M35a2 knock

[cattlerepairman]

Hairline cracks on the heads are normal to an extent, especially if the heads are older and are not from the last castings in the late 1980' . The TM specifically mentions that the cracks within specs do not make a head unserviceable.

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[TAZZJR]

Hairline cracks on the heads are normal to an extent, especially if the heads are older and are not from the last castings in the late 1980' . The TM specifically mentions that the cracks within specs do not make a head unserviceable.

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Not to discredit you I just want to read to insure I know what I'm looking at and for. Where in the tm is this mentioned?

 

[ToddJK]

Did your truck have any blowby? Depending on how bad that crack is could be a source to one issue, but I don't think that helps the knocking issue though. I'm curious to see what you discover as you dig deeper as to what the knock was caused from.

 

[rustystud]

Honestly it's a rod knock, or severe piston slap. That test you did by eliminating the injector is a classic test for rod knock. Remove the fuel and there's no pressure so no knock. Same applies to gas engines. Remove the spark plug wire and listen for the knock to go away. You don't always have a pressure drop either. That would mean severe bearing failure.

 

[TAZZJR]

Honestly it's a rod knock, or severe piston slap. That test you did by eliminating the injector is a classic test for rod knock. Remove the fuel and there's no pressure so no knock. Same applies to gas engines. Remove the spark plug wire and listen for the knock to go away. You don't always have a pressure drop either. That would mean severe bearing failure.

I'll be dropping the pan soon and checking the rod bearings.

 

[cattlerepairman]

Not to discredit you I just want to read to insure I know what I'm looking at and for. Where in the tm is this mentioned?

Look into the Troubleshooting manual for the LDS 465-1 engine, page 49:

 

[Mullaney]

I'll be dropping the pan soon and checking the rod bearings.

.
There is a low tech tool to test the bearings.
Unbolt the rod cap, apply some Plastigage.
That will show you what the bearings are doing...

 

[TAZZJR]

My mistake I ment to say that the pistons have cracks not the heads.

 

[rustystud]

.
There is a low tech tool to test the bearings.
Unbolt the rod cap, apply some Plastigage.
That will show you what the bearings are doing...

That will check the rod bearings, but the wrist pin bushing and piston skirt collapse cannot be tested without pulling out the piston assembly. Though you can get a feel for the piston by grabbing the rod and pulling it hard back and forth and see how the piston moves in the bore. Should be no movement.
I once checked an engine's pistons this way and found one that was ready to swap bores !

 

[TAZZJR]

Without getting into things that are not truck related that delayed me, I was finally able to finish the rebuild. I rebuilt the heads a while back, replaced the pistons and barrings, added spin on oil filters, and added a thermocoupler to the exhaust manifold.

The final issue that has held me up for months has been getting it to simply crank.
Turned out to be a fix of some residual air in the diesel lines and fine adjustment of the valves. Once the valves were finally adjusted correctly it started like it had ran for years.

I just wanted to say a big thank you to everyone that helped me out. I couldn't have done it with out yall.

 

[m715mike]

Awesome job TJ!

 

[ToddJK]

That's a great feeling of an accomplishment when you do all that work and it pays off in the end!

 

[rustystud]

Glad to hear your back on the road again !

 

[M37M35]

Without getting into things that are not truck related that delayed me, I was finally able to finish the rebuild. I rebuilt the heads a while back, replaced the pistons and barrings, added spin on oil filters, and added a thermocoupler to the exhaust manifold.

The final issue that has held me up for months has been getting it to simply crank.
Turned out to be a fix of some residual air in the diesel lines and fine adjustment of the valves. Once the valves were finally adjusted correctly it started like it had ran for years.

I just wanted to say a big thank you to everyone that helped me out. I couldn't have done it with out yall.

Glad you got her going again!
So what went bad to cause the knock?

 

[TAZZJR]

Glad you got her going again!
So what went bad to cause the knock?

Head gasket and pistons were the only thing I saw that was bad in the entire rebuild. I believe the rhythmic noise was the gasket blowing by between the heads. I did alot of troubleshooting to follow the noise to find it between the heads. I have a video somewhere that I shoved a paper towl between the heads and watched it blow by.

I called it a knock but I never found any metal on metal wear to cause a knock. The noise is gone. So the head gasket is the only thing I know that would cause the rhythmic noise.