The Stovebolt Site Forums The Shop Area Engine Shop Polishing crankshaft journals

I haven’t started yet but have been looking at YouTube videos.
Question is, should I remove & look at the crankshaft main bearings as I should probably replace them too?
I think I just answered my own question!
The journals have fine grooves but I didn’t see any material burned into them.
This is the worst one.
Thanks.

If you're doing a "shoeshine" job with hand held emery cloth instead of using a powered belt polisher, be sure to do a thorough cleanup afterwards. Any leftover abrasive material plus motor oil makes a good grinding compound that will trash the new bearings in record time. I spin up a crankshaft in my lathe at low speed and use an ultra-fine grit sanding belt powered by a small angle grinder motor to polish cranks. Some machinists insist that the direction the polishing is done makes a difference, but that's not a factor in hand polishing a bearing journal. You don't need to remove the crank to polish main journals- - - -just roll the upper bearing shell out and slip the polishing cloth through the gap the missing bearing leaves. Use lots of spray brake cleaner and an air hose blow gun to flush away any leftover grit.
Jerry

That journal is not really a candidate for just a simple polish and new bearings. Besides the grooving, if you look close, its either got some debris embedded, or it was rusty at one time as you can see the pitting, or both. If the rest look similar, you might consider pulling the crank and have it machined to whatever undersize needed to get the journals cleaned up. Your new bearings will certainly last longer. If you decide to go down that road, also ask the machinist to drill and tap the crank snout for a balance bolt, small block chevy will work. Makes removing and installing the balancer much much easier.

I wouldn't go racing with that crank, but if it's round and doesn't have any deep scores, it will last a long time in a street machine. Grooves or shallow pits don't damage bearings- - - -high spots or debris do that. A groove is just an oil reservoir. If that's a standard diameter journal that's round but a bit undersize, a .001 or .002 undersize bearing will get the oil clearance back where it needs to be with just a good polish job and a thorough cleanup. Measure the crank with an accurate micrometer- - - -"Test, Not Guess!" I've done that dozens of times.
Jerry

I’m getting a good micrometer. If they are round I’ll polish them & re measure. Do I need to remove the main bearings & check them?

It doesn't hurt to check the bearings for condition, but it will be just about impossible to measure the diameter of the shaft with it in the block. You won't be able to get a micrometer far enough over the main journal to get an accurate measurement. Do you know if you're dealing with a standard diameter shaft, or one that's been reground? The best guesstimate of main bearing size will be by using Plastigauge to measure the oil clearance. CAREFULLY checking the main journal with a dial or digital caliper will give you an idea if the shaft is standard or ground undersize, and most replacement bearings will have STD. or an undersize stamped on the back of the bearing shell. OEM bearings, not so much.
Jerry

That’s probably a photo illusion. No color that I see.

If there is an oil supply hole in the journal, I like to stuff some small paper wads in there, so the grit really can't get any further than that.

I did not say anything about “color.” Look carefully at the photo. Besides the grooving, there is what looks like pitting in the metal and some embedded debris. Almost like the motor sat for a good while without being turned. Moisture of some sort rusting maybe, or rust that acted as the abrasive and cause the grooving. Could be anything really. Polishing a crank that is grooved, even minor grooving, only polishes the high spots. You will not polish those grooves out, particularly using the shoe string method. So then when you measure the journal, you are really measuring for the high spot.

I will be very interested in seeing what a good shoeshine with the appropriate sanding cloth can do to rehab that bearing surface.
I see the pits mentioned but all in all it seems to me the grooves are not deep and a (reasonably) successful outcome is within reach.
Keep us posted on your process and results….
Chuck

This week I’ll do one journal (I understand that I could spend hours doing each one)? If so I’ll pull the crank & have it machined or look to buy a new one.

Rig up an motor to spin the crank in the block, you will cut your sanding time way down and get better results. Even your starter would work, though it may get hot.

Things we did as a matter of routine in commercial shops back when these old engines were in daily drivers are suddenly too "shade tree" to be acceptable to modern stovebolters. Farmer John who needed to get his broken-down truck running at harvest time really did some oddball stuff, and the thing went right back to work. I'm amazed any of them survived long enough to be the subject of all that obsessive-compulsive attention to detail!

One 235 engine I tore down had a piece of creosote fence post whittled down and driven into a cylinder instead of a piston. The connecting rod was torched off just above the crankshaft and clamped around a piece of leather to keep the oil pressure up. The engine had spun a rod bearing and got reassembled as a "5 cylinder". It ran a long time that way.
Jerry

Here is the thing, polishing a crank journal is what the machinist does as the last step in machining a fresh crank. The machinist drops the rotating flex belt on the journal and gives it a little touch. It’s not minutes on the polishing belt, it’s seconds. For a crank that has been sitting a bit and has a little surface rust, it’s essentially the same deal, even with the shoestring method. It’s a few cycles of the abrasive cloth. If the journal won’t clean up with a few cycles, it has to be recut.

On a crank that is in really good shape, say a standard size crank that is in near perfect shape, yes, a touch up with the polishing belt may be all that is necessary. Any more then a touch up you are changing the size of the journals and thus what you really need is a full cut and polish to the next size. Look at the photo below. That is the best crank I have ever had. A 56 235. When the machinist mic’d the crank he said it was standard and that the only thing I would do is have it polished. It got a couple of seconds on the belt and that was it. Look at the journal, it’s not perfect but it’s pretty close and it started out pretty close.

Hours of polishing? I suppose it’s possible but you would need to be polishing to a measurement certain matching each journal just to get to the right size bearing, .001, 002 and for that you need a mic and full access to the crank journal. Really what you are doing is cutting the crank using Emory paper.

If you are just looking to get this motor running, take out a crank bearing and a rod bearing shell and look on the back for the size. Order replacement bearings. Give the crank journals a quick polish with the Emory and string. If you have a mic, mic the journals and the bearings (installed) and see what your clearance is. If no mic or you don’t have the skill set to do those kinds of measurements, Put it together and use some plasticguage and see if you can discern a general clearance. If the clearance is not too great, run it. You might very well get some mileage out of it.

If you want to do a better job, have the crank cut and polished to an available bearing size, .010, .020 whatever, and put it back together and eliminate the risk of having to do the job over again.

People who grew up shim-adjusting the oil clearance on Babbit bearing rods and mains aren't quite as persnickety as the young sprouts who have never had that kind of experience. Precision-fit bearings are a luxury, not a necessity.
Jerry

What year is your engine? Do the main bearings have shims? If so, you will have more wiggle room if you need to do a little bit more than light polishing. The final oil clearance is obtained by removing a layer or two from the stack of shims which are currently there.
Since the connecting rods are in the way of freely spinning the crank to feel for resistance as you remove a shim, I recommend that you use plasti-gauge to check your bearing clearance.

I don’t know anything about shims on the crank or bearings. Whatever I do I want the engine to be in top condition when it’s back together!
I just looked at the cam. I it might need some work too? It’s not wiped clean.

Regarding the cam, the condition of the lifters will tell you a lot. If they're worn concave, you should have the cam reground or replaced if you can find one and have the lifters resurfaced.

For your crank project bear in mind that not all crank grinders are created equal. I have seen some pretty sloppy crank grinding with journals several thousanths off from any standard size. These require shimming behind the bearings with tapered shims unless your engine has the factory shim pack between the block and the main cap; nothing after 55 2nd production did that I know about. Canadian production might vary.

The engine in question is a late model 250 with standard type bearings, no shims like the older engines.

Check the lifters, but if you have already pulled them and not labeled or numbered them, then a new cam and lifter set is required. Get a generic factory replacement, Mellings would be my choice. If you go this route, you will need a new timing set and possibly a camshaft retainer plate if you don't want to mess with the old one. You will need some break-in oil, camshaft break-in grease to coat the lobes, and new valve springs probably wouldn't hurt. The engine will require a full 20 minute break-in run. Even though the cam has easy rise lobes and little lift, there will be some risk of lobe failure due to cam or lifter fail, it's part of the risk of flat tappet cams. I would really try to keep each lifter marked and use the factory cam if possible. Measure each lobe lift and check each lifter face, use a dial indicator and run each lifter under the indicator to check for a .002" to .003" crown on the lifter face. Even if you purchase new lifters, they also need checked, quality control is not where it should be at any of the manufacturers at this time.

Before you ask, you need to heat the timing gear in an oven ( 250* or more ) and have the camshaft in a freezer to get get cold, have retainer plate and keyway installed, and in one quick motion drop the gear on and drive it down till it seats. Just pressing them on works but doesn't have the grip that heated gears do.

I have a low mileage used Blue Racer camshaft I will give you, I might even have a set of lifters somewhere. I will look up the spec's of the cam, it slightly bigger than a stock one.

Along with the cylinders needing boring and the journals being worn, needing a new cam and lifters. I bought a rebuilt engine. I hate to scrap the old engine but I don't know what else to do with it all!

You roll your sleeves up and rebuild it. It’s pretty fun and you might enjoy the process.