Compresion test

[Luke Davey]

When i do a compresion test do i need to measure the air pressure/humidity/temperature ect. I have tested it before and it read 100psi with 6.7:1 compression, this is at 1000ft above sea level, i am also wondering what the standard air pressure is? (im told it is about 14psi). any help appreciated

 

[Jaybird]

The compression test will not vary enough at differnt elevations for you to notice with conventional guaging equipment. Just make sure your tester is seated in the hole good (use the o-ring) and be sure to kick it several times to get a good reading. You have some issues if you still show 100psi. Measure your piston (and jug) and if it is still within spec without any signs of bad blow-by past the ring, you may get by with just re-ringing it.

 

[Luke Davey]

The tester is cheapo it does not have a threaded head but a taperd piece of rubber that inserts into the spark plug hole, it is very hard to hold in and kick at the same time. What is the atmospheric pressure?, and what is the acceptable limits for a 6.7:1 compresion engine, im taking it is more than 100psi.I want to do this before i pull the engine apart.

 

[Luke Davey]

The tester is cheapo it does not have a threaded head but a taperd piece of rubber that inserts into the spark plug hole, it is very hard to hold in and kick at the same time. What is the atmospheric pressure?, and what is the acceptable limits for a 6.7:1 compresion engine, im taking it is more than 100psi.I want to do this before i pull the engine apart.

 

[Jaybird]

I suggest a new tester.

Luke, those little testers with the rubber end are OK if you want to find a dramatic difference in a v8 real fast, but for reading a correct compression you need one that threads into your head.

 

[bigred455]

I took a spark plug washer and put it on with the seal they give you with the tester,it seals great for a good reading.

 

[Dsharp]

How much do the compresion testers go for?

 

[Luke Davey]

OK i will change to a non cheapo, or use my local workshops one. Can anyone answer my question about what the atmospheric pressure is and what the acceptable limits are for a 6.7:1 compresion engine? It's no good doing this if i dont know if i get agood or bad result. Any help appreciated.

 

[Luke Davey]

Sorry i forgot to say that the bike has done 20'000km on these piston and rings, i have taken off the pipe and looked into the cylinder and can see the cross-hatching and some places where it has worn the bore to stright up and down lines this is just behind the piston, so i'm thinking it could be piston slap.
The bike is a 1997 CRM250 (non AR)

 

[steve33]

$40.00 at napa

 

[Eggnchips]

I believe ( and I could be wrong) but atmospheric pressure at sea level is 1.014 bar or approx 14psi.

Look at the weather forcast as they give the air pressure in millibars. e.g. 1014 millibars.