Compression Test

Hi,

Just need a quick bit of advice. I have just refitted my cylinder head
although I have not yet refilled the coolant or started the car.

I decided to do a quick compression test to check everything was in order
before I filled the coolant and so on.

The first cylinder I checked showed very low pressure. (about 40psi)
Bearing in mind that the oil pressure isn't up and the engine temp is still
stone cold, is this reading totally inaccurate.

Is it worth me filling the coolant up and running the car for a while before
doing the test again, or is something wrong and should I take the head off
again now?

Cheers,
Dave

That's a bitch.....

I would take a couple tablespoons of oil and pour it into that cylinder,
then do another test.

If the compression comes up, your rings are bad. If the compression
stays low, you may as well pull the head because either that gasket is
no good or you have a burned valve.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Dave Skirrow wrote:
>
> Hi,
>
> Just need a quick bit of advice. I have just refitted my cylinder head
> although I have not yet refilled the coolant or started the car.
>
> I decided to do a quick compression test to check everything was in order
> before I filled the coolant and so on.
>
> The first cylinder I checked showed very low pressure. (about 40psi)
> Bearing in mind that the oil pressure isn't up and the engine temp is still
> stone cold, is this reading totally inaccurate.
>
> Is it worth me filling the coolant up and running the car for a while before
> doing the test again, or is something wrong and should I take the head off
> again now?
>
> Cheers,
> Dave

So, the fact that the temp is cold and there's no coolant or oil pressure
yet doesn't make too much difference to the test then?



Dave


"Mike Romain" > wrote in message
...
> That's a bitch.....
>
> I would take a couple tablespoons of oil and pour it into that cylinder,
> then do another test.
>
> If the compression comes up, your rings are bad. If the compression
> stays low, you may as well pull the head because either that gasket is
> no good or you have a burned valve.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
>
> Dave Skirrow wrote:
>>
>> Hi,
>>
>> Just need a quick bit of advice. I have just refitted my cylinder head
>> although I have not yet refilled the coolant or started the car.
>>
>> I decided to do a quick compression test to check everything was in order
>> before I filled the coolant and so on.
>>
>> The first cylinder I checked showed very low pressure. (about 40psi)
>> Bearing in mind that the oil pressure isn't up and the engine temp is
>> still
>> stone cold, is this reading totally inaccurate.
>>
>> Is it worth me filling the coolant up and running the car for a while
>> before
>> doing the test again, or is something wrong and should I take the head
>> off
>> again now?
>>
>> Cheers,
>> Dave

The valve looked ok, hopefully I have just damaged the gasket when I put it
on or something. It wasn't even the cylinder that I was repairing.



"Mike Romain" > wrote in message
...
> That's a bitch.....
>
> I would take a couple tablespoons of oil and pour it into that cylinder,
> then do another test.
>
> If the compression comes up, your rings are bad. If the compression
> stays low, you may as well pull the head because either that gasket is
> no good or you have a burned valve.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
>
> Dave Skirrow wrote:
>>
>> Hi,
>>
>> Just need a quick bit of advice. I have just refitted my cylinder head
>> although I have not yet refilled the coolant or started the car.
>>
>> I decided to do a quick compression test to check everything was in order
>> before I filled the coolant and so on.
>>
>> The first cylinder I checked showed very low pressure. (about 40psi)
>> Bearing in mind that the oil pressure isn't up and the engine temp is
>> still
>> stone cold, is this reading totally inaccurate.
>>
>> Is it worth me filling the coolant up and running the car for a while
>> before
>> doing the test again, or is something wrong and should I take the head
>> off
>> again now?
>>
>> Cheers,
>> Dave

"Dave Skirrow" > wrote in message
...
> Hi,
>
> Just need a quick bit of advice. I have just refitted my cylinder head
> although I have not yet refilled the coolant or started the car.
>
> I decided to do a quick compression test to check everything was in order
> before I filled the coolant and so on.
>
> The first cylinder I checked showed very low pressure. (about 40psi)
> Bearing in mind that the oil pressure isn't up and the engine temp is
still
> stone cold, is this reading totally inaccurate.
>
> Is it worth me filling the coolant up and running the car for a while
before
> doing the test again, or is something wrong and should I take the head off
> again now?
>
> Cheers,
> Dave

Why was the head removed?

No, because you are comparing all the cylinders in the same state, cold
and dry. It is more how even they are vs how high they are at that
point.

The wet test tells a lot. You can do it in all the cylinders to see how
much they come up if any.

Mike

Dave Skirrow wrote:
>
> So, the fact that the temp is cold and there's no coolant or oil pressure
> yet doesn't make too much difference to the test then?
>
>
>
> Dave
>
> "Mike Romain" > wrote in message
> ...
> > That's a bitch.....
> >
> > I would take a couple tablespoons of oil and pour it into that cylinder,
> > then do another test.
> >
> > If the compression comes up, your rings are bad. If the compression
> > stays low, you may as well pull the head because either that gasket is
> > no good or you have a burned valve.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> >
> > Dave Skirrow wrote:
> >>
> >> Hi,
> >>
> >> Just need a quick bit of advice. I have just refitted my cylinder head
> >> although I have not yet refilled the coolant or started the car.
> >>
> >> I decided to do a quick compression test to check everything was in order
> >> before I filled the coolant and so on.
> >>
> >> The first cylinder I checked showed very low pressure. (about 40psi)
> >> Bearing in mind that the oil pressure isn't up and the engine temp is
> >> still
> >> stone cold, is this reading totally inaccurate.
> >>
> >> Is it worth me filling the coolant up and running the car for a while
> >> before
> >> doing the test again, or is something wrong and should I take the head
> >> off
> >> again now?
> >>
> >> Cheers,
> >> Dave

New rings usually need to seat in. Is that what you repaired and if so
how was that cylinder's compression?

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Dave Skirrow wrote:
>
> The valve looked ok, hopefully I have just damaged the gasket when I put it
> on or something. It wasn't even the cylinder that I was repairing.
>
> "Mike Romain" > wrote in message
> ...
> > That's a bitch.....
> >
> > I would take a couple tablespoons of oil and pour it into that cylinder,
> > then do another test.
> >
> > If the compression comes up, your rings are bad. If the compression
> > stays low, you may as well pull the head because either that gasket is
> > no good or you have a burned valve.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> >
> > Dave Skirrow wrote:
> >>
> >> Hi,
> >>
> >> Just need a quick bit of advice. I have just refitted my cylinder head
> >> although I have not yet refilled the coolant or started the car.
> >>
> >> I decided to do a quick compression test to check everything was in order
> >> before I filled the coolant and so on.
> >>
> >> The first cylinder I checked showed very low pressure. (about 40psi)
> >> Bearing in mind that the oil pressure isn't up and the engine temp is
> >> still
> >> stone cold, is this reading totally inaccurate.
> >>
> >> Is it worth me filling the coolant up and running the car for a while
> >> before
> >> doing the test again, or is something wrong and should I take the head
> >> off
> >> again now?
> >>
> >> Cheers,
> >> Dave

Dave Skirrow wrote:
> Hi,
>
> Just need a quick bit of advice. I have just refitted my cylinder head
> although I have not yet refilled the coolant or started the car.
>
> I decided to do a quick compression test to check everything was in order
> before I filled the coolant and so on.
>
> The first cylinder I checked showed very low pressure. (about 40psi)
> Bearing in mind that the oil pressure isn't up and the engine temp is still
> stone cold, is this reading totally inaccurate.
>
> Is it worth me filling the coolant up and running the car for a while before
> doing the test again, or is something wrong and should I take the head off
> again now?
>
> Cheers,
> Dave
>
>
Not knowing what kind of car or valvetrain - do you have the valves
adjusted properly? On my Camaro with a small block chevy, the lash on
one of the valves had been "adjusted" so far that there was zero
compression. Amazingly enough, the motor ran fine - I thought I broke
my tester. Backed off the lash and reset it and got 150 psi.

(I was checking compression before the first race with the car.)

Ray

ray wrote:
>
> Dave Skirrow wrote:
> > Hi,
> >
> > Just need a quick bit of advice. I have just refitted my cylinder head
> > although I have not yet refilled the coolant or started the car.
> >
> > I decided to do a quick compression test to check everything was in order
> > before I filled the coolant and so on.
> >
> > The first cylinder I checked showed very low pressure. (about 40psi)
> > Bearing in mind that the oil pressure isn't up and the engine temp is still
> > stone cold, is this reading totally inaccurate.
> >
> > Is it worth me filling the coolant up and running the car for a while before
> > doing the test again, or is something wrong and should I take the head off
> > again now?
> >
> > Cheers,
> > Dave
> >
> >
> Not knowing what kind of car or valvetrain - do you have the valves
> adjusted properly? On my Camaro with a small block chevy, the lash on
> one of the valves had been "adjusted" so far that there was zero
> compression. Amazingly enough, the motor ran fine - I thought I broke
> my tester. Backed off the lash and reset it and got 150 psi.
>
> (I was checking compression before the first race with the car.)
>
> Ray

Good point, I also have seen zero with a hydraulic because the push rod
wasn't centered in the lifter.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Mike Romain > wrote in
:


If there is no oil in the lifters....the valves won't open to the proper
dimension, hence cutting off airflow to the cylinder.



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

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