Stripped manifold bolt thread (V8)

[adam quantrill]

While investigating a 'tick tick'ing which turned out to be an exhaust gasket, I decided to nip up all the maniold bolts to make sure they wre all tight.
However I found that one of the bolts appears to be turning and not tightening - someone has stripped the thread. This looks like the first mechanical fault I've found on the 400SX.

Lickily it's right at the front of the engine on the drivers side, so easy to get to (the ones behind the supercharger are a pig!)

So - what do I do next? I don't want to take off the manifold and as that gasket isn't leaking (yet), perhaps the easiest thing is to put in a stud. Or maybe I could tap the hole with a slightly bigger diameter tap and stick in another bolt, or a stud.

Any other ideas?


>> Edited by adam quantrill on Monday 3rd October 10:15

[dickymint]

Maybe a longer bolt would find some 'unused' thread?

[adam quantrill]

Possible - I could grind one down to the required length, thus giving it a square end - the thread would then reach all the way down. Haave to be careful not to hit the bottom of the hole or it'll definitely strip what's left.

[tallbloke]

Square the end of some studding and use two locknuts to find the bottom of the hole (A plug tap first would remove corrosion and crud at the bottom)and then wind the lower nut down tight onto the manifold. That way, you'll avoid the risk of stripping the thread in the cylinder head through bottoming before the bolt head is tight against the manifold.

[adam quantrill]

Yeah if I use studding I'll probably leave it a bit longer and grind a hex end onto it, that way there'll be a fighting chance of extracting it again when the time comes. It'll also be much easier to install.

[350matt]

Alternativly drill it out and helicoil it?
These are usually stronger than the origianl thread

Matt

[chassis 33]

350matt said:

Alternativly drill it out and helicoil it? These are usually stronger than the origianl thread Matt

Thats the proper solution yes, but a bit of a bugger with the head still in the car, one hell of a job removing the head, for something so silly as a stripped thread.

Regards
Iain

[wedg1e]

chassis 33 said:

350matt said: Alternativly drill it out and helicoil it? These are usually stronger than the origianl thread Matt Thats the proper solution yes, but a bit of a bugger with the head still in the car, one hell of a job removing the head, for something so silly as a stripped thread. Regards Iain

Ah well you see, that's what happened to me! I had the same probs as Adam, but couldn't get in to Helicoil as it was the rearmost cylinder on the left bank.
So I resigned myself to whipping the head off (which isn't THAT much work really) and eventually found that between both heads, FIVE of the threads were knackered. Helicoiled the lot, job done
Alas I then took the opportunity to inspect the cylinder bores, and that's where it really went wonky...

[adam quantrill]

At the front there might just be enough room to get the helicoil tap in there with the engine in situ. Not enough room for a drill though, unless on a remote chuck.

So what size helicoils did you guys use? There seem to be quite a few part-used kits on eBay which seems like a bargain way to go.

[wedg1e]

adam quantrill said:

At the front there might just be enough room to get the helicoil tap in there with the engine in situ. Not enough room for a drill though, unless on a remote chuck. So what size helicoils did you guys use? There seem to be quite a few part-used kits on eBay which seems like a bargain way to go.

IIRC I was able to use the original size, 3/8" UNC rings a bell.

[GreenV8S]

Would you consider using Timeserts instead of helicoils? It looks like a rather better solution.

[adam quantrill]

If I had the manifold off, then yes, but I think they are a bit wider than helicoils (for the same bolt diameter) and thus won't go through the hole in the manifold retaining plate.

I hope to fix this without disturbing the manifold (as that gasket seems gas-tight right now).

[SLB]

One problem is drilling the hole for the helicoil perfectly straight with the head in the car. You could use a drill with a 90 degree head but it's harder to keep on the right line.

[adam quantrill]

Well I'm wondering that with the thread being non-existent, whther the hole is now wide enough for the tap without more drilling. It is tapping alloy after all. And yes, I do remember my metalwork lessons, two turns in, one turn out...

[leorest]

I'd second, cleaning thread and using a stud and two nuts to hold it for now and Helicoil it when the head/engine is next out.

When choosing the stud material be aware that using stainless steel and aluminium together promotes galvanic corrosion.

IMO threads in ali are always a problem area as is stopping corrosion. Only way round it is to use wire thread inserts in Ali and choose fixings to avoid corrosion.

There are other thread inserts which have their merits but Helicoils are relatively cheap (tooling wise) and easy to put in.

Leo

[wedg1e]

SLB said:

One problem is drilling the hole for the helicoil perfectly straight with the head in the car. You could use a drill with a 90 degree head but it's harder to keep on the right line.

Tried this; there wasn't room once you got a drill bit in the chuck! Maybe easier towards the front...

[wedg1e]

leorest said:

When choosing the stud material be aware that using stainless steel and aluminium together promotes galvanic corrosion. Leo

I considered this, but reasoned that the bolts were being screwed into the Helicoils so should still be removeable. Bit of copper grease and last time I tried, they still turned. Unless it was the Heli's turning in the head, of course...

[tallbloke]

adam quantrill said:

Well I'm wondering that with the thread being non-existent, whther the hole is now wide enough for the tap without more drilling. It is tapping alloy after all. And yes, I do remember my metalwork lessons, two turns in, one turn out...

Stick a 3/8 bsf tap and a m10 tap down before the helicoil tap, the different pitches will help cut it out to the helicoil tapping size.

[leorest]

wedg1e said:

I considered this, but reasoned that the bolts were being screwed into the Helicoils so should still be removeable. Bit of copper grease and last time I tried, they still turned

The galvanic corrosion is only a problem when the stainless is touching the ali, so stainless bolts/studs into thread inserts would be fine, provided the inserts (or their plating) are reasonably compatible with aluminium.

wedg1e said:

Unless it was the Heli's turning in the head, of course...

If this does happen, then it's simplicity itself to fit a new Helicoil, this time with a little thread lock selected to cope with the temperature! Threads direct into ali are a nightmare for stripping/crossing/corroding/binding/snapping, but thread inserts can be changed if there are any probs.

I always assemble everything with copper grease and have wondered how to adjust torque figures.
I have heard it said, mainly on other forums, "torque values should be increased to compensate for the lubricant, which would otherwise allow the bolt to undo easier", but I am not so sure.
My thinking is that the dry torque value was set to give a calculated stretch to the fastening and the addition of assembly lubricant would increase this for a given torque measurement. Anyone know which is correct?
Angular torque setting would give constant stretch regardless of dry/lubricated assembly but converting ft-lbs. into degrees isn't easy.
Leo

[adam quantrill]

> Stick a 3/8 bsf tap and a m10 tap down before the helicoil tap, the different pitches will help cut it out to the helicoil tapping size.

If I can tap it to M10 then I may as well just use an M10 bolt - or stud - in that hole and be done with it. I'll be sure to label that bolt though - don't want a garage numpty trying it in all the other holes before finding the one that fits!!!

I have a spare couple of heads I can try tapping to see how easy it is out of the car.