The installation trick for the new guys is to get them slightly undersize
and stretch them over a plywood form for a few days so they lie in the slot
perfectly when assembly the engine. They tend to take a set once they
sit around in a given position. This was discovered after Don installed
his O-rings and his o-rings might have been slightly oversize.

Paul Lamar

So are the ones Bruce T sells a littel undersize, and I need to stretch
them, or should I Ebay these and get smaller ones? I haven't assebled the
motor yet, but it was a bad (stock) Oring that caused the motor to die in
the first place.

Mike Harrington

How much under size is the over all diameter of the O-ring Mike?
If it is less than about 5% it is best to stretch them slightly. 
The exact dimension is not important as long as you can stretch them
slightly.

The very important dimension is the section diameter.

Going on Bill's recommendations to not completely fill the slot
what is the section diameter of the ones Bruce T sent?
I measure the outer slot width at .130 inch and 0.070 inch deep.

What do your outer O-ring section diameter measure Don?

Looking at the Creavey catalog I just uploaded it looks like
a 0.098 or 0.093 section diameter is called for. 
Note this is not a 3/32 section diameter O-ring. A 3/32 O-ring is 
actually well over .11 and may be too large. McMaster Carr only sells
the 3/32 section diameter which may be too large for the outer slot.
I know that was the case for the oil scraper O-rings.
Best to order the exact size directly from Creavey.

The outer slot dimensions are 305 mm ( 12 inches) top to bottom and 
248 mm (9.76 inches) side to side. These measurements are inner 
slot wall to inner slot wall.

The inner slot is 191 mm (7.52 inches) across and 248 mm (9.76 inches) 
top to bottom. Interesting.

These measurements are inner slot wall to inner slot wall.
In other words it is an elongated circle with a radius of
about 95 mm (3.74 inches) at both top and bottom.

The inner slot width is a bit wider at .150 inches.
This could be why the 3/32 section diameter rings work from McMaster Carr.

The depth of the inner slot is about the same at .070 inches.
The same 0.098 or 0.093 section diameter is called for.

Check my measurements carefully on your engine.


Paul Lamar
 
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