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14th January 2020
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Chief Master Mechanic
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Join Date: Sep 2019
Posts: 455 Sportster/Buell Model: XLH Sportster/Buell Year: 1969 Other Motorcycle Model: 111 Ironhorse Outlaw Other Motorcycle Year: 2004
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LOL, I don't feel so bad now almost 500 people have viewed this thread and no one has taken a stab at the math question.
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14th January 2020
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Senior Master Custom Bike Builder
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Join Date: Jun 2008
Location: Cornelius, OR
Posts: 9,504
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Quote:
Originally Posted by RicThompson
I have new S&S 4 and 5/8 stroker pistons and no rings.
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It'll run better if you put some rings in it!
Even a one piece oil ring is better than none. 
__________________
Ryder Rick "I know right from wrong, but sometimes, wrong feels right"
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14th January 2020
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XL FORUM LIFE MEMBER
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Join Date: May 2014
Posts: 1,339 Sportster/Buell Model: xlh Sportster/Buell Year: 1974
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Quote:
Originally Posted by RicThompson
LOL, I don't feel so bad now almost 500 people have viewed this thread and no one has taken a stab at the math question.
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I thought the math question was : How does Dennis Kirk get the numbers given in post one for the ring sets he sells? The numbers given are for 1000 sportsters. I thought the answer as to how they are computed was pretty clear in post #4.
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14th January 2020
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Chief Master Mechanic
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Join Date: Sep 2019
Posts: 455 Sportster/Buell Model: XLH Sportster/Buell Year: 1969 Other Motorcycle Model: 111 Ironhorse Outlaw Other Motorcycle Year: 2004
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Quote:
Originally Posted by ryder rick
It'll run better if you put some rings in it!
Even a one piece oil ring is better than none. 
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Actually no, a one piece oil ring on these short forged pistons would not likely control oil very well at all. A cast one piece oil ring will work with the tight tolerances of a cast piston but set up loose for a forged piston not so well.
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14th January 2020
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Senior Master Custom Bike Builder
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Join Date: Jun 2008
Location: Cornelius, OR
Posts: 9,504
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Ya, I can see how a one piece would not work well on a short piston.
I noticed in other reading that 1 piece rings don't always work well even with a long piston.
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14th January 2020
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XL FORUM LIFE MEMBER
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Join Date: May 2014
Posts: 1,339 Sportster/Buell Model: xlh Sportster/Buell Year: 1974
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Quote:
Originally Posted by RicThompson
…. A cast one piece oil ring will work with the tight tolerances of a cast piston but set up loose for a forged piston not so well.
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This is somewhat of a misconception. Take two pistons with two different rates of expansion. The one with the higher rate of expansion needs more clearance when the engine is cold, but if the clearances are figured right both will have about the same running clearance when hot at operating temperature. So the loose one is no longer loose.
True, shorter skirts don't help with ring seal.
Anyway, I agree, the 3 piece oil ring is better.
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14th January 2020
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Chief Master Mechanic
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Join Date: Sep 2019
Posts: 455 Sportster/Buell Model: XLH Sportster/Buell Year: 1969 Other Motorcycle Model: 111 Ironhorse Outlaw Other Motorcycle Year: 2004
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Quote:
Originally Posted by needspeed
This is somewhat of a misconception. Take two pistons with two different rates of expansion. The one with the higher rate of expansion needs more clearance when the engine is cold, but if the clearances are figured right both will have about the same running clearance when hot at operating temperature. So the loose one is no longer loose.
True, shorter skirts don't help with ring seal.
Anyway, I agree, the 3 piece oil ring is better.
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I have to disagree with you. A cast piston does not thermally expand significantly during normal operation. They can be fit for very close tolerance. I am only concerned with high performance applications utilizing long strokes, short skirts, high heat, piston rock and slap. Not the application for cast pistons nor single cast iron oil rings.
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14th January 2020
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Custom Bike Builder
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Join Date: Dec 2014
Location: Phoenix
Posts: 2,287 Sportster/Buell Model: xlch Sportster/Buell Year: 1964 Sportster/Buell Model #2: XLCH IR EFI Sportster/Buell Year #2: 1971 Other Motorcycle Model: BMW K1200RS Other Motorcycle Year: 2001
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There was an interesting post made by Dr Dick about the difference between cold set up clearances and actual running clearance. it was a very interesting read and it spelled it out pretty clearly. I will try to find it instead of trying to explain through my own recollection.
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14th January 2020
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Senior Custom Bike Builder
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Join Date: Nov 2006
Posts: 2,990 Sportster/Buell Model: KHK Sportster/Buell Year: 1954 Sportster/Buell Model #2: IronHead XLH Sportster/Buell Year #2: 1978 Other Motorcycle Model: XLRTT Other Motorcycle Year: 1966
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Ric,
With maths like yours on post #5:
""900 standard bore is 3.0, 900 standard ring would be 3.005""
I wouldn't want to buy any engine that's been near you!!!!!!!!!!!!!!
Patrick
__________________
Flat Head Forever
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15th January 2020
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Custom Bike Builder
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Join Date: Dec 2014
Location: Phoenix
Posts: 2,287 Sportster/Buell Model: xlch Sportster/Buell Year: 1964 Sportster/Buell Model #2: XLCH IR EFI Sportster/Buell Year #2: 1971 Other Motorcycle Model: BMW K1200RS Other Motorcycle Year: 2001
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Quote:
Originally Posted by Iron Mike
There was an interesting post made by Dr Dick about the difference between cold set up clearances and actual running clearance. it was a very interesting read and it spelled it out pretty clearly. I will try to find it instead of trying to explain through my own recollection.
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Well I cant find it. Basically regarding the proper BENCH clearances used, taking in account expansion rates of given materials, heat applied and derived from power output ect ect, arrives at desired predetermined RUNNING clearances. Maintaining the proper warmup and and initial desired state of tune holds these RUNNING clearances. Straying from one of these variables throws all of it out the window. It does not matter what material you are starting with, it is what clearances you want to maintain in operating conditions.
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