Grade 8 cap screws for head bolts?

I'm thinking about using the following hex head bolts and washers available from mcmaster.com:

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Grade 8 Alloy Steel Hex Head Cap Screw Zinc Yellow-Plated, 1/2"-13 Thread, 3-3/4" Length, Packs of 5 ($5.64/pack)

18-8 Stainless Steel AN 960 Flat Washer 1/2" Sz, No. C816, .515" Id, .875" Od, .059"-.067" Thk, Packs of 50 ($8.56/pack)
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Would cost approximately $31 (including shipping) for enough of these bolts and washers to do the 14 locations on the cylinder head. That's about $2.22 each.

I'd also need to cut about an additional 1 to 2 inches of threads on each bolt, but that's pretty easy.

The bolts that came off are grade 8, 1/2"-13, 3 3/4" length and the hex head size and washer size available at mcmaster.com will fit the locations, even though the original hex heads are 5/8" and the replacements would be 3/4". Washer size is the same as the flange size on the original bolts - 7/8".

Has anyone tried using grade 8 bolts like I'm thinking of using? I realize I'd have to find a different place to ground the body to the engine, because the original left rear head bolt has a stud on top for the grounding strap to be attached.. but I should be able to use another bolt or nut on the engine for that purpose.

I know I might be able to find a new original set for about $60 - $80 with shipping, but I'm just wondering why not use regular grade 8 cap screws and good washers? Any thoughts on this? Rick

I've been considering this myself - I think they use a "Torque-To-Yield" (TTY) variation of SAE Grade 8 - I'll have to check the head markings again.

You are correct that you'd have to relocate the engine-firewall ground, but any convenient point on the intake should work.

I was actually thinking about using socket head capscrews and washers - because I like socket heads. You'll want to use a "hardened" washer as opposed to the standard SAE stuff, but it's doable, I'm sure.

I just haven't had a chance to experiment with anything just yet...

5-90

5-90, thanks for the insights about the hardened washer. I decided to order the following washers to go with the grade 8 bolts:

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Znc Yellow Pltd Stl Hvy Dty Spring Lck Washer 1/2" Screw Sz, .512" Id, .869" Od, .125" Min Thk, Packs of 100
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About $11 for 100, which is 86 more than I need, but they are hardened and the heavy duty designation is intended for use with grade 5 or 8 fasterners, unlike the stainless steel washers I was considering before. These are "lock washers", but once flattened should serve the same function as a flat washer and I don't think the tightening torque will be affected (only the loosening torque..). Has anyone else tried this approach? Holler, if you think it's a crazy idea. Otherwise I may use this bolt arrangement when I reassemble the engine in a couple days. Then I can let you know what happens if you're interested..

If you're going to be doing this soon (sounds like you are...) I'd definitely like to hear more about it!

I've use SAE Grade 8 Hex Head Capscrews and Hardened Washers on industrial engines (PC12.9 on metric applications) - typically around 8.2 to 8.8:1 compression. I've had good results - and with the low compression we see in the AMC242 (8.7 - 8.9:1) I see no reason why this wouldn't work for us as well.

I just happen to prefer socket heads - for which hardened washers are mandatory! Having the screw head "pull into" the casting really sucks...

Installation torque should not be affected by the use of a "spring lock" washer - I just don't care for them. You can usually find hardened washers from an MRO supply shop. Here are my choices...

MSC Direct - www.mscdirect.com

USS L9 Flat Washers, 1/2" Nominal
.526-.536" ID
1.055-1.092" OD
.090-.112" thick
$26.41/100

1/2"-13 x 3-3/4" Socket Head Capscrew
Holo-Krome #75524371, $110.18/100 (order qty. 25)
1/2"-13 x 4-1/2" Socket Head Capscrew
Holo-Krome #75524454, $138.43/100 (order qty. 25)

1/2"-13 x 4" Hex Head Capscrew, SAE Grade L9
Lake Erie #67506246, $169.35/100 (order qty. 25)
1/2"-13 x 4-1/2" Hex Head Capscrew, SAE Grade L9
Lake Erie #67506287, $222.98/100 (order qty. 25)

That may be a bit more spendy than most people tend to think, but I'm known for being picky. I don't use "imported" fasteners in critical applications, unless I know where they're being imported from. Germany, Japan, England - all fine. Pacific Rim? Not so much.

5-90

5-90, I'll let you know how it works out, if I decide to use them.

The problem with the washers you have listed is the OD -- 1.055-1.092". I measured the area adjacent to the valve cover, and I don't think a 1" washer will fit, that's why I went with the lock washers, which are available with an OD of .869". The flange diameter on the original headbolts is 7/8" (.875"), so I need to stay pretty close to that.

I'll take at look at the socket head capscrews you mention and see if that's something I'd want to try. Thanks for the followup. Rick

I looked at the socket head bolts (part # 91251A120 at mcmaster.com - $7.45 per pack of 5). The tensile strength is 180,000 psi compared to 150,000 psi for the grade 8 hex head bolts I ordered and aren't that much more expensive.

The downside is that I'd need to order a 3/8" hex head drive, as I don't think I have one. (That's the size hex key for the 1/2"-13 socket head bolts...)

I like the looks of the socket heads better than the hex heads, and it seems like the circular bearing area would provide a more uniform holding force than the hexagonal bearing area of the hex head. However, I've already ordered the hex heads. Don't think I want to spring for yet another set.. Maybe next time. Or, if the hex heads work for me, maybe you can let us know how the socket heads work for you.

Have a good day. Rick

The hex head bolts arrived today from mcmaster-carr -- they are quick! Turns out I won't need to cut more threads on the bolts as there are plenty - about 1 - 1/2 inches of threads which is about 1/4" more than needed. The stainless steel washers are a perfect diameter match to the old flanges.

Based on what 5-90 wrote (above) I went ahead and ordered the socket head bolts and some hardened lock washers as well. Decided to give them a try if they arrive before it's time to put the head back on. Ordered a hex socket, as well. Heck, I just couldn't resist the looks of those beauties...

Just hope I can torque those socket heads to 110 ft-lbs with the 3/8" drive socket... without busting something.

Well, I couldn't recall how large the spotfaces are for the head screws, so I was operating on limited recall there. I could probably get out Wicks Aircraft or Aircraft Spruce & Specialty and find some AN or NAS hardware that would work better - but I've got those catalogues crated up pending a re-arrangement of house.

If the hex heads work for you, there's no reason at all why the socket heads wouldn't - and I can probably get access to a mill to make the spotfaces for the screw heads larger (which would allow the use of the larger hardened washers, and help to spread clamp loads more evenly.) It will probably be a little while before I try something like that, but I don't see any reason not to - so I'm sure I'll try it eventually.

I would probably go ahead and replace the screws that get used (hex heads or socket heads!) every time the head comes off tho - especially since they'll be cheaper than the TTY screws used by OEM. That, and I'm still not sure where the OEM screws are made - knowing that I can get Unbrako, Holo-Krome, or ARP replacements would make me feel rather better (I don't care for PacRim hardware... Except for Japan - they can actually do things right. China and sundry still haven't mastered the art of heat treatment...)

Hell, I'd rather use Polish or Yugoslav hardware than PacRim - at least they do things right!

5-90

I was searching around today and found this and was wondering if there is any update? It would be nice to not have to spend so much money on those darn TTY head screws!

Heh. I saw it and thought we had an update!

Again, theoretically, there's no reason it shouldn't work. I just saw some head screws yesterday while I was cleaning up out in the garage, and they've got standard SAE8 markings on them (with a black oxide coating.) So, there's no particular reason that regular SAE8 hex heads or standard socket head screws shouldn't work - apart from having to relocate the cylinder head ground, as I'd mentioned above.

Socket heads, as noted, are H&T to somewhere between SAE8 and SAE9 as a matter of routine (in inch sized. ISO would be roughly "ISO PC 11.9".)

If you used socket heads, you'll want a "flanged" socket head (to spread the bearing force) or a "hardened" washer as I mentioned - a "hardened" washer differs from the typical zinc chromate plated SAE8 washer by being about twice as thick. Typical flat washers aren't really meant for spreading bearing loads - they're there to keep surfaces from galling. If you want to spread a bearing load, you'll want a hardened washer or a series of Belleville spring washers (hmmm.....)

As far as underhead bearing surfaces - take a hex head capscrew and flip it over - look at the underside of the head. The typical hex head actually has a flattened round bearing area under the head, and the "points" of the hex are a few thousandths above this surface. Makes sense, else you'd risk having the points of the thing digging into whatever you're tightening it against...

It's been awhile since I installed those socket-head bolts that 5-90 and I talked about, but they are holding nicely, and I'm still glad I opted for them. Just order them from mcmaster.com as I indicated. You'll be pleased with the results. Best, Rick

rickoregon said:

It's been awhile since I installed those socket-head bolts that 5-90 and I talked about, but they are holding nicely, and I'm still glad I opted for them. Just order them from mcmaster.com as I indicated. You'll be pleased with the results. Best, Rick

Click to expand...

Excellent. Just how bloody long has it been, anyhow?:gag:

Did you use washers under the heads, or are the heads bearing directly against the casting?

NB - you don't just have to go to McMaster - you can also hit MSC Direct, J&L Industrial, or any other MRO outfit as well. While they may not be able to tell you specifically where their "import" screws come from, the "upper" stuff is usually called out (USA/Germany/Japan/wherever,) and if you can find a source for SPS/Unbrako, their stuff is first-rate (and made here in Souther CA, as I recall. They do a lot of aero stuff as well.)

I tend to prefer US-made stuff, with European being a close second, and then Japan/Taiwan for PacRim. Everything else can be considered "Made in China" (although Hong Kong is catching up, but they're better for electronics,) and China never has gotten the hang of proper heat-treatment. A couple of years ago in Materials & Processes, I tested screws from various sources - and the Chinese SAE8s I tested failed before the Taiwanese SAE5s did!