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Old 05-20-2018, 01:08 AM   #1
VinceS2
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Member#: 353338
Join Date: Apr 2013
Chapter/Region: International
Location: Newcastle Australia
Vehicle:
2005 EVO 8 WRX + STi
gold

Angry Head Bolt Thread Manufacture Errors - Is this common; How Fix?

Hi,

Has anyone else experienced M11x1.25mm head bolts pitch not being quite right on an EJ20? As in up to a thread out of pitch over their threaded length? Doesn't sound much, but is pretty confronting 'in the flesh'.

I am quietly doing a minor rebuild to an '04 STi (rings, timing gear, clutch & full head service) and am up to installing the heads. Bought new bolts, purely as a 'good practice' preventative measure. Oiled washer & thread and found they were going tight just screwing in with speed brace. These are supposed to be M11x1.25mm threads and it turns out that, over 50mm, the OEM one is a smidge under on diam (unimportant) but out by half a thread, and the replacement bolt is slightly better on diam but out by a whole thread. So my OEM's are M11x1.266mm and the new bolts are M11x1.282mm, marvellous eh?

See pic, which I originally took just to count the threads on a big screen, but it turned out to be a useful comparison technique. The green and red number sets are identical copies, placed in different places to allow comparison between them.



Any other time I would just revert to the old bolts, but the shirty thing is that I destroyed 3 using them by being bent (by me) to be used for something else, so need to decide if to force the new ones in, or go hunting wreckers for similar-to-OEM ones made just a bit wrong too!

This seems all pretty unbelievable to me, but you can see simply from the misalignment between the threads of the adjacent bolts that it is the wrong thread so using the new ones seems silly, despite the seemingly only minor discrepancy! An M11 nut screws on each and both feel perfect, just that the engagement length in the block is much longer, so it matters.

Have others seen this / got a particular recommended solution? Thank you.

Oh, in case it is not obvious, that pic comes from the following arrgt; all diams were via a micrometer, not the verniers; thread font is Courier New, being a fixed space no kern font:
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Old 05-20-2018, 02:07 AM   #2
Bram
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Join Date: Aug 2011
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I see your in Australia too. I have some used ARP2000s and some used ARP625s if you want buy them and use them. Either of those 2 options will be better than OEM bolts.
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Old 05-20-2018, 03:53 AM   #3
VinceS2
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Member#: 353338
Join Date: Apr 2013
Chapter/Region: International
Location: Newcastle Australia
Vehicle:
2005 EVO 8 WRX + STi
gold

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Thanks for your kind offer Bram, PM sent.
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Old 06-10-2018, 02:26 AM   #4
VinceS2
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Member#: 353338
Join Date: Apr 2013
Chapter/Region: International
Location: Newcastle Australia
Vehicle:
2005 EVO 8 WRX + STi
gold

Wink Head Bolts might be wonky, but supplier was good, gotta love that!

Just to tidy this one up, Bram kindly gave me his used ARP 2,000's for a good price and that sorted the assembly issue. The supplier of the kit also handled the problem well and accepted the problem was real and at least gave me a full refund for the bolts, so all kudos to them.

The supplier was https://www.ebay.com.au/str/anbbroth...cat=4481063016 which I found the rest of their stuff (gasket kit, rings, 12mm oil pump) was great quality at an excellent price. As suppliers go, these guys are clearly setting themselves up to proudly do really good work. I can see lots of little touches that were 'done right' and obviously some supplier-side issue has let them down on the bolts. They say they have not figured out the problem completely yet and I was the first report, but they will sort it.

Given how it was only half a thread I am guessing anyone else just treats them as new bolts and 'a bit stiff', so there are happily mis-torqued heads out there everywhere waiting to fail! Or maybe not, as I only got about half way in (on a speed brace) and was unhappy with what I was feeling. 'Getting boofy' might not have got it in to the base position where turn of the nut method would get an acceptable result. No interest in testing these theories out!

I did check for consistency and every new bolt was exactly the same; not quite right thread pitch. The ARP 2000's screwed in by hand, after I ran an old bolt in the two I put the new ones into, just to reset the threads a little anyway. Beats me why it seems the OEM threads are a smidge off 1.25 pitch too, maybe that's a tolerance thing - I haven't checked... or care now!!!
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