6.2 compression test.. HELP ME!

[76chevyc10]

I found a 6.2 diesel engine to replace the gas engine in my 76 chevy 1/2ton pickup, I'm going down to look at the motor on Thursday.

I want to do a compression test to see how tight the engine is, does anyone know how many PSI would be considered a good reading?

I'm not sure what year this engine is, all I know is its a 1 ton chevy pickup between 1982- 1986 and the seller says it runs good.

I have an old book that says compression should be 22:1 but I don't know what that means, I need PSI. Any help would be appreciated

[Robyn]

Howdy and welcome

The 22:1 is the compression ratio. This is the swept volume of the cylinder with the piston at BDC as compared to the volume left when the piston is at TDC. In other words the volume of the cylinder and combustion chamber is 22 times that of the combustion chamber alone

The compression pressure while cranking at good healthy starter speed should be 320 to 400 psi after about 4 hits
Look for comparable values on the cylinders. For example if you have six at 340, one at 380 and one at 240 I would worry about that one.
If they are all close at or above 320 things should be fine.
they will vary some so dont worry about 10-15 pounds or so up or down.

A red painted engine is an 82 all others were black, unless someone got busy with a rattle can.

Also warm the engine up good before doing the comp. test. This will allow all cylinders to be well lubricated and everything working well. Doing a test on a cold engine can give erroneous readings.

Another thing, if you can run this engine warm it real good and check for air bubbles in the coolant tank which could mean a bad head or head gasket.
If the seller gets real nervous when you ask to warm it up good be very suspicious that he is hiding something.
These engines can and will run well even with a leaking gasket or head.



Hope this helps

Robyn

[76chevyc10]

Thanks that helps alot!

[Robyn]

You betcha

have fun

Robyn

[Destroyer]

Howdy and welcome

The 22:1 is the compression ratio. This is the swept volume of the cylinder with the piston at BDC as compared to the volume left when the piston is at TDC. In other words the volume of the cylinder and combustion chamber is 22 times that of the combustion chamber alone

The compression pressure while cranking at good healthy starter speed should be 320 to 400 psi after about 4 hits
Look for comparable values on the cylinders. For example if you have six at 340, one at 380 and one at 240 I would worry about that one.
If they are all close at or above 320 things should be fine.
they will vary some so dont worry about 10-15 pounds or so up or down.

A red painted engine is an 82 all others were black, unless someone got busy with a rattle can.

Also warm the engine up good before doing the comp. test. This will allow all cylinders to be well lubricated and everything working well. Doing a test on a cold engine can give erroneous readings.

Another thing, if you can run this engine warm it real good and check for air bubbles in the coolant tank which could mean a bad head or head gasket.
If the seller gets real nervous when you ask to warm it up good be very suspicious that he is hiding something.
These engines can and will run well even with a leaking gasket or head.



Hope this helps

Robyn

The girl of our dreams , who ever he is thats one lucky guy that got you.

My 6.2 military hates to start with out hours of charging has new plugs and filter has two brand new batts and alternator and starter but won't budge with less than 13 volts any ideas like starting fluid. did notice smoke comming from the starter area last time it ran which is a new developement. It did stop after cranking.

[Robyn]

Good bet you have some battery cable issues. Gounds are critical as are the connections at the batteries.
These engines need loads of amperage flowing to the starter to get them rolling.

Thanks for all the compliments ;0)

[Destroyer]

Hmmm now that you mention it I did repair (poorly I am guessing now) the connection to the starter.

[Robyn]

The connections need to be the heavy soldered eyes.
Welding cable with soldered ends and top terminal or the dual terminal jello batteries are best.
use the marine type ends that allow you to bolt the eye to the terminal end, or in many cases the terminal has a wing nut.
Poor connection results in very high amp draw and then the voltage drops off rapidly resulting in a brown out effect and hence the poor starting.

The side terminal cables can become all coroded back under the red plastic cover and you can't see it without cutting the cover off.
All that corosion will result in very poor starting and charging too.
The stock GM cables have the end soldered to the cable, but only the outer strands are soldered and the core of the cable gets coroded and loses its ability to carry the amp draw.
Bad cables will really sink your operation and quick.


Many of the 6.5's have tha alternator wired to the LH battery and then the cable crosses the header support to the main battery. The ground to the LH battery may also go south in the crimp at the engine end eye resulting in a poor charging condition.

Fix it all and be done with it and it will work sweet.
Another neat trick I did was to install a Ford starter relay right behind the RH battery and wire the solenoid wire that activates the starter to it and then come from the battery directly through the relay to the starter.

This will take all the stress off of the ignition switch and allow far more current to the solenoid.

On the 94 and later units the solenoid wire also manages the fuel lift pump on start up so there is another draw.

It will really help save the ignition switch.

Robyn

[Destroyer]

Wow you are like Ninja mech or something sure know your stuff I am going to replace the whole mess as it a 1984 retired miliary blazer and God knows what it have been thru.

After I do that I will get back with you as I still think I am have a charging issue and want to see what yousay about that.

Right now it starts easy with a full charge to both batts but the right pipe blows white smoke till it warms up. could that be fuel as opposed to a ring seating?

[Robyn]

Well now.
If the compression is good, most likely you have some tired injectors.
Maybe even the IP getting weak.
My first point to check after a good compression test would be the injectors.
Once they get many miles on them the inner parts start to wear and get carboned up and the "POP" pressure falls off and they squirt instead of spraying a fine mist.

This condition will make for a smokey start up as well as some rough running for a few minutes.

A quicky, just unscrew the squirts and stuff in a fresh set.
You can get a nice install kit that comes with all the little hoses and new coppers cheap.

I think that you will be amazed at how well your little diesel rat will run with just a new set of squirts.
Ya might also toss in a set of new glow sticks while your there too.

My 94 had some squirts that were on the way out and it would cough up enough smoke to take care of 100 acres of mosquitoes real quick.

Good luck

Robyn

[Destroyer]

Mine smokes and kills the neighbors and the bugs, thx the squirts are next did the glow stick already. I am used to doing 350 work so when it comes to the 376 I am befuddled so thanks my M9001 cucv will live again after I do the squirts, the seats reinstalled after breaking off bolts opps
, and redoing dash(the Army seems to love ripping these out for some reason, like I think it might be like this fight wars tear out the instrument panels as I have not seen a pic online that did not show a gutted dash) and fixing a few leaks.

[Turbo Al]

Robyn,
Hi, I really don't have much of an option because the engine is out of the truck so more or less have to do a cold compression test -- what is the best way?? This engine was running before I pulled it. I could probably start it but oil lines are off.
1. crank it over (with glow plugs out) for a few mins before checking compression.
2. Crank it over spray some WD40 or light motor oil in the glow plug holes to simulate oil on walls.

Thanks in advance,.

Al