Regrinding a crankshaft

You would be laughed at by all concerned!

New bearing shells are supplied as a set.

Once the hardwork of removing the crankshaft has been done it would be foolish to try and only regrind some bearings...in fact I don't suppose you would find anyone who would do it! Once the machine is set up, you may as well do 'em all.

This would be the worst sort of 'false economy'

So that's a 'no'....

That was me ...wha'd'a ya mean you could guess? Not logged in

The car industry has for decades supplied the NEW engines with a standard grind but in some instances, one or two journals would not clean up so they were ground to the closest undersize diameter and the engine was assembled using one or two undersize bearings. The reason the did this was there was no performance or changes to specifications. It was also a financial benefit not to throw out a good crank and any engine rebuilder like myself always checks the journal diameters BEFORE ordering a set of journals bearings because of this. GM,Ford,Leyland and just about all major manufacturers do this and it forms part of the Mechanics trade training. It has been a common practice to re-grind a single journal without removing the crankshaft and done insitu in the vehicle. I have such a machining machine for such applications which has been used on machinery and trucks like Caterpillar D8's and International, Ford, Cummins engines to mention a few. As for bearings comming in a set, the set can also be ordered with the appropriate undersize bearing shells at no extra cost.

Been there and done that so many times.

There is no technical disadvantages or stress concentration points. But as our un-logged in Del-Gato suggests, there is not much economic advantage and tons of risks. Yup, you can save some money (price of a coffee) if the two scratched ones are on the same offset (same grinder set point) and you intend to re-use the old bearings and buy only 2 oversize bearings and save a few bucks. If you intend to do this and sell the car please let your ethics be your guide.

This is something I might have done 30 years ago if it meant grinding all or eating mac and cheese for a week when grinders were manual and not automatic as now. Today, if I caught my 12 YO daughter doing this I send her to bed with no supper and take away her torque wrench for a month !

Hi PetroPower,

Back in the 60's I too have machined individual crank throws without removing the crank from the engine (just as Guest said in post #9). If Elias is wondering if grinding a single throw might cause the crank to be out of balance, forget it. Unless he's dealing with a blueprinted racing engine, he'll never notice it.

Back in those days we did what we had to do! I remember the mac and cheese dinners as well. Don't know if you other guys remember this or not but up until the late 40's Chevrolet used brass shims to adjust the rod to crank clearance. I've used enough Plasti-gage to fill a good sized box trying to get clearances just right.

Also, in the vein of do what you have to, when I was discharged from the Navy in 1964 I was driving my 53 Chevy from Pensacola to Atlanta and about 100 miles up the road I threw a rod. Middle of nowhere except for an old farmers place off in the distance. I borrowed enough tools to remove head and the oil pan (saved the oil). I removed the offending rod and piston, left out the pushrods for that cylinder then put it back together.

I drove the car 100 miles back to Pensacola on 5 cylinders! If I got over about 20mph, the vibration would shake it to pieces. Might have done better if I'd removed another piston/rod on opposite throw. Betcha money there's not many kids around today that could improvise like that. Anyway, just thought I'd pass that on...

-John

Johnjohn you revived some old memories for me. I also removed a thrown rod from an International K11 while on the Alcan highway about 300 miles from Alaska.

I did one thing different however. I knew I would lose oil pressure if the crank oil holes for that rod were not plugged so I wrapped the journal with a piece cut from a eigth inch thick lead sheet (which I was delivering to a battery rebuilder)and held it in place with two hose clamps.

This not only solved the oil loss problem but provided a rudimentary balance as well.

Hey that's cunning...

A guy I work with won't even change a wheel himself...calls out the AA what a wus!

I bet you even wrestled a bear just fun while you were stopped?

Hi taejonkwando,

I don't know which was worse, 95º in the shade in S. Alabama or doing it on the Alcan Hwy. in winter (what time of year was your misfortune?). You know, I don't think plugging the oil hole in the crank throw even occurred to me at the time. I must have maintained sufficient oil pressure though, since I made it for 100 miles. When you used lead sheet to plug the hole, were you considering balance also or was it just something you had on hand to plug the hole? How far were you able to drive it?

Kudos to you taejonkwando! I thought I was the only person on earth that had done that. Lets start a club; the only folks that can belong are those that have had a catastropic engine failure in the middle of Podunk and were able to repair it with only tools available at the failure site and then drive it _______ miles/km. Repair, in this case, means making it functional enough to get you either to civilization or to your original destination. You fill in the miles blank.

"THE GLORIFIED CYLINDER REDUCTION ENGINE REPAIR CLUB"

(or something more all inclusive).

Regards,

-John

You guys were probably lucky that the crankshaft on some engines does not get a continuous flow of oil if I remember correctly, it gets oil for only a short time in every revolution......so the pressure loss, without the lead, was probably not too great.

I do like the lead idea as a counterbalance of the missing parts.

Sadly I cannot join your club as I have never had one of my cars do such a thing, even in the middle of town next to a good hardware store and a repair shop..... All of my cars got good oil and frequent changes at the correct mileage with a new OEM filter.

If I ever saw low oil pressure, the problem was identified and corrected before something broke.....

No shortcuts.

"You guys were probably lucky".

Actually Andy, that was a very unlucky day for me. I mean dropping a rod is not exactly my idea of a fun day...

You said "All of my cars got good oil and frequent changes at the correct mileage with a new OEM filter". Even in those wild and younger days I was pretty fastidious about changing oil. I probably changed it more ofter than necessary. Even to this day the first thing I do whenever I crank my truck is to watch the oil pressure gage for a few seconds. Just a habit I guess.

Don't know about taejonkwando, but in my case I think the gods of destruction just decided to rain on me that day.

You are probably right!

Remember if God wants to empty his bladder, get out from under there pretty damn quick!!

Have a good one.

"the crankshaft on some engines does not get a continuous flow of oil if I remember correctly, it gets oil for only a short time in every revolution" ?

I can't think of a case now, not since splash-fed big ends went out. The 20's for most people but I think Hudson used it untill later.

On the subject of lead weights I recently helped a friend balance a V-twin engine in a vintage GN. Only one main bearing, big-end pin cantilevered off it. We removed a rather large lump of lead and replaced ti with something he reckoned was denser. I asked him what it's half life was so we could work how long it would be before any density change menat we'd have to balance it again!

As I recall, some engines only have two holes, one in the crankshaft and one in a bearing, when the two holes are opposite each other, oil gets transferred from the fixed part (block) to the moving part (crankshaft), probably only for 10 ° degs of movement.

Which is why oil must be liberally applied when building up an engine, to such parts.....

Maybe modern engines have a continuous ring to allow oil to be transferred during all 360° deg of movement.....

I was not referring to splash lubrication, that was before my time!!

I can't think of and cases of main bearings where a circumferential groove doesn't distribute the oil in a main bearing, or practically any plain bush. Not many seem to have thought it necessary for a big end though. Anyone??

I know of cases where putting in the bearing(s) upside down cuts off the oil altogether though!

I know of cases where putting in the bearing(s) upside down cuts off the oil altogether though!

Seen it and NEARLY done it myself, I think my colleague noticed it before I buttoned up or as I was mounting stuff. Can't remember any more than that!!

No reason as to why not. If you were real cleaver you could remetal and machine the old shells to suit. I have done a recondition on an obsolete JAP industrial motor and not only did a friend grind the shaft for me he had one of his retired mates metal the shells and machine them to suit his grind. At the end of the day in a practicle sense grind the lot and buy a set of shells if you want it to be reliable. As a side note my engine reconditioning tutor in Wellington told me that one of the worlds larger auto makers at one stage would fit the odd oversize piston to a new motor if a bore had not cleaned up from new. The same lot would not sell an odd sized set of pistons so you had to take the lot out to the larger size to clean up the block. When challenged they said as it is listed as a part for the motor they could do it.

I think that was a common thing in the car industry, at least in the UK in the 50s & 60s that I know of......Each bore was cut by a different tool and the results had to be within a three or four piston tolerance. Each bore was then measured and the correct size piston inserted.

When re-boring an engine, the difference is that the same tool was used for each cylinder bore and accuracy was much much better and a piston set could be installed....all the same size.

How its handled today, I haven't a clue, it would be nice to hear from someone who knows....

It depends what your trying to accomplish .

I have worked on a few crankshafts in the vehicle .

It is possible to polish a journal to remove scaring and replace those damaged bearings .

I fixed an International back hoe that way .It had seized from over torquing the motor and I was able to fix it in place and drive it away for years of service .

A good trick is to wrap sandpaper around the journal and take a shoe lace with about 3 wraps and pull in a sawing motion ,this will evenly and effectively prep the surface.

Obviously if you have the engine disassembled you might want to get a full recon

in "the old days' we used plasti gauge to order oversized bearings .

Hope that helps

Plastic -gauge is still used today, great stuff.

I suggest you determine whether the scratch is severe enough to justify a regrind. Small scratches can be polished out without affecting reliability. If the condition of the journal warrents regrinding, check the form of the remaining journals for roundness and other possible defects before regrinding a single journal.

i have had this done it was popular in the 50's and now is become almost a lost art some large trucks commenly use this practice as they can be rebuilt with out removing the motor also used on large yachts i actually had this done on a 1972 240 z race car i built you remove the head and oilpan and the starter the regrinder attaches a motor to where your starter went and the regrinding machine bolts to the oil pan rail { it looks like a strange sawsall } and as the motor turns over it follows the crank around' cost 125 for the first journal and 50 for any after the guy that did mine was great took about 35 mins and job was perfect also you do not need to buy bearings in sets they are available individually from most oem auto/marine/truck high places ,preformance bearing offered by nissan ,ford and chevy offer sizes in increments of one thousanth not ten thous and some come with extra groove to hold more oil ' in race motors you mic crank after a few races and replace bearings as necessary not going to regrind for a few thous when you can simply buy a bearing that fits

You could build-up the scratched pin or journal by metallizing it. During my work in the metallizing industry, I have refurbished damaged or wornout crank pins and journals on hundreds of crankshafts varying in size from one inch to 8 inches with great success. I have done it on crankshafts of my own trucks, air compressor engines etc and never had to worry about any failure. In fact the metallized pins or journals are not only as good as the original but are better as the coatings have a mocroporosity that holds oil. Try this and you will be surprised how good it is and you will be able to bring the damaged journal to standard size and use original standar set of bearings for the engine Only caution is to find a reliable shop that will use the proper process which is undercutting the pin or journal, using a Nickel-Aluminum bond coat and then building up with either 420 stainless steel or High Carbon steel to finish to size plus at least 20 thousands for finish grinding.

I worked for a major re-manufacturer, supplying remans to major retail companies for two years. It was not uncommon to see .010", .020", .030" under on the same crank on a regular basis.

I really can't tell you what the difference in stress is on each journal, but if this is not a racing engine I would suspect that the results of doing only one or two journals would not be significant. Don't really know though.

If you just have a scratch --- polish all journals then measure to determine the requirements. If you only have a scratch and all other wear measurements are OK then do as minimal as possible.

We did over 500 engines, domestic and foreign, each month with no problems regarding this issue.

Have I missed something, or has the odd conclusion been jumped to. I'd have thought the economics of pulling the whole thing apart and regrinding all the pins depended on what this is for an engine, not to mention where it is. If this is a fairly ordinary, fairly modern car (1940's) and engineering services are nearby, get it reground and fit new 'thinwall' bearing. If it's a marine diesel in a ship on an eight-week voyage, do what you can in-situ! If the bearings are white-metalled and machined it makes less sense to do the while lot, especially on a large engine.

My father in law aparently did the trick of tying up a rod after a bearing failure on a Bentley during an Alpine holiday, don't think it affected their itinerary much! Grandfather used to suffer frequent big-end failures on his Meadows (splash-fed) powered Lea-Francis; Usually when pulling their caravan up hill. He kept spare bearings on board and reckoned to be able to change them in about the time it took grandma to get the primus lit and make tea.

Sure, if you're not going to put alot of load on this engine (High RPM, heavy pulling, etc.) you could probably get away with polishing/grinding the one journal. But, as someone stated before, new bearings come as sets, and any machinist who is going to grind the crank is going to charge you the same amount regardless if its only one journal or 6 because his time is spent more on setting up to do the job, rather then actually doing it. I just got a crank ground and balenced for a Chevy small block 400 engine for around $100, and new bearings cost less then $50 for a set typically.

Something you should consider though is why the journals got scratched up in the first place. If there's metal shavings floating around in the oil, chances are this will be a recurring problem untill you get the engine completely disassembled and hot tanked.

Coating the journals with a metal layer as someone stated above may or may not work. My concern would be many crank manufacturers nitride the journals to make them more wear resistant, and a coating may not have those same properties.

My opinion: Get the whole thing ground, its not that expensive, and it'll give you an extra margin of reliabillity and a little more power in the upper end because your engine wont be fighting its own harmonics.

Grinding stands a chance of removing some types of surface treatment, I would have thought; tuftriding for instance? I admit I was assuming that we were dealing with a situation where grinding was known to be appropriate.

Nothing! It might screw up the next mechanic that has the bad luck to follow you.

Some say that you will mess up the balance. What ever you take off the rod journal is added in the bearing wall thickness.

Good point!!

just make sure you grind the fillet radii correctly.