4 spark plugs 1984 FLTHC
#11
As far as the compression check goes, I didn't open the throttle at all. Didn't know I was supposed to.(still learning) I'll check it again today if I get time. Thanks for all the input, knowledge is fairly easy to come by on this forum. Lot's of good people with good ideas! Dale - New compression check with throttle wide open, front 145#, rear 140#
Last edited by Learch; 11-21-2008 at 08:51 AM.
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Ben221 (04-19-2020)
#12
Yea, you're good!
Rear is most always less, unless the rear piston is really carboned up bad and/or there's a problem with the front. Anything less than 5% difference is real good - the book says 10% is acceptable.
Mine had about that first time I checked it at 28,000 miles, put another 27K on it before I did the top end, but it was piston rattle rather than low comp. or oil usage that made me want to do it.
And I ran my original plugs 45,000 so I wouldn't worry much about the 2 that are hard to get out - just leave them alone
Ride Safe and enjoy!
Rear is most always less, unless the rear piston is really carboned up bad and/or there's a problem with the front. Anything less than 5% difference is real good - the book says 10% is acceptable.
Mine had about that first time I checked it at 28,000 miles, put another 27K on it before I did the top end, but it was piston rattle rather than low comp. or oil usage that made me want to do it.
And I ran my original plugs 45,000 so I wouldn't worry much about the 2 that are hard to get out - just leave them alone
Ride Safe and enjoy!
#13
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#15
Not to say you don't have domed, high compression pistons. I'm assuming with a domed cut head and domed pistons, one sorta offsets the other. But that arrangement would give more even combustion area in the entire chamber. Again, I'm not up on the "high-peform" stuff.
If you take out the plugs on the primary side and use a tiny light, like a rifle bore light, you could probably see well enough to tell. Main thing is that it runs great!
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Learch-
My 45" flathead with only a 4.75:1 C/R had 90 lbs (before I stroked it)...
For a stock bore evo @ 8.5:1 C/R, 120-145 is good operating compression
Any over-boring will (of course) add additional psi readings.
I'd be glad it runs good, & ride when ya can...
My 45" flathead with only a 4.75:1 C/R had 90 lbs (before I stroked it)...
For a stock bore evo @ 8.5:1 C/R, 120-145 is good operating compression
Any over-boring will (of course) add additional psi readings.
I'd be glad it runs good, & ride when ya can...
Last edited by Buddy7394; 11-26-2008 at 01:21 AM.
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