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cross / threaded seat bolt

knw911

Silverstone
Joined
19 Oct 2016
Messages
128
Hey guys - some of you will have seen my previous thread and the troubles in getting my new seats installed. Long story short, I had been sent incorrect fitting kits, and the seats not compatable without extensive modification. Watch this space for replacements.

However, on trying to put the original seat back in, I one of the bolts seems to be cross threaded. You can screw it down so far, and then it wont budge. Assumption is that in the processes of trying to put the new seats in, the tension may have damaged the thread.

The bolt looks fine, so assume its the thread in the chassis.

How to overcome? I've seen suggestions of oil up with WD40 and force it, cutting a slit into the bolt, re-cutting the thread, drilling it out and replacing... etc etc.

Any suggestions welcomed.
 
I would recut with a tap.

MC
 
MisterCorn said:
I would recut with a tap.

MC

+1

They're only cheap, not worth buggering the job up.
 
+ 2

They are essential tools, I've got a cheap Draper Tap & die set and use it frequently as we have a fleet of old cars and bikes. Anytime a bolt is stiff I run it through the die and tap the hole if access is easy, If you don't you'll end up having problems next time it needs to come out.
 
Most Tap and Die sets will come with a gauge like a set of combs, so you can determine the pitch of the thread. Use a bolt to do this, then use a die on the bolt to determine the size.

Once you know, use the correct tap by going in a turn or two, then backing off a bit. Repeat this until it cleans it.

I've done stripped wheel bolts threads in hubs with this method. :thumb:
 
thanks guys for the really helpful input!

So I need a tap and die kit. Anyone have a clue as to the size of the 996 seat bolts so i know what size kit to buy?
 
and what do you do when the tap wrench is too long / wide so that when you turn it it hits the interior trip of the car? ahah
 
You use one of these :



or a 1/4 drive "T" bar with an extension and an 8 sided socket that fits the end of the tap, or if you're careful, a small pair of adjustables.

 
knw911 said:
thanks guys for the really helpful input!

So I need a tap and die kit. Anyone have a clue as to the size of the 996 seat bolts so i know what size kit to buy?

M10, not sure on the pitch, but they'll be either 1.5 or 1.25.
 
Donkey's years ago a bought a little credit-card sized Pro-Bolt "bolt measuring guide" that has M12 - M4 sized holes in it that I use if I need to know what size a particular bolt is and also has various serrated edges with all the pitches.

Just searched and they're only £6.50, definitely a good addition to anyone's toolbox!

https://www.pro-bolt.com/bolt-measuring-guide/
 
Space Cadet said:
Donkey's years ago a bought a little credit-card sized Pro-Bolt "bolt measuring guide" that has M12 - M4 sized holes in it that I use if I need to know what size a particular bolt is and also has various serrated edges with all the pitches.

Just searched and they're only £6.50, definitely a good addition to anyone's toolbox!

https://www.pro-bolt.com/bolt-measuring-guide/

There's a bad echo in here ... :mrgreen:

911munKy said:
My cheap Draper set covers M6 to M12, that should do it.

Also another invaluable tool that get loads of use is this, it might seem expensive but it's been used hundreds of times.
https://www.ebay.co.uk/itm/3247645...WV4Mk2E6QOMZ1c_6KC_PmfZ6lCO_2ythoCxqkQAvD_BwE
 
To measure the pitch, just count the number of threads over a 10mm distance, then divide 10 by the number of threads. Worked for me for 40 years. See image below.

..........and don't ever run a tap down a hole with without using equal force from either side, i.e. never use a spanner to turn a tap, always use something 2 handed (with a tommy bar).


550px-nowatermark-Measure-Thread-Step-6-Version-2.jpg
 
Use the tapered tap with the most missing threads and try to pick up the correct threads lower down when recutting. If you go in with a plug be careful not to pickup the cross threaded part and recut the cross thread all the way down!

There is a bit of an art to it.
 

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