I got 4 Old Nelsons what are these "Counter Balanced Drive Washers" for?

[robbietrumpet]

HI this Is Robbie Smith, I met a number of you at the Texas Pylon Classic Race last year, I eeked out a win in 424, I had the low wing Yellow planes..

I got my hands on all these old Nelsons. Yeah I know their NOT legal in AMA 426 anymore...there's NO races anywhere in Texas anymore anyway, so I'm just gonna toy with them... Four of these babies will be viable... I might build up a Quickie just for these engines and go out and fly fast, turn left and impress my friends....

QUESTION what are these "Counter Balanced Drive Washers" for?
How do you "CLOCK" them?? Here's a picture of one next to a STOCK one: and a picture of an add for them from 1998:

Could I just put the Stock drive washers ones back on? but I only have two of the stock ones...

Anyone?
Robbie
Any information would be great!
Robbie

[rocket]

What you have there is 5 Nelson 428 Short Stroke Motors. That counter balanced drive washer came in about the same time the short Strokes were going out.

[Joe Tropea]

Hi Robbie:

The point of the counter balance is to offset the mass of the piston assembly at the top/bottom of the stroke. Because this is a single cylinder, this was introduced to minimize vibration. Multi-cylinder engines use opposing pistons to offset vibrations. See attached pic where 2 pistons are always at the top and two at the bottom at the end of a stroke.

To install the counter balance:

1. install a prop loosely on the engine and turn it slowly until you feel it click in one spot. This is Top Dead Center (TDC)
2. Loosen the prop WITHOUT TURNING THE ENGINE
3. Align the notch on the prop washer with the venturi opening
4. set the prop at the 8 and 2 o'clock position
5. tighten the assembly.

Test it by flipping the engine over by hand a few times and bring it back to that TDC "click" and check both the notch and prop position

[robbietrumpet]

Thanks Joe, This is a great explanation... I always thought all engines were balanced within themselves. Single cylinder engines running at high RPM might be a different animal.... I was really racking my brain on this. Now I can feel good about moving forward and running these things...
Robbie