A very special specialoid

davidd

davidd

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Here is a photo of the last Specialoid piston that was run in the Flash. During the 1972 season, the bearing races walked out of the journals. The Flash engine was removed and stripped. The engine from Don Jone's side car rig was removed and the Flash components, but not the flywheel, were installed in the Comet engine. The engine did pretty well for the rest of the season until the piston came apart. Fortunately, no Flash components were hurt in the making of these photos.

Failure_1.jpg


Failure_2.jpg


Failure_3.jpg


David
 
Bill Thomas

Bill Thomas

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Hello David, Any idea why? I thought Specialoids were the best, Like Brick Toilets !! I Still run them in my bikes, And I have run the Big ones on petrol !!, The amount that sticks out the top of the barrel has to be seen !! All The Best Bill.
 
Howard

Howard

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I've still got an 11:1 Specialoid I took out of the racer, it has a very fine crack in the gudgin pin bore, so they weren't all perfect.

H
 
davidd

davidd

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Bill Thomas said:
Hello David, Any idea why? I thought Specialoids were the best, Like Brick Toilets !! I Still run them in my bikes, And I have run the Big ones on petrol !!, The amount that sticks out the top of the barrel has to be seen !! All The Best Bill.
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Coburn Benson, who built an tuned the engine, came to the conclusion that there was a very minor amount of play in the lower end that throughout the season caused higher than normal stress on the piston. He was using 8000 as a redline, but it turned out that the chronometric was lagging slightly and he estimated that the engine was running up to 8300. He speculated that the piston separated at the pin (maybe aided by one of those cracks that Howard noticed) and then the con rod rose outside the barrel until it hit the lip at the crank case mouth and bent.

I think the Specialiods were great for their time, but as someone who changes out hubs, brake drums and brake plates in the interest of safety, I would not run a Specialoid piston today, at least in a performance engine.

David
 
davidd

davidd

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vince998 said:
Was the crankcase also damaged David? (by the conrod?)
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Yes. You can see the crack eminating from the contact area. There is no crack on the gasket surface. This is the timing side and that is the front stud you are seeing.

Failure_4.jpg


David
 
davidd

davidd

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mercurycrest said:
Definitely and I'll bet with a long enough bar in the little end of it, so's to twist it back a bit and a fresh bushing, that rod and big end can be used again too!:rolleyes:
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The con rod bend is interesting. I wonder if a Vibrac would have done the same. From what I have been told, it might not.

David
 
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