Want to Talk to Experienced Engine Rebuilder

3 principal methods are employed for reconditionnning the crankshaft pins and main journals (a)grinding to underzise dimensions, (b)metallizing the surface to original size and (c)chrome plating to original size. Building up surfaces by submerged arc welding is also used but to a lesser degree.

When grinding undersize, bearing journals are ground and polished to original specifications and standard undersize dimensions. Journals can be re-hardened if necessary but in regrinding to standard undersizes, depth of the original hardening is generally adequate to retain hardness.

Diesel engineering handbook.

It appears that you are quoting the old crank myth , read the post below. Undersize bearings do NOT have thicker bearing material, they have the same amount of bearing material, but have thicker steel backing .therefore the strength of the bearing has not changed. Most automotive engines and the older tractor cranks are not heat treated or surface hardened, so grinding deeper is not a problem . Grinding is not the problem , why it had to be ground can
be the problem . Heat treated cranks that have
had a heat related failure are subject to a change
in the hardness or strength due to excessive heat.
Those with nitriding or tufftriding come with a completely different set of guide lines . Basically ,if the shaft is not nitrided and is not a heat treated shaft with a heat related failure , you can grind it to any size that you
can buy bearings to fit. george

And to think... I thought that just the outer surface of the crank was hardened (usually somewhere near .100 thick on the radius) in order to resist the abrasive wear from contaminants in the oil. Now I learn that it is hardened to resist the inherent torque of the engine. If the designers needed strength from hardening the crank... then why didn't they just harden the entire radius of the metal (hardened to the core of the crank)? Maybe it is because they want some "flex" to the crankshaft so it won't break from the torque stresses.

I believe that there are folks like you that believe that the hardening (tempering) of the surface (bearing face) of the journals is for the purpose of extra torque strength (strength against twist). In my opinion, your belief of such... is a falacy! It makes almost no design sense to just harden the bearing surface area to add strength against torque! Especially since there is no "surface hardening" on any other part of the crank except the bearing faces... the webbing and connective material between the journals usually have no surface hardening whatsoever! They are usually just rough cast!

It does however make sense to temper the bearing surface area in order to resist errant abrasion from particulates in the lubricant!

This is the crank maximum grind myth referred to by George from Maryland below.

We used Sealed Power, Federal Mogul and Perfect Circle bearing books (still have some of those parts books) for guidelines on what was available in bearing sizes. We ground old tractor cranks (many for '49 and older pulling tractors, one year three tractors went to the State pulls in Springfield and won 1st, 2nd, and 3rd), and all types of truck and automobile cranks. Some of the cranks that were too large for our crank machine would be sent to "Effingham Regrinding" in Effingham Illinois (if you really want an answer to your question, call them. They are still in business!)

As for the surface hardening... Yes cranks are surface hardened but according to most of the tech info that I ever read, most of the surface hardening was at least .070 to .100 deep (that is on a radius) Where as grinding .060 off the crank only removed .030 off the radius. We tried to not grind to .060 "because" it was such a pain in the backside (took too much time, we worked on commission). Plus, if a crank needed that much taken off it was usually due to burning a bearing (and extremely galling the crank) and if it was burned and galled bad enough to warrant turning that far... the crank was probably bent (twisted) anyway! So we usually recommended either sending it to Eff. Regrind. to be checked out (including magna-fluxing, straightening, and regrinding).

The process of grinding a crank uses a "wet" grinding wheel and a stream of coolant on the journal as it is ground (cut). There is no loss of surface temper unless some operator tries to rush the grinding job and starts heating the journal face (which will take the temper out of the face). A machinist will use his ears to tell just how a cut is progressing (can tell instantly if there is a slight change in sound) along with watching the surface and using a special "swing-away" micrometer that is fastened right to the machine. The mic can be swung into position and will give a constant reading as metal is removed so that the cut will be accurate. I HAVE NEVER "heard" the stone change pitch as it would if it were to cut beyond the tempered face of the journal. And believe me, a machinist CAN tell by the "singing" of the wheel how it is cutting.

As I said, we ground a lot of cranks, most between .020 and .040 (that is .010 to .020 on the radius) and some to the .060 size with NEVER a return. The shop had been in business since the late '30s.

The shop closed it's doors sometime in the late '80s because it was bought out and liquidated by another company. A lot of that happened back then!

"Sixth and Green" was the place to be during the summer time up there (the traffic was slow though). College girls running around in shorts.... Never visited any bars, and didn't like the taste of beer (still don't) but I would drive near campus about everyday on my way home for lunch those first few years.

And now, I live in southern Illinois with corn fields outside my front door... MY corn fields! I will take corn fields anyday, as opposed to city life!!! ;-)

Yup, I worked for ya... Never did hear the full story about what happened to the shop. Just rumors! I had left the area by the time it closed. And I never believe rumors too much. Always wondered what happened to you and the store!

Do ya still have the "G"?

I live about 100 miles south of Champaign now! Been farming for the last 20 years! Dad retired in '87 and I saw the opportunity in '84 to quit the automotive mechanic life and get back to my roots... farming!

When I left the Champaign/Urbana area... I never looked back! :-)

Good to hear from ya!

I can't say that I am "collecting old tractors" ...that is, none of them are for restoration purposes. I own 7 tractors and a IH1460 combine. All red! 28 hp up to 190+hp All the equipment is for farming purposes, even though the newest tractor was made in '78. I also own 135 acres, 2 planters (corn planter and bean planter) and various assortment of implements (these are mostly all red too!). I farm over 350 acres all by myself... corn, soybeans and hay! Plus, I drive a semi hauling propane in the wintertime for a propane supplier.

there are a few nitrated shafts that if ground need to be renitrated . The tuftriding is very shallow but the old nitriding was .015 to .017 deep and could be ground .010 .

george

So if you were serious... you missed the target!

If someone will post it ,I have a copy of the myth and the answers to it . I would but don't know how , can email to someone who will .

george

I can post it for you.

Also, I noticed you mentioned salt bath nitriding - adding nitrogen to steel or iron - which makes me think you know what you're talking about.