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Compression Test Results - PSI Correct?

sal@dmoto

sal@dmoto

AFM#434
Joined
Aug 26, 2015
Location
San Francisco, CA
Moto(s)
2011 R6 Race
Name
Sal
My bike had some overheating issues last season due to some issues with the coolant system (all taken care of now). I haven't had a chance to run the bike through its paces since the season ended so I decided to run a compression test to see if everything is ok inside.

Rented a tester from O'Reilly's (had to buy an adapter for our tiny threads) and my numbers were as follows

Cyl 1: 150 psi
Cyl 2: 150 psi
Cyl 3: 149 psi
Cyl 4: 146 psi

(2006 CBR600RR, basically stock motor, unknown miles)

Now my question is this, are these numbers ok? I've read different things online, like I should be around the 150psi mark, but the service manual says 178 psi. However I've also seen that the number could be lower depending on the tester itself and that I can't be 100% unless I did a leak down test or something of that sort.

I know that you want each cylinder to be within 5% of the others (7.5psi in my case) and I at least have consistency across the board.

Any reason for concern or should I be ok?

Thanks
 
sal@dmoto said:
My bike had some overheating issues last season due to some issues with the coolant system (all taken care of now). I haven't had a chance to run the bike through its paces since the season ended so I decided to run a compression test to see if everything is ok inside.

Rented a tester from O'Reilly's (had to buy an adapter for our tiny threads) and my numbers were as follows

Cyl 1: 150 psi
Cyl 2: 150 psi
Cyl 3: 149 psi
Cyl 4: 146 psi

(2006 CBR600RR, basically stock motor, unknown miles)

Now my question is this, are these numbers ok? I've read different things online, like I should be around the 150psi mark, but the service manual says 178 psi. However I've also seen that the number could be lower depending on the tester itself and that I can't be 100% unless I did a leak down test or something of that sort.

I know that you want each cylinder to be within 5% of the others (7.5psi in my case) and I at least have consistency across the board.

Any reason for concern or should I be ok?

Thanks
Click to expand...

When I doubt the tester is reading too low, I just check a cylinder each on one or two of my other vehicles.

Edit: u had the throttle wide open when testing.. Right?
 
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Good call. kind of a pain to get to on my car but I should have thought of that when I had it around...

Yup! Wide open. Ran a couple tests fuel/spark disconnected, throttle open. Averaged the results
 
I don't know if those results are good. I am used to seeing close to 200 psi on most of my bikes that I have tested.

I'd assume that the tester was reading low since you got consistent numbers across the board.

Then again I'd think a well maintained engine will wear evenly and compression will reduce similarly across all cylinders.

I am an amateur when it comes to mechanic stuff. So I'll wait for someone more experienced to chime in.
 
Given the variability in the tester itself, the technique, and that each cylinder will wear/age differently, I'd say you're good to go. If one cylinder was considerably off from the others, I'd say you might have a problem, but that spread looks normal for a used motor.
 
the spread looks good. unless you have numbers to compare with you need to do a leakdown test to get a better idea.
 
+1 on leakdown. If the bike runs to begin with, a compression test is almost useless in diagnosing where the sealing issue happens. Leak down testing is seriously a pro mechanic's biggest secret. It's really unfortunate that your typical auto parts store don't carry 'em.
 
The variance is nearly perfect. Was it up to temp? IIRC, it should be in the 170# range.
 
PSI figures seem low, my 14.6:1 RSV4 does 262psi
 
14.6:1?

Wow that seems high!
 
Karbon said:
+1 on leakdown. If the bike runs to begin with, a compression test is almost useless in diagnosing where the sealing issue happens. Leak down testing is seriously a pro mechanic's biggest secret. It's really unfortunate that your typical auto parts store don't carry 'em.
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compression tests are such a waste of time. LEAKDOWN FTMFW!!!!!!!!!!!!!!!!!!
 
Compression tests are good for a general (and somewhat vague) sense of engine health. As mentioned, a leak down test is superior for telling you what's going on and where problems may be.

Also note that many things can affect compression readings and even if a bike is in perfect new condition, there will still be differences from cylinder to cylinder. And it's no good comparing the readings from one bike to a different bike. Things like compression ratio, intake and exhaust tract efficiency, cam lift and timing, valve lash settings, ring design and where the ring gap is positioned, etc., etc., will all have an effect on the readings.

OP: For a street bike the readings seem decent. Ride and enjoy.
 
ST Guy said:
Compression tests are good for a general (and somewhat vague) sense of engine health.
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:rofl a no! a compression test is about the same as a meter that tells how much air you blow into a balloon...... with a hole in it. it doesn't give any indication of overall motor health. it tells you how much air the piston pushes on the up stroke. compression tests are for idiots!
 
elskipador said:
:rofl a no! a compression test is about the same as a meter that tells how much air you blow into a balloon...... with a hole in it. it doesn't give any indication of overall motor health. it tells you how much air the piston pushes on the up stroke. compression tests are for idiots!
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What a load of shit. Compression tests are very useful. And one of the easiest ways to lead you to a problem. If they were so useless, service manuals would point you in that direction first.
 
I think the key thing about compression tests are they are fast and easy. It takes more skill to setup a leak down test and more tools. It's a better test for sure BUT not all folks are exactly good mechanics. For me it's just another tool in the toolbox. At the shop it's all leak down tests as all my tools are there. In the field I throw the compression tester on there to see if I need to go get the leak down tools and come back before I tear into it any further. Simple.
 
msethhunter said:
What a load of shit. Compression tests are very useful. And one of the easiest ways to lead you to a problem. If they were so useless, service manuals would point you in that direction first.
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Service manual say lots of things that are far from correct. My OEM cbr manual says the fork cartridges aren't serviceable, but in actuality they're completely serviceable. As Jim pointed out, its about the knowledge of the mechanic, & I just don't have time to waste of silly tests that don't tell you any real info, other than "there's a problem" to which you will then need to do more testing. I'll stick with just using the much more useful test.
 
elskipador said:
Service manual say lots of things that are far from correct. My OEM cbr manual says the fork cartridges aren't serviceable, but in actuality they're completely serviceable. As Jim pointed out, its about the knowledge of the mechanic, & I just don't have time to waste of silly tests that don't tell you any real info, other than "there's a problem" to which you will then need to do more testing. I'll stick with just using the much more useful test.
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Do what you want. But calling a compression test usless is factually wrong. It's a starting point, that will lead you to which cylinder to do a leak down on.

I spent 9 years turning WRENCHES at dealerships before I changed careers. I'll stick to what the industry recommends, and follow the service manual. The manual also says that you can overhaul/repair engines. But most people buy used instead of repairing what they have.
 
compression test is a quick way to show a leaking or blown HG or issues with a cylinder. I used it for years.

leakdown is useful for gauging the overall health of the engine

since the OP didn't find a problem with one cylinder and he's questioning the overall health of the cylinder leakdown should be done.
 
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msethhunter said:
Do what you want. But calling a compression test usless is factually wrong. It's a starting point, that will lead you to which cylinder to do a leak down on.

I spent 9 years turning WRENCHES at dealerships...
Click to expand...

Well yay for that. Shawn has wrenched on race bikes that are in considerably higher states of tune, as well as innumerable stock engines. When you're a go-to forum mechanic then you can trash talk. Until then you're nothing but a hater. :twofinger

buellistic said:
Rings my be dry
Squirt some oil down and do it again.
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How can rings be dry? There's always an oil film on the cylinder walls. :dunno
 
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