Hello!

I am breaking in a new (to me) McCoy .29 blue-head motor. It was converted from R/C to C/L by getting a new straight venturi.  I ran it once for a few minutes, wet 4-stroke with peaks of wet 2-stroke, using 10% nitro 29% oil (1/2 castor 1/2 synthetic) and using a 9 x 4 prop. All was going well.  Second run, it suddenly leaned out, seized up, and stopped mid-run. It is now very hard to turn over.  I pulled the motor apart. Crank pin is not bent. Piston is difficult to crank through piston sleeve for a full rotation.  If I take the sleeve out, engine turns over fine.  Piston seems to bind in the sleeve now. Perhaps, there seems to be more wear on one side of the piston (exhaust side) compared to the opposite (intake) side.  What just happened to me?   Do I need to get a new piston to rectify this?

C R

Just guessing, I would expect either a cracked piston or it ate a wristpin pad. If it was a ringed engine, then I'd expand the options to include a broken ring or collapsed ring land. Pull the piston/rod out and look carefully at the piston, wristpin pads, and for scoring in the cylinder bore. Mark the rear of the rod beforehand! Remember that the piston baffle goes on the bypass side, and the high side of the ports goes on the exhaust side!

Additonally, some folks did install ringed McCoy Series 21 piston/cylinders into the earlier redhead or bluehead engines. It's apparently not that difficult to do, so you never know who may have done the conversion in their home shop.  Steve

Can't say specifically, but for such a very short run time, sounds like may be you may have had a bad engine to start with (defective?).

You can find another .29 / .35 Red Head / Blue Head engine fairly easy. They don't go for too much on E-Bay, and you might find someone in the community to reasonably get you another that is in much better shape.

A month ago I won on E-Bay a .35 Blue Head RC (similar crankcase to early 1960's Red Heads - not lightning bolt case) complete with exhaust baffle and RC carb for $15 + $8 shipping. Head paint has tool drawer scuffing but appears to be new inside and never run, so deals are out there. Several years ago I found a .19 Red Head with tool drawer rash that had been unrun, too.

Sorry to hear of the bad breaks, Christopher, hope all things work out for you.

We know that all things work together for good for those who love God, to those who are called according to his purpose.

Or it sucked up some debris from the original machining, or found its way inside since then. Usually, stuff gets sucked through the gas path, and gets stuck on the way out.

Brett, back in the 1980's I purchased on close out from now defunct Hobby Shack in Fountain Valley, CA, 2 brand new Fuji .099S-II ABC engines on closeout. I paid $10.00 each for them. Upon opening the nose on them (they are basically a copy of the Enya .09-III design but with right exhaust instead - the Enya is .099 in displacement although the bore and stroke differ slightly), I found the crankcase had significant aluminum shaving grit from the machining process inside. I promptly disassembled the engines, flushed them out with solvent, then reassembled them. I learned something, that even with the later Japanese engines, you'd think they would be meticulous with cleanliness. (This particular engine is odd in that it is the last of their cross scavenge engines but in ABC, of all things.)

From that point on, I have disassembled every engine I have received to peak inside the crankcase and combustion chamber. Once on E-Bay I've received a used engine with the piston and cylinder installed backwards. It was a fine engine once I corrected that problem. I wonder how much success the previous owner had with it.

Yes, when I look more closely at the cylinder liner, there is a gauge on the exhaust side, near the port.  If anyone has a piston and liner they want to get rid of, let me know!

C R

   I agree with Jim. At this point, you don't have anything to loose, and it's not a Ferrari engine for crying out loud! I would examine the parts and make sure that nothing is stuck in the gouges and grooves and scrape at them with an exacto knife point to dig out anything that may be stuck. Then polish the wounds a little bit to make sure there are no high spots. Rotate the piston in the liner with a some oil to lightly lap it and check the fit. Clean up with solvent, reassemble  and test run. If it works, you have an engine to use while you look for parts or a parts donor. If not, at least you tried! Back in my Kart racing days, we would get a little heavy handed with the mixture needle and seize an engine. I kept a bottle of muratic acid, a battery drill, hone, 600 wet or dry paper, and some spare rings in the tool box. You would be surprised how quick you could do a tear down, clean up, , reassemble and be ready to run by the next heat! The muratic acid was to eat off any aluminum from the piston that was galled to the cylinder wall. Water, vinegar, and baking soda was also a part of the kit. WHen you have nothing to loose otherwise, there is always a way! I got to try the hammer and punch routine on a McCoy one of these days just for giggle and grins.
   Type at you later,
     Dan McEntee

Thank you all!  This advice has been most helpful. I am almost certain that the engine ate a metal chip and seized.  I've polished the inside of the piston cylinder, and the outside of the piston, with crocus cloth. That is making an improvement--I can get the piston perhaps 30%-40% up into the piston sleeve now. I'll try to get to 70-80%, then break it in on the bench again. Just for my curiosity sake, what is the piston made of, cast iron?   Is it heat treated?   Other then the wrist pin attachement, is there any machining in the piston?

    I think it is sintered iron, meaning, it's iron dust compressed into the shape of a piston. At least most McCoys and Johnsons (whose pistons were apparently made by McCoy) of the 50's and early 60's were made that way. It's porous until broken in and you get some carbo/varnish built up to fill the pores.  Otherwise, it's cast iron.

    At this point, it doesn't hurt anything to try, and you might try the brake cylinder hone to help round it out. But don't be too disappointed if you wind up with poor compression.

    In any case, the solution is the same whether you don't try, or if you fail, so nothing to lose. These engines were known to be semi-disposable and were *extremely inexpensive* even by the standards of the day, so decades of reliable service was really never in the plan.

    Still, it's a shame to fall victim to a built-in 60-year-old land mine.

    Brett

It’s good to match expectations (with this engine, low!) with reality!

Christopher, personally I don't take quite a glum outlook on the McCoys and the sintering process isn't as bad as it would seem. After doing a little reading, they use temperatures in the the range of something like 600 - 1100 deg C (1100 - 2000 deg F, cast iron melts at 2200 deg F) or so temperature and pressure fuse the iron particles together.

I guess now you know it doesn't hurt to check an engine's internals (pop the head and back) prior to running. Regarding swarf, I was surprised to read in one of the modeling magazines may be 20 years ago that it was common even with import engines. Recommendation was to inspect engine internals before running.

I don't think anyone is knocking the sintering process. It is an unusual idea for those unfamiliar, but the process works well. For example, beryllium stock is produced by sintering. One of the steps is called HIP, or Hot Isostatic Pressing. It creates the density you want (voidless) so that the stock behaves much like wrought materials. For the McCoy, they were probably taking advantage, cost-wise, of near-net-shape coming out of the mold.

But with a sintered iron part, when you are all done--you still have an iron part. And in a McCoy, you have a mild steel liner, probably a leadloy alloy or similar. These need a bit of clearance to keep from binding. And if the materials are not stress-relieved adequately somewhere along the way, they will warp as they settle in. So the heat cycles during break-in are important. With wrist pins, if the fit is too loose, they get knocked around in the piston. I think you'd rather have the relative motion between the rod and the pin than the pin and the piston.

I should go look at the differences in properties of a fine-grain cast iron like Meehanite vs. a sintered part. It might be interesting....

Dave

PS--One of the guys we were flying with yesterday related a story about a recent break-in run on an old K&B .15.  He fired it up in a test stand and it ran for a minute or so, and seized. The bottom of the liner separated from the top of the liner right thru the ports. I imagine it would take a new piston, liner, rod, maybe wrist pin, etc. to get that one up and running again. It happens....

Regarding pulling off backs and heads for a look see, I guess I was brought up in a different generation. You see, I have no problems with doing it, because somewhere in the life of the engine, I'm going to have to do it anyway. I've done it enough times to be comfortable with it. And, regarding whether there's swarf or not, normally you'd expect that not to happen even in our so called modern engines, but it does happen.

    It happens so rarely that the odds of damaging the engine by taking it apart is vastly higher than saving it from enclosed debris. You aren't that different a generation than I am, but, if this was 1965, and we were talking Fox/McCoy/Johnson/Forster, etc. I would have a different opinion. Now, no way from any mainline manufacturer (OS right now) or the common semi-custom engines (PA and Jett). That pretty much covers it for competitive engines in 2019.

   The reason I say that is that I have seen people who are highly skilled and experienced (including world and national champions) take brand new engines apart to do the old "disassemble/clean/lube" routine, and have the engine never run right again. Or in one case, return the engine to the manufacturer for a refund, get a replacement, have the manufacturer put it back correctly, and beat him with the "defective" engine in a contest. You just paid $500 for an engine to be made for you, do you think Randy or Dub is going to forget to clean it out?

   My other exception would be almost all of the aftermarket reworkers aside from Randy or Dub. There are a few who, hate to say it, are not exactly machinists and not at all careful , and I have seen many "Super Joe Blow 40 Stunt Dremel Tool Specials" eat themselves up in a few runs from debris.

   And I am not sure why you think you will eventually have to take it apart anyway - I haven't taken the backplate off of any of my RO-Jetts at any time, and last removed the head of the #1 engine right after the 2003 TT (*to put it back to the stock setting*  after experimenting both ways on the compression). I have done it many times for rework, and if you know for sure something is wrong, then go ahead, it's not brain surgery, but that's when you don't have any options. I wore out a 40VF (which is A LOT of flights, essentially the entire decade of the 90's) and had never had the head off of it, and only looked when someone asked me how much carbon I had.

     Brett