General Stripped thread

[Bettegacci]

So a dodgy repair by the previous owner of my 500 and left this to happen yesterday ??? the top hole is also worn, but I’m hoping I can heli coil it, now I know why my exhaust kept rattling loose, any advice? Could the bottom hole be tig welded up and re drilled and tapped?

 

[the hobbler]

This is quite a common occurrence with the 500, but there is a way to permanently cure it. When I was at Radbourne racing we carried a small Abarth recommended modification to prevent this from happening.
The trick is to use the "self tapping steel inserts" as available from either "MEMFAST" or, "THE STEEL INSERT COMPANY"---their inserts are practically identical to the 'pukka' Abarth supplied items. Basically, you drill out the damaged hole to the required size, make the small insert tool, and screw in the steel insert. I would also recommend that you make up some new studs (instead of bolts) to hold the manifold in place---make them long enough on the 'inside' so that they 'lock' against the cylinder head webs and long enough on the 'outside' to allow you to use 2 plain nuts. 1 nut to tighten the manifold in place and the 2nd nut to lock onto the 1st nut. Do NOT use 'locking' nuts as these can 'grab' and pull your stud out. Lastly, if you have to go up to a 10mm stud (the standard is 8mm), make up a 'stepped' stud so that 8mm still goes through the elbow---if you drill the elbow to accept 10mm studs you will end up with very thin walls on the elbow manifold.
If you require more help with this problem, contact me direct by e-mail. Just for interest,where do you live? I am just outside Chester.

 

[varesecrazy]

This is quite a common occurrence with the 500,
Just for interest,where do you live? I am just outside Chester.

Oz.tralia apparently..

I did wonder ..as the post equated to 04:00 hrs UK time.


I am not familiar with the quoted brands.. but assume it is essentially a 'tube' of thread.
Similar to a helicoil.. but not twisted wire.

Termed
steel_self_threading_inserts.php

 

[Bettegacci]

Perth Australia here ? 500f, Thanks this sounds similar to the helicoil system, I’m going go down the stud idea instead of bolts and I’ll use the double nut idea too, am I right to presume the head is cast Aluminium? If I can tig weld it I’ll be a happy lad, this is my first fist 500, I’m still very green on learning all about them. Thanks for the reply

 

[the hobbler]

The inserts have an external thread to 'grip' the metal it is being inserted into--in the case of the 500 head, aluminium. The insert with the correct 8 x 1.25mm INTERNAL thread is part number:---STT1M8-CR3 and has an EXTERNAL thread of 12 x 1.5mm---you drill a hole of 11.00/11.2mm. Looking at your photo,it looks like a lot of head (previous insert?) has come out with the bolt. If it has and you do need to tig-fill and then re-drill/tap the hole, do one side at a time if you can---this enables you to use the elbow as a drill guide. If you have any problem getting the inserts in Perth, contact me direct, with your address and I will put 4 into the post to you. If you have to do one end of the head, you might as well do both ends and prevent any future problems.
A company in Perth that might be able to help you with the inserts (from either of the companies) is "GoGear". An old mate of mine, Dick Ward, as far as I am aware, still owns this company. Dick has some history with Abarth---I helped him strip his road car and rebuild it as a 'full-blown' "Abarth 850tc Radiale" when we both worked together at Radbourne Racing. If Dick is there, feel free to use my name as a contact (Tom Montagu) and please give him my regards.

 

[Bettegacci]

Can you pm your email tom, wouldn’t mind asking some advise and sending a quick video I can’t seen to upload here.

 

[Fiat Down Under]

Hi Bettegacci. How did you get on with your repair? I have the exact same issue with my '65 500 D. I've had to remove the engine as it was the inside mount and it wasnt until the engine was removed I could see the damage. The 2 bolt inserts into the block have previously been drilled and maybe tapped (no sign of helicoils?) and the manifold bolts used were a M10/M8 version. The lower hole hasn't torn quite like yours but has ovalized and looks very weak. I think my only option is TIG weld infill and re-tapp? I'd like to be able to stick to M8 bolts again if possible.

 

[the hobbler]

Hi Bettegacci. How did you get on with your repair? I have the exact same issue with my '65 500 D. I've had to remove the engine as it was the inside mount and it wasnt until the engine was removed I could see the damage. The 2 bolt inserts into the block have previously been drilled and maybe tapped (no sign of helicoils?) and the manifold bolts used were a M10/M8 version. The lower hole hasn't torn quite like yours but has ovalized and looks very weak. I think my only option is TIG weld infill and re-tapp? I'd like to be able to stick to M8 bolts again if possible.

From all my experience with 500 and 126 cylinder heads (and yes, they are aluminium Bettegacci) it is wise to retain 8mm as the hole size in the 'elbow' exhaust manifolds' If you go up to 10mm, the walls of the holes in the 'elbow' get very thin. If you have to (due to the amount of hole destruction in the head) go to 10mm thread, you will require to fit 'stepped' studs---10mm into the head repair and 8mm 'shank' through the exhaust 'elbow'. From new, the retaining-bolt/stud hole in the manifold 'elbow' is about 8.5mm to 9mm (depending on supplier!)
My e-mail address Bettegacci is:--- [email protected] --feel free to drop me a line with your questions---keeps what few grey cells that I have left between my ears rattling around!
If you DO have to go up to a 10mm fixing in the cylinder head, you WILL need to go the stud route. This size IS available in the "self-tapping" inserts, but might leave little metal around the holes in the head. In these curcumstances, welding up the hole and going back to 8mm (and using studs) is often the best way to go. If the engine is out of the car, try and repair/thread-tap just one hole at a time---that way you might be able to use the exhaust AND the manifold/elbow as a drill guide. The last time that I had to do this sort of repair, I used differing sizes of tubing, one size inside another size etc. until I achieved a small hole in the guide-tubing for the initial pilot drill, and then removed 1 piece of tubing at a time so that I could go up 1 drill size at a time. For a 8mm x 1.25mm thread, the final drill size is 6.8mm (17/64th)---I normally finish with a 6.5mm drill as 6.8mm drills are difficult to fo find