8-71 engine compression tester

[Larry B]

Two months ago I took my unit to a local shop to recheck all my clearances and set governor. After three days they said it would not run proper because timing was wrong. I pulled engine,  timing was correct. I found a lot of the mistakes that were made in those three days. But I am not sure what all happened, so for my own piece of mind I would like to do a compression check before I reinstall engine. Please explain how to make a compression tester from an old injector and the proper procedure for the test. Engine is running on shop floor to a water barrel now and it is a lot easier to work on than in bus.

[luvrbus]

Take the barrel off the injector off and weld a pipe in the barrel and build the hold down for the injector clamp, adapt to your gauge, remove one injector at a time install the unit you made and clamp down run the engine @ 900 rpm depending on the altitude you have 450 to 550 psi on each cylinder reinstall each injector and set everything on that cylinder go to the next one it takes a while to do a compression test on a 2 stroke.

Don't try and test one without a barrel in the tube 99.9% of the time you will blow the injector tube then more work lol some just use a plate on top of the barrel with a tap and use the clamp bolt hole to hold it down I never tried that.

Have you tried to borrow one from a dealer most of the time they will loan you one,if it wasn't so far I would lend you my Kent/Moore

[artvonne]

 If your pulling the injector, why not do a leakdown test?

[bevans6]

At this point, if you are pretty convinced something is wrong in that hole, I think I would take the head off and look at it.  The engine is out, you obviously know how to swing a wrench, so getting the head off and pulling the piston would not be an insurmountable challenge.  Or - are you more at the point where you think it's come good, and just want a little more insurance?

I found this:  for $45 I would buy one rather than make one.  http://www.toolsource.com/diesel-engine-compression-test-adapter-detroit-diesel-p-58487.html

Brian

[Larry B]

I am about 90% convinced there is nothing wrong. I would like a little more insurance. To reinstall a head after the engine is in the bus would be really hard.

[Larry B]

Explain the leak down test. I may as well do this also. The more insurance I have the better I will fell.   

[luvrbus]

Larry, no such thing as a leak down test on a DD 2 stroke 

good luck

[wg4t50]

I never heard of a leak down test on a Detroit either, BUT with a little effort you could pull it off, all you need is the air compressor, the tester that has the two gauges. Never seen one for this high of compression, but have done my Lycoming aircraft engine many times, of course you only use 80 psi at TDC and read the leak down number.  Simple to  determine where the leak is, intake, exhaust or in crankcase.
Would guess on the Detroit, you would need about 200 psi for that test if it were tried.
AS they say, that is my opinion or FWIW
Merry Christmas

[artvonne]

Larry, no such thing as a leak down test on a DD 2 stroke 

good luck

 Clifford. In another thread you explained doing a compression test using a modified injector or Kent Moore tool, running the engine at 900 rpm and reading pressure.

 I am curious as to why you say you could not do a leakage test using the same type tooling, holding the engine stationary at TDC (valves closed), and pressurizing the cylinder through that same type of tooling.

[artvonne]

I never heard of a leak down test on a Detroit either, BUT with a little effort you could pull it off, all you need is the air compressor, the tester that has the two gauges. Never seen one for this high of compression, but have done my Lycoming aircraft engine many times, of course you only use 80 psi at TDC and read the leak down number.  Simple to  determine where the leak is, intake, exhaust or in crankcase.
Would guess on the Detroit, you would need about 200 psi for that test if it were tried.
AS they say, that is my opinion or FWIW
Merry Christmas

  Engine compression ratio has nothing to do with a leakdown test. 80 psi is an arbitrary number, you could use any PSI but the testers are generally calibrated (orificed) for 80 psi so thats what you use. The cylinders in a big aircraft engine like a 540 Lycoming are larger than a DD, and holding the prop from turning with 80 psi applied to that big piston can take two men if it gets very much either side of TDC. But we actually did rotate the engine a bit while under pressure to seat the rings.

  You would be hearing a great deal of loss through the crankcase oil filler and if you pushed and pulled the prop back and forth would hear a "snap" of the rings popping into position and feel a sudden increase of pressure on the prop (and gauge), and a drop in the audible sound of air coming from the crankcase.

  We often saw 79 over 80 on good tight engines, 75 over 80 on mid time/older engines, and low 70's on tired ones. Once they fell into the 60's you would generally ground the plane. Thats if all the loss was past the rings. You really want zero loss through a valve. Whether it was an airplane or a lawnmower, or a Bus or a car, diesel or gas the readings should be looked at with equal value as to the engines condition....leakage is leakage

[wg4t50]

Paul, Exactly, I had the IO-360, still the same cylinders as the 540, 90 CID each.  Yup, been there, done that.
Now that I gave up the MCI with the 12V-71, I settled for a ISM500 Cummins in a 36' Foretravel, miss the MCI but too old to maintain a physical or a MCI, so needed a store bought RV so I could take to factory and have serviced correctly.
Old age sucks !
Dave

[luvrbus]

I know how a leak down test is done Paul do one a a 8v71 and please post your results for us

[Larry B]

Didn't seem to get much done today. Got the tester built, will try it tomorrow. had visitors stop by with Christmas wishes.

[Rick 74 MC-8]

Be careful that Diesel can start if it spins over


Rick 74 MC-8

[artvonne]

I know how a leak down test is done Paul do one a a 8v71 and please post your results for us

  I may just try it some day if I have a need. I cannot see any physical (mechanical) reason it wouldn't work, and your obviously not going to share if you know of one. 

  Rick, one would hope that anyone with enough knowledge to do a compression test or leakdown test would know to have a diesel in a no fuel condition. Kind of like knowing why you dont arbitrarily walk up to airplanes and turn props by hand.