turning crank shaft

[badsix]

yes its std. now. its nice to see experts all in agreement makes me feel good.
thanks Jay D.

[Jack Staggs]

Roy, I am not an expert by any means on hardening of 356 crank journals, but I think that your estimate of hardening depths reaching .040" is highly optimistic.
I deal with several high end grinders on a regular basis. I have been told that on some cranks hardening depth may be as little as .006", so on a .010" grind, .005" will be taken off the radius of the journal. bThat's too close for me. Another grinder told me that earlier cranks used different forging materials/hardening procedure and hardening is not needed. I usually have re- hardening done anyway.
Some well known experts assert that hardening makes the surface too brittle, and more prone to cracking. Perhaps, but I'm sticking with the factory boys on this.
Another area of concern is ginding the crank down to the lowest size that bearings are made to fit (.030"), weakening the crank due to less overlap on the cheeks. If both the rods and mains are ground to .030", the overlap will be the reduced by the full .030". If either rods or mains are ground less, the reduction will be less by the factor of the size, but .030" seems like a lot to some folks. Lets think about it a bit.
Cracks ALWAYS start at the small radius. Cracks on the journal surface fore and aft are of little concern to me. These are usually from oil starvation or overheating. I have never seen a crank break from these defects. It's interesting to note that of all the dozens of forged broken cranks that I have seen, every one has visible rings, like a tree stump, as the crack increases incrementally, not breaking suddenly. Cast cranks do not have as easily visible rings.
Magnafluxing is an inexact science. Aviation techs routinely are tested for proficiency on this process. I have had cranks brought to me that have been tested OK by unknown shops that customers wanted me to install in their engines. Further testing revealed existing cracks. Not good.
OK, let's get back to cheek overlap. Earlier 356 pushrod engines used 50mm main bearings. When the super 90 was introduced for the '60 model, all main bearing journals were increased by a whopping 5mm, to 55mm (I know I am going from inches to MM here on some measurements.) So good, cheek overlap gained a huge advantage at that journal. They still broke sometimes, most likely due to the higher 6k rpm limit (remember, stresses increase exponentially at higher rpm). Well, the the factory boys (?), decided to REDUCE the #1 main journal back down to 50mm, from the 55mm for the "C" cars, even though the SC produced more power, and the flywheel was brought back up to the full weight of the previous of the "B" normal and super, (19+ lbs) from the weight of the S90 14.3 lbs flywheel, adding more stress to the now smaller again #1. Why? The 911 is in the works so let's get this 356 out of production, and not have oddball stuff. Anyways 912/C/SC cranks seem to break more often at #1. Out of balance clutch/flywheel/ not pinned clutches by sloppy mechanics are the biggest problem, IMHO. Viewing of the wonderful "Made By Hand" video shows that cranks/flywheel/clutch were balanced as a unit, prior to installation in the cases. We do not have that luxury when doing simple clutch job. The best that we can achieve here is to pin and balance the clutch as a unit before installation, with the rest of the engine intact. In these cases, full installation may be required to determine if further corrective balancing will be needed. Do not trust that a pressure plate that comes in a box with balance drill marks/added weights will be adequate. Most likely it will not. If your pressure plate does not have pins to locate it into an exact spot, your pressure plate will not be balanced. Some preA pressure plates that fit in to a relief MAY be an exception.
Why am I going on to adnausium about this? It's not because I like typing. I hate it. The topic of crank stress risers was brought up, and it's not a simple subject.
So let's go back to journal over lap. The factory over time increased the overlap by a substantial amount on some engines. They then decreased the amount in one place. They decreased the flywheel weight, them increased it back.
Several folks over the year have attempted to increase displacement on 356 engines. My friend Dean, of Polo fame built several stroked engines with titanium rods, with offset caps to clear the camshaft. I engineered a few huge bore engines with 1903cc, using stock crank throws. The Current offering is by John Wilhoit, with stroker cranks having engine displacement around 2.2 liters. It is my understanding that these stroker cranks are using rod journals that may be .200" or more smaller than the cheek overlay of stock cranks. I will apologize to John if I am far off the mark here. I congratulate him for bringing these large displacement engines to be. It's not an easy task.
With all this being said, "How much stress can be put on a 356 crank without it breaking? " I don't know.
Ps: Jay, you might want to have your crank mag checked again. I probably would, by a known shop.
Pss: Some Scat cranks seem to have greater small radiuses on the journals, requiring trimming of the # 2 main bearings to give adequate clearance for end play.

[bbspdstr]

I used to build engines for 356s. Alas, some of us restorers are finally waking up to the realization that we should identify the best area for our own abilities and not try to do everything on every 356 but identify others who have other areas of expertize.....and collaborate.

There are specialists within a specialty and it makes sense that one gets good doing something repetitively, not just once-in-a-while.

I used to have magnaflux and any other testing done on original cranks and once the power was put back in, the tired puppies occasionally broke anyway.

Especially when the happy customers got excited and over-rev'd that new motor...but I didn't have a 'tell-tale' tach to prove anything.

My mentors always told me never to go past first under and never use submerged arc built-up journals to save a crank...find a better one.

I waited for the vintage racers to proof Scat cranks before I bought one for my race car, then every high end engine got one for "insurance." I still wonder about billet and forged, but I'm too busy on the whole of a 356 to take engineering courses.... again.

Scat cranks come through with the assumption that someone who knows what they are doing is going to balance everything ("blueprint") and are therefore not an 'out of the box' unit...but I've never heard of one breaking.

I never guaranteed anything other than my own work. NO parts.

Ray Litz and then Walt Watson did the majority of the machine work on my 'good' engines. Worth the wait and cost.....never a problem for over 30 years and lots of engines.

Cleanliness is actually the most important part of a rebuild. I was bit there once and thereafter the aluminum case galley plugs came out and the ends tapped and sealed with threaded plugs. Even if you think you are being careful, the galleys can hide enough crud to ruin a new crank and bearings in a few minutes, so full-flow filtration became a normal addition.

Late rods and tappets, too. Those tiny rust pits just allow a little more oil to lubricate...worry more about the pressure and volume of a small pump that's worn in it's parallel of the gears and at it's tach drive end.

Soon, a 'safe' engine isn't "original" anymore, so.......if you use an original old crank with unknown heat cycles and rpms, then you are trusting to luck anyway and the little rust pits become the least of your worries.

I just know that like the crank that I am, I can't do what I used to do over 50 years ago either.....but I do have that degree from the School of Hard Knocks goin' for me.....

Gerry, any dinner plans next month?

-Bruce

[roy mawbey]

Jack,

It is possible to gas nitride to a case depth of 0.040" but there are other forms of nitriding like plasma where the depth is as small as 20 microns. ( its all dependant on application)

Gas nitriding seems to be mainly used for crankshafts and camshafts as well as other parts used in car engines.

But you are correct, possibly the depth is dependand on cost! The longer the process the higher the cost.

When I think back to the 50's and my apprenticeship the old fashioned carborizing of mild steel, nitriding was then in its infancy. Goodness how that case hardening process has changed especially in aerospace applications.

Thanks guys for such an interesting thread. Jay, best of luck with your engine.

Roy

[Jack Staggs]

Oh, one more thing, Jay. Some of the earlier rods have the tang on the opposite side than the 912 type. You may have to buy new bearing shells for the rods.

BTW, if anyone has .030"/.75mm rod bearings, I would like to buy them. Broken sets of main or rod bearings, any size, as well.
Thanks

[badsix]

yes, I have the late 912 style rods and the correct bearings. I believe I sold the old rods and bearings years ago. I will look to make sure.
thanks Jay D.

Roy, some very interesting conversation I will agree.

[bbspdstr]

BTW, if anyone has .030"/.75mm rod bearings, I would like to buy them. Broken sets of main or rod bearings, any size, as well.
Thanks

Jack, as I recently decided not to build any more 356 engines at BBE, I gave all my bearings (and other 'stuff') to the very qualified younger man doing that work, Eric Wills, of Wills Werks, in Fairfax, VA. 703-266-1356

I had broken sets, sets for older engines, undersize sets, etc. He wasn't interested in much of what I've been saving all these years, so he may be worth a call.

Hershey is where the cases, heads, used P&C sets will be heading along with many other goodies I no longer need to shelve.

-Bruce