crankshaft grinding tolerances

[Dave1]

When grinding a crankshaft, what are the acceptable tolerances for run out or (out of round)?

I understand the engine mfg will have the tolerances for run out (bend) which I believe is usually about .001", more I am concerning with the runout of an individual journal.

First off, .... I am new to crank grinding , you might say I am in "Learning Mode".

My Storm Vulcan 15 Special is I believe an early 1970's model and by the looks of it when I bought it,
it had ground Alot of cranks in its day.

I have had the bed resurfaced along with the wear strips under the head and tail stocks, also I have verified the head and tailstock alignment by grinding two short pieces of 2" round stock in two places, then measured the diameters, adjusting the position until both diameters are identical, similar to setting up a lathe.

At this point the taper along the width of the journal seems good, however the run out or out of round varies between cranks and even between a crank being ground. I am able to hold a tolerance of .00015" to .0005"

I am using junk cranks to practise on , example a Chevy 454 and a Ford 302.

I guess my question is, what kind of accuracy can I expect from this type of machine, and what are the factors that affect accuracy??

Dave

[Monzsta]

I ran an old Storm Vulcan, can't remember the model but it had a big steam boat type wheel for bed traverse You'd pull it our for hi or lo speed. Also ran an AMC K2000U. Loved that thing, but the hydraulics could get you in trouble.

How are you measuring your out of round?

[Dave1]

Using the Arnold gauge on the grinder

[MotionMachine]

.0002" is the most I would consider acceptable. .0005" is too much. Having said that, I've seen high dollar cranks with as much as .0007". I had to make a video of one to prove to the manufacturer how bad it was. I was able to re-grind it to .0001" OOR (with one hand holding a camera), so I didn't even have perfect steady rest pressure. Having a dull wheel or an improperly dressed wheel for that crank material will amplify an OOR problem. I've found that some cranks like very little bottom shoe pressure, some like more, some like none at all, it all depends on the crank. It's a learning curve, glad I'm done learning.

[modok]

Read the bearing catalogs, it's all in there.
Clevite, king, ect

[PackardV8]

First off, .... I am new to crank grinding , you might say I am in "Learning Mode".

My Storm Vulcan 15 Special . . . what kind of accuracy can I expect from this type of machine, and what are the factors that affect accuracy??

Dave

Hi, Dave,

First question any crank grinder will ask of a Storm-Vulcan 15 Special user is,
"on chucks or on centers?" Then, "rods or mains?"

[Monzsta]

First off, .... I am new to crank grinding , you might say I am in "Learning Mode".

My Storm Vulcan 15 Special . . . what kind of accuracy can I expect from this type of machine, and what are the factors that affect accuracy??

Dave

Hi, Dave,

First question any crank grinder will ask of a Storm-Vulcan 15 Special user is,
"on chucks or on centers?" Then, "rods or mains?"

Very true. I had an antique big spindley 4 cylinder crankshaft teach me a lesson. IN the AMC, despite it's size I regularly turned Kohler cranks without issue, but when I chucked up this piece of linguinie, no matter what I did I couldn't keep it true due to the inertia of the rather large chucks and spindles of the AMC. I ended up on the Storm Vulcan where I found that any sort of spindle pressure would blow it out of the water too. I ended up wadding the chucks with rags for a soft grip and spending an inordinate amout of time on the balance weights of the machine stealing all kinds of centers from the lathe in order to get this spaghetti to turn without whipsawing or oscillating. After a few touch and gos and a very light hand on the steady rest I managed to grind these skinny journals.

The crank looked a lot like the one in this thread. viewtopic.php?t=59050

[Dave1]

My machine is equipped with chucks. Had a talk with a crankshaft grinder who has about 50 years of experience, one of the tips he offered was to pay attention to wheel dresser. Following this I bought a new 2 carat single point diamond.
This made a huge improvement.

Dave