Compression test question
#1
#2
#3
You will need a good compression tester; Sears has several that will work well and don't cost an arm and leg.
http://www.sears.com/shc/s/search=co...e=CAT_REC_PRED
Just make sure that whatever you get has the 12mm adapater.
Remove both spark plugs and connect the tester to either cylinder; make sure the connnections are tight. No need for wrenches; the connections are all fitted with o-rings so you just need to get them good and finger tight; no leaks.
If the bike is EFI, hold the throttle wide open and spin the engine; watch the gauge and after about 5-6 strokes, it will stop increasing. Record the reading and repeat on the next cylinder. If the bike is carbureted (CV) the slide is vacuum operated and you can open throttle plate but the slide will not raise without engine vacuum and will restrict the air flow to the cylinder. So, I just pull the carb off; you can leave cables connected, just pull it from the intake and push it to the side to allow unobstructed air flow to the intake so the cylinder can fill. Repeat the above process.
The two cylinders should be within 10psi of each other; a larger variance is an indication that rings are worn, valves are worn or guide seals are failing. If one cyliner reads much lower than another, squirt some motor oil into the cylnder, spin is a bit and take another reading. If the second reading (with oil) shows higher than the first, rings are going. If the reading is the same, valves or guide seals are going. Check the service manual for what the compression should be.
There is a second test to isolate the problem; a leakdown test which will require another tester.
Google search on compression and leakdown test and you will find more information.
http://www.sears.com/shc/s/search=co...e=CAT_REC_PRED
Just make sure that whatever you get has the 12mm adapater.
Remove both spark plugs and connect the tester to either cylinder; make sure the connnections are tight. No need for wrenches; the connections are all fitted with o-rings so you just need to get them good and finger tight; no leaks.
If the bike is EFI, hold the throttle wide open and spin the engine; watch the gauge and after about 5-6 strokes, it will stop increasing. Record the reading and repeat on the next cylinder. If the bike is carbureted (CV) the slide is vacuum operated and you can open throttle plate but the slide will not raise without engine vacuum and will restrict the air flow to the cylinder. So, I just pull the carb off; you can leave cables connected, just pull it from the intake and push it to the side to allow unobstructed air flow to the intake so the cylinder can fill. Repeat the above process.
The two cylinders should be within 10psi of each other; a larger variance is an indication that rings are worn, valves are worn or guide seals are failing. If one cyliner reads much lower than another, squirt some motor oil into the cylnder, spin is a bit and take another reading. If the second reading (with oil) shows higher than the first, rings are going. If the reading is the same, valves or guide seals are going. Check the service manual for what the compression should be.
There is a second test to isolate the problem; a leakdown test which will require another tester.
Google search on compression and leakdown test and you will find more information.
Last edited by djl; 07-16-2012 at 09:59 AM.
#4
#5
8 complete cranks on the starter, battery charger in place, throttle plate wide open.
Scott
Scott
__________________
HILLSIDE MOTORCYCLE & MACHINE, INC.
HARLEY-DAVIDSON SPEED & SERVICE CENTER
5225 SOUTH MAIN ST., MUNNSVILLE, N.Y. 13409
Sales/Support 315-495-6650
www.hillsidecycle.com
Walk-in Retail Showroom
Complete H-D Machine Shop
Case & cylinder boring
Complete Cylinder Head Shop
High-Performance Engine Kits
Crank Rebuilding
Direct Link & PowerVision Tuning
Goodson HD Tooling Manufacturer
Maxton Mile World Record
4500 sq ft. facility
OVER 35 YEARS OF H-D ENGINE BUILDING.
See us on Facebook.
HILLSIDE MOTORCYCLE & MACHINE, INC.
HARLEY-DAVIDSON SPEED & SERVICE CENTER
5225 SOUTH MAIN ST., MUNNSVILLE, N.Y. 13409
Sales/Support 315-495-6650
www.hillsidecycle.com
Walk-in Retail Showroom
Complete H-D Machine Shop
Case & cylinder boring
Complete Cylinder Head Shop
High-Performance Engine Kits
Crank Rebuilding
Direct Link & PowerVision Tuning
Goodson HD Tooling Manufacturer
Maxton Mile World Record
4500 sq ft. facility
OVER 35 YEARS OF H-D ENGINE BUILDING.
See us on Facebook.
#6
I am getting a tester this weekend. looks like a simple procedure enough...The reason i am doing this is recently my bike seems to have a little less ooomph! I was riding on the interstate... about 75-80 mph on cruise control and going up a slight incline it dropped down to 70mph then back up to set speed on level road...
My bike is still under extended warranty but the dealer is backed up for 2 weeks with work...
I'm gonna ride it for the summer and when it get a bit cooler i will drop it off...I am curious about the compression though , it has 72000 miles.
My bike is still under extended warranty but the dealer is backed up for 2 weeks with work...
I'm gonna ride it for the summer and when it get a bit cooler i will drop it off...I am curious about the compression though , it has 72000 miles.
#7
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#8
Well i did the test myself and it was apparently good... dry test at 175 psi on both front and rear... One of the Mechanics at my dealer said it may be the cruise control or the throttle cables??? My plugs were a bit dirty but looked pretty good...I am happy it's not a compression problem but baffled at what is the issue.
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