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rc plane crash - 68% pitts challenger robbie skipton at raf cosford

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Denis Watkins23/07/2016 17:42:12
4177 forum posts
83 photos

Just on taper seat guys, both taper and flat seats are parallel threaded.

What changes is the plug seat that originally was flat on our Ford Anglias, but designed tapered to increase the gas/seat surface area for a better seal, so Robbie's motor had the improved version.

But neither are interchangeable, so just the same, you would not get a good seal with a flat seat plug in a taper seat motor

G194023/07/2016 17:52:41
3523 forum posts
1 photos

It puzzles me why losing a plug on one cylinder should cause loss of vital crankcase pressure on the other 3. The only multi cylinder 2 strokes I've had much to with is Scotts and the crankcases are completely isolated from each other as they are on the Scott look-a-like engines and motor cycles manufactured by a friend of ours a few years back (Silk 700s). In fact George Silk was an ace 2 stroke tuner and one of his must dos was improving crankcase compression which he did to great effect. I know plugs whiskered regularly on my 1932 TT Replica and, if I guessed right, I could change the whiskered plug with one of the cleaned ones I kept in my pocket without stopping the engine - or even getting out of the saddle

So on the ZDZ does each cylinder share the same crankcase volume somehow? Not trying to stir things up. I'm merely curious. Or did I completely misunderstand?

Paul Marsh24/09/2016 16:16:01
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3840 forum posts
1110 photos

I asked Robbie why losing one plug would lose the engine - it shares the same crankcase pressure. As it's a two stroke, when that happens, all pressure is lost and fuel shut off. If it was a flat four 4 Stroke, it would run on 3, just a little lumpy on every other stroke (when the dead-side cylinder fires).

That's why it stopped.

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