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.
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
If your pulling the injector, why not do a leakdown test?
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 (http://www.toolsource.com/diesel-engine-compression-test-adapter-detroit-diesel-p-58487.html)
Brian
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.
Explain the leak down test. I may as well do this also. The more insurance I have the better I will fell.
Larry, no such thing as a leak down test on a DD 2 stroke
good luck
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
Quote from: luvrbus on December 22, 2011, 04:25:51 AM
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.
Quote from: wg4t50 on December 22, 2011, 12:35:22 PM
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
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
I know how a leak down test is done Paul do one a a 8v71 and please post your results for us
Didn't seem to get much done today. Got the tester built, will try it tomorrow. had visitors stop by with Christmas wishes.
Be careful that Diesel can start if it spins over
Rick 74 MC-8
Quote from: luvrbus on December 22, 2011, 03:46:58 PM
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. ;D
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.
Larry,don't forget and take a old fuel jumper line to make a bypass line so when you start the engine fuel it doesn't spray everywhere .
I made a jumper for fuel lines . I need to question a few other things. Used old whole injector. Removed all internal and seal welded all open holes. Top hole (where spring was) welded a 3/8" pipe nipple. All I have left in head is three push rods sticking up and valve springs on test hole. Plugged rocker arm mount holes with short bolt to stop oil flow. Installed test unit with hose and gauge. When engine was started I expected it to run rougher than it did. 15 seconds after starting engine the test unit started to smoke. I was NOT expecting this smoking. Glanced at gauge and shut engine down.Is it normal for the compression tester to get so hot that when oil lands on it, the oil will smoke light blue? First glance at gauge was 200psi. I might have too large and too long a hose between test unit and gauge. A lot of my compression is used to fill hose. I am going to mount direct on top of test unit. Should I expect gauge to bounce a lot? I do have a check valve I could add between test unit and gauge. Gauge is 600psi liquid filled. Hose was 3ft. long- 1/2" i.d.
Reinstall the rocker stands the exhaust valves have to be in the loop and operational only the injector is out of the loop and it will bounce around , the gauge should be a direct mount with no hose only a bleeder valve which is not necessary IMO
good luck
Artvonne,, you are correct on the 80 pound pressure being an arbitrary number,, the regs state that a cylinder cannot loose more than 25 percent of what is applied. With the exception of the large bore Continentals, which now use a "calibrated orifice" method of testing. ( SB 03-3).>>>Dan ( 32 year I/A and counting)
Did the test over the last two days. The home built tester from an injector seems to work only I don't like what it is telling me. I have a problem on both sides. Only 225 to 240 lb. compression. I ordered a tester today off ebay. Should have done what Brian suggested to start with. Was not expecting boths sides to read bad. An odd thing was I got a little higher reading at 600rpm than I did at 900 rpm. I believe I got pictures figured out will try and send one of tester.
Check the manual 600 rpm maybe right for a 8v71 n/a
good luck