Stripped thread


I've found an upper front engine mounting bolt (photo) has stripped its thread in the engine block. "Copper" wire strands came out of the hole with the bolt, and now it turns freely.
I've a new metric bolt a size up, and a hand tap to suit. I'll have to drill the mounting hole slot to the new size.

Has anyone got a moment to recommend whether I should go with this, or use an helical thread repair, or think again ?

Many thanks all


  • 20240206_135247.jpg
    1.5 MB · Views: 31
If the metric bolt tap drill is roughly the same size as a helicoil I think it’s a toss up. If the metric is significantly larger, that would favour the helicoil.

Personally, I’d helicoil it so I could retain the original bolt, they don't make them that good anymore.

By the way, one thing to look for is that the bolt is the right length. The two there, going throught the engine stay, should be 7/8”. The other two are 3/4”. It’s possible to install those backwards, which makes it easier to strip the thread.

Go for a helicoil. I had the same happen on mine last year, helicoil repairs are also stronger than the original threads in the ally head.
Thanks Vern and Sdibbers, The car is located many kilometers from a screw gauge in Greece. I know the nominal length is 40mm with 32 threads, but not the sure what gauge/pitch that mades it. (It's marked APO 88 on the head.)
While I'm back in blighty, would you know the size of this screw? I'll be chasing a helicoil and drill that suits.
Thats not what I would call an engine mount? Its the front steady post attaching to the head isnt it?
JP, I'm very happy to agree, or now that I've found it in the workshop manual, even refer to it as the stabliser mounting bracket, with its bottom end bracing the engine tie rod. It also braces the front lifting bracket, which I'll need to drill if I have to tap in a larger replacement bolt. It looks like someone packed the thread in the head with copper strands when the deed was done.
(I used the word 'bolt' as the WM uses the term :D )
go for the helicoil but note when buying the kit that the little springs come in different lengths and some are quite short and you will want a longish one
May I suggest opting for a time-sert, which is an even better way of fixing a stripped thread than a helicoil.
They were installed from new by Rolls Royce, which is surely the best recommendation.
Ugh - they suggest the 10 insert kit at . . . over $550.00. Anyone got a second hand P6 2000 head ?
To be fair, they thought my reference to 'Rover' actually meant Range Rover . . .
Ugh - they suggest the 10 insert kit at . . . over $550.00. Anyone got a second hand P6 2000 head ?
To be fair, they thought my reference to 'Rover' actually meant Range Rover . . .

Ouch. You could try re-tapping the hole next size up and getting a local engineering shop to make a stepped stud to go in the head and present a smaller / right size thread to fit a nut to.

I have used these kits from eBay available in many sizes to great effect. easy to use with the correct size drill etc. The drilling is easy as all the drill does is remove the old threads so it self centres. Then just tap the hole with the supplied tap and fit the insert with the tool. Word of warning though. Make sure you tap the hole deep enough for the length of the insert. The tap has a tapered end and if you don't go in far enough, the insert will become smaller in diameter as it is screwed in and then the bolt will lock up as you screw it in. (Speaking from experience obviously!!) The insets are a bugger to get out too!

When I had my Porsche, the Porsche community liked time-certs but you do need a large oversize hole to fit them which seemed a but overkill and a lot of good material removed to me to repair a thread.

If you’re repairing the threads in situ (head in place) you may have to remove the radiator so you can get the drill in place to drill out the old hole. If I recall correctly I had to cut down the drill bit a little too.
It is an issue, isnt it. do you know approximately how much bigger the existing hole should need to be to accept an helicoil that will suit the original screw ? I was looking at some numbers found randomly on the hinternet and it seems to be saying the hole is only drilled 1/64th bigger.
I wonder if (with a bit of patience & the effect Keynsham mentioned) I could keep the drill on the straight and narrow and turn by hand with a rig that can exert a suitable inward pressure. Its aluminium, but accuracy might suffer, I see that.
Colnerov's suggestion of a stud would be good if there was a local engineering firm. Things around Poros tend to the make do and mend school of thought - hence the original copper wire in the stripped thread - & importantly my Greek still struggles with communicating Imperial dimentions :rolleyes:. I'll try the drill, tap and use the original screw I think.
Thinking aloud:
I must say that the stabaliser fitting itself seems very solid with one good fixture and the substantial flat face of the bracket. The top screw also locates the front lifting bracket, which isn't "operationally crucial". Does anything else hang onto the lifting bracket that I'd need to remove ? I cant see anything.
I wonder if there is scope to drill the existing hole deeper, and tap further into the block? Not 'proper' but if a 5mm longer screw fulfills the role to locate the top of the stabaliser mounting bracket . . . just wondering . . .
Last edited:
It’s been a while, but I think even with the rad out I used a pair of pliers to turn a drill bit while holding it square on. It’s not a huge amount of material being removed (especially now the old threads are gone!). Then I used a spanner to turn the repair tap while making sure it was also square on to the head. It’s worth doing, and the finished repair will be stronger than the original thread.