Crank regrinding
 

If a crank is round, and not scored ect, why does it need to be turned? Talking Babbitt bearings.

Re: Crank regrinding
 

It doesn't unless it was previously turned off center

Other than its hard to get odd sized already finished rods

Re: Crank regrinding
 

It not only doesn't, but shouldn't be turned unless there is good reason to do so. No point in removing good metal. The same goes for generator and starter armatures. Unfortunately some people think they have to remove good material to show it's been worked on. :mad:

Re: Crank regrinding
 

My brother was pointing out that you need to check all the dimensions. It may be round, but are the centers of the mains centered to the flywheel flange pins center?
Are the journel raduses correct?
Are the crank throws the same length?
Are the center lines of the mains in line (yes they can be out)?

All these areas can be messed up. Of course, if the round size is also the factory size then you likely have a NOS crank and you do not have to worry. If the crank has been ground then the odds are very very good that the centerline of the mains are not in line with the flywheel flange.

Re: Crank regrinding
 

Magnafluxing is also a good idea.

Re: Crank regrinding
 

Kevin in NJ
Why would you ever think that a crank that has been previously ground is now off-center?
What would lead you to that conclusion?
Jim

Re: Crank regrinding
 

Round means that there is no ovality. On the crankpins it is not unusual to have a journal that shows little wear at 90 degrees to TDC and BDC but 0.003 of wear in the TDC and BDC locations.

Re: Crank regrinding
 

As I understand it, machinists average the dimensions of a worn (out-of-round) crank and use that dimension to set up the crank in the grinder. This gives a new center line to the crank which is off center from the factory dimension. They also won't redress their grinding wheels to put the proper radius on an A crank. All to save them time and money even though they are giving you an inferior, substandard job!
Look up how to grind a crankshaft on youtube and they will show how this is done.

Re: Crank regrinding
 

Model A cranks can and do bend over time because of the forces on the crank caused by the lack of counter weights. Set your crank on V blocks on the first and third main bearing journal and put an indicator on the second journal. If you get a small amount of runout regrinding the crank could fix it.

Re: Crank regrinding
 

As a rule a ground crank is likely not done right. It is worse for the A crank because they are not likely to know about the rear flange.

Keep in mind the first statement is for any crank.

This is based on my brother experience checking machinists work before putting inengines he rebuilds. What he also learned when learning how to operate his crank grinder he bought because he got tired of the crappy work. It really takes skills, experience, and care to re-grind a crank accurately.

It is truly a sad state of machine shops and lack of quality. Even to get modern stuff done right.

Re: Crank regrinding
 

WHY do MANY post WORST CENARIO cases & "assume" that most crank grinders DON'T know what they're doing????---THOSE GUYS ARE EXPERTS, IN THEIR FIELD!!!
Do something USEFULL, like, OIL YOUR LAZY BOY RECLINER MECHANISMS!!!----Then go watch a crank grinder in ACTION & REPORT back!!!
Bill W.

Re: Crank regrinding
 

Umm, because the fact is most do not do it right.

This is based on local experience and talking with numerous experienced professionals that prefer to check the work of others.

Then throw in the number of people that seem to have vibrating engines.

Oh and I guess I will go to my brothers hobby shop and work with him as he fine tunes his repeatable sub-thousands accuracy on grinding A cranks. Then checking his work on the large surface plate he bought just so he could double check his work.

Sorry Bill, but you are talking where you maybe should not.

Re: Crank regrinding
 

I'm offended by the use of the word, "MOST"---------Just crude RHETORIC!!!
Bill W.

Re: Crank regrinding
 

Search crankshaft grinding on youtube and watch as they show you how they do their "averaging" method instead of grinding on the original center. It seem that this "quicker cheaper good-enough" method is industry standard!

Re: Crank regrinding
 

The model A crank center main is hard to grind with out bending the crank. This is because it bends very easy from the pressure of the grinding wheel. When we ground cranks like that back in the day in my Dads repair garage, we use the grinding support to control this. But it takes skill to use it correctly. The ones that grind today are use to big strong cranks.

No you do not grind off the old mains, you use the centers. and make sure they were not messed with. You can also double check run out where the timing gear goes on the crank. Then check the flywheel flange for the rear of the crank.

Re: Crank regrinding
 

I agree with Kev, and George.

In 53 years, I would say that 80% of crank grinders don't know how to grind a crank that takes a gear on it. No crank of any kind should be ground off worn main journals for a center line.


Kev is also right about the ones that don't radius their stone to match the Radius in
the crank. That is real common, they grind up to the Radius with a flat grind wheel, and leave it at a Right Angle, which will brake, more then not.


A good way to tell how a crank was ground is if the very front of the first main Journal has a ridge on it as the gear was in the way to grind it all.

George also brought up the center main which is true. The Model T is even worse!

Here are some pictures of a ground crank by Vern in Fort Dodge, Iowa. They are always Perfect, with high polish on mains and crank pins, straighten rear flange by grinding, that bolts to the flywheel, while it is still set up for center line, correct Radius, crack checked with Black light. On Model T's he also, if wore will straighten the pulley and seal area.

Herm.

Re: Crank regrinding
 

Herm is correct. I have been grinding Model A shafts for over 35 years and I always remove the gear and set up on the groove on the front journal and then the rear flange. You have to be careful of nicks and gouges. I always resurface the rear flange where the flywheel attaches so everything is running true.

Re: Crank regrinding
 

More Model A Complications:

Appears if 80% of the Model A crank grinders do not know what they are doing; maybe this means that 20% of the Model A crank grinders do know what they are doing.

Then if the 20& of the Model A crank grinders get 80% of the bad Model A cranks to re-grind, then possibly 20% of the Model A crank grinders could easily get cranky.

Seems if A Model A owner needs to get his Model A crank re-ground, it would be easier to look for a cranky, Model A crank grinder so he doesn't have to get involved with all of the complicated math and algebraic equations required for finding a good Model A crank grinder.

In 1640, (just in case anyone is interested in conic sections within a circle), there was a 16 year old child prodigy we studied, where he wrote about his Mystic Hexagram with intersecting lines within a circle ......... so when it comes to checking the centering of one's Model A crank, rather than referring to this most often used Mystic Hexagram, it again appears so simple to just start looking for a cranky, Model A crank grinder.

Hope this helps.

Re: Crank regrinding
 

Life is "SHORT" & I just get tired of folks "BAD MOUTHING" others, as a HABIT.
Bill Slack

Re: Crank regrinding
 

If when presenting a "Model A" crankshaft to a machinist for regrinding one if not the first question asked should be, "insert grind or babbitt grind? That is usually a good indication of the quality of the finished crank. Word of mouth is the best way to find the most expert service.