JD 1971 2520 Knock/Cause?

2-3 years ago I purchased a 1971 2520 with an engine knock. The owner said it had been overhauled. It seems his mechanic must of overhauled the head and maybe the rings. Compression is 370-380 psi (very good) on all four cylinders as tested by a diesel injection shop. The same shop felt the knock was coming from the number 4 cylinder. The reason I had it at a diesel injection shop is I was wondering if the knock was fuel related. They said it wasn't, the injectors and pump were setup correctly.

The next step is I removed the timing gear cover. To make a long story short, backlash, idler gear bearings, and balancer shaft bearings all seemed good.

The next step is I removed the pan and crank. The rod bearings and crank did not look bad at all. I did send the crank to a machine shop for inspection. They felt it needed a 10/10 machining, a light machining on the rod and bearing lands (terminology?). By the way, rod bearings were date coded 1989.

Now my question, I removed the pistons and cylinders (sleeves). Note in the picture the wear on the sides of the pistons 90 degrees from the wrist pins. What would cause this? Is this my knock? Note #4 piston is the worst.

Comments sure would be welcome. Paul

Here is a picture of all 4 pistons. Paul

What is a 10/10 machining? .010" under on the mains and rods?
The diesel engine is not the original in my 1969 2520(was factory gas) The tractor has about 6000 hours on it. I had to put new sleeves in it a couple years ago. The crank measures standard, and the pistons still look like new.
Looks like at least some lubrication issues.

Could be the rods have stretched from the looks of the pistons.(not uncommon for a Deere) I would take them to an engine machine shop and have them checked to eliminate that as a reason for the knock.

Were you at an auction over in Middlesex, NY last week? A fellow with the same name bought a very old Ontario drill there.

Just wondering if you eliminated the hyd. pump coupler and the water pump by unhooking them first ? these can really make a racket !

Very nice pictures. Looking at your pistons I can still see the machining in the skirts, and thats a good sign. You say that the compression is good, and thats a better sign. That number 4 has some scoring, but you verified compression which is a good indicator of the walls and rings. Its hard to see your rings though from the photo, but that don't sound like it. .010 over on the grind is normal wear and tear and aint going to give you a knock, so I'm guessing not down there either. How do your wrist pins feel at the rod ends or in the pistons themselves? From what I can see, that wear on number 4 is in direct line with the movement and number 4 is wear the torque meets the drivetrain. Its hard to see, but is that bottom ring broke on No. 4 at about 1 o'clock just before it gets to the wrist pin on the right side in the photo? It does look like its missing a piece from what I can see. By the way, the most pressure on the skirts will be 90 degrees from the wrist pins, hence the longer skirt in that area.

Mark

measure the skirt clearances. I will bet your #4 piston has collapsed and you have excessive clearance making the knock. we have 2510 that did the same thing. Played hell finding that funny rattle- knock ended up replacing two pistons.Paul

I disassembled a complete diesel engine awhile back chasing a bad knock, only had about 500 hrs since I had done sleeves and pistons,bearings and heads redone. Loooooong story short the flywheel had come loose. Just something to check. the OH was an inframe so the flywheel was never touched from the factory.

No. I have enough old stuff. Same first name too? I know there's some over toward Dansville- maybe one of them.

A wrist pin bushing that is too tight can cause a knock and piston skirt wear. Will the piston fall side to side with it"s own weight?? If not then the bushing is too tight.

Your pistons should be cam ground, which means their largest diameter is opposite the pins. That area is also major and minor thrust for the combustion event. While I cannot see the depth of the scoring; cold start hard running (not letting it warm up) and/or overheating can cause this. This is probly not the source of the noise. I assume the noise was at crank speed? I also assume you didn't see copper on any of the bearings, but did you plastigage the mains and rods? Tedious yes, but you need to know on start-up if the knock will be gone. The wrist pins can't be too loose. Lightly oiled, you should not feel any looseness as you rock the rod in the piston. Did you check the flywheel for looseness? Did you check for adequate oil pressure cold and hot? And was the knock deep sounding or a rap on acceleration. How the knock sounded would give you a lot of information. Since a shop ruled out injectors could it be carbon. They can give a rod type knock. Stick to your evidence. Hope this helps. Gerard

Bob, Yes 10/10 is .010 undersize for mains and rods. First number is mains, second is for rods. Usually the bigger the number the cheaper the crank. Gerard

I get the feeling that piston number four is on backwards while looking at the second picture.

Yeah, another Bob Bancroft apparently. Dansville would be about a half an hour drive from Middlesex so that must be it.

At a glance, I'd say that engine was run low on coolant and overheated . . or abused with ether starting in cold weather. I've had to rebuild many Deere 300 series engines that looked exactly like that.
When an engine gets overheated, the piston-skirts are the first thing to suffer. High heat causes the skirts to swell, and the oil on the cylinder wall to exceed its "flash point."
When an engine gets overloaded with ether, pistons with conventional square-sided rings tend to break on top. Pistons with Keystone triangle-shaped rings tend to gaul the skirts.

As to a machine shop suggesting a "10/10." I'd run away and go elsewhere - unless your crank journals are actually damaged. Grinding a crank undersize just makes it a little weaker and it's a shame to do it unless absolutely necessary. Even when slightly worn, polishing the journals an and installing .001" undersize bearings is often all that is needed.

I think, you are "overthinking." That engine is rugged and fairly simple. When piston skirts get damaged like that, they knock. Nothing complicated and nothing uncommon.

By the way, a stuck wrist-pin is near impossible, because in your engine, they are "free floating."
They move in the rod bushing and in the piston bore.

I'd put in new sleeve and pistons. Hand polish the crank journals, install standard bearings and check clearance with Plastigauge. Easy to do.

One thing that ought to done though, is . . . get the big-end (bottom) of the rods checked. Many shops over-look that. Deere rods tend to get slighly out-of-round after a few in-frame rebuilds. The big ends that hold the shell bearings need to be "resized" once in awhile. In our Deere shop, it was standard procedure for any diesel rebuild. If a little out. the rod cap is shaved, and the hole rebored to original specs. It can only be done once or twice, and then the rods get too short.

I also advise you check your balancing shafts and bushings very closely.

Also, since your mechanic said the injection pump was fine - ask exactly what that means? Did he/she actuall check timing advance and make sure it's working correctly?

Thanks everyone for the comments and the time you took to make them. I beleive I got some good advice. I will post again later and give an update.

It is likely too late to stop the 10/10 machining, otherwise I am on the path jdemaris suggested.

I measured one balancing shaft journal, looked good. But the bushings show a lot of copper color so I will replace them.

I really appreciate the comments regarding root cause.

I am including a picture of the tractor when I brought it home. It now has new brakes, painted wheels, new seat, new tires, new radiator and new load shaft/seals.
Paul

I absolutely agree on not turning the crank and do expect that of course there is wear and tear. I didn't know could get bearings .001, but that would be best. I thought first undersized journal/oversized bearing were .010. You are 100% correct, undersized journals absolutely do weaken the crank, but if push comes to shove he can have the journals welded up and then ground down to standard size. I know, unnecessary cost, but can be done. I've had that done ONLY because I know cut or undersized journals with oversized bearing are no way to go for long, or on anything one plans to keep and working.

Your advice was excellent and I too appreciate it.

Mark

By the way in advance JD, when I say weld up and grind the crank, I'm talking about if has to turn the crank down. Not if he can go .001 which I didn't know could go until now. Thanks for the lesson. No one (me) is ever too old to learn.

Mark

I used to work in a shop & ran the crank grinder. .010 is only .005 on a side & hardly enough to weaken a shaft that size. If you weld on them is will be at risk of breaking from stress cracks. Just make sure the grinding wheel has a good radius on it, and not grind too close to the edges. Bearings come in .010, .020 & .030 & if they thought it would make the shaft too weak, they wouldn't be made that small.

Is that just the camera or is the #4 sleeve darker? If so , why??

.010" undersize requires a journal that is .010" smaller diameter, regardless is only .005" per side. Making any journal smaller makes it less strong.

I never said using undersize journals breaks cranks. I said it makes them weaker. Take a high-hour engine that will already have some metal fatique, and then grind it undersize - and it has to make it weaker - unless you have some magic process that makes less metal, MORE strong.
We had a few .030" under cranks break. Now - as to why? I assume there were long-hour fatique cracks, and grinding .030" under was the "straw that broke the camel's back." Also, Deere claims that any crank-dampener with over 10,000 hours should be renewed it it also leads to broken cranks.

My point was, an still is - to blindly grind a crank that might not need it - is foolish. On the other hand, if a crank has bad journals - then there's aren't many options. Spray-weld the journals, grind undersize, or buy a new crank.

Deere sold .001" and .002" undersize bearings to install in standard cranks with slght wear. We did many and it's a very fix for machines that are only slightly out of tolerance and have low hot oil pressure at engine idle.

Just because a company sells a product to fix engines, does not mean, or prove - they certify it a fix "as good as new." Often the purpose is to get more use, that's all. Deere also allows undercutting armatures on diesel starter-motors - but also says they will not have the endurance of a new armature with a full-size commutator.

There are some old Deere #s for .002" bearings. Knowing the way Deere has dropped much of its parts support, they probably have to be source aftermarket now.

AT21108 0.05MM (.002" under) US, PLAIN (PKG. OF 2 HALVES) (2 USED GASOLINE) (4 USED DIESEL) Mains

AT21122 BEARING 4 0.05MM (.002" under) US (PKG. OF 2 HALVES) Rods