Compression test
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Joined: Feb 2026
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Compression test
Thank you all
I ran a compression test on my 07 Dyna wide glide. My numbers was 200 on front cylinder and exactly 200 on rear, I know my numbers match up. Very happy. What I was wondering is what is the normal max pressure on the cylinders. Anybody do a compression check what was your starting your highest pressure?
Thank you, Howard
I ran a compression test on my 07 Dyna wide glide. My numbers was 200 on front cylinder and exactly 200 on rear, I know my numbers match up. Very happy. What I was wondering is what is the normal max pressure on the cylinders. Anybody do a compression check what was your starting your highest pressure?
Thank you, Howard
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Yes sr very happy with match, also used my bore scope and can see cross hatch. Bike only has 16000 miles, I just bought it 4 months ago. Traded owner my KLR 650. my Harley was never used by him so it was sitting collecting dust. Was very happy about the equalization, but also surprised by the amount of compression. It had expected it to only be around 180 psi. thought these bikes were low compression, anyways I was just trying to find out what’s a normal compression pressure on a Harley. I don’t mind at least 9 1/2 to one. Thank you again, sir and you have a blessed day.
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Joined: Jul 2024
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From: Ca.
"~170–210 PSI cranking compression (depends heavily on cam and model)" For an M8 by chat gpt.
My understanding showed me in an old Honda spec book, most engines showed (153 - 187) PSI. The way I read the abstract was adding both together then divided it, showed me its blueprinted compression as 170. Back to the abstract showed me that 153 was the cutoff number to rebuild the top end.
Now scan thru a Ducati shop manual showing me in cap letters, POOR right next to the number 150 psi. This made me think that 150 is the cutoff for most bike engines or engines in general... abstract wise.
So this shows me now that 190 psi is your blueprinted number for your bike. So when you take a reading down the road and it reads 150 Pea Yes I said, it is due for a top end rebuild.
I prefer a leak down test myself. I was given a bike with 20k miles on it and it sat for about 30yrs in a garage. I used a LD test on fresh rebuilds and it would read 2%. The sitter blew down 4% in each cylinder and knew I had a runner. It also came with a factory shop manual, as if I needed help at that website... they threw me off LOL.
My understanding showed me in an old Honda spec book, most engines showed (153 - 187) PSI. The way I read the abstract was adding both together then divided it, showed me its blueprinted compression as 170. Back to the abstract showed me that 153 was the cutoff number to rebuild the top end.
Now scan thru a Ducati shop manual showing me in cap letters, POOR right next to the number 150 psi. This made me think that 150 is the cutoff for most bike engines or engines in general... abstract wise.
So this shows me now that 190 psi is your blueprinted number for your bike. So when you take a reading down the road and it reads 150 Pea Yes I said, it is due for a top end rebuild.
I prefer a leak down test myself. I was given a bike with 20k miles on it and it sat for about 30yrs in a garage. I used a LD test on fresh rebuilds and it would read 2%. The sitter blew down 4% in each cylinder and knew I had a runner. It also came with a factory shop manual, as if I needed help at that website... they threw me off LOL.
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Joined: Aug 2018
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From: Stockholm
Do you know if anything is done to your engine? I mean if it is a stock cam and the heads are not milled, 200 psi is a lot. I have noticed that meters differ and to know your engines exact psi, you should have your meter tested or calibrated. During the test, the plug should be uninstalled in the other cylinder and the throttle should be wide open. Also the battery should be fully charged. One thing that increases compression is carbon build up. When this is said, the fact that the pressures are even tells your engine is healthy.
Last edited by OakMountainRider; Feb 16, 2026 at 08:24 AM.
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From: South Carolina
When working on a Honda, use a Honda manual...
What matters here is what the Harley Davidson service manual calls out as acceptable readings.
100 psi. minimum, no more than 10% difference between cylinders.
In my opinion the leakdown test is an archaic way of testing an engine`s compression, it is a holdover from aircraft maintenance.
A leakdown test only measures the leakage with the piston and rings in one stationary position (TDC) and are often not repeatable between engine runs (but it can be a great tool to use to sell aircraft engine cylinders to aircraft owners
).
The best way to check an engine`s condition is a borescope inspection and a compression check.
If the compression is low use a leak down tester to push air into the cylinder so you can hear where it is leaking out, you don`t even need gauges on the tester for this.
What matters here is what the Harley Davidson service manual calls out as acceptable readings.
100 psi. minimum, no more than 10% difference between cylinders.
In my opinion the leakdown test is an archaic way of testing an engine`s compression, it is a holdover from aircraft maintenance.
A leakdown test only measures the leakage with the piston and rings in one stationary position (TDC) and are often not repeatable between engine runs (but it can be a great tool to use to sell aircraft engine cylinders to aircraft owners
).The best way to check an engine`s condition is a borescope inspection and a compression check.
If the compression is low use a leak down tester to push air into the cylinder so you can hear where it is leaking out, you don`t even need gauges on the tester for this.
Last edited by Dan89FLSTC; Feb 16, 2026 at 07:12 AM.
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From: South Carolina
The other cylinder`s spark plug should be removed.
Last edited by Dan89FLSTC; Feb 16, 2026 at 07:37 AM.
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From: Bates County MO
Stock 96" from that era cranked 190-194 when they were new, and a small carbon build up would bring that # up another few pounds. Low battery voltage and weak compensators can cause hard starts & starter ring gear damage.
If you're concerned, machining those heads for Automatic Compression Releases (ACR part number is 28861-07A), install them and the wiring harness (70623-06) & activate them via digital tech or your tuner, and starting issues became a distant memory.
If you're concerned, machining those heads for Automatic Compression Releases (ACR part number is 28861-07A), install them and the wiring harness (70623-06) & activate them via digital tech or your tuner, and starting issues became a distant memory.
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You hit the nail on the head, I know my jugs are good. Bike only has 16000 miles. I did bore scope and didn’t see any real carbon build up. Same reading with two different compression gauges / same hose. I do from time to time get a hard start, but I quickly disengage starter. If the motor doesn’t start right up I stop and wait 30 seconds. Don’t want to eat a starter. Thank you sr