ARP head bolts shorter than oem

Phoenix440 · Oct 24, 2025

I am installing reco iron heads on a 440.
Decided to buy ARP bolts, Felpro marine gasket, trying to avoid the previous leaks that were in the motor.
Was about to install one of the heads and thought it might be a good idea to make sure the bolt lengths are correct.
The long centre bolts with washer installed are exactly the same length from bolt tip to under the head ( washers installed on ARP).
The short ARP bolts with washers installed are a bit over 3/16 shorter than oem ( so this much less thread engages in the block).
The kit is AR145-3606 which is standard replacement.
I have contacted ARP, havnt heard back, but just wondering if anyone has seen this or did they mix up the bolts?
Any help appreciated

Geoff 2 · Saturday at 12:00 AM

I have had ARP bolts that are the other way: too long [ & too short ]. You have to double check ARP stuff, their QC is terrible..if it exists at all.
Nothing wrong with the factory bolts.

Kern Dog · Saturday at 12:35 AM

I have a set of ARP bolts that were on a 1990 360 that I bought from a friend. Those were shorter than factory head bolts by a good 3/16".
Not good.

Bird 426 · Saturday at 2:24 AM

As long as your threads are engaged, you should be alright. If this was airplane stuff, they like 3 threads showing. My Hemi has about 1 thread showing with Edelbrock heads.

Geoff 2 · Saturday at 4:09 AM

No, you want as many threads as possible engaged, especially cyl heads & main brg cap bolts. Head bolts can distort the cyl bore when tightened. You want as many threads as possible to reduce distortion. For this reason, one of the benefits of studs over bolts is more thread engagement.

69Bee · Saturday at 8:11 AM

You won't have any problems. If you are concerned with the shorter bolts, don't use the washers. The ARP bolts already have a flanged head, so they will work fine as is. When using main studs, and there was not enough thread above the nut, ARP said to just eliminate the washer, and everything worked out fine.

Bird 426 · Saturday at 5:00 PM

Sorry, I had studs, not bolts in mind

Phoenix440 · Saturday at 7:02 PM

Thanks for the replies everyone. Head studs seem to be the best solution, but may go with short bolts no washers if I can't get refunded.

Phoenix440 · Saturday at 7:04 PM

Geoff 2 said:
No, you want as many threads as possible engaged, especially cyl heads & main brg cap bolts. Head bolts can distort the cyl bore when tightened. You want as many threads as possible to reduce distortion. For this reason, one of the benefits of studs over bolts is more thread engagement.

Thanks for the info, makes sense. I would have gone for head studs if id known arp bolts were shorter.

Phoenix440 · Saturday at 7:07 PM

69Bee said:
You won't have any problems. If you are concerned with the shorter bolts, don't use the washers. The ARP bolts already have a flanged head, so they will work fine as is. When using main studs, and there was not enough thread above the nut, ARP said to just eliminate the washer, and everything worked out fine.

Goid idea,Might be the easiest way to go, now I have bought the bolts, other than trying for refund and buying studs.

ARP head bolts shorter than oem

Phoenix440

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Geoff 2

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Kern Dog

Life is full of turns. Build your car to handle.

Bird 426

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Geoff 2

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69Bee

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Bird 426

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Phoenix440

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Phoenix440

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Phoenix440

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