Hi Chris,

Thanks for your input and I'm in the same boat as you as I'm neither of those mentioned too.

I'm in no way as knowledgable as Klaus with these all aluminum engines and Volvo models.
But bolts, to me, are to be as a standard as they can get everywhere. Limits are mostly cost driven with a dose of physics thrown in to keep it real.
There are so many types of fitted joints and stress analyses with or without heat related applications, that the bolts are the least of the problems.

I have seen high speed camera films of engine heads actually moving around on the head gaskets from all the combustion "banging." They don't call engines "bangers" for nothing.
They were furnished by Caterpillar diesels for my classes in machine tool metalworking back when I was an instructor in the eighties. Stationary engines with bores that you could stick your head into.

Things like casting the head and the block poured as one piece was thought up a long time ago and is another story all by itself!

When we start having to use gaskets mediums for containments of gases, fluids and what have you, then bolts or rivets, are your choices for fasteners.
As we know with home products, Rivets can make many things a non repairable throwaway? Luckily they haven't gone that far... yet?


In the case of those rod bolts, it's ludicrous to pay $20 a piece for them IMO. I believe they are even made of stainless steel so since I'm in the boat like you and being an old salt maybe ARP 's special steel might be an option someplace on that? 304 stainless is not so exotic but still very affordable. If, you don't go crazy with extra chromium for rust resistance and nickel for heat resistance in a 250 degree environment of an oil bath?

Talking about down there in the sump and crankshaft and rod loading from combustion down forces over side thrust of the crankshaft against exiting combusted gases and creating vacuum is probably why they are only using those small headed (external torx) bolts as you see in the package the poster provided.
Are they after a weight reduction or selling more tools?
I guess Volvo uses them there? I have no clue about it.

I have read about those newer engines having special tricks and tools.
Oil seals that are put in from the backside of housing enclosures, so you have to pull it. Nuts! But I bet they reuse the bolts.

Another rule of thumb I learned, in being an unofficial machine shop to engineering liaison, is that the bolts diameter is used in calculating or limiting the thickness of joint plates. There is a relationship in that marriage.
The rod cap only needs to be so thick and the calculation goes back and forth to reason things out.

Everything was prototyped that we used today and lots of it was trail and error or "lucky we got it to work longer that time."
(:-)

Yep, a 240 man, without a car or mechanic payment since 1978.
I take aspirin, if I get new car fever and if that doesn't work, I buy a quality used one!

Phil