Causes of low compression

[Tractorboy88]

Where you take the compression readings - connect an air hose from your air compressor(adapter needed) then with the piston at top dead center and locking the crank if possible. Slowly add air pressure and check where the air escapes. Out the carb bad intake valve. Out the exhaust - bad exhaust valve. Bubbles in cooling system - blown head gasket or cracked block. Out oil filler - blow by on rings. Have fun.

My compression tester has a quick attach air line fitting, luckily the same as my air lines. I attached my shop air lines (@~100 psi) and the engine holds compression except for a small leak out of the exhaust. No pressure out of radiator or blow by.

 

[Tractorboy88]

One thing that hasn't been mention yet, Has the engine ever been bored out? If it was, are you sure you rec the correct rings for it? The leakdown test is what should give you a good pointer as to the true problem. Good luck.

The engine is at standard bore. The rings were checked before being installed on the pistons and were within the correct gap.

 

[kencunningham]

One thing that hasn't been mention yet, Has the engine ever been bored out? If it was, are you sure you rec the correct rings for it? The leakdown test is what should give you a good pointer as to the true problem. Good luck.

 

[davesl708]

Tractorboy88. When the valves were done were the guides replaced too? Your leak test indicated exhaust leak. Was it on all cylinders or just one?

 

[KYErik]

I have an old diesel backhoe that was hard to start- I had to crank it for at least 20-30 seconds. It turned out that the starter was dragging so bad that it was only cranking about half as fast as it was supposed to (it was like that when I bought it so I didn't know it was supposed to crank faster). I replaced the starter and wow- now it fires right up in 3-4 seconds.

It wouldn't explain the white exhaust, exhuast leak and crankcase blowby, but are you sure it is cranking at full speed? Slow cranking would result in a lower compression reading.

 

[Tractorboy88]

Tractorboy88. When the valves were done were the guides replaced too? Your leak test indicated exhaust leak. Was it on all cylinders or just one?

All 6 guides were replaced. The same valves were used, just ground.

All 3 cylinders leaked by exhaust valve and out through muffler, with enough force to push open the rain cap.

 

[Tractorboy88]

I removed the timing cover today. After rolling the engine over several times, all the timing gears lined up perfectly, dot to dot.

I set up a dial indicator atop the number 1 intake tappet and read off a lift reading of .310".

 

[banjodunn]

G'day as your leakdown test indicates you have got exh valves not seating correctly did you check to make sure you had valve clearance on both valves with the cyl at TDC? I always have to go back to the book for setting 3 cyl valves as i can never remember the sequence for them. I would try your leakdown test again and back your valve adj right off to make sure you do not have a clearance issue. If not I'm afraid it will be head off again if you have to do this then carefully pour some gas in the exh ports with the cyl head on its side and check for leaking around the valve face a good valve job will not leak.

Jon

 

[jimmysisson]

I had a jeep CJ2 flathead rebuilt in around 1967 by a good old mechanic. Drove it from VT to Idaho before the rings seated and it stopped burning oil. At 52 mph, all she wanted to go. Ran fine after that for years. Check valves first.
Jim

 

[Tractorboy88]

Thanks guys. I'm gonna try to put it back together tomorrow and check some other things.

 

[oldpilgrim]

If you replaced the rings, you really need to hone the cyl walls. That friction is needed to seat the rings properly otherwise it could take a long time or maybe never.

 

[sd455dan]

sounds like the valve job wan't done correctly... were the seats ground ??
There should not be anywhere near enough air getting past the exhaust valve /seat at tdc on a leak down test to push open a rain cap/flapper...
If the valves were ground but not the seats , will likely loose compression and increase leakage over matched worn valve/seat sets.

Hope I didn't read your posts incorrectly?

 

[SimS]

^^X2 I agree with Super Duty Dan. If you are applying air to one cylinder and the rain cap is lifting there is a serious valve leak. If the valve and seat check out then it has something to do with the valve clearances or camshaft timing. Good luck.

SimS

 

[tjflicek]

Check for anything preventing air from being drawn into the cylinders on the intake stroke. If a diesel can't get air in it has nothing to compress.

Good Luck

Jeff

 

[Tractorboy88]

Ok folks.

I reinstalled the head today.
I torqued down the head, but left out the pushrods intentionally. I attached my air line to each cylinder and have an audible amount of air escaping through the intake and or exhaust valves, and a small amount escaping by the rings into the oil pan.
I then reinstalled the pushrods and used a long 1/4" extension to gauge piston location, rolling the engine over to TDC of compression on each cylinder and checking/adjusting valve lash. I set intake at .014" and exhaust and .017".
After setting the valve lash, i checked compression with all injectors removed. All 3 cylinders tested at 290-295 psi.

 

[Tractorboy88]

Check for anything preventing air from being drawn into the cylinders on the intake stroke. If a diesel can't get air in it has nothing to compress.

Good Luck

Jeff

The intake elbow boot/hose is removed and is flowing into an open intake. The muffler is also removed, so its also an open exhaust manifold.

 

[Tractorboy88]

If you replaced the rings, you really need to hone the cyl walls. That friction is needed to seat the rings properly otherwise it could take a long time or maybe never.

The cylinder walls were honed with a ball type hone.

 

[Tractorboy88]

sounds like the valve job wan't done correctly... were the seats ground ??
There should not be anywhere near enough air getting past the exhaust valve /seat at tdc on a leak down test to push open a rain cap/flapper...
If the valves were ground but not the seats , will likely loose compression and increase leakage over matched worn valve/seat sets.

Hope I didn't read your posts incorrectly?

I specifically told the machine shop it needed a valve job and also had the owner inspect the valves and valve seats. He pointed out the guides needed replacement. I also disassembled the head myself before i took it to the machine shop so that i could inspect the valves and i picked up a reassembled head. The bill simply stated "serviced head, replaced 6 guides, trued head".

I will say this, this was the first time i had used this machine shop and he does not specialize in diesels, but he has been in business for 30+ years and saw no issue with performing the work due to its size and weight. The last diesel head i had serviced (Ford 2000) i took to another shop, which did exceptionally nice work (cleaning, truing, replacing the guides, replacing the seats, valves, springs, and retainers) and i had no issue with that engine as i have this one. This shop was closed however, for a few weeks during the time i began working on the 3000.

 

[Texasmark]

One more time do a wet compression check. If ok, go back to the starter and ensure it is spinning fast enough to get you the compression you need. Personally, I'd think 200 psig loss on all cylinders being caused by a bad valve or two, slightly amiss is a SWAG. If you flunk the wet test, take it out and work it hard for a couple of hours and back off it starts to overheat to the point where it quits.

Is your starter a 5" diameter. Have you had your battery load tested such that at 200 amperes of current you maintain at least 11v at the battery terminals? Have you tested the voltage at the starter power terminal to STARTER CASE and had at least 10v during cranking? If you fail any of these tests, they go after your starting system.

After sitting on the side lines and reading all this, I don't know what other bases are left uncovered. You have done an extremely thorough job and the problem is still there........apparently you are looking in the wrong place for the smoking gun.
======
I bought a 3000 years ago that the salesman had to use ether to start it in April, in Texas! It was my first diesel and was an education. The $3500 got my attention but had I known what was in store (he surely did....was a tractor roller) I would have passed on it. The problem with this tractor was that the PO had worked it really hard for it's 4500 roughly hours and there was no hose between the oil bath air cleaner and the intake manifold.....top end was shot.

Other thing I found out later was the it was running a gasser 4" starter and diesels require a 5" diameter. Then the connecting wires from the battery to the starter were old and frayed with bad connections. Then the battery wouldn't properly load test. Then I found that the starting solenoid was pitted and wouldn't carry the proper current.

So getting through all that I was in pretty good shape but not quite there.
---------------------
Moving on I realized that an overhaul was necessary. Getting into it, found that the pistons were shot where the rings ride so I had to have new pistons, rings, inserts, got mains anyway and rod bearings. Had the guy work the head over...don't remember what he did but he was recommended by the local Ford house so I used him. I did tell him to do what ever it needs and that included resurfacing.

I did a rough check of the cylinder walls and they were close enough so I was able to continue with my "in frame". I did the ball 30 degree cross hatch hone. After I got it all back together and injectors bled and all that, it fired right up. I took it out and worked it hard for awhile, several hours, watching the temp gauge for overheating which it didn't.....had it done that I would have backed off till it cooled down and do it again.

Have had the tractor now for about 15 years. Have put about 1500 hours on it since the OH. Nar a problem. Didn't even go back and tweak the valves. Passes the start in the Texas winters usually with no thermostart pre heater slobber. I do have a good size 31 battery.

In summary I think two things may help you that are herein.......go out and set your rings and ensure your starting system is up to par.

Good luck and I compliment you on your thoroughness,.

Mark

 

[Tractorboy88]

One more time do a wet compression check. If ok, go back to the starter and ensure it is spinning fast enough to get you the compression you need. Personally, I'd think 200 psig loss on all cylinders being caused by a bad valve or two, slightly amiss is a SWAG. If you flunk the wet test, take it out and work it hard for a couple of hours and back off it starts to overheat to the point where it quits.

Is your starter a 5" diameter. Have you had your battery load tested such that at 200 amperes of current you maintain at least 11v at the battery terminals? Have you tested the voltage at the starter power terminal to STARTER CASE and had at least 10v during cranking? If you fail any of these tests, they go after your starting system.

After sitting on the side lines and reading all this, I don't know what other bases are left uncovered. You have done an extremely thorough job and the problem is still there........apparently you are looking in the wrong place for the smoking gun.
======
I bought a 3000 years ago that the salesman had to use ether to start it in April, in Texas! It was my first diesel and was an education. The $3500 got my attention but had I known what was in store (he surely did....was a tractor roller) I would have passed on it. The problem with this tractor was that the PO had worked it really hard for it's 4500 roughly hours and there was no hose between the oil bath air cleaner and the intake manifold.....top end was shot.

Other thing I found out later was the it was running a gasser 4" starter and diesels require a 5" diameter. Then the connecting wires from the battery to the starter were old and frayed with bad connections. Then the battery wouldn't properly load test. Then I found that the starting solenoid was pitted and wouldn't carry the proper current.

So getting through all that I was in pretty good shape but not quite there.
---------------------
Moving on I realized that an overhaul was necessary. Getting into it, found that the pistons were shot where the rings ride so I had to have new pistons, rings, inserts, got mains anyway and rod bearings. Had the guy work the head over...don't remember what he did but he was recommended by the local Ford house so I used him. I did tell him to do what ever it needs and that included resurfacing.

I did a rough check of the cylinder walls and they were close enough so I was able to continue with my "in frame". I did the ball 30 degree cross hatch hone. After I got it all back together and injectors bled and all that, it fired right up. I took it out and worked it hard for awhile, several hours, watching the temp gauge for overheating which it didn't.....had it done that I would have backed off till it cooled down and do it again.

Have had the tractor now for about 15 years. Have put about 1500 hours on it since the OH. Nar a problem. Didn't even go back and tweak the valves. Passes the start in the Texas winters usually with no thermostart pre heater slobber. I do have a good size 31 battery.

In summary I think two things may help you that are herein.......go out and set your rings and ensure your starting system is up to par.

Good luck and I compliment you on your thoroughness,.

Mark

Its equipped with a new fully charged 4DLT, and i have a set of jumper cables connected to another 4DLT sitting beside it in a 555 backhoe.

You did just say something that has caught my curiosity. The starter on this tractor sounds different, has a different growl than i'm used to hearing on all the 3 cylinder diesels, and it does seem to look different. There seems to be a little more room around it. Maybe its just me doing some optimistic thinking, but first thing ill check tomorrow is the size! Thanks for letting me know that! 3 cylinder Ford gassers are rare around here, although i do have one on my junk pile mated to a 6 speed.