Why are "steel main caps" a good thing?

[anthonym]

and do they go with other bits likely also to be present,

here why I ask

[Roger King]

Simple, they're stronger, but not generally necessary on a 711m or AX block because the originals are almost bullet proof. On second thoughts, maybe a good idea on a turbo or super charged engine running a lot of boost. Provided they have been done properly though, I can't see any actual down side to them. What does seem odd here is that the crankshaft appears to be standard and any engine with one of those ain't going to need steel caps.

[anthonym]

Thank you Roger, I was hoping you would be along :-) . Is it possible the original purchaser specified them to Cosworth without realising it might not be necessary? Any idea what sort of pistons are in there? I thought he said "steel" but maybe he meant "forged".. was 20 years ago so all a bit faded and I have no paperwork for this aspect of the car.

He said it came direct from Cosworth so CC refused a BDR chassis number because they did not supply it.

I have recently been told Cosworth never sold direct. 

Anthony

[Roger King]

I can't help with the origin of your engine, although I am not aware that Cosworth ever supplied the BDR in anything but kit form, so maybe that was what was meant. I've bought numerous BDR kits from them in the past so I suppose I could describe them as having come from Cosworth. But steel caps may have been fitted for a number of reasons - second hand block that had lost the original caps, ignorance of the capability of the standard caps, an intention to tune further in the future, etc.

I would be amazed if it had steel pistons so I'm sure as I can be that they meant forged as you say. Steel or iron pistons did exist in the early days of the internal combustion engine, but I'm not aware of anything current using them. Cosworth supplied the pistons as part of the BDR kit and they were most definitely forgings. Basically, the kit contained all you needed except the bottom end of the engine (mainly block, crank, rods, bearings, sump, oil pump, etc. The idea was that it was a conversion kit for an existing Crossflow.

[rj]

Roger

The Audi LeMans TDI engine had iron pistons. (I was surprised too)
https://www.mpulse.mahle.com/en/article/consequences%20for%20pistons

 

[Roger King]

Gobsmacked.

[anthonym]

"Cosworth supplied the pistons as part of the BDR kit and they were most definitely forgings."

That aligns with my recollection of what he said, though I am sure he said "steel", but I readily accept that was his interpretation of "forged".

[anthonym]

regrettably I would need to lift the head to be able to see the engine number if it is from Cosworth as I gather the (then) modern head obscures the engine number that is stamped in to a horizontal surface at the top of the block.

Comments about this most welcome.

edit: the V5 engine number is COSxxxx