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 Post subject: Stripped head stud hole
PostPosted: Thu Feb 15, 2018 8:14 pm 
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848cc
848cc

Joined: Fri Jul 21, 2017 1:14 pm
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Location: Branxton, NSW
When re-torquing my head today, one stud thread in the block has started to pull! Not pleased. I guess I'll helicoil it but need to know if someone has any advice and especially is it a blind hole? Dont want metal in the engine

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1972 UK built Mk3 mini with 1098cc engine


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PostPosted: Fri Feb 16, 2018 5:24 am 
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Joined: Fri Mar 19, 2004 6:19 pm
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Location: near Baulkham Hills, NSW
Yes it's a blind hole.
You can either helicoil it or tap 7/16" UNC for a custom made stud.
Either way, it needs to be done so the stud is dead vertical or you will have grief fitting the gasket. So I would not do it in the car unless you hire a magnetic base drill.
And use it also to start the tap square.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank @7000+, 45 Dellorto, RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. Going harder with Stealth Black Box in.:mrgreen:


Last edited by drmini in aust on Fri Feb 16, 2018 6:43 am, edited 1 time in total.

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PostPosted: Fri Feb 16, 2018 6:40 am 
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848cc
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Location: Branxton, NSW
Thanks. is it 3/8" unc thread? I have heard use an old rocker post to get the drill square as well, mag base also an option

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PostPosted: Fri Feb 16, 2018 6:42 am 
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Yes it is 3/8 UNC.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank @7000+, 45 Dellorto, RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. Going harder with Stealth Black Box in.:mrgreen:


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PostPosted: Sat Feb 17, 2018 5:28 am 
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848cc
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Joined: Fri Jan 02, 2015 3:59 am
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When drilling a block for 11 studs I used the cylinder head to get in right place. Plus some valve guides drilled out to 8mm internal and turned for sliding fit in the head drilling (note, there are different sizes depending on which one). The drilling was then just done using electric hand drill.

An old rocker post works well to keep the 3/8 UNC tap dead vertical, but it is too small for use with a 7/16 UNC tap or a 3/8 helicoil tap. Best used with an old rocker shaft and a second rocker post which you can clamp using spare 3/8 stud to keep from wandering about.

All lined up perfect, head slips on without touching the 10th stud - other one is the bolt at thermostat end which uses a 5/16 UNC helicoil.

But have not tried this with a stripped head stud.


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PostPosted: Sat Feb 17, 2018 7:21 am 
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I made a custom stud once from a 1/2" UNC grade 8 bolt, I turned it down to 3/8 except at the bottom then threaded 3/8" UNF at the top.
Someone had already done a bad job of tapping the S block to 7/16", it was drilled and tapped crooked. Hence my comment above.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank @7000+, 45 Dellorto, RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. Going harder with Stealth Black Box in.:mrgreen:


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