John Deere 3020 - Rocker arm shaft clamp / bolt failure

[Glen D Anderson]

Good evening.

So.....while using the 3020 the other day, with it idling, it started runing rough(missing) and popping from the exhaust. A few minutes later there was single light knock, a minute later, a few more light knocks, so then we figured we better try to limp it back the shop. On the way there it made a couple of louder knocks which scared me so I shut down thinking we had a dropped valve.

I removed the manifolds to inspect, sure there was an exhaust valve dropped only to find all the valve heads in their proper spot. WTF? LOL Removed the valve cover to find the rear clamp, bolt & washer, for the rocker shaft were broke. All of the parts, with the exception of the broken 1/3 of the washer were sitting in the top of the head. The missing 1/3 of the washer was found down in the intake lifter for #4. None of the broken pieces were hammered up so we were puzzled as to where the knocking noise was coming from? Then we wondered if the broken 1/3 of the washer that we found in the lifter was getting jammed under the pushrod causing to valve to hit the top of the piston?

So, we did a leak down test and all of the valves with the exception of the intakes on #1 & #2 were leaking like sieves along with all of the rings so we removed the head. No sign of the valve/s contacting the pistons anywhere? Further inspection revealed the rocker shaft was bent(at the #3 clamp location) but the pushrods were straight / fine.

Given the age of the engine & leakdown test results this will be getting an overhaul but my question is what caused this???

We're thinking: The washer broke / failed allowing the clamp to come loose which then started hammering on the bolt. The bolt & clamp eventually broke from the constant hammering. Without the clamp to retain the rocker shaft, the shaft bent as a result.

Another question & maybe a moot one, what was making the random knocking noise? The rocker shaft smacking against the head where the broken clamp was?

Anyone see this before? Thoughts?

 

[Cliff Nelson]

I have seen that several times. The aluminum clamp breaking is the most common but I have seen the bolt break too. Always one of the end clamps and usually cracks the shaft.

 

[SVcummins]

My 3020 has it done it once my 4020 done it twice . Note to
self replace the bolts when doing a major over haul . It will
scare you to death when one breaks I think I have a set of
rocker arms and bolts on hand . These dang 55 year old
tractors . A quick test with the old stethoscope which in my
case is a screwdriver or ratchet or long bolt on the valve cover
will tell you right where the problem is

 

[SVcummins]

Not always been in the middle of the engine all three times for me broken clamp twice bolt once

 

[tomstractorsandtoys]

Never broke a clamp but my 4020 had one of the rocker arms break. New ones are made heavier. Tom

 

[Glen D Anderson]

Thanks for the replies.

Thinking I'll be replacing the factory grade 5 bolts with grade 8 and using thicker hardened flat washers. Might consider replacing all of the aluminum clamps too but I can just imagine the price will be enough to scare ya...LOL

 

[SVcummins]

About 20$ each for the clamp the last ones I bought

 

[matthies]

The clamp broke the bolt and washer from where the clamp cracked. Replace the clamps, bolts, washers, with factory stuff and be down. My 2 cents.

 

[matthies]

Sorry be done.

 

[Glen D Anderson]

Looking at the pieces closer, I think you're right.

(quoted from post at 06:34:49 02/16/22) The clamp broke the bolt and washer from where the clamp cracked. My 2 cents.