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Stuck ud18 project thread. Insights welcome!


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I imagine this will be an ongoing thread as I have this old ud18 that was my fathers and it got left in the rain with one exhaust open for several years.  There was a tin can over the exhaust but eventually it rusted through.   The engine has sentimental value for me as I remember my father running it on his sawmill when I was kid circa 1983, and I'd love to see it live again, after 40 years of sitting.  The engine was in great shape before it sat, so no known mechanical problems.

My tIme, funds, and expertise are limited and the engine will almost certainly have to be torn down and rebuilt... so this could take a while, maybe years as I tend to get sidetracked with other projects around the farm.  It will be the first engine I attempt to rebuild all by myself, and a tricky one since parts are hard to come by and $$$.  So I'm definitely gonna be asking y'all for advice from time to time.

Other times I will just post some pics, updates, etc.

Initial status of the engine was:

  • engine stuck, stuck, stuck.
  • no obvious cracks in block or head(s).
  • compression release mechanism stuck.
  • 3 valves appear stuck
  • injection pump:  unknown if stuck or free.  (Bosch)
  • fan blade (water pump) rotates
  • clutch works.   (unit has a flat belt drive, which spins in neutral, stops when engaged)
  • has an electric starter.  untested, presumed dead.
  • has a bigass manual crank.  It seems something is broken, so the crank only barely engages.
  • thick grime in the rear head when I removed the exposed exhaust manifold.   manifold itself seems surprisingly ok.  (not all rusted away)
  • front head comparitively clean after removing intake and exhaust manifolds.
  • minor rust visible in the cups underneath injectors. 

Tomorrow I may have some pics to share. I just got a new endoscope also, so I can check out condition of pistons/cylinders.

Right now I am hoping that someone out there has a service (or parts) manual for an old ud18 with the two separate exhaust manifolds and the rounded intake manifold.  I need the pages that discuss (dis)assembly of the intake manifold and the funky housing above it that does compression release stuff.  The older intake manifold is identifiable because it has 3 bolt holes at top center.   The newer (i think) one has 4 bolt holes and removable covers at left and right side.

My problem (one of many) is that the compression release mechanism is stuck inside either the intake manifold or the above housing or both.  There appears to be a single valve, much like an engine valve, that extends into the intake from the housing above and I'm guessing it is this valve that is stuck.   So the housing can't be removed from the intake yet.

I have the intake and housing off the engine, soaking first with penetrating oil and now with diesel.  There is a little 2 inch lever that is supposed to actuate the mechanism that gives me a place I can (lightly) tap with a hammer in both directions.

I actually have 3 different service manuals that say ud18 and ud18a, but all three discuss the other (newer) type of intake manifold which seems to work quite differently.   I found on ebay just now a parts manual that clearly shows my type of intake manifold, so I will order that.

The good news is that I got all the rest of the compression release mechanism working:  lever freed up, starting valves are free, carb is free, linkage is free, and it will catch in start position and release to diesel like it is supposed to.  So I'm calling that a win.

My immediate goals are:

  • get the intake manifold freed up.  
  • get pictures inside the cylinders.  (might have to suck out some diesel).
  • either get everything back together, or create a proper way to store/label parts and prevent further dust/corrosion of exposed parts while I work on it.   The engine is under a metal roof, but no walls, so exposed to dust, humidity, etc.


Sorry no pics yet.  My phone was dead this morning.  






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If the cooling system is still intact you can heat cycle the engine with a block heater.

 find a heavy-duty electric timer, set the block heater/ coolant heater for 12hrs 0n ,12hrs  off.

 fill the cylinders with whatever magic concoction you believe is the best rust dissolver, and let it heat cycle for a week or two.  if it is still stuck, you have the knowledge you covered all the bases.

 King of Obsolete (google this) makes a gadget he calls the bar starter. Worth a try.

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yeah, I was thinking about something like that, with heating it, maybe a propane heater under oil pan.   The block heater + timer is a nice idea for getting lots of cycles.  Coolant system is intact but empty, and might have leaks (untested).

I put the endoscope down the cylinders and intake/exhaust ports yesterday.   Cylinder #4 is not letting any diesel past the piston, but the other 5 have drained.  Significant rust in all of the cylinders.  Two valves are stuck and lots of rusty grime above them.

I had about resolved just to pull the heads and go through it.  I figure that even if I get them all moving, there will be some stuck rings, and maybe enough crap on the cylinder walls to damage piston(s) anyway.

Now though I'm thinking that the heat cycle thing may be my best bet to free them up first without having to drop crankshaft and beat out with sledge and torch.

I don't presently have a block heater and the engine is a few hundred feet from nearest electrical outlet so I'd have to run a long extension cord, but it's doable.

I have some other concerns/doubts:

  • If I just fill up the radiator, will this fill the engine block around the cylinders without the water pump running?
  • If I remove the head first, can I still try this trick...   seems like I could still fill up water jacket in the block, right?
  • If I drain the coolant, will it fully drain from the block?   My concern is if some water remained, that could freeze over the winter.  (if I haven't gotten it fixed or fully torn down by then).  I see there is a dedicated drain in the block, so probably it should be fine.


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Progress!    I was able to get the intake manifold valve mechanism to free up today.

I put a C clamp on the spring.  It still didn't want to budge, but then I tapped on the lever thingy again and boing! it popped free.  After working it some, movement is pretty good except it is a bit sticky going from starting position (valve up) to diesel position.   I poured a can of Coke in there which should settle below the diesel and maybe eat some rust or dried grease.

Anyway at least now I can compress the spring and disassemble the unit for a proper cleaning and greasing and probably painting.  All that can wait until the engine is freed up.

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Also yesterday I brought over an old and wide metal filing cabinet and cleaned it up.  It's a bit rusty but makes a great place to organize and store parts, ziploc bags, boxes, etc.

I put all the bolts, nuts, etc in labeled zip-loc bags.  And larger items in cardboard box inside the cabinet or else in tough construction trash bags outside.  With this system in place, I am no longer concerned about opening up the engine for possibly a lengthy time and parts being exposed to dust, bugs, or worse yet lost.

Today I ordered a block heater and some oxalic acid.  The acid is supposed to gently chelate rust and liquify it while leaving good metal mostly alone.  I figure I will try some heat/cool cycles with some of that in the cylinders.

I'm ready to take the heads off in the next day or two, but I'd like to confirm I can still put water in the block and do the heat/cool cycles with the heads off.   Does anyone see any problem with that?


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Ok, time for some photos.

Here's the engine, from Diesel injectors side.  Note the bucket of bricks hanging off the hand crank.    I don't want to load it too heavy though, because the crank slips pretty easily.



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Here's the gas spark plug side with intake and exhaust manifolds removed.   Rainwater entered the exhaust ports which are the 1st and 3rd holes from the left.  Affecting cylinders 4, 5, 6.


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No rust or sludge to speak of inside the valve cover housing.   Though exhaust valves for cylinder 4&5 are stuck.  These both share the same exhaust port.


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Here's the intake manifold+housing assembly in the Diesel (valve down) position, as it was stuck.  To the left of spring is a valve guide.

When the lever is operated, the spring compresses until center point is passed, and then snaps into the opposite position.

Notice that the manifold pipe is just round. Unlike the newer style discussed in the service books I have, it doesn't have separate passageways for gas/diesel, nor butterfly valves at the ends.  Just the single valve, which I surmise allows more air in for diesel when raised, and less for gasoline when lowered.

There is also a separate chamber in the upper housing with an electric switch that enables the magneto in gas mode, and grounds it out in diesel mode.  (not pictured)

I haven't found any other photos or video of this assembly on the internet after a search.   Mine is full of diesel in these pics, I will try to remember to take a picture after I drain it.



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This is odd/concerning to me.  These two round extrusions are located just above the injection pump.  The one on the right has a shallow circular hole which may have been machined for some reason.  Inside that hole, is a smaller irregular hole just under 1/8 inch, which appears to have rusted through to/from the inside.

Maybe they are some kind of freeze plug?   But there are flat freeze plugs elsewhere on the block, that appear just fine.

And it kinda seems that a past owner attempted to drill it out for some reason.

If anyone knows what these extrusions are for, please let me know.  Anyway, I figure I'll just weld up the "drill bit" hole and call it good.


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Pictures of cylinder walls/piston after soaking in diesel for a few days.   From cylinder 1 to 6.  The light is not terribly bright, but you get the idea.  Kind of a horror show.  Cylinder 4 has red diesel in it, and now I know for sure my endoscope is diesel proof.  heh.  Cylinder 3 is near TDC, so it didn't capture any cylinder wall.

I'm kinda surprised how bad cylinder 1 wall looks considering that it wasn't catching rainwater.   But it has a valve open, and 40 winters of humidity.... 

note: timestamp in the images says 2022, should say 2023.







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Progress:  I finally was able to get the compression release shaft out which then allowed me to remove the rocker arm assembly.

There were a couple of headaches, which I will describe with photos below.

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Ok, I've gotta remove this compression release shaft that crosses through the valve rocker assembly, and before the shaft can be removed I've gotta pop a pin out of a linkage rod.   Of course, the pin (at bottom) is good and stuck.

The little lever (spring retainer) near the top will have to be removed also, but lets not get ahead of ourselves.



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Well the pin finally came out, but it took about an hour of convincing with torch, prybar, hammer, and penetrating oil.

At the top of the picture, you can see there is another smaller pin, which I also removed and took about another hour.  But that one I did later on the vice so it was a bit easier.  I have to be careful and patient as I don't want to break any of these brittle old linkages.


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Next I had to get that lever off.   There was a nut and locknut that came off.  At first I thought the lever just clamped the shaft like a battery post clamp, but no, it is solid all the way around.

I wasn't sure how to proceed, so decided to check the service manual.  Strangely, the first service manual I checked doesn't even mention this part during disassembly.  The 2nd service manual is just the same.  Finally I checked a military service manual I have and it says to "gently and carefully" tap the pin out.    Duh!   but somehow looking at it before I couldn't see that the pin extended all the way through.

Ok, cool, I'll just gently tap it out.

yeah right.

An hour later, with more use of the propane torch, penetrating fluid, and a big bolt for a punch, the pin finally came out.  threads are okay and nothing broken.  hurray!

Anyway, the assembly is kind of interesting.  The compression release shaft actually has very elongated threads that make it move left/right across the rocker arm assembly as it is operated.  I'm not sure yet why this is useful, possibly has to do with torquing down on the starting valves. 

Then the shaft has a groove in where the pin sits, and the pin itself has a tapered flat edge that fits up against the shaft's groove and binds as the nut is tightened.   I'm glad I didn't mess up that pin, as it would be a "fun" machining exercise if so.



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The tops of the valve stems do not seem worn, so I consider that something of a good sign.

I tapped on the 2 stuck exhaust valves in cylinders 4 and 5 and was able to get them to release and pop back up.  They still seem sticky compared to the others, but I guess that's no surprise.

I hope I didn't damage the valve seats doing this.  It might have been better just to leave them for now and soak the entire head in rust-911 or hot tank first.    Oh well, that ship has sailed.


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I took some pictures of the identification tags and accessories.

Engine -- model: ud-18, serial: UDR 2361

Stamped on block: UDRM 2517     (why is this different from serial on id plate???)

Injection Pump:  American Bosch, GVA 225/700 A F   (GVA225/700AF for anyone searching)

Starter: Delco Remy, model: 665, serial: 156, volts: 12.

Magneto: International Harvester, F6-48431.    (model F6, and I guess the rest is a serial #)


If anyone can tell me what year this thing was made that would be good to know.  I'm guessing maybe '38 or '39.


That's all for today.









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I didn't spend a lot of time on the website but the Wisconsin Historical Society (in it's IH collection) model UDR-18 with serial numbers from 2351 to 2367 were built in April 1942.  I cannot find UDRM-18 serial # 2517  which is stamped in your block which suggests to me that this is an ENGINE serial # (UDR "M" = "motor") separate from the complete UNIT serial #. 

The first UDR-18 power units were built in 1940.  1942 seems to be a logical year of build for your unit.

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