Unbelievable Crank Case Pressure

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After fitting some pistons I had around here with new gapless rings and discovering the top lands were very close to the wrist pins which resulted in a 1/4"distance from the top of the piston to the top of the barrels at TDC, I thought it should give the old Norton an easy long life with such low compression. I has also installed a special crank seal from the aviation industry which had 6 fine contact surfaces instead of the usual 1 where the circular seal presses the rubber into the crank shaft. I was told it would be leak proof. However what I didn't anticipate was the increase in crank case pressure on the other side of the pistons as this inadvertently increased the compression rate below the pistons. Aside from lacking much power I noticed oil everywhere and oil tank farts when shutting down. The chaincase oil had bits of metal and was black from the ground down rubber of the seal. The seal was pushed clear into the engine sprocket where it was ground to nothing.

Unbelievable Crank Case Pressure
 
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RennieK said:
After fitting some pistons I had around here with new gapless rings and discovering the top lands were very close to the wrist pins which resulted in a 1/4"distance from the top of the piston to the top of the barrels at TDC, I thought it should give the old Norton an easy long life with such low compression. I has also installed a special crank seal from the aviation industry which had 6 fine contact surfaces instead of the usual 1 where the circular seal presses the rubber into the crank shaft. I was told it would be leak proof. However what I didn't anticipate was the increase in crank case pressure on the other side of the pistons as this inadvertently increased the compression rate below the pistons. Aside from lacking much power I noticed oil everywhere and oil tank farts when shutting down. The chaincase oil had bits of metal and was black from the ground down rubber of the seal. The seal was pushed clear into the engine sprocket where it was ground to nothing.

Unbelievable Crank Case Pressure


No no will not continue the thread promise :)
 
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The seal was ovbviously not intended for this type of usage, if it was ground to scrap. There is a fine line between a perfect seal and too much friction, and this looks like a case of the latter. If, in all the years of production, virtually the same type of seal was used (not to mention racing) why fix what wasn't broken?
 
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Danno said:
The seal was ovbviously not intended for this type of usage, if it was ground to scrap. There is a fine line between a perfect seal and too much friction, and this looks like a case of the latter. If, in all the years of production, virtually the same type of seal was used (not to mention racing) why fix what wasn't broken?

I think he was just baiting someone into another crankcase breather discussion. :roll:
 
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nortonspeed said:
April 01 :!: :?:
Do you know something about this?. Looks to be a spoof on all the breather posts.

This looks to be an issue where the inner race pushed through the machined surface for the seal. Possible the inner race beinging galled on the crankshaft and the cases tightened up together or from hammering on it from the timing side. POP!

Internal pressure? Good one!
 
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I reckon that someone fitted a pcv to the primary chaincase and it sucked the rollers out :shock:
 
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I think Harley big twins use the chaincase volume to help mitigate case pressure.
 

rvich

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Too bad you don't have an extra set of plugs installed in the case, you would practically have a Wankel!
 
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nortonspeed said:
April 01 :!: :?:
You Nailed it nortonspeed, it's my attempt at an April Fools Joke! I didn't expect to drag this on but my internet provider was working on the pole outside just when I was posting and they screwed my internet till just now.

In reality the damage was from a green horn drifting out the seal from the inside but they didn't realize they were pounding on the case itself.
 
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