I'm picking up the new/used 5.9 tomorrow. Still up in the air about how deep I want to go with it before actually doing the swap. I think I'll check the compression and do a leak down test...if things look good, I may just replace bearings, pumps, timing chain, etc. and leave all of the "rotating things" alone. If it catches me in the right mood I may end up tearing it completely down and starting from scratch.

What's the best way to check compression on a stand? Rig up battery/starter/start switch? I've seen the test type start switches with alligator clips before...

My first instinct was to rip it all apart and take the block to be cleaned, honed and have new cam bearings/freeze plugs installed. I intended to put a decent cam in it but after talking with Comp Cams I'm not sure I can pull off anything reasonable given my local emissions laws. If the compression is good with minimal leak down, is there any real point in gutting the block? Not sure I want to do it just for the sake of doing it.

Opinions?

 

Compression test on a stand is gonna be difficult at best. Better bet would be cylinder leak down test. Only need to turn the motor so the cylinder you want to test is at TDC on the compression stroke. (both valves closed) You can do that by hand. Needs a neat gauge, and a source of compressed air though.

 

I have a leak down tester/compressor...I guess it kinda overrules a standard comp test anyway, huh? So, with the cylinder at TDC you are testing leak down with the smallest cylinder capacity correct? Why not with the max cylinder capacity? Is the intake valve open at the bottom of the stroke?

 

What you are interested in is how well things are sealing. (rings and valves) using the smallest volume gives more accurate results..... (so I was led to believe.....) Not to mention that at TDC is where you are most interested in what things are like, as that is where pressures are going to be highest when the engine is running.

I usually run input pressure at 100 PSI, that way, percent leakdown is very easily calculated.... not to mention it makes hearing where its going MUCH easier. According to theory, anything up to 25% leakdown is "acceptable".......

 

ok, thanks.

So, if one is to expect up to 25% leakdown, and the input pressure is 100psi...should the overall pressure level out at no less than 75psi? And if so, over what time interval. I would think that if 25psi was able to leak out (at all), eventually the rest would do the same. What factors would allow a percentage of leak and not eventually a total leak down?

 

On a somewhat related note, I'd like to thank everyone on this site. Thanks to you guys, I took a perfectly fine (although weak) V6 with a few minor issues and turned it into a full blown V8 build and swap. The way I see it...you guys are gonna owe me somewhere in the neighborhood of 2-3000 bucks by the time this is said and done

...now accepting donations.

No, seriously...I've been dying to do something like this for a while and the things I've read/learned here gave me the extra motivation. Of course, my truck isn't a daily driver either so if I FUBAR it at least it won't be a major inconvenience.

I just wish my truck was 6 years older, then I could do whatever I wanted with the engine withour fear of the emissions police. If I were a smarter man, I would sell the V6 truck and buy a V8 4x4. Here's to boredom and the need to fix something!

 

Leak down test is constant flow. You don't just pressurize the cylinder, and turn off the air. The way it works is, one gauge will read input pressure, the other gauge will read the pressure the cylinder will maintain. Your assessment of the numbers is correct, at 100PSI input pressure, cylinder should maintain AT LEAST 75 PSI. Even it it does, you will still be able to hear where any leakage is going. (make sure you have the oil fill cap off, and throttle cracked all the way open when you do this.) This is an excellent way to diagnose leaky valves and such.

 

Got the 5.9 on the stand today. Now to start tearing it apart...

 

I'm not sure this tester I have is accurate or reliable...either that or I have valve issues. Every cylinder that I checked, at TDC of compression stroke, shows ~80% loss. By the way the tester manual says to calibrate it to zero percent loss it is only pumping 15-20 psi into the cylinder. If I crank the regulator up to ~80-100psi the loss gauge pegs itself clockwise(which is beyond the 'green' acceptable range). It should move CCwise to one of the percentage ranges.

 

Can you tell where the air is going?
If its going out the exhaust you may be top dead center on the exhaust stroke, exhaust valve would be open.
Pull the valve covers that way you know for sure your on compression stroke.

Dave