When Should A Crankshaft Be Reground?

So, it appears that I've found myself looking at a rebuild for a naturally-aspirated 4 cylinder diesel, which I really didnt want to mess with, but it is what it is.

Regardless, I'd perfer to stick to an in-frame overhaul if possible.

When I take this thing apart, what should I be looking at/for in regards to the inspection of the crankshaft, to tell if it will need to come out and be reground, or if I can simply give it the fresh bearings that come with the wet sleeve overhaul kit, and continue on with life?

Thanks in advance...

Measure it !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Using an accurate micrometer (not a caliper) that is of the range needed. 2 to 3" or 3 to 4' probably, measure 9 places on each journal. Start at the front of the crank, and make a spread sheet, or paper copy of the measurements. On each journal (rod and main) measure three places at the front of the journal at 120 degree separation. Then go to the middle of the journal and again measure 120 degrees apart. Then at the crank edge of each journal. These nine measurements give you taper of the journal and eccentricity (egg shapeness) write each measurement even if it matches the one before it.
Be very touch sensitive when adjusting the micrometer. Assure it is flat front to back, and measuring directly across the diameter. Be sure to apply only enough pressure to just barely let it be stable and flat to the work. Practice measuring on the same piece of material (Like an old wrist pin) for 15 trys to make sure you are consistent. More than .ooo8 out of round (egg shape) and .0005 taper wil need to be ground. Jim

Hi The first thing you could do is ask Steve when it's apart L.O.L.

From my point of view there will be things you might see before it gets to measuring it that will decide the crank regrind anyway. when I pull an oil pan and bearing caps the first things I look for if it's knocking or got low oil pressure are,

Is there any copper backing material showing where the white metal on some types of bearing could be worn from the bearing inserts, the crank should be measured for wear then.

is there any ridge where some bearing types wear the crank either side of the oil grooves leaving a high narrow band in the middle on what should be an otherwise flat surface across each journal.

Are there any bad scratches or gouges/ white metal stuck to the crank shaft where the bearing got hot/ maybe pounded out and run rod metal to crank metal or welded stuff to the crank messing up what should be a mirror polished surface. the odd time a guy might get lucky and white metal polishes off and the cranks ok.

I've never done a Zetor motor but there are some engines you can't "roll" the rear main bearings in anyway as you can't get the cap off without splitting the tractor to undo bolts in the bell housing behind the flywheel. That might also decide whats coming apart from your findings with that to.
anyhow thats what I got to say from general experience looking before getting real technical with a micrometer. Good luck with what you find in there.

Seriously, this can be a very expensive thing to do. If you are unsure what to look for or are unsure what to do, you will be money ahead to take it to a mechanic that is familiar with tractors to get it done. You will also be money ahead to purchase a manual. This is not something you want to do a you tube video on not knowing what you are doing, it can cost you a lot more than what you make. Just my thoughts, take them or leave them, You also will need to figure out what caused the problem, it did not happen all by its self, something, either mechanical or man caused it and most times it is man. Zetors are darned good tractors and will last years and years if treated properly (same as the hay baler you had trouble with. Did you find out what's wrong with it let us know) Keith

I will point out that a major part of this SHOULD BE "what do the inserts look like? and what will this tractor be used for?" While it is a great opportunity for all us YTers to expound on how nothing should ever be done in any manner except for the absolute best, that no tractor should be touched without making it like new again, there are always economic realities. If it is your own, figure out your potential loss for what you will save. If it is for a customer give him an estimate both ways, and let him decide knowing exactly what he plans to do.

X 2. It's very rare that a visual doesn't let you know a crank needs reground.

Like others said, measure it. Don't guess or assume anything, especially with a diesel.

My first purchase would be a shop manual. That will give the tolerances that are allowable. Without that information it is impossible to know what needs to be done.

What kind of problem is it having? If it has low oil pressure, hammering in the bottom end, might as well pull it out, do it right. Diesels are extremely unforgiving. Any shortcut will come back, multiplied $everal times over!

I'll add to check it carefully as well! I just did one without grinding the crank and it turned a bearing the first day. Don't know yet what I did wrong because I haven't had time to read it down again. Make sure you check both for wear and for out of round. Nothing worse than putting a bunch of time and money into something and having it turn bad on you.

I agree with the others, do a visual, then micrometer for wear and roundness.

Shop manual should give you specifications.

About how many hours are on the motor?

no one mentioned checking the big ends of the rods, a new bearing in an out of round or shrunken big end won't last long, I always take them in to the machine shop and have them checked and re-sized if needed