3B Compression Numbers (1 Viewer)

Joined
Dec 17, 2009
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49
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MN
Well, I finally did my compression check before I go into restoration mode. 1984 AU 42 with Turbo (installed about 3000 km ago), truck has ~370,000km, guessing all original.
Did the test with the Harbor Ft. cheapy comp gauge, edic unplugged, all plugs out, crank 6-10revs until gauge is stable.
Did the first set cold. 1-420, 2-390, 3-390, 4-420
Warmed up close to operating temp (fast idle, did not drive it)..1-460, 2-420, 3-430, 4-460

What do you guys think, #2 does seem the weakest (seems to take a couple more revs to top out). The truck runs great, no smoke, burning oil, etc. that I can see. After the turbo install, I do have a little more blow by (or oil drip from the tube), but sounds like that is normal.

I am planning on a full resto (like Rob's if I can pull it off), plan was if the numbers looked pretty good and close, I was not going to open up the motor, It sounds like close is supposed to be within 10-20psi of each other.
If the recommendation is to take a look, what are the norm's (Head VS Block issues).

Thanks
Troy
 
Joined
Jan 11, 2010
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1,116
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WA & BC
Troy , those look fine . leave it and since you have added, a turbo ,
most important , and missed is poor rads and under maintained /sized cooling system.
extracting more power , means better cooling systems are required.

VT
 
Joined
Dec 17, 2009
Messages
49
Location
MN
Thanks VT

I am running 10-12psi max. I did turn up the fuel some, but have not seen temps over 900F.
Not many big hills or grades in MN and the temps have been cooler since the turbo has been installed (did not drive it in the winter), so far, the cooling looks to be fine.
During my rebuild, are there some nice radiators out there that I should look at?
 
Joined
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Im not talking EGT's or the flat running driving down the road.

Im talking bumper 2 bumper traffic in 100f for an hour, then your asked to climb that long steep grade behind all of them.

Your 4 core rad & fan system / fan clutch must be able to dump all that heat and more without having the thermostat fully open and now the rad is limiting the heat.A rad that's just doing it's job or can only transfer enough till the thermostat is fully open and then the coolant coming out of the bottom of the rad is the same temp as it engine runs at will cause an overheat.
That Rad is at it's limit, the coolant boils in the cyl head causing pockets of hot spots , and the head get's hotter. It might not blow off steam as you see the TV adds, but this is the start of headgasket / bolt stretching and IMO cup movement till it starts to pound the gasket till it cracks and drops.

I have purchased 2 60's from the dry belt , and the coolant was rusty water..Whats with that ??
Antifreeze is more than just that ,anti rust / cavitation plus it adds a factor to increase the boiling point . same as the radiator cap.
In imperial terms 1 pound of pressure raises the boiling point 3 F so boiling point sea level 212F for a standard day add 12 pound cap 3 X 12 = 36 + 212 = 248 F the geyser blows, the metal is heat stressed. So if your just under 230 , and it never blows , has the metal / gaskets / seals etc all been stressed.

Thats what I'm getting at.

VT
 
Joined
Dec 17, 2009
Messages
49
Location
MN
Thanks..I will definatey look at making sure I have good cooling capacity after my resto.
Any other opinions or experiences on a 42 w/turbo regarding temp issues.

Also, amy more opions on the compression numbers would be great.
 

RufusTheDufus

SILVER Star
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Jan 9, 2008
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Moronville, ME
 
 
Have you adjusted the valves? I noticed that a valve adjustment can sometimes impact compression numbers for a cylinder that doesn't quite match the others.
 
Joined
Dec 17, 2009
Messages
49
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MN
thanks guys, valve check makes sense, will check and redo comp. check.
 

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