Flywheel Bolts for the 60-degree V6

[Series8217]

The 60* V6 crankshaft has six M10x1.0 holes. The GM flywheel bolts (p/n 476576) are 23mm long with a 1mm unthreaded chamfered nose and a 6mm unthreaded shoulder (9.9 mm diameter). The bolts engage to a depth of 18 mm in my 1992 3.4 DOHC (LQ1) crankshaft. However, that depth utilizes the conical nose. The fully tapped thread depth is around 16.6 mm, and it seems to be up to a millimeter less on some holes (or the threads in my crankshaft have gunk at the very ends).

The steel 60*V6 flywheel (Sachs NFW1006) is 8.4mm thick in the mounting area. This limits the shoulder length to 8.4 mm minus shoulder stretch. The crankshaft holes are slightly chamfered, and could potentially accommodate 1mm of extra shoulder / thread roots.

So in order to meet the minimum 10 mm thread engagement, the bolt must have at least 19.4mm of under-head length and enough threads.

The maximum length is 25 mm minus bolt stretch, and assuming that all holes have 16.6 mm of usable thread.

ARP makes 6 different bolts sets with an M10x1.0 thread:
* 147-2801 - M10x1.0 x 25.4mm (5.7/6.1/6.4 Hemi)
* 251-2803 - M10x1.0 x 29.21mm (2.0L YB Cosworth)
* 151-2801 - M10x1.0 x 29.21mm (2.0L Pinto)
* 254-2801 - M10x1.0 x 25.4mm (4.6/5.4 Modular V8)
* 156-2801 - M10x1.0 x 24.765mm (5.0L Coyote V8)
* 206-2803 - M10x1.0 x 21mm (Rover K-series)

151-2801 appears to be the infamous Pinto bolts that I've seen mentioned on this forum and others. They do not fit. It is possible that in the past they were made in a different length, short enough to fit the 60*V6 but they are not anymore. Blue Shift mentions this and includes pictures of it in another thread.

156-2801 is new (that motor just came out recently). Based on catalog specs, it looks just about perfect, so I ordered some from Summit. Unfortunately, I can't install the bolts deep enough in the crankshaft in most holes, because the end of the bolt is not chamfered at all. It hits the ends of the crankshaft threads before it goes in far enough to squeeze the flywheel.

If there is a way to safely shorten the 156-2801 bolts without messing up the start of the threads, they might work. Unfortunately that's not the only problem. At 8.5 mm, the shoulder on these bolts is slightly longer than the thickness of the steel flywheel. It's a fight between bolt stretch and the chamfer on the crankshaft holes.

The only shorter bolts are 206-2803, but with how much shorter those are, just 1.5 mm of end chamfer is enough to be very close to the minimum thread engagement.

Note that some aluminum flywheels are thicker than the steel one. The 156-2801 bolts might work with flywheels that are at least 10mm thick.

I noticed the other day that WOT Tech (basically the 60degreev6.com web store) sells "ARP Flywheel Bolts". They look like 156-2801 but might be shorter. If that's true, those are the 206-2803, and they don't have a chamfer so they should be safe to use with the steel flywheel, but not a thicker one.

[The Dark Side of Will]

Interesting info. Also be careful going with thicker heads than stock, as there isn't much room between the stock bolt heads and clutch disk, if you have a sprung hub disk.

Are the GM bolts still available?

There is a similar situation with the Getrag 282 ring gear bolts... they are an odd length stock (I think 22mm) and there isn't room in the transmission for a 25mm bolt. I have faced 25mm 12.9 bolts off at 22mm using a lathe, and with an abrasive foam polishing wheel the threads cleaned right up and were useable... That's a heck of a way to have to make bolts, though.

[Series8217]

Interesting info. Also be careful going with thicker heads than stock, as there isn't much room between the stock bolt heads and clutch disk, if you have a sprung hub disk.
Are the GM bolts still available?

I'm not sure how thick the heads would have to be to cause a problem. Blue Shift is using TWO washers under the Pinto bolts and it still clears the clutch, and I think that was on a Fidanza flywheel too. Then again, he mentioned there has been some unidentified noise coming from his transmission lately, and it could be that the clutch and flywheel have worn down enough that the clearance has been taken up.

The GM bolts are still available, and ATP also makes replacements: http://www.rockauto.com/dbphp/x,catalog ... ZX200.html

I'm trying to find a place that has the GM ones in stock, otherwise I'll try the ATP bolts. I have no experience with ATP though. I did already order the bolts; they're only $10 shipped from Rockauto for a set of 6.

There is a similar situation with the Getrag 282 ring gear bolts... they are an odd length stock (I think 22mm) and there isn't room in the transmission for a 25mm bolt. I have faced 25mm 12.9 bolts off at 22mm using a lathe, and with an abrasive foam polishing wheel the threads cleaned right up and were useable... That's a heck of a way to have to make bolts, though.

I used some socket cap screws from OSH or McMaster for the 282. I just had to grind down the heads a bit to clear the retaining plate / oil deflector for one of the carrier bearing outer races.

[Series8217]

I found some previous discussion here:
phpBB/viewtopic.php?p=76502&sid=8aa00c9 ... 0769ec30f5

Kohburn mentions using the Pinto bolts with the addition of "lock washers from the stock flexplate". Note that ARP's instructions explicitly say to NOT use washers. That said, Blue Shift has been using washers on his, but I don't know how long it will hold up for (or if the noise he's been hearing is from the bolts having loosened up).

Since there has been a lot of discussion about flywheel bolts looseing, please note that the general consensus (NASA, Carroll Smith) is that lock washers are useless, so that's another reason to avoid using them. Red loctite and proper bolt torque are, as far as I can tell, the best way to stop traditional bolts from loosening. (There are other effective methods listed in the NASA document starting on page 6, but they require modified bolts or a different thread profile). Safety wiring is also effective, but the heads of our flywheel bolts are too thin.

I found out that one of my friends has some M10x1.0 thread reforming tools, so I'm going to try shortening these bolts. Then I can thread them into the crank and see if there is enough engagement before the unthreaded portion hits the crankshaft nose.

[The Dark Side of Will]

The entire purpose of a washer is to spread out the contact load from the bolt head. They are neither necessary nor productive on a steel/iron flywheel, especially with properly profiled, large diameter bolt heads on flywheel bolts.

The reinforcement plate you mentioned for use with an aluminum flywheel would be an extreme example of a washer, but that's the only situation in which its use is desirable.

Edit: I thought I'd had some problems with washers under conventional thickness hex head 12.9 bolts on the Northstar, but I was remembering incorrectly. The washers under the heads WERE quite close, but the real problem was that the bolts were too long and had impacted the rear main bearing bulkhead.

[Series8217]

I received the ATP "OEM replacement" bolts, part no. ZX-200. I'm not happy with them.... they're lightly stamped "11.9", and obviously not during the head forming process. The head has round maching marks as if it was turned. They're Made in China according to the packaging. They have an unthreaded shank like the GM bolts, but it doesn't smoothly transition to the threads. There's just a step. There are no foundry markings.

I do have some extra ones on the way, since I was going to try drilling some for safety wire. Since I have extras, I could do some testing. How do I find out if they actually meet 11.9 class requirements?

[Series8217]

The ARP bolts were much easier to cut with a hacksaw than I thought. A 32-tpi blade makes quick work of them. I cleaned up the ends with a file and they thread in just fine, even without using a thread reforming die.

I shortened them by a few mm, and then threaded them into the crank. They end up having 90* to 180* left from where they contact the flywheel to where the shoulder bottoms out on the crankshaft nose. It looks like that gives just enough space to tighten them down to spec. I'll know for sure when I get the torque wrench on it, but I doubt these ARP bolts will turn 90* with only 70 ft-lbs of torque on them, especially with 10mm of thread engagement and a 1.0mm thread pitch. Stretch wouldn't be more than 0.2 mm on a fastener this size right?

[Series8217]

I received the ATP "OEM replacement" bolts, part no. ZX-200. I'm not happy with them.... they're lightly stamped "11.9", and obviously not during the head forming process. The head has round maching marks as if it was turned. They're Made in China according to the packaging. They have an unthreaded shank like the GM bolts, but it doesn't smoothly transition to the threads. There's just a step. There are no foundry markings.

I do have some extra ones on the way, since I was going to try drilling some for safety wire. Since I have extras, I could do some testing. How do I find out if they actually meet 11.9 class requirements?

Update on that... I sent an e-mail to ATP detailing my concerns. Their reply:

The ZX-200 bolts are sourced from an overseas supplier. We rely on the
supplier's engineering expertise to provide us with parts that are
functionally equivalent to the OE parts. We have not experienced any
problems with the ZX-200s.

What they seem to be saying is their Chinese supplier "copied" the GM bolts (and apparently made them even cheaper). The GM bolts are probably optimized to be as cheap as possible already, so I'm not sure that's such a great idea. Also, ATP did not admit to any due diligence on their part. Due to this fact, and my above observations my recommendation is to use the GM bolts instead of ATP ZX-200.

[The Dark Side of Will]

Put a high strength nut and a few washers in a vice and see how hard you have to pull the overseas bolts until they break, then compare with published torque guidlines. Maybe get some hardware store 8.8's to compare.

Of course that's a good way to waste a lot of time when you could just buy the bolts you know are right.

Also, 11.9 is a WEIRD class... I @$$ume there's a DIN definition for it, but it may be very uncommon or unrecommended. For example, DIN recommends against the use of 11mm threads because there are so few applications in use. Of course that didn't stop GM and VAG from using them for head bolts...

[Series8217]

Put a high strength nut and a few washers in a vice and see how hard you have to pull the overseas bolts until they break, then compare with published torque guidlines. Maybe get some hardware store 8.8's to compare.

Good idea, but I can't find any 12.9 nuts in M10x1.0.

Also, 11.9 is a WEIRD class... I @$$ume there's a DIN definition for it, but it may be very uncommon or unrecommended. For example, DIN recommends against the use of 11mm threads because there are so few applications in use. Of course that didn't stop GM and VAG from using them for head bolts...

ISO 8676 and ISO 8765 (equivalent to DIN 960 and DIN 961, respectively) are the standards for fine pitch metric hex cap screws.

There's nothing weird about 11.9, except perhaps that there isn't an SAE grade equivalent. The 11 means the minimum ultimate tensile strength is 1100 Mpa. The 9 after the decimal means that the yield strength is ~90% of the ultimate tensile strength.

Do you think that GM and VAG may have used 11 mm head bolts precisely because they aren't used in other applications? I assume most if not all of them are torque-to-yield, and using a weird thread would prevent service personnel from replacing the bolts with other ones that don't follow the same tension profile in yield.

[The Dark Side of Will]

I know there's a definition for class 11 metric fasteners, just like there's a definition for 11mm threads... both are very uncommon.

I'm not aware of any production head bolts that are actually torque to yield. The involved torque+angle process is used to correctly compress the OE composition head gaskets.
I think that VW and GM were both thinking that they could achieve the clamp loads they needed with 11mm fasteners. Since 1 ton of steel can make 19% more 11mm fasteners than 12mm fasteners... I think it's purely economies of scale. For the numbers they needed, the fact that it's not standard across the industry wasn't a consideration.

[Series8217]

The plot thickens on the ATP bolts.

I just received the second set of ZX-200 bolts I had ordered. They are NOT the same as the ones I posted about above. These appear to be of a much higher quality; more in line with what I would expect to see on an OE replacement part.

The ones I received most recently have the following features:
* an apparently forged head (the "11.9" lettering is -raised-)
* a smooth transition between the shank and the threads
* overall darker in color, indicating either a different alloy, surface treatment, or perhaps they just have more oil on them
* larger chamfer from the hex sides to the round part of the head
* slightly shorter overall length than the other ZX-200 set and the GM bolts

I now seriously doubt the quality and authenticity of the first set I received. If I had received these new ones initially I would have probably used them.

[The Dark Side of Will]

The color difference just means that the black oxide coating on the new batch is thicker than the old batch.

The "offshore" first batch is sounding more and more like a good candidate for destructive testing.

[Series8217]

The dark ones are oiled and the light ones are dry, so they might look the same if I clean off the oiled ones.

Yeah I do want to see how they fare, but I haven't solved the nut problem yet.

[Series8217]

ATPs reply regarding the second batch I received:

We used to purchase these bolts from a different supplier here in the U.S. Unfortunately, they are no longer in business and we were forced to find an alternate. We occasionally get product returns of old inventory from our customers. This is what you received on your second purchase.

Better to sell a crappy (potentially dangerous?) product rather than none at all, right?

[ericjon262]

Thought I would add,

WOT tech ARP bolts Vs GM bolts. Gm=Longer, the last MM or so is tapered on the GM bolt, and useless from a thread engagement standpoint. the threads on the ARP bolt go all the way to the end.



Approx 23.1mm length below head.



Approx 20.2mm length below head.

[Series8217]

Thank you for sharing the photos and measurements. Those are the ARP bolts for the Rover K series engines:
206-2803 - M10x1.0 x 21mm (Rover K-series)

I was afraid they might have too much of an end chamfer and give to little thread engagement. However your photos and measurements show that there is effectively no chamfer at the end, much like the bolts I used. That's great, they should have enoughvbthread engagement when using a stock-thickness flywheel. The short shoulder is interesting.. I don't know if that can cause any problems.

[ericjon262]

one of my bigger concerns was not the bolt itself, but that the hole in the flywheel for the bolt is much larger than the bolt, effectively allowing the flywheel to shift 10 degrees or so(going by memory on the numbers). I was thinking about having a machine shop make a set of sleeves for a snugger fit.

[The Dark Side of Will]

Ten degrees seems like a lot... I could believe 1.

Not relevant if the bolts are torqued and have complete circumferential contact.

[ericjon262]

it's been a while since I had looked at it, but it was enough play for me to not like it. I'll break out the calipers and measure the differences in the size of the bolt vs the hole.