AP Wasp .061 retrofit

Ken Cook Mon Jun 04, 2012 5:54 pm

A few years ago, the price of the AP .061 was in the $30.00 range. I was reluctant at first as Chinese products aren't on the top of my list. All control line users of this engine were wiring the stock r/c carb open at the time. No one was coming up with a way to introduce a venturi set up for this engine. The stock r/c carb has many air leaks in my opinion. The engine wouldn't initially start for me. It was probably the tightest pinch ABC engine I ever encountered in this displacement.

I removed some of the pinch by lapping in the piston sleeve followed by a thorough cleaning in hot soapy water and nylon bristle brush. I assembled the engine using a 4.6 x 3 APC and proceeded to start break in. I ran the engine up for 2 minutes followed by cool down. This only yielded a high 22k. Knowing that I'm using the stock plug I figured a bit more time on running it in. I knew after a few more runs that the stock carb was the culprit. Removing the carb I found the case has round hole as opposed to the bathtub shaped hole like the Norvel.

This was good news as I figured I could make a adapter and drill and tap the center for the Cox Tee Dee unit. I had a Ace replacement needle valve body for the TD(poor man's Kirn Kraft unit) with the fine threaded needle valve installed. I cut the stem down and soldered a washer onto it so in the event the plane goes into terra firma there would be no needle valve breakage. (fingers crossed)

For the most part, the engine could also be run using the stock TD needle valve and or different size venturi's. I run bladder on all of my engines so I opted for the largest. This setup was quite surprising. The instructions have a rpm rating around 23K. Just using my setup and prop I was above 26k and my launch rpm is about 25800 k. Surprisingly I was turning out some pretty good rpm's on this engine. Ken

andrew Mon Jun 04, 2012 10:39 pm

Sounds like you've got this one dialed in pretty well. There are a couple of other things you can do, if you haven't already, to tweak it a bit more.

The OEM head gaskets on the AP are awful. The COX copper gasket will fit and seals much better than the original.

At high RPM, a Galbreath head/NELSON plug will likely last longer and probably add a few RPM, sometimes 200 to 500.

The cylinder screws are a little brittle --- I replace mine, both AP and NORVEL, with socket head screws that are a little longer. The standard screw for the AP and NORVEL is a 2x5mm. If you will replace it with a 2x8mm, it will extend below the crankcase flange. Should you ever snap one off flush with the case flange, it is almost impossible to get out --- if it extends below the flange, you can back it out with long nose pliers.

andrew

Ken Cook Tue Jun 05, 2012 2:20 am

Hello Andrew, the aluminum shim is terrible. I found that out immediately. My stock plug was short lived. I ended up using Merlin plugs, which jumped the compression up a fair amount and these plugs required yet even more shims. I have a total thickness of .021" of shims . The piston in this engine doesn't come to the top of the cylinder and is down from the top another .020". Every Norvel I have, the piston is almost flush to the top of the cylinder. Generally, if the plugs are blowing, keep adding shims until it stops blowing. I just don't have any other engine with this much space.

I had a total of about 7 -8 shims. Now it hasn't blown anymore plugs but I find that a bit strange. I figured if it's working leave it. I've since removed 1-2 shims and dropped the nitro to 10%. Setting the needle is finicky now as it has to run on the ground prior to launching a few seconds until the engine heats up. If launched prematurely, the engine cools and proceeds to go dead rich and quits. I will also take your advice on the screws. They're very soft in fact you can see one of the screws up front in the pic is slightly buggered due to this. Ken

andrew Tue Jun 05, 2012 1:22 pm

Ken -
One other thing to keep an eye on with the AP is lateral play (not endplay) in the crankshaft. I've also seen some where the oilite bushing seemed to be drilled off center --- it's a little hard to tell since you can get some crankcase flash swaged over the end of the bushing making it appear off center.

The lateral play may not be uniform, in other words, you get more at 90 degrees to the cylinder than in-line with the cylinder. To check, I usually just mount a prop and holding the engine in one hand and prop in the other, rock the prop to sideload the crank, then rotate about 30 degrees and do it again. There's no known fix that I'm aware of, other than a new case or to re-bush the case. Given the nice carb adapter you made, the latter may certainly be an option for you. High castor content fuel seems to help reduce crankshaft blowby as it wears.

From what I've read, the AP Wasp is being discontinued, so stocking up on a few high stress parts may be in order.

Whose combat mount are you using with your AP?

andrew

PS: I think the OEM head shims probably came from a Bud Lite can and were cut out with scissors. Very Happy

Ken Cook Tue Jun 05, 2012 3:11 pm

That's funny you mentioned the play. The bushing completely wore out and egged to the point that I had almost .006" play. I tried to purchase a new case and at the time had no luck. Horizon listed the case and showed it in stock but the shopping cart would double my quanity. I took it over to my friend who has a lathe at his house and he was able to rebush the case. This was actually a pretty neat process. He's installed many bushings in various engines

My father made those particular mounts but they were copied from a set I already owned. He's now retired and I wish he made more of them. Ken

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AP Wasp .061 retrofit

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