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Head Bolts


48ply1stcar

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Since head bolts for flatheads don't stretch and I had no problem reusing head bolts in the past.

 

Is there any reason that one can not use Grade 8 bolts from the hardware store?

 

We have a store in my area "Fleet Farm" still sells bolts by the pound.  Grade 8 at $4 a pound - that's less than a dollar a bolt.

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Not me. Too much risk, blown head gaskets for one, probably caused by one bolt not holding the torque. To replace a head when the engine is in the car would not be easy, especially torquing the bolts. In my opinion this is not a place to skimp. The performance and the life of the engine is based upon those bolts and I'm not so sure they DON'T STRETCH. Don't they stretch when they are torqued? JMHO

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On the original head bolts the shank (portion of the bolt between the top end of the threads and the head of the bolt) is undercut. On a standard grade 8 bolt the shank is not undercut. Withoout this undercut the shank will rust fast to the engine head and potentially make bolt and head removal very difficult thus it is not a good idea to use standard grade 8 bolts.

 

Pictured are head studs where you can clearly see the undercut.

 

studs.jpg

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Don, I did NOT know that. I don't think my new bolts were undercut. I asked for top quality head bolts. Could one change them one at a time and NOT have to remove the head? Gonna be more careful on the convertible.

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Since head bolts for flatheads don't stretch and I had no problem reusing head bolts in the past.

 

Is there any reason that one can not use Grade 8 bolts from the hardware store?

 

We have a store in my area "Fleet Farm" still sells bolts by the pound.  Grade 8 at $4 a pound - that's less than a dollar a bolt.

Who told you this........? All torque is accomplished by the bolt stretching as it is tightened. Then why do they have torque values for the head bolts......?

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Confusion here is modern engines now use a head bolt that deforms when fully torqued and cannot be reused. Stock head bolts do not use this technology and can safely be re-used. 

 

For stock bolts it is more important to chase and clean the threads on on the block and bolt, so plan on investing in a tap and die for that job. Also make sure you have an accurate torque wrench. 

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I have grade 8 bolts in my old 218 engine, I ran it 4 years without problems till I decided to replace it with a rebuilt P28 engine.  In that engine I used a bolt for a chevy V8 application.  They are a pioneer part.  Search for pioneer as Ihave posted the number 3 or more time to this forum.  they have a slightly smaller head than stock but the under cut and thread length is nearly identical, 10 years with no issues.  They were about 79 cents a piece when I got them.

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I made replacement head bolts for my D25 from Grade 8 fastener-store bolts, but it was a lot of work — cutting the shank, grinding off the head markings, sandblasting and blueing. My goal was new bolts that looked like old. Second picture far right is an original. Greg G's suggestion sounds a lot easier.

post-1019-0-15765700-1374334661_thumb.jpg

post-1019-0-35490800-1374334734_thumb.jpg

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I used grade 8's on my 218 with ally head and nearly cost myself dearly, threads all properly cleaned, thread seal applied then torqued in sequence. Re torqued after first heat cycle and all seemed well. Truck was idling when I heard a strange metal bang noise, engine was still running but I could not see anything odd until later that day I was admiring my handy work and noticed one bolt head didn't look as tight down as all the rest. Turns out it had snapped inside the head level with the top of the block.

All bolts were immediately replaced with ARP studs and nuts which can be torqued down more as well, not cheap but cheaper than a new Edgy head, since then no problems head wise, plenty elsewhere but head good!

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I used grade 8's on my 218 with ally head and nearly cost myself dearly, threads all properly cleaned, thread seal applied then torqued in sequence. Re torqued after first heat cycle and all seemed well. Truck was idling when I heard a strange metal bang noise, engine was still running but I could not see anything odd until later that day I was admiring my handy work and noticed one bolt head didn't look as tight down as all the rest. Turns out it had snapped inside the head level with the top of the block.

All bolts were immediately replaced with ARP studs and nuts which can be torqued down more as well, not cheap but cheaper than a new Edgy head, since then no problems head wise, plenty elsewhere but head good!

 

The bolt breaking sounds like an coincidence, since there is no way you put anywhere near a breaking stress on the bolt.  As for the ARP studs (which I use as well), I hope you remembered to reduce the torque value when you tightened them down.  The nut uses a fine pitch thread, which increases the clamping force for a given torque value.  Working off of the top of my head, I believe that the bolt torque value is something like 75 lb/ft, where the stud torque value is about 55 lb/ft.  If you torqued the stud to 75 you may be bending that Edgy head!

 

Marty

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