Omega Owners Forum

Chat Area => General Car Chat => Topic started by: The Sheriff on 22 August 2014, 20:31:13

Title: Probably a daft question....
Post by: The Sheriff on 22 August 2014, 20:31:13
.....and, no doubt, I will be mocked. But I can take it, so.......

Just been watching an old Wheeler Dealers, the DB7 one. Exhaust manifolds are cracked and, as this happens with so many cars, my question is: Why are they made of cast iron? Why not steel or alloy or anything that won't crack?
Title: Re: Probably a daft question....
Post by: RobG on 22 August 2014, 20:40:24
Longevity and cheap to produce
Title: Re: Probably a daft question....
Post by: The Sheriff on 22 August 2014, 20:43:05
Longevity and cheap to produce
Hmmm......longevity.....they keep fick breaking  ;D
Title: Re: Probably a daft question....
Post by: RobG on 22 August 2014, 20:45:01
Longevity and cheap to produce
Hmmm......longevity.....they keep fick breaking  ;D
Taking into account the numerous heat cycles that they endure they last quite well.
Title: Re: Probably a daft question....
Post by: The Sheriff on 22 August 2014, 20:50:48
Longevity and cheap to produce
Hmmm......longevity.....they keep fick breaking  ;D
Taking into account the numerous heat cycles that they endure they last quite well.
Yeah....well....I could have had a look at 1aauto.com I suppose. ;D
Title: Re: Probably a daft question....
Post by: cem_devecioglu on 22 August 2014, 20:53:27
there are alternative steel mixtures like 310 which has extreme strength but prices are definitely incomparable..  and its very hard to machine it..
Title: Re: Probably a daft question....
Post by: Vamps on 22 August 2014, 21:08:32
.....and, no doubt, I will be mocked. But I can take it, so.......

Just been watching an old Wheeler Dealers, the DB7 one. Exhaust manifolds are cracked and, as this happens with so many cars, my question is: Why are they made of cast iron? Why not steel or alloy or anything that won't crack?

See, no one mocked you Steve............ :D :D :y
Title: Re: Probably a daft question....
Post by: Broomies Mate on 22 August 2014, 21:12:28
Mock Mock Mock Mock Mock.  ;D


It's a cast part, which means it's cheap to reproduce in large numbers.  It is subject to extreme temperatures from an automotive POV.  Heat cycles mean it has to be durable.  Unless you use an extremely expensive material, which would mean using an extremely expensive manufacturing procedure, you wont beat cast iron.
Title: Re: Probably a daft question....
Post by: Broomies Mate on 22 August 2014, 21:13:39
I hear Daewoo use Vac-Formed Plastic for their exhaust manifolds?  ::)
Title: Re: Probably a daft question....
Post by: Lizzie_Zoom on 22 August 2014, 21:29:37
Not a daft question indeed!

I have always doubted the worth of using cast iron in machines, but it appears it is great for engine parts, be it on the internal combustion engines (once commonly with the main cylinder block) and on steam engines.  My suspicion comes from railway history when most early bridges were made of cast iron.  As engines became heavier they found the cast iron would become brittle, cack, and under bridges often gave way as trains crossed them. After some engines disappeared into black holes where bridges had been a few seconds before, all load bearing bridges were replaced with steel ones once that technology became available.

So cast iron parts for our cars seem to be not ideal, but as others have stated, is a cheap second best solution.

Remember those cast iron cylinder blocks of yesterday cracking all so readily? Thank God for the alloy alternative of today!  :y
Title: Re: Probably a daft question....
Post by: Andy B on 22 August 2014, 21:40:36
..... they found the cast iron would become brittle, ......

Cast iron IS brittle ....... it doesn't become brittle  ;)
Title: Re: Probably a daft question....
Post by: Broomies Mate on 22 August 2014, 22:02:19
Remember those cast iron cylinder blocks of yesterday cracking all so readily? Thank God for the alloy alternative of today!  :y

I'm not sure the Alloy alternative is used for longevity Lizzie.

I think the Alloy alternative is used as a weight saving feature to provide a more 50/50 weight distribution.  'All Alloy' engines have been proven to suffer problems earlier in their life than the Iron blocks they replaced.

Manufacturing practices have come a long way and will continue to progress, though.  :y
Title: Re: Probably a daft question....
Post by: Lizzie_Zoom on 24 August 2014, 14:59:12
Remember those cast iron cylinder blocks of yesterday cracking all so readily? Thank God for the alloy alternative of today!  :y

I'm not sure the Alloy alternative is used for longevity Lizzie.

I think the Alloy alternative is used as a weight saving feature to provide a more 50/50 weight distribution. 'All Alloy' engines have been proven to suffer problems earlier in their life than the Iron blocks they replaced.

Manufacturing practices have come a long way and will continue to progress, though.  :y

That is interesting BM. :)

I remember when cracked cylinder blocks were a regular feature in ending a car's life when under 80-100K miles in the 50s/60/70s.  Yet look at our Omega's, and so many more cars that get to 200K+ without that ending.  In fact, for me at least, I hear little about cracked cylinder blocks, or indeed other old flaws (like broken rockers, push rods, crankshafts, big ends, etc) that used to end a cars life on many a lonely road.  I personally drove a 1955 Humber Hawke in 1970 that ended it's life on the outskirts of Bromley after a rocker broke and did other damage. ;)
Title: Re: Probably a daft question....
Post by: Nick W on 24 August 2014, 16:24:37
Lizzie, may I recommend a book called Structures or why things don't fall down by JE Gordon? This clearly explains why cast iron was an unsuitable material to build bridges with, among many other things. A nice clear explanation of tensile strength and the difference between stress and strain are well worth the cost.
Title: Re: Probably a daft question....
Post by: The Sheriff on 24 August 2014, 20:19:15
Lizzie, may I recommend a book called Structures or why things don't fall down by JE Gordon? This clearly explains why cast iron was an unsuitable material to build bridges with, among many other things. A nice clear explanation of tensile strength and the difference between stress and strain are well worth the cost.
She'll be all over that, Nick  :y
Title: Re: Probably a daft question....
Post by: Lizzie_Zoom on 25 August 2014, 10:38:35
Lizzie, may I recommend a book called Structures or why things don't fall down by JE Gordon? This clearly explains why cast iron was an unsuitable material to build bridges with, among many other things. A nice clear explanation of tensile strength and the difference between stress and strain are well worth the cost.

Thanks for that Nick :y :y :y
Title: Re: Probably a daft question....
Post by: Rods2 on 27 August 2014, 19:07:03
The purity of metal components has improved due to better production techniques along with better designs using CAD systems and much closer machining tolerances. With cars we have the Japanese to thank in many ways for this. The Ford technique of selecting the piton to fit each bore, such were the production tolerances, is now thankfully a thing of the past.

Broken half-shafts was a very common problem on cars that were produced before the mid-1960's, but not something you hear of these days.