Terex 72-41

[monsterchuck]

Hello all,
I recently picked up an older Terex 72-41 loader. She's definitely a little rough but should work well for what I plan to do with it. I plan on servicing all the fluids and filters eventually, but first I need to get the engine straightened out. It's a 4-71N Detroit that ran when I brought it to my shop but missed on cylinder 2. I pulled the air box cover and found coolant leaking down the cylinder wall. I got the head pulled off and found the compression ring around cylinder two very obviously failed. Where it failed, it looks like it overheated and slightly deformed the liner. I know I need to put at least a new liner and rings on cylinder 2, but my problem is getting the piston out. I read that there was a way to remove the pistons and liners from a Detroit without removing the oil pan, but for the life of me I can't figure it out. Do I have to remove the blower? Or is it just not possible without pulling the oil pan?

 

[Rustyfender]

Last winter I spent a lot of time fixing a 471N 2 valve, I am pretty sure you have to take piston's out the top, but the only way I could get the bearings unbolted would be by removing the oil pan.

 

[monsterchuck]

Well, looks like I have to get the oil pan out of the way somehow. That's not going to be fun. Thanks for the insight.

 

[Rustyfender]

Good luck. Take your time, it is fairly straight forward piston has to be installed with sleeve

 

[monsterchuck]

I managed to get everything apart, and I'm trying to find replacement parts. I had 3 N75 injectors and one N65, the N65 being on the failed cylinder. I'm guessing the yahoo who replaced that injector didn't time it or run the rack afterwards, and that's what cooked the liner and head gasket. Which is unfortunate, the engine had apparently been rebuilt and didn't look to have too many hours before the head gasket and liner failure. Anyway, can someone please explain to me the difference between the crosshead and trunk pistons in a Detroit 71 series? I've read that the crosshead is a two piece design, but also that a trunk piston has a cast iron upper and an aluminum lower piece. Is it that the wristpin on a crosshead piston bolts to the connecting rod while the trunk piston uses a more standard wrist pin? Old Detroit Diesel info is hard to come by it seems, that or I need to give up my black belt in Google-Fu.

 

[Rustyfender]

Is your engine a 2 valve , or a 4 valve head?

 

[John C.]

I can confirm that there is no way to remove the piston without pulling the oil pan and unbolting the piston rod and removing the cap. You don't have to remove the blower to work on the pistons and liners.

Coolant in the cylinder is usually from a leaking injector copper sleeve in the head so you should address that by having the head pressure tested. You don't have to load the liner in the block with the piston in the liner. You do have to fit the liner to the block. The 71 series engine use dry liners and they have to have as much contact with the block as possible in order to transfer heat to the block and then to the coolant. You should consider hiring someone with experience on Detroit engines to work with to repair your motor.

 

[monsterchuck]

The engine does have a 4-valve head.

I was worried about the injector sleeve being the source of my leak, but I confirmed the badly blown head gasket before teardown by pulling the air box cover on the dead cylinder, turning the engine to bottom dead center, and sticking a borescope in the intake ports. There was an obvious stream of coolant coming from between the head and the liner, right where the compression ring was burned out when I got it apart.

I was hoping I might be able to get some Detroit tips from some guys on here. The only shop that works on these near me (that I'm aware of, anyway) is a bit of a drive, and I doubt they'd be too keen on dealing with my old hunk of iron. I know a guy from a truck stop that I worked at when I first started wrenching, but he's retired. I guess I'll keep bumbling on and learning as I go.

 

[John C.]

If that is the case you are still going to get that head to a shop to make sure it is flat. Head gaskets and firing rings don't fail on their own. There is always a reason it happened.

 

[Simon C]

Put lots of these motors together in the Thunder Bay Ontario area. The liners need to be fit like " John C " said. That being said make sure you have someone around who knows what vice grips on the fuel rack means before start up to prevent a run away. I have a complete 53 Series Manual but not a 71 Series manual.
As you said , Trunk type pistons were one piece with a regular style wrist pin and seals pounded into the end to seal the oil.
Crosshead pistons had the wrist pin bolted to the rod.
You will need to check that rod to make sure it is not bent, and will need a special loader to squeeze the rings tight enough to be able to enter the cylinder. You cannot use a band style compressor to load the piston with rod into the liner. Have the Cylinder head pressure tested, and you need to know what paper matches are for when putting the head Gasket Rubber Quad Ring in. Dont forget to back of the buffer screw on the governor before strarting the unit or you may have a run away.
Post an add in the local paper to see if some old guy who built them can sit in a chair and coach you along.
40 Years ago this month I tore down my first Detroit Diesel Engine.
Did travel From Marathon Ontario into the Upper Peninsula of Michigan to tune up a friends Detroit 353 Engine about 25 Years ago.
Ask the old timer about everything I have mentioned to you, and if he doesn't know what I mean he is the wrong guy for the job.
Many of these engines have started and grenaded in less than 1 min., for not following the procedures properly. All the best to you.
Simon C

 

[Bluox]

The liner height is likely too low which let the gasket burn out and cut a water grommet.
There is a ring under the liner flange that sets the liner depth.
It comes in different thicknesses and shims are sometimes used under them.
Liners come in several different sizes.
these engines require a lot of precision measuring.
You need to track down a service manual and someone who has the tools and expertise to use them.
Bad Bob