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what are the compression specs for the g180? I cant find it in my chiltons-thank you

According to Haynes, it's 163.56 psi @ 300 rpm : max variance 8.53 psi

Edit, obviously a misprint in the manual...series 5-6 section states 170.64 @ 3000 rpm

Couldn't find info on the series 8-12


Dunno about yours, but good luck getting it to run at 300 rpm

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FIAA: Color Guard

My series 8 manual says 170.64 psi at 300 rpm. When doing compression test you don't want to run the engine you just want to crank it over a few times without starting it.

"When doing compression test you don't want to run the engine you just want to crank it over a few times without starting it."

That's what I was thinking...

Am I crazy or are there 2 misprints?

Page 16 of he Haynes Series 1-12 manual shows 163.56 psi @ 300 rpm
page 39 shows 170.64 @ 3000 rpm

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FIAA: Color Guard

Cranking speed with all plugs out and compression gauge in 1 cylinder is about 300 rpm, especially with a good battery...

i got 125 across the board, seems strange their all low but in sync with each other-ill wet test it tomorrow along with my hitachi rebuild thanks for the help guys

I got 125 on 1,3,2 &120 on #4. Would that suggest blowby on the rings?
Truck runs great, not planning anything as major as a re-ring anytime soon. My hope is to find a decent G200 somewhere to rebuild, mostly for the learning experience, and for the fun of it.

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yeah im thinkin rings, i plan on doin a little rebuild this summer. The truck runs great, i was kind of suprised when i got the compression result s.

My series 8 book says for compression test you start engine and bring it up to normal operating temp. turn it off and remove spark plugs. It says standard psi is 170.64. Limit psi is 119.45. It says if compression is lower than limit, engine should be overhauled. Sounds like you are borderline.

I say just keep driving it until you notice a lack of power.

Could be valves too.

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'78 1.8L 4-speed Fleetside

The only thing more beautiful than a sunset is a sunrise.

Make sure throttle is wide open when you check compression. Otherwise may read lower than normal.

Added to all that be a good idle to take the fuel pump off line and disconnect the fuel line to keep from flooding the carb.

Same here, but mine runs to well for me to dare rip it apart just yet..... knocking on wood

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FIAA: Color Guard

The float in the carb should not let any fuel in. Also with the plugs out there is no compression to draw any fuel mixture in. Unless maybe you want to disable the pump for safety reasons.

Not to egg on you but the chevy luv manual says to push the throttle wide open which would let gas in, and since you are cranking the engine over the fuel pump will run.

I'm not trying to jump on anyone here, but here are my theories on compression testing. If I already think I have a problem sometimes I will run a quick test, just pull the plugs and crank. If something is seriously wrong it will show up pretty quick. If I really want to get an accurate reading, like evaluating a newly bought LUV or giving mine a yearly checkup I'll put a bit more effort into it. For the absolute best reading here is my method:

Start the truck and warm it up to normal operating temp
Disconnect power from the fuel pump and let the motor die
Pull the coil wire out of the coil, or better yet disconnect the + side wires
Pull all four plugs, keeping them in order and inspect them

For each cylinder:
Hook up the tester
Mash the gas pedal to the floor
Crank the motor over (I usually do about 8 cycles, you can hear it compress, just enough for the guage to stop climbing basically)
Note the guage reading and repeat once for accuracy before moving to the next hole

Once that is all done, what happens next depends on the readings. If low, a squirt of motor oil in the cylinder and repeat the test. If it comes up a lot, the problem is rings. If it doesn't change much, it is valves or a head/headgasket issue. In that case, I check/reset the valve clearance and retest.

Burning off the fuel is a good idea for two reasons. First, it will pull some of it through the carb, and unburnt fuel will wash down the cylinder walls and could give a bit lower reading. Second, fuel/air mix coming out of the spark plug holes could find a spark and ignite. The cylinder you are testing will be sealed and will draw fuel in just fine. In my experience even open plug holes gets enough air moving through the carb to get gas into the cylinder.

Opening up the throttle is just getting a good airflow into the motor. Propping the choke open is a good idea too if it isn't opened on its own. If you don't you might find that continued cranking will get you a higher and higher reading before it peaks out. With the throttle open wide it shouldn't take more than a few revs for the needle to peak. Seems like most service manuals I've read also give this as one of the steps in a compression test so I've generally stuck by it.

Just a little FYI, A g200 with a g180 head on it apparently gives around 195psi. Imagine my shock when I bought that truck and first ran a comp test on it.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

That sounds pretty thorough 800xl, I will re-check mine this weekend using the method you describe and see what different readings I get.

Thanks for the info

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FIAA: Color Guard

It good to have a couple luv daddies around here to put things straight.

There are allot of reasons for doing a comp. test NOT doing a comp. test is basically to check comp. in the engine from cyl.to. cyl. If you want a true test of your engines condition then use a leak down tester.Any motor with 100lbs of comp. will run (all though it's tired) and motor with 200lbs will run real good but you have to have the whole combo. working together and any motor with 300 or more will be diesel or alky. keep in mine that there are a lot of things change this as you cam shaft and cam timing will change the comp. the most. there is more but this rant is over for now thanks for your time

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1978 pro street step/side 455Buick, 4sp,4.11s, 31/18.5s