Range for compression on 2f (1 Viewer)

[Liam]

Just got my test results back on my 87 FJ60. Dont have the exact numbers on the cylinders but the mechanic said they were between 131 and 135.

Is this good for an engine with 143K?? What should be the range (high/low)?

 

[Doc]

Dude, that's way WAY W A Y low. I'll give you $2.5K for it.





I have no idea.

 

[Liam]

Dude, that's way WAY W A Y low. I'll give you $2.5K for it.





I have no idea.

make it an even 5K and it is yours....i'll even throw in the fuzzy dice

 

[lowtideride]

my rig hovers around 120-130....

 

[Liam]

but is that good???

 

[lowtideride]

um i dont notice....haha....as long as they are with in 10-15 of each other dont worry about it.

 

[chitown40]

Per FSM, 149/cylinder is what it should have started with back in '87. So, like Al said, as long as there is less than a 10% difference between cylinders you should be ok.

 

[airon23]

I'm a little dumb but what exactly does high compression/low compression mean?

 

[Doc]

Higher compression means your piston rings are doing a better job of sealing the combustion chamber shut, giving higher compression on the up-stroke.

 

[NocalFJ60]

It also depends on your altitude.The higher the altitude the lower the pressure.

Your numbers sound fine. Also the guage could be off some. Like said above even if the guage is off it is just as important if they all are within 10%.

 

[Liam]

what about wet and dry testing...what does that actually mean. What would a typical service dept do?

 

[NocalFJ60]

If it is low then you can add some oil to the cylinder and retest. If the pressure comes up then that means the oil helped seal up the rings to increase the pressure. The dry measurement is just after the engine is warm without adding oil. The typical service dept. would just do a dry probably unless one was low and then you can use the wet to tell if it the rings.

 

[Liam]

Per FSM, 149/cylinder is what it should have started with back in '87. So, like Al said, as long as there is less than a 10% difference between cylinders you should be ok.

so i am guessing that a range of 131 to 135 is good compression...

 

[lowtideride]

yulp sure is.

 

[Liam]

yulp sure is.

good...now sumone buy it then....

 

[cruiser4life]

If it is low then you can add some oil to the cylinder and retest. If the pressure comes up then that means the oil helped seal up the rings to increase the pressure. The dry measurement is just after the engine is warm without adding oil. The typical service dept. would just do a dry probably unless one was low and then you can use the wet to tell if it the rings.

Good thread. Been wondering about some of this stuff for a while.

What is a typical increase (percentage-wise) when the transition is made from dry to wet?

In other words, how much will the wet test typically help raise the compression?

How much of a delta between the wet and dry test indicates a problem with the rings?

If they are within 10% on both dry and wet (no matter the increased compression with the wet) is everything OK?

Thanks!!

 

[chitown40]

If your compression is good dry, then you don't need to do a wet test. You can do a wet test to try to determine if the rings are bad or if the problem is in the head. Also a leakdown test using shop air can give you lots of info. I never did a leakdown test, as I was able to determine most of my engine problems with a dry and wet test. NO change in my one bad cylinder and it turned out to be a bad valve from a cracked intake manifold. This is common on the 2F's because the heat risers sometimes stick in the closed position thereby overheating the aluminum intakes and causing them to crack right under the carb.

 

[cruiser4life]

If your compression is good dry, then you don't need to do a wet test. You can do a wet test to try to determine if the rings are bad or if the problem is in the head. Also a leakdown test using shop air can give you lots of info. I never did a leakdown test, as I was able to determine most of my engine problems with a dry and wet test. NO change in my one bad cylinder and it turned out to be a bad valve from a cracked intake manifold. This is common on the 2F's because the heat risers sometimes stick in the closed position thereby overheating the aluminum intakes and causing them to crack right under the carb.

Thanks for the added detail.

I guess a better way to approach it would be to define good. You mention above that 149 per cylinder is the "new" value.

You also mention that as long as all cyclinders are within 10%, then everything is OK.

So, if let's say the dry test produced all 110's and 115's and the wet test produced all 125's and 130's, then it would be OK or good?

Trying to understand what number is too low even if the variance is within 10%.

Thanks.