11-11-2018, 02:07 AM
The three bearing had a reputation for failure in its day. When I was running my car as everyday transport through the 60s several strangers volunteered that encouraging info. No one ever suggested that the 2 bearing were somewhat prone and my father who ran the car previously never heard mention of. (The later big bang came as no mean surprise!)
For any that may be interested, for multi main bearing engines rigidity of support of the crank is vital for extended life. The large bore Model T had a bent wire crank but supported in a rigid cast iron crankcase. I have been involved with Jowett Javelin cars. These have a short robust looking crank but were notorious for failure (partly due poor heat treatment process), It is evident from bearing wear patterns (and engine thump!) that the split alloy crankcase deflects markedly.
The centre bearing of the Seven dangles from the thin roof of the alloy crankcase so deflection under load must be significant. The mountings are frequently distorted out of static alignment which makes matters worse. The Big Seven went to the other extreme with bearing housings checked into the rigid deep iron crankcase. Hi performance engines, including the Merlin, have bearing caps bolted both vertically and horizontally to ensure rigidity.
Rolled fillets were later common on modern cars. As with most compressive processes considerable gains were obtained. Nitriding, presumably what gives Phoenic cranks their life, develops a compressed layer.
For any that may be interested, for multi main bearing engines rigidity of support of the crank is vital for extended life. The large bore Model T had a bent wire crank but supported in a rigid cast iron crankcase. I have been involved with Jowett Javelin cars. These have a short robust looking crank but were notorious for failure (partly due poor heat treatment process), It is evident from bearing wear patterns (and engine thump!) that the split alloy crankcase deflects markedly.
The centre bearing of the Seven dangles from the thin roof of the alloy crankcase so deflection under load must be significant. The mountings are frequently distorted out of static alignment which makes matters worse. The Big Seven went to the other extreme with bearing housings checked into the rigid deep iron crankcase. Hi performance engines, including the Merlin, have bearing caps bolted both vertically and horizontally to ensure rigidity.
Rolled fillets were later common on modern cars. As with most compressive processes considerable gains were obtained. Nitriding, presumably what gives Phoenic cranks their life, develops a compressed layer.