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LDT 465 Multifuel. Andy3's Broken Camshaft

oddshot

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LDT 465 Multifuel broken cam. Andy3's M35A2

A couple months ago, Andy3 posted that the multifuel engine in his M35A2 had died on the road. He heard a “thump” and that was it. The truck was towed to 73m819 (Ron)'s shop who found that the engine had broken a cam shaft.

This truck was subsequently towed to the Steel Soldiers Rally where the old engine was lifted out and a used engine installed. These events are covered in the following threads and in the interest of brevity, I would ask that you read them if interested.


http://www.steelsoldiers.com/showthread.php?128165-Deuce-was-dead-on-side-of-the-road



http://www.steelsoldiers.com/showthread.php?130298-SSGR14-Engine-and-Bed-Swap


I remembered reading on this forum that quite a large number of engines has suffered this failure. Although a number of folks have put forth theories about the causes of this failure, I have not seen a thread where somebody disassembled the engine to find the cause, and only one instance where somebody replaced the cam, timing gears, bent valves and bent push-rods and got the truck running. Most folks just find a used engine and trash the old one.

I picked up Andy3's engine at the rally and have begun to disassemble it in the hopes of finding the cause of these broken camshafts. Perhaps there may be a bit of PM we can do to prevent this failure OR maybe we can find out if a repair could be done to these engines ... maybe even in the chassis.

Andy3's engine was built by White in 2-84. Andy3's M35A2 is a 1971 and has about 54,000 miles on it at the time of the failure, obviously this is a replacement engine but there is no way to determine the number of hours on it. There are NO rebuild tags on it, and, so far, I do not see any signs of anyone having been inside this engine. The inside of this engine is VERY clean, it appears to have had frequent oil changes and so far I find no sign of abuse, harsh treatment or evidence of overheating. Andy reports that the engine had been running well at the time of the failure.

Unfortunately, folks who have had this failure did not post any background info on their engines, such as who built it, when it was built or if it had been rebuilt at some time. Most owners did not do any diagnosis beyond establishing that a cam had broken. All of the owners report that their engines had been regularly maintained and running well at the time of the failure.

As I do the tear-down, I will share what I find. Where I can, I will include pictures.
 

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oddshot

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I began by removing the rocker arm assemblies and push-rods. The rocker arms were free and not binding. 5 of 12 push-rods are bent. By measuring their heights, I could see that at least 3 valves are bent to the point that they are hanging open a bit. This is consistent with an engine who's crankshaft and camshaft have gone out of sync. I checked all of the valves to make sure that they were not frozen in their guides, all of them moved freely. I was able to move all of the cam followers (lifters) by lifting the up and down with just the suction created in the oil by the pushrods.
 

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oddshot

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I removed the crankshaft pulley/harmonic balancer assembly and front engine cover. I checked all of the gears to make sure that none were bent or had teeth chipped, worn or missing. I could see no evidence that a foreign object dropped into the gear set and jammed.

Using a wrench, I spun the engine to make sure that the engine was free and the gears meshed and turned correctly and found no problem.

I did find that I could rock the cam gear quite a bit. I removed the retaining bolts from the front of the cam and removed the gear and front portion (i.e., the broken piece) of the camshaft.

The cam shaft had broken immediately behind the first bearing. I found no evidence galling, excessive heat, or oil starvation on the bearing journal of the camshaft, and none on the camshaft bearing. Both are worn smoothly and the broken bit of the cam shat spins freely in its bearing.

Some people have speculated that the front camshaft bearing may have spun in the block and starved the bearing of oil. I can report that is not the case in this engine.

I reached into the block and found that I can spin the remainder of the camshaft with my fingers, no tools are needed. The cam shaft spins freely and has no up and down play that I can feel.

The pictures below are of the cam shaft and its bearing still in the block. The picture that looks like the surface of the moon is the broken end of the cam. Note the crystallized appearance of the broken piece.

At this point, I have to admit to a bit of impatience on my part. I got way too curious and started doing this teardown while the engine is still on my truck, and the truck is in my driveway. The tools I need to measure the cam journal and the ID of the cam bearing are in my toolbox at work. As soon as I get this measurement, I will post the info here.
 

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oddshot

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Below are pictures of the cam gear and the broken nose of the cam. Please note that the bearing surface does not show any galling or oil starvation, and that this side of the break shows the same crystalline appearance with no evidence of grinding or friction wear.

For the record, the cam's bearing surface measures 1 3/16 inch across. That is a fairly large supporting structure.

My plan is to remove the rest of the cam and get a measurement of the cam bearings. I am sending a sample of the oil from the engine out for analysis and will be cutting the filters open to see what I might find in there. I have friends who can help determine the nature of the break.

I find the place where the cam shaft broke very interesting. A radius molded into that corner could have prevented a possible stress riser, but at this point, this is just speculation.

As the undertaker said, "Remains to be seen".
 

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61sleepercab

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Could it be that from the amount of fracture prior to breakage that this camshaft was defective during manufacturing and the outside edges was the only thing holding the pieces together? Looks from the pictures a prior break waiting to snap at any time?
 

oddshot

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A side note: I didn't have a puller suitable to remove the crank pulley/harmonic balancer assembly, so I spent some time this morning making a very nice tool for the job so as not to break anything.

It turns out I wasted my time ...

At least it didn't land on my foot.
 

oddshot

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Jasper, Georgia
Could it be that from the amount of fracture prior to breakage that this camshaft was defective during manufacturing and the outside edges was the only thing holding the pieces together? Looks from the pictures a prior break waiting to snap at any time?
No ... its just the pictures. The color of the break was uniform throughout. The high spots along the edges do show just a *little* shine where the two pieces of the cam touched while Andy tried to restart the engine.
 
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oddshot

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I'm interested in seeing the bottoms of heads and tops of pistons!
Yeah ... me too. No doubt at least 5 valves touched pistons, I'd like to see what else is going on in there.

I'm gonna get to all that after I get the engine out of the back of my truck and down on the ground where it would be a bit more stable and I don't have to climb up and down all day.

If you guys think of anything I may have missed or have any information on camshaft failures in this engine, please let me know.
 

Keith_J

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My thoughts - could be wrong. Sharp corner = stress raiser. Cyclical torque loading of shaft causes cyclical deflection and metal fatigue.
Most excellent hypothesis. Now, what is the camshaft material? Nodular cast iron? Probably. Look at the Goodman endurance limit for this material. Realize cams in four stroke engines spin at half crank speed. 12 valves then load it 12 times per revolution.
 

John S-B

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I nominate Oddshot for Official SS Deuce Coroner... Was that blue fabric an actual sterile surgical drape?? :D
 

rustystud

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Most excellent hypothesis. Now, what is the camshaft material? Nodular cast iron? Probably. Look at the Goodman endurance limit for this material. Realize cams in four stroke engines spin at half crank speed. 12 valves then load it 12 times per revolution.
The cams are forged steel, they should not break like this. I believe it is a manufacturer error in the steel billet used. Also it could use a radius on those sharp corners. The last time I saw a break like this was on a tractor spindle. They said it was worked hardened, and due to stress it broke. But what kind of stress would a cam experience at this point ? Metal fatigue is also a factor, but the engine is only about 30yrs old. Must be manufacturer error.
 
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cattlerepairman

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The breadth and depth of knowledge on this site never ceases to amaze me. Coroner oddshot is doing a rather thorough autopsy and I enjoy watching it!
 
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