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Compression / Leak Down Testing Procedure
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=69052		 Page 1 of 1
Author:  mtgstuber [ Sat Jun 02, 2012 8:54 pm ]
Post subject:  Compression / Leak Down Testing Procedure
Hi folks,
After almost three months of waiting, my VM.1072 adapter came in. My goal in getting it was to check my cylinders and see if I needed to tear down the engine further or if I can simply drop new rockers arms in and put it back together.
So I started by hooking up a compression gauge and simply turning the engine by hand. Keep in mind that I have the top of the engine torn down right now, so I used a block of wood to hold support the foot, and used a shorter bolt so that it wouldn't bottom out.
Image
Here's my problem: When I turn over the engine by hand, I get (at most) 30 pounds of pressure on the compression guage. When I switch to doing a leakdown test, my results vary based on the crank position. In some positions I get a loss of around 40%. In others, I end up close to zero. Recall there are are no camshafts installed right now, so (theoretically) all the valves should be closed all the time. I would think in this state it wouldn't actually matter what position the piston is in.
Can some one point me towards the right procedure for doing a compression test or leakdown test on this engine when the cylinder head cover has been removed?
Author:  msilbernagel [ Sat Jun 02, 2012 9:56 pm ]
Post subject:  Re: Compression / Leak Down Testing Procedure
I'd recommend you locate and download the service manual - links are available at the top of the CRD forum, through the FAQs.

To use that tool and test compression, you probably have to have the rocker arms and engine cover installed - otherwise, there's nothing to open the valves to let air in to be compressed. This may answer your questions about why some positions get you a little and some almost none.. it's sucking air past rings, etc.

If you want to try a leak down test - feed compressed air into the VM.1072 so that it pressurizes the combustion chamber and listen to see where the air is leaking about approximately how much. You should be able to tell intake valve leaks especially well, exhaust you may be able to hear out the tailpipe, and rings would send air back up through the oil galleys (and sound too).. all depending upon the volume of air getting by.

To see if your valves are bent, you might try begin by cleaning off the top of the head and then lay a straight edge along the valve stems both alongside near the top and then across the top. Look for any valve top that's slightly away from the edge - signs of being bent. If they all appear to be true you're probably in pretty good shape.

If not - your question's answered and you can remove the head.

If so (all straight) - put it back together far enough that you can put the cam gears and timing belt (tensioner), etc back on.

Once you can get it timed and able to spin safely, and have cams overhead to open the valves - you can test compression.

?

Mark
Author:  mtgstuber [ Sat Jun 02, 2012 10:08 pm ]
Post subject:  Re: Compression / Leak Down Testing Procedure
So I'm an impatient sort, and after posting went back out to fight with the beast. What I found was this: On cylinders 1 and 3 (I didn't bother checking #4), I can attach my tester and they'll sit at around 40% leakage. As I rotate the crank shaft with a breaker bar, I can get to close to 10%, and it becomes about impossible to turn.

On cylinder 2, I can't get it above 60%. :(

I'd still love some pointers from those in the know on the best way to do this test properly. That said, it seems I've got more wrong than some broken rocker arms. Is it possible I just have a bad valve? What's the best way to check?

Any thoughts on where I should go from here? (Other than scrapping it entirely?)
Author:  mtgstuber [ Sat Jun 02, 2012 10:16 pm ]
Post subject:  Re: Compression / Leak Down Testing Procedure
msilbernagel wrote:

To see if your valves are bent, you might try begin by cleaning off the top of the head and then lay a straight edge along the valve stems both alongside near the top and then across the top. Look for any valve top that's slightly away from the edge - signs of being bent. If they all appear to be true you're probably in pretty good shape.



I'll grab a straight edge and check things out . . .

I'm currently reading the valve removal procedure. Ugh. Do I really need the $300 special tool Image, or can I use an off-the-shelf valve spring compressor? Any recommendations on ones that work, or ones to avoid?
Author:  mtgstuber [ Sat Jun 02, 2012 10:29 pm ]
Post subject:  Re: Compression / Leak Down Testing Procedure
The tops of the valve stems all seem to be true, but I'm not sure how close they should be. I'm assuming within a hundreth of an inch or two is okay.
Author:  msilbernagel [ Sat Jun 02, 2012 11:47 pm ]
Post subject:  Re: Compression / Leak Down Testing Procedure
You might spray a little motor oil in #2 to be sure the rings are sealing.

You've got the coolant system dismantled? Be nice to see if air/compression was finding it's way into the coolant.. perhaps the leak is headgasket...

Perhaps one of the diesel greyhairs has a good test procedure they could share. the Service manual doesn't seem helpful.. but perhaps I missed it.

Mark
Author:  mtgstuber [ Sun Jun 03, 2012 12:13 am ]
Post subject:  Re: Compression / Leak Down Testing Procedure
Well, I realized that I had loosened the glow plugs. I had this moment of hope -- hope that I was simply an idiot, and that tightening up the glow plug and rerunning the test would make it all right. I was looking forward to admitting my utter stupidity, but having an engine I didn't have to more to. No such luck. :banghead:

I may still be an idiot, but tightening the glow plug didn't make a difference.

I ran the test again, with the tightened glow plug, and found I have a steady stream of air coming out the exhaust. Am I correct in assuming that this means my exhaust valves are likely toast, and that I should proceed with pulling the head?

Assuming so, does anyone have any tips for taking off the exhaust manifold? The FSM seems to imply that you can (after removing the support bracket) simply slide the turbo and exhaust manifold off the studs as a unit; however, there's a nut hidden behind the turbo that I can't get to. Has anybody managed to pull the exhaust manifold without first removing the turbo?
Author:  tjkj2002 [ Sun Jun 03, 2012 8:02 am ]
Post subject:  Re: Compression / Leak Down Testing Procedure
You can not do a compression test by turning the engine by hand,you must achieve at least 250rpm's via the starter to get a good read.Do one test while cold and one test will hot for the best results.
Author:  mtgstuber [ Sun Jun 03, 2012 12:56 pm ]
Post subject:  Re: Compression / Leak Down Testing Procedure
Given how little is still connected, I don't think the starter motor would even spin at this point. Good to know for future reference though.

Anybody have thoughts on taking the intake manifold off? I'm debating the relative merits of driving into town to hunt for more tools versus just sucking it up and taking the turbo off.
Author:  EAB [ Sun Jun 03, 2012 2:42 pm ]
Post subject:  Re: Compression / Leak Down Testing Procedure
My thought is put it together and see how it runs instead of speculating and performing test procedures incorrectly.
Author:  mtgstuber [ Sun Jun 03, 2012 4:49 pm ]
Post subject:  Re: Compression / Leak Down Testing Procedure
While I can understand your thought, that doesn't explain the large difference between cylinder two and the other cylinders. Note that I switched from doing a compression test to a leak down test. It seems like a lot of hassle to put it back together only to find that I have to tear it all back apart.

In particular, I seem to be getting a large and steady leak out through the exhaust system. Mark suggested putting some oil in the cylinder and retesting. (haven't done yet, but will do)

As for the cooling system, yes it's torn apart. I've checked the various outlets and didn't
seem to get any air coming out of them, but, unlike the exhaust, I don't have the luxury of just a single outlet to check.

I'm open to advice on how to improve my testing procedures w/r/t the leak down test.
Author:  EAB [ Sun Jun 03, 2012 5:17 pm ]
Post subject:  Re: Compression / Leak Down Testing Procedure
Double check you leak out the exhaust. With no cams, the only way out the exhaust is a bent valve.
Author:  Joe Romas [ Fri Jun 08, 2012 11:53 am ]
Post subject:  Re: Compression / Leak Down Testing Procedure
Have you read this thread :?:
Sounds to me like what your looking at :furious:
viewtopic.php?f=5&t=66774
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