What material for billet main caps?

[la360]

What steel is most commonly used and why?
AL....

[CNC BLOCKS]

Al we use all of Kenny's caps at Po-Gram Engineering and have had no problems with there caps, We feel there caps are the best in the industry so we offer them to our customers as they have been around for a long time.

Here is a link with some info for you Hope this helps.

http://www.pro-gram.com/tech_info.jsp

[la360]

Thanks for the reply Carl, I have actually checked out the Pro Gram site, and it seems they use either SAE 1045, or 4140. I think for what I am doing, the K1045 will be sufficient.
AL...

[OldSStroker]

What steel is most commonly used and why?
AL....

Most are either low carbon ("mild") steel like 1018 or 1025. Some use a medium carbon steel like 1045, which is perhaps 15% stronger. High-end GM Bowtie blocks use 8620, a nickel chrome moly alloy steel. It's maybe another 10-15% stronger "in the bar" than the 1045.

Generally billet caps are not heat treated, so the higher carbon (1045) or alloy (8620) steels are used because they are stronger in the non-heat treated form. 4130 (chrome moly) could also be used.

There is not a ton of difference in the material cost, and they all machine about the same, but the 8620 and 4130 caps do cost some more to manufature and therefore cost more to buy. If you are pushing hp numbers way beyond what the OEM intended for your production block, the alloy caps are probably a wise choice. If you are into 4 figures of hp with a production block, they should be mandatory, IMO.

Most retrofit billet caps do NOT include a rear main cap because it is so much more work to machine. CNC Bowtie blocks have all 5 made from 8620 and even have 4 bolts on the rear cap. You pay a lot for those blocks however.

[la360]

I did actually think about making caps out of 7075 T6 Aluminium, but I was a little reluctant to do so, because of the rear cap, and to be perfectly honest, I am not sure how many blocks my machine shop has done that were running aluminium caps. As stated, the rear cap does require alot more maching and set ups etc, even if a 5 axis machine is being used. I will have to do some more investigation I guess. I still have to draw the caps up in MasterCAM anyway.
Thanks for the replies
AL...

[OldSStroker]

I did actually think about making caps out of 7075 T6 Aluminium, but I was a little reluctant to do so, because of the rear cap, and to be perfectly honest, I am not sure how many blocks my machine shop has done that were running aluminium caps. As stated, the rear cap does require alot more maching and set ups etc, even if a 5 axis machine is being used. I will have to do some more investigation I guess. I still have to draw the caps up in MasterCAM anyway.
Thanks for the replies
AL...

Why aluminum for caps? What kind of engine?

[CNC BLOCKS]

[/quote]Most retrofit billet caps do NOT include a rear main cap because it is so much more work to machine. CNC Bowtie blocks have all 5 made from 8620 and even have 4 bolts on the rear cap. You pay a lot for those blocks however.[/quote]

The rear caps that Pro-Gram makes the rear seal is cut in all but the ID and the thrust is all done as well making it not much work to install a rear main cap just a lot of money as most of the time we use straps on the rear main caps

[OldSStroker]

About time I read your link, Carl. Thanks.

148,000 psi tensile 4140 is definitely heat treated. Bet than is a tough one to line bore.

I wonder why Pro-Gram quote expansion coefficients at 1000-1800F. It doesn' seem to relate to the caps in use.

[la360]

It's a factory Chrysler 360 block with a half fill. I will be making up a set of 2 bolt caps, and if time prevails, i will make up a rear cap. Alot of Big Block Mopar guys seem to prefer using Aluminium caps, and the stuff is easy to machine. I have personally never machined the 8620 steel, but have done plenty of 1045, and mainly tempered 4140 (50 odd rockwell). Have not machined 4130 though, I don't imagine it being much different to 4140.
Thanks for the replies
AL...

[hotrod]

Not sure you need anything this strong, but if I were making a part that I absolutely did not want to fail but had good machining characteristics I'd go with "stress-proof" steel.

http://www.niagaralasalle.com/pdf/stressproof.pdf


We used to machine loader pins out of it for a construction company ( the pivot pins for back hoes etc.) The stuff is 100,000 psi steel without heat treating and machines well for a high strength steel (83% of 1212 steel). The other thing I like about it is it does not move around much as you machine it as the production process relieves internal stresses pretty well.

If you can get your main caps out of a slice of a 4.5 inch round you might want to take a look at it.

Larry

[Harbinger]

If you can get your main caps out of a slice of a 4.5 inch round you might want to take a look at it.

Larry

I like the idea of using 1144 but the max available diameters, as Larry mentioned above, might leave you a little short on making a four bolt cap.

If I were machining caps I'd probably use 4140.

If you've already spent thousands of dollars in block and cylinder heads lightening, it might make sense to use a 7075 aluminum cap. Manufacturing costs are much lower.

Perhaps 7075 is a good choice for blocks that don't fair well with big doses of nitrous? Just a guess.

[OldSStroker]

Not sure you need anything this strong, but if I were making a part that I absolutely did not want to fail but had good machining characteristics I'd go with "stress-proof" steel.

http://www.niagaralasalle.com/pdf/stressproof.pdf


We used to machine loader pins out of it for a construction company ( the pivot pins for back hoes etc.) The stuff is 100,000 psi steel without heat treating and machines well for a high strength steel (83% of 1212 steel). The other thing I like about it is it does not move around much as you machine it as the production process relieves internal stresses pretty well.

If you can get your main caps out of a slice of a 4.5 inch round you might want to take a look at it.

Larry

Stressproof and its stronger brother Fatigueproof are great steels, but because of the way they are made, only come in rounds and hexagons.

The strength (and good machining properties) come from severe cold working. Normal cold finished bars are made by pulling annealed hot finished bars thru a die for round/hex or rolls that reduces their diameter somthing like 10% or less. This "strain hardens" the material by reducing the diameter and increasing the length and results in elongated grains along the axis of the bar. Stressproof is reduced many more % to achieve the hardness (Rc 26-30 or so) and 100 ksi yield and 125 ksi tensile, but in doing so the grain is even longer and more directional. This makes for great shafts, pins, bolts, etc, where you want the grain along the axis, but when you slice off pieces across the grain you don't get a lot of the the benefit of the grain structure.

4140, 8620, 1045, etc. come as rolled or drawn flats where the grain can be used in the plane of the cap instead of thru it from front to back. You can decide how you want the grain to be in you cap by how you cut it from a flat. Sorta like carving a nice piece of beef.

All that being said, Stressproof is probably still a very good choice for billet caps, even if it's not the best choice. It's probably overkill in most applications.

Any steel you use for caps, if you don't plan to harden it by heating and quenching, should be "cold finished" (cold rolled or cold drawn), not "hot rolled" bars. If you plan to thru harden your caps by heat treating, remember that only steels with more than .3% carbon content are going to respond to this direct hardening. 1018-1026 and 8620 won't. The last 2 digits are the nominal % carbon (if you put a decimal point in front). 1045, 1144, 4130, 4140 will direct harden.

If I had to make the ultimate cap, I'd probably start with hot rolled (?) Aircraft Quality (AQ) E4340. It's usually not available cold finished. I'd rough machine it then direct harden and temper it to the strength I wanted, then finish machine it. I'd use AQ because it is a cleaner steel with less chance of impurities or inclusions which might spoil your whole day if they caused a cap to let go. OK, so this might not be the ultimate cap; you could use VAR steel, assuming you could buy it, and do about the same processing. If it wasn't for a high end endurance engine lie Cup or F1, I wouldn't consider it.

My $.02

[Unkl Ian]

8620 machined nice in my exerience.

[Harbinger]

My $.02

A bargain at even twice that amount.

Good points about grain direction.

BTW, your aircraft quality E4340 is pretty common in cold finish, annealed, normalized & tempered condition. Easy enough to find in bars as well. VAR on the other hand is something I've never seen in a flat, just rounds. Don't even want to think about the price.

Have you seen VAR in flats? Any sources?

Thanks

[OldSStroker]

My $.02

A bargain at even twice that amount.

Good points about grain direction.

BTW, your aircraft quality E4340 is pretty common in cold finish, annealed, normalized & tempered condition. Easy enough to find in bars as well. VAR on the other hand is something I've never seen in a flat, just rounds. Don't even want to think about the price.

Have you seen VAR in flats? Any sources?

Thanks

Thanks, Herald

Recently some of the round sizes of E4340 (3-1/2 eg) haven't been so easy to find in CF. We make a number of high-end supercharger ( Roots style) drive parts for high-rpm drag engines from E4340. The smaller stuff is CF, if you consider "turned and polished " HT to be cold finished. I don't if we are talking strength and not OD condition/tolerance. No matter, we do a nice (proprietary) heat-treating to all of them.

I doubt you could find VAR 4340, etc in flats, but you could saw slugs out of large diameter round with any grain direction you desired. Kinda like cutting up a log in a sawmill. How fa$t do you want to go?

VAR billets used for high-end cranks (F1 etc and maybe some Cup and PS teams) are sold out thru 2007 production in many cases, from what I read in the trades. Most VAR is used for aircraft, of course, and those guys have deep pockets and are hard to outbid, unless you are Ferrari, Renault, etc.