McCoy .29 RR Engine disassembly

Stuka Stunt Main Forum · 6 of 6 known posts recovered

Kurt · Aug 24, 2001 02:38 PM

I recently acquired an old McCoy .29 Sportsman rear intake that will not turn over. It looks fairly clean, not gummed up with castor oil but the crankshaft will not rotate. I would like to disassemble the engine and try to fix it if possible. How do you disassemble these engines? The front cover is held onto the case by 4 phillip's head screws but there is a black anodized front piece that the prop screw threads into that seems to be press fit onto the nose of the crankshaft. I believe I need to pull that off to try and get the engine apart? The front cover screws are loosened up and can be removed . The head is off and the head gasket is in good shape. Is the cylinder press fit into the case? What am I going to find at the back of the engine? Any tips on how I should proceed would be appreciated.

Thanks,
Kurt

Kurt

Jake · Aug 24, 2001 06:01 PM

#1 source

LAST EDITED ON Aug-24-01 AT 06:07 PM (CDT)

I have two of them, nice motors by the way. The early slant intake Sportsman was only made a couple years and is rather scarce today. The crank itself is probably not stuck, it is likely the piston gummed up in the liner. You shouldn't have to fool with the front end (pulling off the prop drive) beyond removing the screws and pulling the front end off once it is loosened up, and yes the prop drive "spool" is a press fit on the crank, and it is blackened steel, not aluminum. On the liner, no it is held in, in the conventional way by the head bolts. Try the soaking in a crockpot with anti-freeze method to loosen it all up. The only thing at the back of the crank is the drum intake valve, again, not a problem.
By the way the motor is usually identified as a "rear intake" rather than a true rear rotor. The .29 RR of the same era is a completely different engine with a detachable rear plate, and ball bearings.

"It'll probably feel real good again, once it quits hurting".

De Hill · Aug 24, 2001 06:10 PM

#2 source

Bolt an old wooden prop to the engine and heat it in the oven at 300 degrees for 15 minutes. Take it out with a potholder and try to turn it over. It will probably free up. When you remove the screws from an engine that has been run, heat it in the oven before you dissassemble it. The screws will come out easily and you won't booger up the screw slots when you take them out.

If you are careful, you can save the paper gaskets by using this method.

De Hill

Kurt · Aug 27, 2001 09:18 AM

#3 source

This engine is the rear intake version of the .29 like Jake said. It has the slanted intake on the rear. I have been using lacquer thinner to loosen up the brown crud in the thing. The funny thing about this engine is that it doesn't show any signs of being mounted on the lugs. No marks from washers or screws that you would normaly expect to see. The cylinder still has what looks to me like honing marks in it. Yet it has this brown crud that I would assume is old castor oil. Anyway, I took the front spool off and got the crankshaft out. The front ball bearing was gummed up solid. The piston came out fine and the two rings look brand new. The piston rod big end is in perfect condition. Should the spool pull out once the crank and piston are removed? How do you get the piston back in? On larger engines I have used a ring compresion tool to get the piston in the cylinder. What is the trick to get these tiny rings compressed so I can slip it into the cylinder?

Kurt

Jake · Aug 27, 2001 03:07 PM

#5 source

LAST EDITED ON Aug-27-01 AT 03:08 PM (CDT)

I forgot this is a single BB main engine. The RR McCoys used twin press-in style bearings which require tools and care to get out. This one should be ok as it is different. By the spool, I assume you mean the disk intake valve, yes it will come out once you get the piston and rod out. These came in a lapped type piston also. Be very careful with the rings, they break easily! By the way Dick McCoy is still around (in his '90s now!) and he still has some parts for some of his motors. He is probably a REAL good source of advice on these if you need it also.

JAK

"It'll probably feel real good again, once it quits hurting".

bkruger · Aug 27, 2001 11:10 AM

#4 source

>
>I have two of them, nice
>motors by the way. The
>early slant intake Sportsman was
>only made a couple years
>and is rather scarce today.
>The crank itself is probably
>not stuck, it is likely
>the piston gummed up in
>the liner. You shouldn't have
>to fool with the front
>end (pulling off the prop
>drive) beyond removing the screws

The weak link in all of this is usually the con rod. Trying to free up a seized engine by the prop may wallow out the con rod or, worse yet, break it or the wrist pin.

My technique is a little different. First thing I do is pull the head. I then make a "plug" that is somewhat smaller than the piston. The plug is designed to go on top of the piston. This plug is relieved if necessary for the raised ridge on the top of the piston. Plug is made of soft pine, although a dowel will probably work as well. Cut the plug so that it is about 3/8" above the top of the cylinder.

Get another piece of 1 inch soft pine about 3 inches x 1.5 inches. Relieve a slot in it about 1/4 in for the bottom of the crank case to go into.

Head to the shop and your favorite vise. Put the channeled piece of pine against one jaw, hold the engine in place, then the shaped plug in the cylinder, then center both up as you bring the vise jaws against them. Close the vise until you start to meet signifigant resistance. Then, using a propane torch, lightly heat the outside of the case around the cylinder. Do this for a minute or so, dancing the flame around the cylinder. Close the vice a quarter turn. Reheat, close again, etc. Once the piston frees and starts to move it should be free enough that you can now lower the piston by turning a prop mounted on the crankshaft. Once the piston is down, you can lube the cylinder with your lube of choice. I tend to like ATF, but that's your choice.

I just recently used this technique on some engines a friend of mine had from his misspent youth. By the time we were done, a Fox 35, McCoy 35, Veco 35, and Veco 45 were now ready run. Now, if he would just build a ship for one of them....

Be careful if dealing with a Fox 35. The case is relatively fragile, and the channeled block needs to be relieved more for the bottom boss holding the screw cover on.

Regards - Bob Kruger