Compression Test Help?

[NocalFJ60]

I am trying to do my first compression test and something seems wrong. I warmed up the cruiser pulled all the plugs and disconnected the coil. I borrowed a guage from a friend which he has used quite a bit. I floored the gas and cranked the engine and got the following numbers.

cyl 1. 65psi
cyl 2. 50psi
cyl 3. 65psi

My book says I should be getting above 120 psi. The guage held the number for well over 5 mins why I was looking around so I think it is making a good seal. I stopped cause I don't think my engine would run at these numbers. These guages seem pretty simple and it is hard to belive it would be off so much.

Any ideas?

 

[IDave]

Don't understand what you were doing with the gas. You just crank using the starter motor. About 20 revs should be enough.

 

[NocalFJ60]

Don't understand what you were doing with the gas. You just crank using the starter motor. About 20 revs should be enough.

It shows in the factory manual the pedal being pushed all the way down.

Step 4

Insert a compression guage into the spark plug hole and fully open the throttle valve. While cranking the engine, measure the compression pressure.


I did about 10 revs probably. Do you let your starter rest half way or just do 20 revs?

THanks

 

[IDave]

Hmm. Never noticed that about the throttle.

I crank it 20 times without a rest.

 

[LandCruiserPhil]

Unrestricted air flow by opening the throttle

 

[NocalFJ60]

Cool.

I guess my next step is to get another guage and compare the numbers? It is possible my truck is at 60 psi? Would it run?

 

[Pighead]

Bingo. Another gauge.
I got all freaked once with my compression readings, used a buddy's gauge and felt all better again.

 

[Ian Rogers]

you know it only takes about 5 cranks you will see the compression getting higher and higher, untill it's maxed out. I use a remote starter swich ($ 5 at Hub auto) that way i can see the gage as i crank. Alos if you do go for about 20 cranks you might want to have a battery charger on there because by the time you get to the 6th cly. you will have far less CA in the battery.

 

[orangefj45]

you should'nt have to crank it more than 5-10 revolutions. normally, it'll show full compression by the 5th rev.

i have a compression tester at home. you're more than welcome to stop my and use it.

 

[NocalFJ60]

you should'nt have to crank it more than 5-10 revolutions. normally, it'll show full compression by the 5th rev.

i have a compression tester at home. you're more than welcome to stop my and use it.

Thanks for the offer but I found another guy from work with one.

 

[Civil1]

Checked my compression today, throttle wide open and all plugs removed, as
described here http://www.ac427.com/html/cobra_52.shtml

Dry Results:

1 = 151psi
2 = 150psi
3 = 151psi
4 = 150psi
5 = 149psi
6 = 150psi

84fj60 stock 240,??? miles.

 

[NocalFJ60]

Checked my compression today, throttle wide open and all plugs removed, as
described here http://www.ac427.com/html/cobra_52.shtml

Dry Results:

1 = 151psi
2 = 150psi
3 = 151psi
4 = 150psi
5 = 149psi
6 = 150psi

84fj60 stock 240,??? miles.

Did you try putting in a little oil to see if the pressure came up to test the rings? I am going to go put everything back together tomorrow and let it warm up and then try again with another guage.

Hope my numbers are that good.

 

[Civil1]

No didn't do the wet test, not that it takes that much longer to do I was just in a big hurry because of family showing up for dinner that I was unaware of. I plan to do a complete test soon probably tomorrow or this weekend sometime I will let you know what numbers I get.

I was real happy with the dry numbers I could only think that with the wet test they would stay the same or go up slightly. I have had a stubborn problem lately that I've been trying chase down. It runs great most of the time, but every once in awhile it starts to buck and kick when trying to maintain a constant speed (30mph). Never does it at highway speeds 55-60mph

I think the factory specs are 149 psi so my compression being a little higher than that might mean some carbon build up on the pistons??(maybe) I plan on doing a seafoam treatment thru the carb and see if that cleans it up some.

 

[CruisinGA]

skip the seafoam. 50/50 brake fluid and water. just take it easy pouring it into the primary only.

Those are damn good numbers. Compression on my '74 is MUCH worse, with half the miles. (10 yrs older though). I'm jealous.

 

[IDave]

Don't have a 2F, but I think I recall that factory spec is more like 170? 150 for an F.

 

[jwest]

2F's are also at 149psi, 114 limit, <14psi difference.

Kinda interesting. Never heard of the brake fluid/water method.
How's the bf supposed to make a difference?

.

 

[Civil1]

yeah, checked the FSM and agree with jwest that 149.3 psi is correct. Don't know about the brake fluid and water, but I have heard about some old timers that used just water. Be careful not to hydrolock the engine.

 

[NocalFJ60]

yeah, checked the FSM and agree with jwest that 149.3 psi is correct. Don't know about the brake fluid and water, but I have heard about some old timers that used just water. Be careful not to hydrolock the engine.

I asked about the water in the carb on this thread. Going to get a guage and test it again tonight.

https://forum.ih8mud.com/showthread.php?t=22163

 

[Civil1]

I've seen that thread before, it is interesting all the different methods that have been tried to clean out carbon and junk. Think I'll start with the seafoam and go from there.

NocalFJ60 good luck with the compression test let us know your numbers. I'll get to mine this weekend and post up my numbers (wet and dry again) and tell ya how the seafoam went.

 

[Civil1]

Ok, so I did the wet test this afternoon. I did not repeat the dry test.
Put about a Tblspn of Marvel Mystery Oil in each cylinder.

Here are both numbers:

Dry____________Wet
1 = 151________1 = 170
2 = 150________2 = 172
3 = 151________3 = 175
4 = 150________4 = 172
5 = 149________5 = 165
6 = 150________6 = 170

Not sure if I am as happy today as I was yesterday, the higher compression numbers lead me to believe that I am losing compression, however if the factory compression is 149psi what gives. If anyone can shed some light on this please do.

I also did the seafoam treatment and it smoked up the neighborhood, got a lot of them asking if it was on fire. I just laughed.

Another little piece of advice is not to add the oil to all cylinders before checking the compression of each cylinder, learned this one the hard way with a face full of oil.

Anyway there they are, let me know what you guys think.