Engine block aluminum vs compacted graphite iron CGI

[Tommy Cookers]

.... iron main caps on alloy blocks ....Chevy LS uses this, has this arrangement ever being problematic?

well ....
billet LS blocks are made from 6061 alloy ....
unlike the usual cast block alloy (357) it has little silicon and so has greater coefficient of expansion

390 alloy (for pistons) has very high silicon content and so unusually low expansion - but isn't used for blocks
presumably GM knew what they were doing

these lowish coefficients of expansion increase a lot with temperature

Well, I'm curious about the claim of the coefficient changing 'a lot' with temperature. Everything I see agrees that it's not linear and does increase with temperature although the changes are minor; we're dealing with pretty low temperatures in an internal combustion engine. Do you have a source for this? I'd appreciate a reference.

matweb.com says for CTE of 390

10 ppm/degF 20 - 100 degC (68-212 degF)
12.5 ppm/degF 20 - 300 degC (68-572 degF)

these of course are mean expansions - so giving an impression of less CTE variation than would the raw data

iirc the change isn't even monotonic (FIA-speak) eg where I was involved eg nickel maraging steels c.ambient temps

[Rodak]

Well, that doesn't seem to be a real issue at engine temperatures. Lucky for us we aren't building engine blocks from plutonium; it undergoes six phase changes before melting, with density varying from 16.00 to 19.86 g/cm3, the most changes of any element.

https://www.globalsecurity.org/wmd/intro/pu-phase.htm

[Tommy Cookers]

afaik
modern engines are running rather hot - close(er) to degrading aluminium alloy wrt fatigue strength etc
when the metal formerly known as bronze might make a good main bearing cap

postwar 'Bentley' Lagonda-design engines made by Aston Martin had mains held in split alloy 'cheese' mounts c.6" dia
fitted axially into that engine - unusually having full-depth CI crankcases though detachable heads
supposedly the mounts expand for rigidity when everything's warm with running

this main bearing mount idea came from early GP cars & eg Miller/Offenhauser - shrink-fitting into hot crankcases
having full-depth alloy 'barrel' crankcases separate from the blocks (as those of course were integral with the heads)

in the AM/Lagonda case the practicalities of fit and function have been questioned - few engines remain as original
(AM offset the liners and rods to get 2.9 litres and so went unsuccessfully to the WEC thing etc)

btw someone I knew had such a Lagonda
he was shocked to find that the sills were part of the body not the chassis
(Stewart Tresilian hated cruciform-braced chassis fashion & said a big front crossmember was crucial to torsional stiffness)

[Martin Keene]

I often see turbo versions splitting the block along the line of the main bolts, i cant help but wonder if a heat differential played small part in the failure as one fights the other with expansion the bolt line becomes the weak point.

The Ferrari F40 turbo engine uses alloy main caps with only 2 bolts, this kind of failure is unheard of, but then we are talking turbos so whoever controls the wastegate is going to be failure point really, I guess.

Ah, I suspect that is more to do with the engine being pushed past its structural capability with the addition of the turbo than anything to do with the difference in cap and block material.

Although, that raises an interesting question about the factory supercharged version, does it have a different bottom end.

Interesting fact about the F40, I never knew that.

[saviour stivala]

The formula 1 engines has done away with bearing caps as we know them for a long time now. Formula 1 engines bearing caps are part of the 'structural intended/designed' lower sump.

[coaster]

This branch of the discussion brings to mind the TJ V10's fabled brass bedplate, it was a thread in itself a long, long time ago, not sure where, but it probably had my comments and echedays prying BrianG for his promised book on the TJ.

Would be nice to track down the owner of the bedplate and get some high resolution pictures.

[saviour stivala]

I do not think the term 'bedplate' is the right term to use when describing the Cosworth TJ lower crankcase/sump. It is the first time I have read such a term to describe the lowermost part of the Formula 1 engine structural member used since the formula 1 engine design eliminated/made do without the traditional removable individual main bearing gaps. At some point in in the F1 V10 engine formula ballast was used in the lower sump. The term 'bedplate' is associated with the marine engine, a design that still incorporates the use of removable individual main bearing gaps. In the 'TJ' old tread mentioned by the above poster there is a photo by Brain G showing the TJ lower sump bolted to the upper sump with the upper sump including the cylinder block as a one piece casting. This photo shows the underside of the lower sump, this was one of the TJ parts that Brain G sold at that time. Good photos showing the same Formula 1 lower sump design incorporating the Main bearing gaps in its cast from, the very inside can be seen in the now famous FERRARI v10 book as well as in the BMW formula 1 v10 paper by Dr. Mario Thessen.

[Martin Keene]

I do not think the term 'bedplate' is the right term to use when describing the Cosworth TJ lower crankcase/sump. It is the first time I have read such a term to describe the lowermost part of the Formula 1 engine structural member used since the formula 1 engine design eliminated/made do without the traditional removable individual main bearing gaps. At some point in in the F1 V10 engine formula ballast was used in the lower sump. The term 'bedplate' is associated with the marine engine, a design that still incorporates the use of removable individual main bearing gaps. In the 'TJ' old tread mentioned by the above poster there is a photo by Brain G showing the TJ lower sump bolted to the upper sump with the upper sump including the cylinder block as a one piece casting. This photo shows the underside of the lower sump, this was one of the TJ parts that Brain G sold at that time. Good photos showing the same Formula 1 lower sump design incorporating the Main bearing gaps in its cast from, the very inside can be seen in the now famous FERRARI v10 book as well as in the BMW formula 1 v10 paper by Dr. Mario Thessen.

I think the term bedplate has become the common term given to a single piece main cap set up that forms the lower half of the cylinder block. Certainly has in off highway diesel where I work. JCB & Kohler both have a single piece main cap set up and it is generally referred to in the industry as a bed plate.

[Tommy Cookers]

and .....

Per RET Issue 136’s deep dive dossier of the Audi R4 TFSI DTM engine uses ... A201Ag alloy for the bedplate .....

[saviour stivala]

An engine 'bedplate' is forever associated with marine and stationary engines of considerable size. When a 'bedplate' design is used, the crankshaft is installed into it with removable bearing caps which are bolted onto it and not into the "framebox'/cylinder blog. It, the 'bedplate' with the crankshaft mounted into it supports the 'framebox', the 'framebox' might contain or not the cylinder frame. In formula one where no separate removable bearing caps are used, common terms used are the 'lower sump', and the "upper sump".

[saviour stivala]

afaik
modern engines are running rather hot - close(er) to degrading aluminium alloy wrt fatigue strength etc
when the metal formerly known as bronze might make a good main bearing cap

postwar 'Bentley' Lagonda-design engines made by Aston Martin had mains held in split alloy 'cheese' mounts c.6" dia
fitted axially into that engine - unusually having full-depth CI crankcases though detachable heads
supposedly the mounts expand for rigidity when everything's warm with running

this main bearing mount idea came from early GP cars & eg Miller/Offenhauser - shrink-fitting into hot crankcases
having full-depth alloy 'barrel' crankcases separate from the blocks (as those of course were integral with the heads)

in the AM/Lagonda case the practicalities of fit and function have been questioned - few engines remain as original
(AM offset the liners and rods to get 2.9 litres and so went unsuccessfully to the WEC thing etc)

btw someone I knew had such a Lagonda
he was shocked to find that the sills were part of the body not the chassis
(Stewart Tresilian hated cruciform-braced chassis fashion & said a big front crossmember was crucial to torsional stiffness)

''The post war Bently barrel type of crankcase''. The 1913 Peugeot L3 3-LITRE FOUR that is said by many to this day as being the one that showed the way forward, used a barrel type of crankcase with front and rear removable main bearing covers plus a central bronze diaphragm which was inserted with the crank from the rear of a heated crankcase.

[saviour stivala]

On the subject of 'replaceable crankshaft big-end bearing shells. The Cosworth engineer talking in 'The story of the development of the 20K rpm CA' when explaining the con-rod big-end bearing problems they ran into stated that 'replaceable bearing shells were still being used in the CA UNLIKE some other engines of the time, meaning that at that time some others were not using 'removable big-end bearing shells but running the crankshaft big-ends directly into the coated con-rods big-ends.

[coaster]

The tradeoff would be less reciprocating mass for the same cross section of material, Eddie Irvine summed f1's v10 era as "rockets to the moon money spending" which that era was notorious for, parts with a months lead time used for 20 minutes and then into the scrap bin.

[saviour stivala]

"Which that era was notorious for, Parts with a month's lead time used for 20 minutes and then into the scrap bin''. Every part of that engine ERA was designed to the limits of what the various rules during that engine formula ERA permitted, That system/way of engine making was and is still adhered too. Besides that, was a formula one engine ERA still regarded by the vast majority of formula one technical followers as the greatest engine ERA ever reached in F1, The NA 3-LITRE V10 ERA.

[Martin Keene]

An engine 'bedplate' is forever associated with marine and stationary engines of considerable size. When a 'bedplate' design is used, the crankshaft is installed into it with removable bearing caps which are bolted onto it and not into the "framebox'/cylinder blog. It, the 'bedplate' with the crankshaft mounted into it supports the 'framebox', the 'framebox' might contain or not the cylinder frame. In formula one where no separate removable bearing caps are used, common terms used are the 'lower sump', and the "upper sump".

I wonder if we are talking about different things. This is what I mean by a bed-plate design:


All of the bearing caps and cast into a single piece that forms the bottom half of the cylinder block. Kohler refers to it as a bedplate in their brochure and that is what that design of cylinder block is know as in the off highway industry.