ARP Head Studs - Opinions

[Arith2]

I woke up in the middle of the night thinking about the ridiculous investment I just made into my cylinder head. Head bolts are an extremely vital component. What are the opinions on ARP head studs? I have stock bolts as a back up in case something doesn't work out. There was someone claiming on a another forum that their S50 had loose nuts their engine builder found even though it was torqued to 64ft lbs. Seems like user error but there's a possibility it could be a shared experience. I figured many use them and it would be easier to consolidate those experiences. What do think of converting to head studs?

[Obioban]

Stock head bolts are fine.

[tlow98]

The stock ones are fine but they are one-time use.

I went with the ARP head studs. Since it was my first time doing the HG job I wanted the assurance that I could take the head off and reuse the ARP bolts in case I missed a step. This way I wouldn’t have any downtime waiting on new OE bolts.

This is one of the least sensitive areas of the motor to bolt specificity. You don’t have to worry about a bore being out of round, etc. Just clamping force.

Either way is fine.

[Slideways]

In the UK, Hack Engineering specialize in S54 rebuilds and they prefer ARP head studs. It would be great if they help prevent head gasket failures, but I'm not sure how much data is out there for using studs.

Another thing to add, BMW head bolt set are a 1/4 the price of the ARP studs.

[Anri]

In the UK, Hack Engineering specialize in S54 rebuilds and they prefer ARP head studs. It would be great if they help prevent head gasket failures, but I'm not sure how much data is out there for using studs.

Hi,

One must understand the physics between both. The downsides and the benefits,
then it will be easier to make single decision.


Regards,
Anri.

[Obioban]

The stock ones are fine but they are one-time use.

I went with the ARP head studs. Since it was my first time doing the HG job I wanted the assurance that I could take the head off and reuse the ARP bolts in case I missed a step. This way I wouldn’t have any downtime waiting on new OE bolts.

This is one of the least sensitive areas of the motor to bolt specificity. You don’t have to worry about a bore being out of round, etc. Just clamping force.

Either way is fine.

I’ve replaced my head bolts one time in almost 20 years of e46 M3 ownership. It’s unlikely I’ll live long enough to have the reusable arp head bolts be cheaper, at 4X the cost.

And, ARP is sometimes worse than stock. E.g. the rod bolts have less clamping force and result in a less round bore than stock (also more expensive than stock and reusable). Who knows what hidden trade offs could exist with these head bolts.

When there’s an area without room for improvement, I’d rather stick with proven. Bonus points when that route is also cheaper.

[tlow98]

I’ve replaced my head bolts one time in almost 20 years of e46 M3 ownership. It’s unlikely I’ll live long enough to have the reusable arp head bolts be cheaper, at 4X the cost.

And, ARP is sometimes worse than stock. E.g. the rod bolts have less clamping force and result in a less round bore than stock (also more expensive than stock and reusable). Who knows what hidden trade offs could exist with these head bolts.

When there’s an area without room for improvement, I’d rather stick with proven. Bonus points when that route is also cheaper.

Yeah, as I said, I didn’t buy them for repeatable longevity I bought them bc when I was rebuilding every other major part of the engine I did it twice bc it was my first time. Effectively, I was practicing. And when I was practicing on the main bolts I learned that I had a lot of downtime waiting for new bolts. I wasn’t trying to be cheap, or spend more to get more. With kids and busy life I get limited time in the garage which I need to maximize. So, for me, that made the most sense.

I’m well aware of the rod bolt and main bolt trade offs. I don’t think they apply here, but I’m happy to learn. What am I missing?

[Obioban]

Yeah, as I said, I didn’t buy them for repeatable longevity I bought them bc when I was rebuilding every other major part of the engine I did it twice bc it was my first time. Effectively, I was practicing. And when I was practicing on the main bolts I learned that I had a lot of downtime waiting for new bolts. I wasn’t trying to be cheap, or spend more to get more. With kids and busy life I get limited time in the garage which I need to maximize. So, for me, that made the most sense.

I’m well aware of the rod bolt and main bolt trade offs. I don’t think they apply here, but I’m happy to learn. What am I missing?

I think when considering going off stock, the question should always be “what am I gaining”— as in, best to stay stock until there’s reason not to. The trade offs are not always known or obvious (as in, the arp rod bolts were being sold as an upgrade for 15 years before we publicly saw someone measure the roundness). If there’s nothing to gain, no reason to move off what is proven.

If you just want practice, you can reuse the old stock.

[digger]

With ARP head bolts you are supposed to retorque them as the gasket relaxes after a few heat cycles. That would be a pain as they aren't accessible just by removing the VC, admittedly the MLS don't relax as much as the old composite gaskets.

[tlow98]

I think when considering going off stock, the question should always be “what am I gaining”— as in, best to stay stock until there’s reason not to. The trade offs are not always known or obvious (as in, the arp rod bolts were being sold as an upgrade for 15 years before we publicly saw someone measure the roundness). If there’s nothing to gain, no reason to move off what is proven.

If you just want practice, you can reuse the old stock.

Indeed. Good thoughts.

[tlow98]

With ARP head bolts you are supposed to retorque them as the gasket relaxes after a few heat cycles. That would be a pain as they aren't accessible just by removing the VC, admittedly the MLS don't relax as much as the old composite gaskets.

They don’t say anything about this in the instructions, nor do I think it’s common practice on modern engines.

https://arpinstructions.com/instructions/201-4303.pdf

if it were it’d be a real pain to remove the camshafts all over again.

[digger]

They don’t say anything about this in the instructions, nor do I think it’s common practice on modern engines.

https://arpinstructions.com/instructions/201-4303.pdf

if it were it’d be a real pain to remove the camshafts all over again.

https://arp-bolts.com/p/faq.php

Do I need to re-torque my head bolts or studs?
If you follow the ARP installation instructions, there should be no need to do a re-torque. However, it may be necessary under certain circumstances if the gasket manufacturer’s instructions require it, particularly if a fire ring has been installed. ARP recommends not doing a re-torque on a hot engine.

My experience on older style gaskets is it is needed to maintain the proper clamp. On the s54 MLS i doubt there would be a need as the gaskets arent as squishy

[Cubieman]

Slightly off topic here.

Can anyone site a specific link or piece of information that says the ARP bolts aren't a good choice for S54 rod bolts?
I have done a few rod bearing jobs on the S54 engine and used OEM bolts as I don't like to deviate from the factory hardware unless there is a known benefit as talked about above. I've already got OEM rod bolts for when I do my own rod bearings.

I imagine the same holds true for an S85, the reason I ask about the ARP's is I'll be doing my S85 rod bearings over the winter and the OEM fasteners I imagine will be a pain in the ass on my 4 post lift at home with a big 1/2" techangle torque wrench on 10 cylinders vs. 6 at opposing angles as well.

I'm not much in the S85 online community but it would seem a lot of those guys use ARP rod bolts, I'll likely just use OEM but some real data or personal experience on the issues of less clamping force and/or bore concentricity would be greatly appreciated.

[tlow98]

Slightly off topic here.

Can anyone site a specific link or piece of information that says the ARP bolts aren't a good choice for S54 rod bolts?
I have done a few rod bearing jobs on the S54 engine and used OEM bolts as I don't like to deviate from the factory hardware unless there is a known benefit as talked about above. I've already got OEM rod bolts for when I do my own rod bearings.

I imagine the same holds true for an S85, the reason I ask about the ARP's is I'll be doing my S85 rod bearings over the winter and the OEM fasteners I imagine will be a pain in the ass on my 4 post lift at home with a big 1/2" techangle torque wrench on 10 cylinders vs. 6 at opposing angles as well.

I'm not much in the S85 online community but it would seem a lot of those guys use ARP rod bolts, I'll likely just use OEM but some real data or personal experience on the issues of less clamping force and/or bore concentricity would be greatly appreciated.

The piece of information most people are referring to is what Lang Racing said about the rod bolts. I believe it’s actually mentioned on their website for the late style M10 bolts. They claim the ARP m11 distorts the bore.

fwiw, if you have the early m11 rod bolts it seems the answer is less clear and the use of those ARP bolts in that case is less frowned upon. I actually used ARP bolts in the m11 case, but I did so bc I couldn’t trust my stockers any longer for a variety of reasons. Since BMW doesn’t sell them I didn’t have much of a choice.

I’d echo Obioban and use stock bolts whenever you can. They’re extremely critical and there are no known issues with the stock bolts. So, they’re the best known quantity.

[bigjae46]

I do know there was a lot of debate and trial and error with head studs on the M54. There was an issue with boost and the head lifting. Common issue with that motor is the head bolts not torquing up because it was overheated and pulled the threads out of the aluminum block. Larger M11 head studs would typically fix those issues.

But this is not an issue with the S54.

I don't see a reason to go with ARP hardware unless the motor is apart, you can do the measurements and you plan on frequently disassembling the motor. Probably only worthwhile if the power will be increased significantly.