Crank Life

[AustinWood]

The Citroen GS has a very short and robust crank, fully balanced. I think they may well be indestructible.


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The large size of the timing belt is another reason the engine is so good.

[Steve kay]

Wives driving Saabs, where would we be without them. My 2CV would still be at the bottom of the hill up which the dear lady in question driving the Trollhatten machine towed it yesterday.

[Steve Jones]

Don't start me on SAABS, great cars!

Malcolm's always told me how good they are - even when they're upside down

Steve

[AustinWood]

We had the Saab for a long time, just routine maintenance. Eventually I needed to replace an engine mounting and couldn't understand why my spanners wouldn't fit. Finally the memory kicked in - it's all unified threads. I hadn't put a spanner on for ages.
(Sorry for the subject drift).

[andrew34ruby]

A thought on sevens breaking crankshafts.... Could another factor be the rather vicious clutch? At some time in their life most cranks will have been driven by someone not accustomed to the clutch.

[Bob Culver]

When cranks finally break only 5% or less of metal is involved in the final fracture. On a road car the crack has existed for thousands of miles and the final situation is largely chance. When the crank on my slightly modified RP failed it had been running for 2 hours extensively at 50-55.  The engine made a resonant like noise on the fast overrun which I attributed to very hot thin oil. Then on next overrun from about 30mph a mighty crash and the engine commenced to idlle like a gold stamp battery. The block had lifted off the crankcase. I was able to refit the conrods to another engine. The rear journal had been heated and turned square. If I had heeded the first unusual sound may have saved the fully polished (by hand) crankcase and  reground cam. The moral is to heed any unusual resonance effect.
 
 
Nothing directly to do with Sevens, but may interest some. The Javelin engine was designed during WW2 by a youngster on his own, not connected with US parent co or Austin or Morris  and being a flat four had nothing to copy. It is a long stroke pre war low c.r style but running 7.2:1. The alloy crankcase lacks basic rigidity, and stock white metal rear main fails early, further stressing cranks.
The crank is short 3 bearing with rectangular webs counterweighted but not with extra to counter the big ends The early cranks were heat treated as a Seven. These often lasted well over 100,000 and are still encountered. But as on the early BMC A engine white metal bearings proved hopeless. So Cu Pb were fitted . These tended to wear the shaft so an induction hardened shaft was introduced and unfortunately used on  the majority  of the cars.  With good performance and handling and well heeled owners, cars were often driven fast. Cranks often broke in first ownership. Sports models with raised cr and on fast US motorways broke cranks at 15, 000 or so!! Blamed on stress from the hardening and cracks caused by factory straightening. Late cars had strengthened crankcase, revised treatment, larger radii, and journals drilled to lighten and to render less rigid. These last as the originals. After production a satisfactory oval web replacement was supplied, but was not very hard. Finally a nitrided version. OK, esp  if nitriding not ground through. Sadly,  as with many other cars, reconditioners hastened failure by ruining radii. And when nitride cranks were uncommon, many unfamiliar generated cracks during  regrinding. Failed cranks are seldom as destructive as often the case with Sevens. Near all cars have later cranks and with modern bearings, larger bores and raised c.r  perform very well and reliably.