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Sportster Motorcycle Engine Conversions Advice, questions, and tips for 1200, 1250, 1340, 1450 etc... for Sportster and Buell motorcycle engine conversions

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Old 7th March 2021
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Default 2003 1275 BFH compression?

Getting it out to enjoy some early spring riding! Checked compression, 210 front cylinder and 240 rear. Maybe that's why it seems to vibrate the gas cap loose at the end of the track. Should I yank it apart and raise compression in the front or lower in the rear to get it closer??
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Old 7th March 2021
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Quote:
Originally Posted by painterdude923 View Post
Getting it out to enjoy some early spring riding! Checked compression, 210 front cylinder and 240 rear. Maybe that's why it seems to vibrate the gas cap loose at the end of the track. Should I yank it apart and raise compression in the front or lower in the rear to get it closer??
I’d assume piston height/quench distance was the same on both at assembly?

Cam timing checked?

Did you test compression after you put the 1275 together?

The low cylinder is the suspect.

Perform a leakdown test to determine cylinder condition. Listen if the low cylinder has air escaping the exhaust, intake or crankcase breather.

Now If leakdown is similar and it vibrates bad, I’d start to think about a bent connecting Rod.
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Last edited by Maxeffort; 7th March 2021 at 19:57..
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Old 8th March 2021
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My hot compression was 210-212psi After a year and 3k miles went up to 215-218psi.
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