compression vs. leakdown - weird results
05-27-2008, 11:49 PM
#1
Junior Member
Squid
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Join Date: May 2008
Posts: 5
compression vs. leakdown - weird results
Background -
I have had my VTR in storage for two years, carport under a cover. I live by the coast, and the salt air chews up everything. Got the bike cleaned off, test drove it, and dropped it off at the shop for a once over. Fluids, brakes, etc, all changed.
Test drove when I got it back, bike died, returned to shop, bad coil. Then it would not run, lots of testing including a compression and leakdown test. Compression came back as 110 lbs PSI on a cold motor, and leakdown as 4%. The mechanic could not get it running to get the motor warm. End result, bad vacum hose got cracked during tank removal and coil replacement.
Now I am wondering about the compression. Bike has 7K miles, I am responsible for half of them. A compression test of 110 PSI is not good, manual says that 160 PSI is what it should be, but a leakdown of 4% is supposedly very good. I am thinking that these two pieces of information contradict each other.
Any ideas here? The bike is rideable, and feels as powerful as I remember. I had a passenger, and I still roll on to 100 mph very easily. I am thinking that one of the tests is bad at this point.
I have had my VTR in storage for two years, carport under a cover. I live by the coast, and the salt air chews up everything. Got the bike cleaned off, test drove it, and dropped it off at the shop for a once over. Fluids, brakes, etc, all changed.
Test drove when I got it back, bike died, returned to shop, bad coil. Then it would not run, lots of testing including a compression and leakdown test. Compression came back as 110 lbs PSI on a cold motor, and leakdown as 4%. The mechanic could not get it running to get the motor warm. End result, bad vacum hose got cracked during tank removal and coil replacement.
Now I am wondering about the compression. Bike has 7K miles, I am responsible for half of them. A compression test of 110 PSI is not good, manual says that 160 PSI is what it should be, but a leakdown of 4% is supposedly very good. I am thinking that these two pieces of information contradict each other.
Any ideas here? The bike is rideable, and feels as powerful as I remember. I had a passenger, and I still roll on to 100 mph very easily. I am thinking that one of the tests is bad at this point.
05-28-2008, 04:26 AM
#2
Senior Member
Superstock
Join Date: Apr 2007
Location: Warren, NH
Posts: 284
The leak down test is testing different things than the compression. I have seen a good leak down test with a low compression motor. The leak down test is testing more the oil rings on the piston than the compresion rings. You can have bad oil rings and still have good compression. The compression number is low, but I would ride it and put some miles on and then recheck it. A bike that has been sitting for as long as your did mite have a ring that is partialy stuck (aluminum piston/steel ring/salt air).
05-28-2008, 08:17 PM
#5
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World Champion
Join Date: Dec 2004
Location: Fulton, MO
Posts: 105,287
And that's why you should do the tests with the motor warm! Your results WILL be off with a cold motor.
If you still think you have a stuck ring after getting a good, correct test then take some Marvel Mystery oil, about an ounce or so and pour it into each cylinder and leave it overnight. Then crank the motor with the plugs out and a towel over the plug holes to get the oil out. Reinstall plugs and restart. It will smoke a bit at first (understatement).
If you still think you have a stuck ring after getting a good, correct test then take some Marvel Mystery oil, about an ounce or so and pour it into each cylinder and leave it overnight. Then crank the motor with the plugs out and a towel over the plug holes to get the oil out. Reinstall plugs and restart. It will smoke a bit at first (understatement).
05-28-2008, 09:16 PM
#8
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Squid
Thread Starter
Join Date: May 2008
Posts: 5
Did 100 mile break-in trip today, no issues. Did some city riding, got the temp up to "halfway" on the indicator (2000 VTR model). Overall, avg speed was 80 to 85 mph, hard to keep it there, wanted to go faster. Ended trip at the gas station I started at, averaged 34 mpg.
I don't think the compression test was done correctly. Does anyone have a recommendation for a compression tester? I would like to buy one online, and check again after a few more rides.
I don't think the compression test was done correctly. Does anyone have a recommendation for a compression tester? I would like to buy one online, and check again after a few more rides.
05-29-2008, 12:37 AM
#9
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MotoGP
Join Date: May 2005
Posts: 2,708
Did 100 mile break-in trip today, no issues. Did some city riding, got the temp up to "halfway" on the indicator (2000 VTR model). Overall, avg speed was 80 to 85 mph, hard to keep it there, wanted to go faster. Ended trip at the gas station I started at, averaged 34 mpg.
I don't think the compression test was done correctly. Does anyone have a recommendation for a compression tester? I would like to buy one online, and check again after a few more rides.
I don't think the compression test was done correctly. Does anyone have a recommendation for a compression tester? I would like to buy one online, and check again after a few more rides.
With the way you say it's running (good) and the results of the leak down test (4%)... I'd guess that the compression test was bogus. It's kinda weird that they could correctly do a leak down test but botch a compression test...
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