Minimum cylinder pressure
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Intermediate
Joined: Jun 2012
Posts: 37
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From: SW Ohio
Minimum cylinder pressure
99 EVO engine, at least 48K miles - giving me hell not starting when it is cold. Only hits on front cylinder. Done all of the ignition checks (plugs, wires, swaps, etc), all AOK. Checked rear cylinder pressure - 88 pounds - did the oil-add - same. No, haven't checked front, have to remove tank to get tester in place. Am I at the point of needing heads done? Dumb question - can heads be removed without pulling engine? Thanks.
Dirt don't hurt
Joined: Jan 2011
Posts: 21,065
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From: Haslet Texas
99 EVO engine, at least 48K miles - giving me hell not starting when it is cold. Only hits on front cylinder. Done all of the ignition checks (plugs, wires, swaps, etc), all AOK. Checked rear cylinder pressure - 88 pounds - did the oil-add - same. No, haven't checked front, have to remove tank to get tester in place. Am I at the point of needing heads done? Dumb question - can heads be removed without pulling engine? Thanks.
I wouldn't stop at the heads though I would take off the jugs too so that you can inspect them and the pistons as well.
All of this can be done with the motor in the frame.
Road Master
Joined: Oct 2011
Posts: 957
Likes: 2
From: Carlsbad Springs Ontario
cyl. comp. test.
99 EVO engine, at least 48K miles - giving me hell not starting when it is cold. Only hits on front cylinder. Done all of the ignition checks (plugs, wires, swaps, etc), all AOK. Checked rear cylinder pressure - 88 pounds - did the oil-add - same. No, haven't checked front, have to remove tank to get tester in place. Am I at the point of needing heads done? Dumb question - can heads be removed without pulling engine? Thanks.
Your description of " did the oil add - same " dosent compute ?
Correct procedure for cylinder compression test is ... run motor to operating temp., ensure you have a fully charged battery , remove both spark plugs , ground out both spark plug wires or disable coils , install cylinder pres. gauge into spark plug hole , open choke , open throttle completely and hold open , rotate engine for 10 seconds and observe the gauge. Comp. should rise evenly to a maximum reading and stabilize there.
Record the reading and do same for other cylinder.
Next ... add an ounce of motor oil into the cyl. to be checked a second time , wait 5 min. for the oil to migrate , do same procedure as above and record the readings for each cylinder.
Last ... You should show approx. 90 lbs. for each cyl. in the first check.
You should show a higher pres. for each cyl. after the oil added step.
What is important is the difference in readings between both cylinders.
If you see a difference of more than 10-15 lbs. between both cylinders you have a rebuild in your future.
Be advised that a compression test is a start point only. Other inexpensive test procedures are available to specify a particular area of possible problems like valves etc.
Dirt don't hurt
Joined: Jan 2011
Posts: 21,065
Likes: 4,561
From: Haslet Texas
How are you doing your cyl. comp. test ? No reason to remove tank.
Your description of " did the oil add - same " dosent compute ?
Correct procedure for cylinder compression test is ... run motor to operating temp., ensure you have a fully charged battery , remove both spark plugs , ground out both spark plug wires or disable coils , install cylinder pres. gauge into spark plug hole , open choke , open throttle completely and hold open , rotate engine for 10 seconds and observe the gauge. Comp. should rise evenly to a maximum reading and stabilize there.
Record the reading and do same for other cylinder.
Next ... add an ounce of motor oil into the cyl. to be checked a second time , wait 5 min. for the oil to migrate , do same procedure as above and record the readings for each cylinder.
Last ... You should show approx. 90 lbs. for each cyl. in the first check.
You should show a higher pres. for each cyl. after the oil added step.
What is important is the difference in readings between both cylinders.
If you see a difference of more than 10-15 lbs. between both cylinders you have a rebuild in your future.
Be advised that a compression test is a start point only. Other inexpensive test procedures are available to specify a particular area of possible problems like valves etc.
Your description of " did the oil add - same " dosent compute ?
Correct procedure for cylinder compression test is ... run motor to operating temp., ensure you have a fully charged battery , remove both spark plugs , ground out both spark plug wires or disable coils , install cylinder pres. gauge into spark plug hole , open choke , open throttle completely and hold open , rotate engine for 10 seconds and observe the gauge. Comp. should rise evenly to a maximum reading and stabilize there.
Record the reading and do same for other cylinder.
Next ... add an ounce of motor oil into the cyl. to be checked a second time , wait 5 min. for the oil to migrate , do same procedure as above and record the readings for each cylinder.
Last ... You should show approx. 90 lbs. for each cyl. in the first check.
You should show a higher pres. for each cyl. after the oil added step.
What is important is the difference in readings between both cylinders.
If you see a difference of more than 10-15 lbs. between both cylinders you have a rebuild in your future.
Be advised that a compression test is a start point only. Other inexpensive test procedures are available to specify a particular area of possible problems like valves etc.
I haven't checked it after the rebuild but I'm sure it is higher now.
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From: Coromandel Peninsula New Zealand
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Intermediate
Joined: Jun 2012
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From: SW Ohio
Thanks Spanners. Any idea why even with only ~ 88 pounds and everything else obvious checking out that my scoot would fail to hit at all on rear cylinder when it is cold (less that 35 degrees)?
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Thread Starter
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Intermediate
Joined: Jun 2012
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From: SW Ohio
Machinehead - there is no room to thread in the comp test tool on the front cylinder unless I remove the left side tank - borrowed comp tool has very rigid hose and scoot has 5 1/2 - 6 gallon set of fat bobs that force a 45 degree bend of the tubing ~ 3 inches above spark plug bore.
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Joined: Jun 2010
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From: Upstate New York
You should be able to buy a compression tester with a more flexible hose for around $20.
FWIW, my motor currently measures 140# in each cylinder at about 100,000 miles. When new (after break-in) it measured 150# in each cylinder. That's with stock cam.
FWIW, my motor currently measures 140# in each cylinder at about 100,000 miles. When new (after break-in) it measured 150# in each cylinder. That's with stock cam.