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Author Topic: ST60 ABC Piston and liner  (Read 272 times)

Offline Greg L Bahrman

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ST60 ABC Piston and liner
« on: August 23, 2017, 03:50:12 PM »
I have bought several of these p/l for different motors from Brian Gardner bristuntataaptdotnetdotau. Although I've had them for several years I've never actually ran one. For the passed two years I've been flying a 64 oz. Sig Magnum with a Tom Lay ST60. It works fine so I really don't have any reason to change. One of my close flying buddies Bill Barber has been bugging me for quite some time to swap out the motor for an ABC unit just to see how it performs compared to what's in it now. The swap was easy except the needle was off a little as Tom liked to put the needle thru the center of the venturi. I normally run a wood Brodak 13 X 5 prop but for the breakin I put an 11 X 5 on. I ran 4 tanks of 6 ounces of fuel thru it on the ground. 3 tanks with the 11 X 5 and the forth tank with the 13 X 5. The first two tanks spit out black oil. The third tank you could see the darkness of the oil was already starting to lighten up and the forth tank the oil came out almost all clear. At this point I'm thinking it's ready to go in the air. The new ABC unit started easy enough but the main problem I had was it would back fire and the prop would come loose., something that never happened with the Tom Lay ring motor. I double nutted the prop to eliminate that problem.
We put the first three flights on it this morning. The fuel is 10% nitro,11% castor and 11% synthetic. Same fuel I used in the Tom Lay unit. I set the needle so the motor was cackleing back and forth between 2 stroke and 4 stroke and with a wave of my hand it was on its way. Half a lap and it dropped into a solid 4 stroke in level flight. As I flew the pattern it seemed to be more intelligent than the Tom Lay motor as it never failed to switch into 2 stroke mode as soon as the motor was loaded or the nosed was raised more than a second or two and immediately returned as soon as the plane was leveled. After three flights I felt they were the best three flights I had ever put on this airframe. Power wise it's really hard to tell. My lap times with the ABC unit were 5 to 5.2 a lap which is where I like it. So as a summery I'm really happy with the ABC unit. I actually like it better than the Tom Lay unit. Nothing wrong with the Tom Lay motor I just like the ABC motor better IMHO. The Tom Lay motor likes to be started a little on the sloppy side of rich where as the ABC unit I could start it with one pull through with my finger on the venturi and it was ready to go. After seven tanks of fuel it's still producing clear oil out the exhaust. I'm hoping as the ABC unit gets more flights on it that the fuel mileage will get better. Right now the engine quits after the first loop of the clover kind of like a cut off loop. Just my experience with the ABC unit. I'm not an expert and don't pretend to be one. My ABC motor was assembled by Randy Smith with his venturi and needle and whatever else he does to them. If I do another I will send it to Randy. Just an old man (75) having fun.

I been giving it more thought as to why I preferred the ABC motor. It was more consistent from the first lap to the last. My Tom Lay motor tended to speed up towards the end of the flight. It's really not a fair comparison because they had different needles and different venturi's and I think even the heads might be different. That being said I"m still sticking with the ABC motor for awhile. I will follow up with more as I get more flights on the ABC motor.
« Last Edit: August 24, 2017, 06:06:36 PM by Greg L Bahrman »
Greg Bahrman, AMA 312522
Simi Valley, Ca.




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