Using PD150 bolts in ALH: Install as bolts or studs?

benhart16

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Greetings everyone.
After reading that the PD150 stock head bolts are grade 12.9 (174,000psi minimum) and that they can be used as an upgrade over the stock 10.9 bolts for the ALH engines simply by trimming them down to 115mm, I got to thinking. I also read that there is less friction variation when torquing a nut on a stud than when torquing a bolt into the block, therefore studs are recommended for heavily modded applications.
The question in my mind: Is is better to trim the end of the bolt off and use it as a bolt, or to cut the head and smooth shank off and use it as a stud?
From the pictures it looks like the threads are more than 115mm long on the PD150 bolts. If I used PD150 bolts as studs, would I still use the same torque sequence as the bolts, torque to spec, then 90*, then 90*? I know the PD150 bolts are torque to yield, so I'm guessing they would still stretch when used as studs.
Background:
Ever since I realized that ARP uses 8740 steel (heat treated to 180,000 psi) for their studs while charging around a couple hundred bucks, I have wanted to search for an alternative that would be equally effective, yet a fraction of the cost. After doing a bit of searching I realized that grade 12.9 bolts are nearly identical to the ARP 8740 studs in terms of tensile strength, but at a fraction of the cost. I have not yet found a mandate on the alloy used for 12.9 fasteners, other than to say it has to be vanadium, molybdenum, or chromium.
 

[486]

Top Post Dawg
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02 golf ALH
rolled threads
the shank is too small OD for cut threads
 

benhart16

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2000 Jetta tdi
Yes, it would not be possible to cut additional threads of the same diameter on the bolt. However, as the PD 150 bolts are 166mm and the ALH bolts are 115mm, they have to be cut to fit. The question is which end should I cut for maximum strength.
 

Mikkijayne

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Now that's a very interesting idea. If the steel is much the same as the ARP stuff would using ARP's torque specs and lube end up not stretching the stud I wonder?

What nuts would you use for it?

Digital Corpus I think used 98ft/lbs on his 12.9 bolts with ARP lube, which was just under the yield threshold, and that seems to be working, so with the right nuts it might work. ARP specify 125ft/lbs.

For the cost of a set of bolts and a head gasket it seems like it's worth a try :)

Edit edit - ARP do M12x1.75 nuts: 300-8396. Stock washers and moly lube and it just might work...?
 
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[486]

Top Post Dawg
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02 golf ALH
Yes, it would not be possible to cut additional threads of the same diameter on the bolt. However, as the PD 150 bolts are 166mm and the ALH bolts are 115mm, they have to be cut to fit. The question is which end should I cut for maximum strength.
I missed the part where the threaded portion is long enough to use as is

go for it, you're eliminating the stress riser at the swell from the shank to the head
 

Mikkijayne

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Yeah there's plenty of thread ^



Bolted in to an AFN the PD150 bolts have 10 threads clear of the head. Take two off for a washer, and thats still ~13-14mm for a nut. If the now-studs are put in 'upside down' with the cut end in the block you then have a bit less usable thread, but a nice lead-in for the nuts, and more thread engagement in the block.



The only downside I can see to this is that the studs wouldn't have a hex in the end to screw them in with the head in place, but for a head-off swap that wouldn't matter.

Definitely going to give this a go on my next engine build :)
 
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Fix_Until_Broke

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If you've got the room in the head, just use the PD150's as is, without cutting them short, and stack a bunch of parallel ground hardened washers between the cylinder head and head of the bolt. This will be far more advantageous than any benefit from using a nut on a stud vs a traditional cap screw. Use the VW PD150 assembly procedure and you should be good.

There are books written about why this is, but basic theory with this is that you have more head bolt material to spread the forces out across, thereby making the joint more robust to assembly variances, thermal expansion, overloading, etc.

The ideal fastener is very stretchy and very strong. You want it to be the lowest rate spring in the system (system being the block, head gasket, head and head bolt). Since very strong and very stretchy are at odds with each other, making the bolt longer is an easy way to gain more stretch without losing any strength. 166mm vs 115mm gives you a lot more of the fastener in tension. More than just the 44% difference in overall length, it's likely closer to 100% because the extra 51mm is all in tension (the bottom threads in the block are not really under any tension).
 

SkyRyder55

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if the above is true, then why not just use a single machined and hardened spacer instead of stacking a bunch of hardened washers.
Now if you have too much spring, your head is going to lift. Maybe this is why the pd150 bolts are of higher grade so that they dont stretch since they are longer.
From what i have learned, headlift is bad. lol.
 

mk1-83

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Holland
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I'm done some hardware store 12.9 hex bolts they are in 120mm length only the last 40mm got threads.
I torq them OEM settings. Holding fine off 2 years abuse from 250 HP to now 300 HP.
 

benhart16

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Thanks Mikkijayne for the pictures, they are perfect!!

I think I finally wrapped my head around the concept of torque to yield fasteners, specifically why the vw head bolts stretch and the ARP studs don't, considering they are similar tensile strength alloy steel.

I believe the answer lies in the fact ARP torque specs, 98ft-lbs for a 12mm stud, will preload the stud to 75% of the stud strength. The VW torque specs, 44ft-lbs, then 90*, then 90* does this, and much more!!

Correct me if I'm wrong, but it appears "Torque to Yield" is a fancy way of saying to get a high quality fastener, and torque the snot out of it so it stretches or yields, so you know that all the bolts are at maximum tension. This seemed to work well for mk1-83 with his hardware 12.9 bolts. I'm going to say the ARP studs will yield too if given enough torque, and thus should not be reused if over-torqued.

My ultimate conclusion: The factory PD150 head bolts, quality hardware store 12.9 bolts, and ARPs 8740 studs (the ARP 2000 studs are stronger) should give similar results. As far as installing the PD150 bolts as studs, I don't see that it will hold better or worse than using them as bolts. Studs do have the advantage of not wearing the threads in the block when torqued. I'll probably go the stud route when I put my ALH together in the near future. Pics to come.
 

benhart16

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Seattle, WA
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Ok, I can't figure out how to post images, so here is a link to the album: https://onedrive.live.com/redir?resid=2D5C9BF4C33A9513!428&authkey=!ADrDR4VSWvimmhk&v=3&ithint=photo%2cjpg

I went through all the trouble to make the studs from the PD150 bolts, and this part works very well. Expect to spend a couple hours grinding everything.

The problem is the M12x1.75 nuts are too big in diameter. You can see the pic where the socket won't fit in the head!

If you could find some lower profile nuts, then this could easily work. I finally gave up and went down the road and bought some M12x1.75 12.9 allen bolts. I followed the standard head bolt torque procedure, though some became very tight on the final 90* turn. I set the torque wrench to 100ft-lbs and stopped when it clicked. Not all the bolts hit the 100lbs mark. I was worried the bolts would strip the threads out of the block. I estimated that the bolts would yield some by 100ft-lbs. The one downside to the allen bolts is the weak spot is concentrated in the short area of threads that is not in the block, as the bolt diameter is slightly larger above the threads. This means the bolts will stretch less than the factory bolts that are fully threaded.
 
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benhart16

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Seattle, WA
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2000 Jetta tdi
If you decide that you want to make a set of studs, I would recommend planning on installing the bolts upside down. When you cut the bolt heads off, it pays to sacrifice one row of threads, otherwise you will spend a long time grinding the stud so it will thread in the block. Then, grind a slot in the nub at the bottom of the bolt for a flat blade screwdriver. This will make installation a ton easier.
 

[486]

Top Post Dawg
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Mar 1, 2014
Location
MN
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02 golf ALH
Didn't think of that! They may make a reduced wrenching surface nut somewhere, I know ARP flange nuts have some real small 12pt heads to them

My ARP studs are torqued to 125 ft/lb and that's on a fine thread nut. I think it is 1/2-20 thread
You don't have to worry about pulling the threads from the block, the 12.9 bolt will break long before that.
 
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