Compression - front vs back??
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Road Master
Joined: Jan 2006
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Compression - front vs back??
Wondering how close the static pressure/compression should be on my TC88 / 1450 stock engine between the fronk and rear cylinders? My compression gauge measured 150 psi on the front (spark plug looks good) and 120 psi on the rear (but plug has shiny/encrusted black deposits on one area of the plug - probably the portion towards the valves?). Also, get quite a bit less air blowing out the left exhaust versus the right exhaust.
Ideas? Does it sound like I'm having problems with my rear cylinder?
05Ultra, 1450, Stage 1, Turing Exhaust, SERT, and recently dyno'd
Ideas? Does it sound like I'm having problems with my rear cylinder?
05Ultra, 1450, Stage 1, Turing Exhaust, SERT, and recently dyno'd
Tourer
Joined: Feb 2006
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From: Southampton, Pa
RE: Compression - front vs back??
With the compression readings this far off I would try to do a leak down test to see if its a problem with the rings or valves. Readings should usually be within 10% max.
Road Captain
Joined: Mar 2006
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RE: Compression - front vs back??
2005UltraNC I wouldnt tear into the engine just yet as 120psi is still good compression but I do agree that there shouldn't be more than 10% difference between cyls. Make sure you are doing the compression check exactly the same for both cyls. (Both spark plugs removed, Throttle wide open and engine cranked till highest reading is noted) Also use a threaded hose and gauge as opposed to the old style that you held into the spark plug hole. Take the readings several times. Take the readings with the engine warm. If readings are still far apart do a leakdown test as suggested. How many miles are on your bike? Has it been using an excessive amount of oil between changes. Shiny crusty black deposits on plugs are usually oil related. Somewhere I read about "05s" having valve guide seal issues. Your last concern was more exhaust air coming out the right pipe than the left. Well looking at the picture of your bike I see the front cyl and rear cyl running to the right muffler where as the rear cylinder has a crossover that only feeds the left muffler. I think the bottom line here is if the bike is running good I wouldnt be too concerned with anything till winter but others may disagree..................BG
RE: Compression - front vs back??
Don't worry about the pressure coming out of your exhaust. You will always get about 80% out of your right due to the cross over. Your cylinders should be close to the same pressure though. I would watch it and let the dealer know what is going on. How many miles did you have on it before you dyno'd it?
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Road Master
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RE: Compression - front vs back??
Thanks guys - sort of what I was thinking also. Bike had about 9K when I did the stage 1 plus exhaust. Rode about another 1400 miles on the canned Stage 1 SERT map (as I understand it's better to "break in the new pipes") before I had it dyno'd.
Stealer dyno'd the bike - AFR flat line below 14 - thinking I'm now running a bit rich. Non-the-less, still think my rear cylinder is having problems.
Will watch and get into the stealer ASAP - still under warranty. Also, fuel gauge still not accurate (sits on 150 miles with 1/2 tank - wish I could get that sort of MPG) - going in for the fifth time.
Bruce
Stealer dyno'd the bike - AFR flat line below 14 - thinking I'm now running a bit rich. Non-the-less, still think my rear cylinder is having problems.
Will watch and get into the stealer ASAP - still under warranty. Also, fuel gauge still not accurate (sits on 150 miles with 1/2 tank - wish I could get that sort of MPG) - going in for the fifth time.
Bruce
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