaper' to get the gallon in the long run, but right now I'd like to spend what I can and get the engine going. I'll post a video when I get it running.
PyroMan is offline Find More Posts by PyroMan
Reply With Quote
Old Nov 27, 2012, 02:10 PM
Registered User
PyroMan's Avatar
United States, KY, Paducah
Joined Mar 2011
590 Posts
Forgot the pictures……Name: ImageUploadedByTapatalk1354046984.834976.jpg
Views: 35
Size: 107.4 KB
Description:
Name: ImageUploadedByTapatalk1354047004.526136.jpg
Views: 32
Size: 96.0 KB
Description: Name: ImageUploadedByTapatalk1354047016.085046.jpg
Views: 34
Size: 109.5 KB
Description:
PyroMan is offline Find More Posts by PyroMan
Reply With Quote
Old Nov 27, 2012, 02:31 PM
Registered User
surfer_kris's Avatar
Sweden
Joined Jan 2008
962 Posts
The first disk should be a press fit, it only serves to keep the spring in place. Remove that and you can access the spring, it might simply be the very end that doesn't catch on to the propshaft. A new J bend might fix it.
surfer_kris is online now Find More Posts by surfer_kris
Reply With Quote
Old Nov 27, 2012, 03:04 PM
Team Compass/KBDD Team Pilot
Ah Clem's Avatar
Joined Mar 2005
3,335 Posts
"The first disk should be a press fit, it only serves to keep the spring in place"

This is not quite correct.

The first disk, the one that serves as a propeller backing plate, is the clutch. Inside is ramp assembly and two, small disks. Turn the prop one way, and the disks roll up the ramps and lock up the clutch (so that it winds the spring). Turn the prop the other way (the direction the engine turns while running) and the clutch does not engage. You cannot see the insides of the clutch, as there is a flat disk/washer, pressed behind it.

The old castor oil effectively glues the ramp/roller clutch assembly together.

The clutch is pressed on. If you removed the backplate and piston, connecting rod, you can press the crankshaft out of the clutch with a vice or arbor press (I just did six of these last Saturday, so it is not hard at all to do).

This will expose the contents of the rear disk/spring housing). You will see the sleeve in the center and probably find that the spring is broken on this end. You can cut the spring off and re-rivet it, or make a very shallow "Z" bend in it, so that it can fit into the larger of the two holes in the sleeve.

Once the spring is repaired/replaced, insert the crankshaft back in the engine from the rear, and press the disk back on. I have been using a small, Torx bit, inserted into the back of the hole in the center of the crankshaft (you don't want to put pressure on the crank pin) to support the crankshaft, and placing a small socket over the front of the crankshaft to press on the disc.

This almost takes longer to explain than it does to do.

Thank you for the pictures of your engine. You did a great job of making it look like new. These are very nicely made-I am sure yours will run like new, also!
Ah Clem is offline Find More Posts by Ah Clem
Last edited by Ah Clem; Nov 27, 2012 at 03:09 PM.
Reply With Quote
Old Nov 27, 2012, 04:06 PM
Registered User
PyroMan's Avatar
United States, KY, Paducah
Joined Mar 2011
590 Posts
Quote:
Originally Posted by Ah Clem View Post
"The first disk should be a press fit, it only serves to keep the spring in place"

This is not quite correct.

The first disk, the one that serves as a propeller backing plate, is the clutch. Inside is ramp assembly and two, small disks. Turn the prop one way, and the disks roll up the ramps and lock up the clutch (so that it winds the spring). Turn the prop the other way (the direction the engine turns while running) and the clutch does not engage. You cannot see the insides of the clutch, as there is a flat disk/washer, pressed behind it.

The old castor oil effectively glues the ramp/roller clutch assembly together.

The clutch is pressed on. If you removed the backplate and piston, connecting rod, you can press the crankshaft out of the clutch with a vice or arbor press (I just did six of these last Saturday, so it is not hard at all to do).

This will expose the contents of the rear disk/spring housing). You will see the sleeve in the center and probably find that the spring is broken on this end. You can cut the spring off and re-rivet it, or make a very shallow "Z" bend in it, so that it can fit into the larger of the two holes in the sleeve.

Once the spring is repaired/replaced, insert the crankshaft back in the engine from the rear, and press the disk back on. I have been using a small, Torx bit, inserted into the back of the hole in the center of the crankshaft (you don't want to put pressure on the crank pin) to support the crankshaft, and placing a small socket over the front of the crankshaft to press on the disc.

This almost takes longer to explain than it does to do.

Thank you for the pictures of your engine. You did a great job of making it look like new. These are very nicely made-I am sure yours will run like new, also!
Awesome, thanks for the instructions. I got the shaft out and have found the problem. The spring is broke in half about an inch from the center. Soooooo, I guess I'll see if I can't take the end of the rest of the spring and afix it to the rivet that is on the center hub.
Name: ImageUploadedByTapatalk1354053924.980597.jpg
Views: 42
Size: 113.0 KB
Description: Name: ImageUploadedByTapatalk1354053960.322497.jpg
Views: 43
Size: 106.9 KB
Description:
PyroMan is offline Find More Posts by PyroMan
Reply With Quote
Old Nov 27, 2012, 04:10 PM
Team Compass/KBDD Team Pilot
Ah Clem's Avatar
Joined Mar 2005
3,335 Posts
That should not be too bad to fix. Looks pretty good in there.

You might want to take the clutch and drop it in some nail polish remover for about a half an hour or so (I had to confess to my wife that I used her's).

That will dissolve all the crud in it (if there is any in it). You can use the keyed end of the sleeve to turn the clutch and work out any tendency to stick.

It looks like someone in the past may have tried to remove the clutch by using a screwdriver (it looks dinged up in the back). I did this once when I was younger and it dented the washer on the back to the clutch disk and rendered it unserviceable (jamming the mechanics inside). If this proves to be the case here, you may need to search for a new clutch.
Ah Clem is offline Find More Posts by Ah Clem
Reply With Quote
Old Nov 27, 2012, 04:48 PM
Registered User
PyroMan's Avatar
United States, KY, Paducah
Joined Mar 2011
590 Posts
Quote:
Originally Posted by Ah Clem View Post
That should not be too bad to fix. Looks pretty good in there.

You might want to take the clutch and drop it in some nail polish remover for about a half an hour or so (I had to confess to my wife that I used her's).

That will dissolve all the crud in it (if there is any in it). You can use the keyed end of the sleeve to turn the clutch and work out any tendency to stick.

It looks like someone in the past may have tried to remove the clutch by using a screwdriver (it looks dinged up in the back). I did this once when I was younger and it dented the washer on the back to the clutch disk and rendered it unserviceable (jamming the mechanics inside). If this proves to be the case here, you may need to search for a new clutch.
Haha, you got me! Those screwdrive markings are from me. I've tried to pop it off in the past with a screwdriver, but I never applied too much pressure because I was scared that I was going to bend it and throw it off kilter. Anyway, it feels quite smooth so I don't think I'm going to soak it right now.
I just got done fixing the spring, it seems to work nicely, but I'm about to put the shaft back in to see for sure.

Thanks so much for all your help in getting this thing apart and fixed!

-Nicholas
PyroMan is offline Find More Posts by PyroMan
Reply With Quote
Old Nov 27, 2012, 05:08 PM
Team Compass/KBDD Team Pilot
Ah Clem's Avatar
Joined Mar 2005
3,335 Posts
I want to see video of it running!

I ran a Wen Mac Mk III this morning in a P-39.

It started on the first try, which was pretty neat.

Yours should start very easily as well.

I am enjoying reading your posts, sir!
Ah Clem is offline Find More Posts by Ah Clem
Reply With Quote
Old Nov 27, 2012, 08:56 PM
Registered User
PyroMan's Avatar
United States, KY, Paducah
Joined Mar 2011
590 Posts
Okay, so fixing the spring took longer than I thought. When I got the engine back together the spring came loose So I fixed it so it shouldn't do that again for a long, long time. I just got the engine back together and played with winding it up for a minute and now I realize a new problem . . .

So when I flip the prop over by hand I heard something that sounded like the engine is leaking. I put some oil around the head of the engine and the back plate. The engine is leaking around the back plate. The original gasket has been broken for sometime so right now I have a temporary cork gasket I made out of cork gasket material. It obviously doesn't work. . . What do ya'll suggest for a new back plate gasket?

I feel like with this engine it goes from "yeah, it's ready to start it just needs fuel" to "Oh man, somethings screwed up" and then back to "It's ready to go!" then back to "Crap this is broke" then back to . . . . :P
PyroMan is offline Find More Posts by PyroMan
Reply With Quote
Old Nov 27, 2012, 09:14 PM
Registered User
GliderJim's Avatar
Michigan, USA
Joined Jul 2006
577 Posts
I believe you can make a gasket from a playing card.
GliderJim is offline Find More Posts by GliderJim
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Cox .049 fuel tank NOI53Y 1/2A Planes 4 Apr 11, 2012 06:57 PM
Discussion How to clamp fuel tubes to a Cox .049 engine arukum17 1/2A Planes 3 Mar 20, 2006 09:32 PM
.049 Supplementary Fuel Tank elaerico Engines 11 May 11, 2005 07:13 PM
Fuel issues for COX 0.049 neniwein 1/2A Planes 9 Mar 06, 2005 05:33 AM