Crank concern

[plmbcrzy]

Thanks for all the help with the cam info. I was grossly misinformed. Opted for the OT10
My concern is 140 heads mated to a 110. Should I try to locate a nitrated crank? I've been dealing with Clark's and was going to order the hardened crank kit, but out of them. Does it really matter, and if so were is a good place to start looking?
Love the forum. Thanks again.

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[66vairguy]

After doing some reading and talking to folks over the years - the 140HP (and Turbo) crankshafts received a nitrided treatment that surface hardened the crankshaft. It was done to reduce wear of the bearing surfaces and that is the ONLY difference I'm aware of compared to the 110HP crankshaft. The old style nitride process was a toxic dip process and now it's done differently. Nitriding only affects a few thousands of depth. It DOES not make the rest of the crank harder. In fact a crankshaft has to tolerate some flexing without cracking. If a nitrided crankshaft is machined, you loose the nitrided (harder) bearing surface. Note the crank bearing surfaces must also be polished to specification AFTER a crankshaft is nitrided.

I've installed a few used nitrided crankshafts that all had at least 50K miles each that were STILL in specification and only needed a mild polish. So yes the nitrided bearing surfaces resist wear, however a nitrided crankshaft is not considered to be stronger. Most of us hobby guys don't drive that many miles and using a 110HP crankshaft with 140HP heads would not be a wear issue. If you are rebuilding the engine and the crankshaft is worn so it is out of specification you'll have to have it cut and use oversized bearings (or find a good used 140HP crankshaft). Also ALWAYS have a crankshaft magnafluxed to check for cracks before spending money to have it cut or polished.

Another thing to do --- replace the harmonic balancer which is a perishable item (the rubber hardens and fails). The harmonic balancer (damper) does protect the crankshaft!! Also make sure the flywheel and pressure plate are balanced as a UNIT with indicator marks to ensure the pressure plate is always installed in the same orientation with the flywheel.

[plmbcrzy]

Thanks again vairguy. I did forget the harmonic balancer. Haven't yet ordered the parts between the clutch and tranny waiting to get it apart, still driving around.


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[66vairguy]

If the flywheel has the original rivets - then it needs to be rebuilt. The rivets WILL come loose by around 80K miles and that will result in damage to the starter and could stress the crankshaft.

At one time there were a few reputable places re-building them, but at this point the only one I can recommend is corventuredave on the other forum. He does bolted or hot rivet, either has a good reputation. Clark's sells his hot rivet units, but NOT the his bolted units. Calif. Corvair sells either of Dave's rebuilt flywheels. If you want to keep the same flywheel you'll have to see if Dave will rebuild it and return it to you.

[rfw66]

The hardening is only .005 deep. When a crank is turned, that hardening is lost.
Of course it depends on what you will be doing with your car. If it is a daily driver or a Sunday driver, use the crank you have. All the LM 8409 cranks are forged and are plenty stout.



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[66vairguy]

Oh - I assume you'll have Clark's install the cam gear (billet NOT cast). If not be weary of machine shops. I learned the hard way. Fortunately Jeff at Calif. Corvairs got it right for me. He has a jig that keeps the gear HOT until the cam is pressed in. Otherwise the gear gets broached and then comes loose.

Also always put a cam on "V" blocks and check for out our round - you'd be surprised how many times a camshaft gets bent - and yes they can be straightened.