Minimum recommended compression. Is this a big problem?

[Pavel]

Hi all, i want to buy MT-07, it will be my first motorcycle. I found a good option IMO and when we started to check compression via tester it appears that 1 cylinder  has 7.8 kgf/cm2 and second has 7.1 kgf/cm2. And service manual says that is almost min required (attached photo of service min-max).  Master who was helping me said to me that air filter may be cause of low compression and if i follow all service requirements - compression won't go lower. MT-07 2017, 20 k miles. They sell it below average price around 10 - 15%. What do you think?  

[Triple Jim]

Well, it's within the max-min specification, so there is no big problem.  Was the throttle held wide open for the test?  The air filter shouldn't have any significant effect at cranking speed, but if the throttle wasn't open it'll read low.  Also, if it has been sitting around for a long time, like months, it could read a little low until it's run a little while.

It's getting close to the mileage of the first valve adjustment.  Do you know if that has been done?

Also, the manual specifies checking the compression with the engine warmed up.  Was it warm?

Edited July 25, 2021 by Triple Jim

[Pavel]

8 hours ago, Triple Jim said:

Was the throttle held wide open for the test? 

Yes, it was completely open. We even double checked.

8 hours ago, Triple Jim said:

Also, if it has been sitting around for a long time, like months, it could read a little low until it's run a little while.

It stayed there for 4-5 months, but they said they were riding it for about one week.
 

8 hours ago, Triple Jim said:

It's getting close to the mileage of the first valve adjustment.  Do you know if that has been done?

No, I don't know, is this very complicated process?

8 hours ago, Triple Jim said:

Also, the manual specifies checking the compression with the engine warmed up.  Was it warm?

Yes, we warmed it up for about 10 minutes and even did a test drive.

Also i wanted to mention that, when we were listening how engine works and holding high revs - 'check engine' light turned on. Then we did a test drive and it disappeared. Very odd.

[Triple Jim]

6 hours ago, Pavel said:

15 hours ago, Triple Jim said:

It's getting close to the mileage of the first valve adjustment.  Do you know if that has been done?

No, I don't know, is this very complicated process?

It's around "moderately complicated".  I'm sure you can find a video about it, and it's in the shop manual.  If the low pressures are due to valves, it's a coincidence that both cylinders are equally near the lower limit though.

I'd probably not buy that one.  I don't think it's a piece of junk or anything, but I wouldn't want to get involved with the lowish compression and the mystery "check engine" light when I could probably get one in better condition for a few more dollars.

Edited July 26, 2021 by Triple Jim

[shinyribs]

Was there a diagnostic code that came on with the check engine light? Something on the dash that said "5D- xx" , the xx being another pair of numbers.

Was the air filter stock or an aftermarket one? Many people don't properly maintain aftermarket gauze type air filters, and that makes them famous for ingesting dust which leads to low compression. Knowing what the spark plugs looked like when you had them out should give you clues if the rings were hurt or not. 

Also, do you 100% trust the reading of  your compression tester gauge? 

[wrxer]

Are you at sea level?

[Pavel]

6 hours ago, wrxer said:

Are you at sea level?

40 m above sea level

[Pavel]

17 hours ago, shinyribs said:

Was there a diagnostic code that came on with the check engine light? Something on the dash that said "5D- xx" , the xx being another pair of numbers.

No, i checked after i came home that there should be diagnostic code, but i didn't notice was there any code or not when we were checking

 

17 hours ago, shinyribs said:

Was the air filter stock or an aftermarket one?

Not stock one

 

17 hours ago, shinyribs said:

Knowing what the spark plugs looked like when you had them out should give you clues if the rings were hurt or not. 

Master said that spark plugs looks good

 

17 hours ago, shinyribs said:

Also, do you 100% trust the reading of  your compression tester gauge? 

Yes, he also said that there may be some inaccuracies using tester

Edited July 27, 2021 by Pavel

[Pavel]

Also i forgot to mention that electronics were connected incorrectly, so when turn on right turn signal front signals shows left and rear right. I will need to reconnect all electronics right away. Maybe that is the reason of  "check"