Switching to M3 screws from self-tappers

[DeadMeat666]

If a car has been built with the stock self tapping screws, is it wise to swap them out for M3 machined screws, or will the screw holes no longer be able to properly accommodate machine screws without risk of getting threaded? This one doubt is what's keeping me from taking on the restoration of any used car, but I don't know if it's a well-founded concern. I'd like to hear from those of you who have actually done it.

[SupraChrgd82]

Likely depends how shredded the holes are from past screw replacement.  If you're the type that's adamant about finding the same thread each time the tapping screw is replaced, there should be enough "meat" left in the holes for the new M3 screws to bite into without stripping.

I just swapped the tapping screws in a 1986 Hornet and the wife's 1.9 Wraith without stripping any. I was gentle with the 'driver and watched closely for the screw heads to seat against the mating surface to assure a succesful swap.

[Carmine A]

AR60 Axles (2.2 Wraith) are notorious for stripping Screw Holes where the Hubs attach.... 

I'm fairly certain that this is in your skill set - I Drill out the Screw Holes to 5.2-5.3mm - and insert THESE.

 https://www.ebay.com/itm/292174792941

A little Epoxy around the knurled area, squeeze them in with Pliers or Vise Grips, and they're PERMANENT!!  Here's the Dimensions...   

I know you can't use these in every location, but where you can, they're MUCH stronger than they've ever been! On my Axles, they've lasted without issue, for 5 years so far - on 4S Brushless Power!!! 😎👍👍

[Carmine A]

....... If at ALL possible, push the insert into the Hole from the INSIDE, with a short (3 x 4mm) Screw into the Insert to protect the Threads. 😉

[Gazzalene]

This might sound a bodge but if I want to put a M3 MS into a old self tapper hole I first put a little bit of CA on a cocktail and and run that up and down the hole. NOT a lot.you don't want to see CA pooled in there,just enough to coat the hole sides.Makes  a very good fit 

[Carmine A]

@Gazzalene - I just did that Today on the Upper Arms on my M05. Works a treat as well, especially on the softer Suspension Parts!!

[DeadMeat666]

2 hours ago, Carmine A said:

AR60 Axles (2.2 Wraith) are notorious for stripping Screw Holes where the Hubs attach.... 

I'm fairly certain that this is in your skill set - I Drill out the Screw Holes to 5.2-5.3mm - and insert THESE.

 https://www.ebay.com/itm/292174792941

A little Epoxy around the knurled area, squeeze them in with Pliers or Vise Grips, and they're PERMANENT!!  Here's the Dimensions...   

I know you can't use these in every location, but where you can, they're MUCH stronger than they've ever been! On my Axles, they've lasted without issue, for 5 years so far - on 4S Brushless Power!!! 😎👍👍

Very interesting. But after looking at my kits again, there really aren't many places where you could drill out the holes to 5.2mm, there's just not enough plastic. This would probably work a treat on 1/8th scale upwards I imagine.

Or am I missing something?

[Gruntfuggly]

I swap from self tappers to machine screws quite often. Never had an issue - they don't seem to back out. 

[ChrisRx718]

Never had any issues swapping from self-tapping to machine thread myself other than on something I didn't build- the previous owner had over-tightened the stock screws and left no plastic for the screw to grab into. New plastics time 

[Carmine A]

3 hours ago, DeadMeat666 said:

Very interesting. But after looking at my kits again, there really aren't many places where you could drill out the holes to 5.2mm, there's just not enough plastic. This would probably work a treat on 1/8th scale upwards I imagine.

Or am I missing something?

..... Not really missing anything. This works as a better than permanent solution - IF you've got enough meat around the Screw Hole. 

This is a last effort for me, after all the usual fixes are exhausted, the Hole is REALLY ripped open, and there's no options left.  There are a few places on a Tamiya that these can fit.

But I never expected this to be a first option. I did put this out there, on here and one other Thread.... 

Maybe you can use it someday - maybe someone else can use it at some point. I know someone who used these on the Front and Rear Shock Towers of a TT-02B, for strong Upper Link Mount points. 😉

[rich_f]

For areas where there isn't enough meat left for those bigger inserts, I wonder if some M3 helicoils would work. According to the ebay ad below, they only require a 3.1mm drill hole. 

https://www.ebay.co.uk/itm/122037614593

Anyone tried these?

[Carmine A]

@rich_f that's BRILLIANT!! 

For the U.S. Guys:  https://www.ebay.com/itm/143464887201 

[Toolmaker72]

I’ve noticed on the vintage plastic parts the self tapped holes actually split over time. Fitting machine screws are much better for longevity.  New parts can easily be drilled and tapped to suit.  Helicoil inserts definitely work also 😊

[Carmine A]

1 hour ago, Toolmaker72 said:

I’ve noticed on the vintage plastic parts the self tapped holes actually split over time. Fitting machine screws are much better for longevity.  New parts can easily be drilled and tapped to suit.  Helicoil inserts definitely work also 😊

Judging just by your username... I'd tend to listen!! 😉

[Toolmaker72]

That made me smile 😊. 

[DeadMeat666]

49 minutes ago, Toolmaker72 said:

I’ve noticed on the vintage plastic parts the self tapped holes actually split over time. Fitting machine screws are much better for longevity.  New parts can easily be drilled and tapped to suit.  Helicoil inserts definitely work also 😊

That's precisely why I preferred to build my NIB M02 with machine screws from the outset. Thank you for confirming my theory!

[Toolmaker72]

Just make sure you drill the correct size to tap m3 or m4 and don’t bottom out the tap otherwise the new screw thread will be cut off.