Parts Store vs Hardware Store Flathead Question

[4woody]

I'm replacing the stock head on my Mopar flat6 with an Edmunds aluminum one. The parts store was closed, but the hardware store had grade 8 bolts and hardened (albiet much thinner)washers, so I got them. (Did I mention how much cheaper they are??) Now I'm wondering if I'm making a mistake. I really don't want to screw up this head.
The stock bolts have a thicker diameter shoulder up near the head that the hardware bolts don't have, but I put the caliper on them and found that thick section goes all the way from head to thread on the HW store bolts. Will that inhibit water flow through the water jacket, or is thick-all-the-way actually stronger and better?
What about modern thin hardened washers vs original mega-thick iron ones (That I can't find anywhere around here)? Are they strong enough?
Should I just say screw it and pay big $ and buy ARP or equivalent high-end bolts? Seems like overkill, but I heard that the shorter SBC bolts actually work on the old Mopar...They'd be strong!

[Fat Hack]

I have to wonder how much of an issue it could really be. If properly torqued, I'd think the hardware store bolts would do the job.

(How much compression are we really talking about here...8:1???)

I don't think I'd try it with any OHV engine, but you might get away with it on a flathead design...I've known people to do it with lawnmower and mini-bike engines...low compression flatheads themselves!

[Paul2748]

I've heard that Ford only used grade 5 for head bolts. Assume other mfgr's did the same. Therefore, hardware grade eights would be much stronger. The washers should be okay along as they don't bend.

[12packo94s]

if stock was grade 5 i would be a little worried using them since torque is also a product of twist and fastner stretch with is now going to change with a different hardness of fastner

[4woody]

I was wondering about torque values too, but ended up figuring that with coarse threads and 1950 technology (Both the fasteners and the torque wrench) it was all very ballpark at best. Am I fooling myself??

[12packo94s]

definately just gonna be ballpark,, for example many high end rod manufactures (oliver being one) go by rod bolt stretch and not torque to eliminate variables in fastners, and even lubricants.

torque can change quite substancially just in a fastner being torqued and retorqued mulktiple times and with any lubricant changes

so changing grade like i said is going to substancially change stretch which is what it's all about in the longrun

[Andy]

The amount that a bolt stretches is not changed by different grade bolts. A constant called Young's Modulus determins the relationship of stress(load) to strain(stretch). This number is the same for all steel.If the bolt is overstressed, a lower grade bolt will yield(deform) at a lower load. If the bolt is not overstressed, there is no difference in stretch. The bolts are fine but would worry about the washers and if thay have enough thickness and diameter to spread the load. Have seen many al. heads where the bolts yield the area under the bolts.

[MercMan1951]

You could take all this technical lingo into account, or, you could use my credo, tighten the hell out of it, and if it fails, on to plan B. http://www.jalopyjournal.com/ubbthreads/images/graemlins/smirk.gif

Seriously, the only area that concerns me is the thickness of the washers. Grade 8 seems like overkill from the info presented here.

[4woody]

The choices were ungraded, or grade 8. Grade 8 wwere 69 cents eacg, so I went all out. The washers claimed to be hardened, but no spec was given, and the old iron washers were really thick. Do I stack up the new ones, or re-use the old ones? Old might be a little bigger O.D. too...but I haven't found any more like them.

[Bugman]

I'd use the old thick washers with the new bolts. Let me know how it turns out 'cause I'm planning on building the 230 in my '55 Ply.

-Bugman Jeff

[Andy]

I might see if flathead Ford washers would fit. Easily found. Next would be a machine tool store or Kerr-McMaster.The thin washers will result in head damage. You actually need washers wider and thicker than stock.