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I finally got around to doing a proper compression test and leakdown test on the '81 Special I picked up recently. Yes, he one with the interesting wiring job on the rear signals. With the engine warmed up and the throttle held wide open, compression was as follows:
#1 125psi
#2 110 psi
#3 75 psi
#4 120 psi
Hmm, that doesn't look too good. The bike seemed to run pretty good when I brought it home, but I suspect it may have been using a bit of oil. There was no noticeable smoke from the muffler, but the level was way down. When I fired it up tonight, I filled the carport with smoke. Not just a bit, but an incredible amount of smoke.
Next step was a leakdown test. My tester calibrates at about 42psi, then the ranges are 10-40 (low), 40-70 (medium), and 70-100 (high) percent leakage.
Test readings came out as follows:
#1 39%
#2 44%
#3 100%
#4 36%
It was clear that the leakage on #1, #2, and #4 was past the rings into the crankcase. With the oil filler plug removed, that is where you could hear the escaping air. Carbs and muffler were quiet. However, on #3, it was obvious the air leakage was all back out through the carb. Both the muffler and the crankcase were quiet.
Clearly, I have an open intake valve in #3 cylinder. My guess is this will probably be just a tight shim. That will be my next job - remove the cam cover and check the valve clearances - especially #3 intake.
The oil burning tonight had me a bit worried too, but the results of the leakdown test make me feel a bit better. The fact that it didn't burn blue on the 4 hour ride home, along with reasonable compression and leakdown results on 3 cylinders tells me the rings are still okay, even if they are a bit tired. I'm sure the 4th cylinder will test okay once the valve closes properly. That makes me believe the valve stem seals are probably shot and tonight's smoke show was a result of the bike sitting for a number of weeks without running. The amount of smoke even seemed to decrease as the engine ran for a few minutes and got warmed up.
More to come....
#1 125psi
#2 110 psi
#3 75 psi
#4 120 psi
Hmm, that doesn't look too good. The bike seemed to run pretty good when I brought it home, but I suspect it may have been using a bit of oil. There was no noticeable smoke from the muffler, but the level was way down. When I fired it up tonight, I filled the carport with smoke. Not just a bit, but an incredible amount of smoke.
Next step was a leakdown test. My tester calibrates at about 42psi, then the ranges are 10-40 (low), 40-70 (medium), and 70-100 (high) percent leakage.
Test readings came out as follows:
#1 39%
#2 44%
#3 100%
#4 36%
It was clear that the leakage on #1, #2, and #4 was past the rings into the crankcase. With the oil filler plug removed, that is where you could hear the escaping air. Carbs and muffler were quiet. However, on #3, it was obvious the air leakage was all back out through the carb. Both the muffler and the crankcase were quiet.
Clearly, I have an open intake valve in #3 cylinder. My guess is this will probably be just a tight shim. That will be my next job - remove the cam cover and check the valve clearances - especially #3 intake.
The oil burning tonight had me a bit worried too, but the results of the leakdown test make me feel a bit better. The fact that it didn't burn blue on the 4 hour ride home, along with reasonable compression and leakdown results on 3 cylinders tells me the rings are still okay, even if they are a bit tired. I'm sure the 4th cylinder will test okay once the valve closes properly. That makes me believe the valve stem seals are probably shot and tonight's smoke show was a result of the bike sitting for a number of weeks without running. The amount of smoke even seemed to decrease as the engine ran for a few minutes and got warmed up.
More to come....
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