Stripped head bolt thread repair

With you again Mushy. BMW also use 10.9s. I bet that most manufacturers use 10.9s? It's a grade that will yield fairly easily and still offer good strength. This is, after all an aluminium head and a cast iron block. Would not want to put too much pre-load in there before yielding the bolt. Also, it is subjected to temperature effects, so it needs to be able to 'breath' to some extent!

Cruched a few numbers:
The short, 96mm, 8V bolts will yield easily with those figures. If you used a 12.9, the load in the bolt would be such that I would worry about stripping threads in the head at 180 deg.
The long, 142 mm, 16v bolts just yield nicely.

The only problem wth the long bolts is that you need to use a proper angle gauge, as the bolts will twist a lot, due to length, and tend to spring back from 180 deg. Without the angle gauge, we used to put a small 'centre punch' mark oh the edge of the bolt head. Them two more. One lining up with the mark on the bolt and another one at 180 deg. This lets you later check if the bolts have moved!

Would not be surprised if diesels, with torque only, and re-torque after 1000 miles, were 12.9s or even 14.9s?

 

Daved,
so with The 96mm's marking the bolt and marking 180deg on head will be ok, I shouldn't expect them to twist?
Also don't really want to use gsf bolts. Is there a better alternative that won't cost the earth?

Cheers

 

The marking with a punch is just a suggestion. You could use three blobs of paint, but it will be oily in there. Angle protactors are about 20 from Sealey, or 40, for a better one, from Sykes Pickavant.

There is no definite bolt to use. VAG ones will be correct. If GSF or Europarts are the same spec. as VAG, they will be OK.
Better does not exist. Stronger than VAG could cause the problems stated below.

40 Nm + 60 Nm + 90 deg + 90 deg, gives the bolts a chance to relax and evens up the loads applied across the head.

 

Ok.
I can only get hold of timesert in m12 in south east!
Are the vag m12 bolts 96mm long and same grade?
Do you think going for 1 m12 will cause probs?

Just a bit worried about heli being man enough for the job!

Thanks again

 

Isn't it an M11 bolt, not an M12?

Helicoils stand up to combustion pressure in spark plug thread repairs. I can't see how you'd have a problem with them.

 

Yep originally an m11!
It's a competition car and I know the heli coil repair will be playing on my mind and will introduce another possible cause of failure.
Then again an m12 with diff torque/stress on head may be just as bad!?

Cheers

 

It is your choice of course. Here are details of ArmaCoils (the original Helicoil made by Armstrong), and Recoil from Australia.









From my own experience, using Armstrong Helicoils and Recoils, can offer the advantages I mentioned in post #5 below. I personally would feel happier with helicoil ArmaCoil inserts in cast iron. In fact, if I had spent a lot of money and bought a set to do M11 x 1.5p, and set up on a solid radial arm drilling machine, I would do the lot and have more confidence in the bolted joint. I have in the past, helicoiled all of the manifold threads in cylinder heads, just to be sure that I could remove the studs more easily. Saab used to helicoil their thin aluminium gearbox casings from new, so as not to strip threads!

 

Yeah m11.
But was thinking of one m12 so I can use timesert.
Will this be worse than using m11 heli coil because of different torque/stress on head?

Cheers

 

Looks like helicoil then!
Cheers for the help!

 

This is a Mk2 8v head bolting arrangement:

There is no way that all of the stretch will occur in the 26mm x 9.9 dia shank! Compared with the 52.85 mm x 9.16 root dia thread!

Crunching numbers gives:
For 1/2 turn on a 1.5mm pitch = 0.75 mm total: 0.23 mm in the shank and 0.52 mm in the thread. This due to proportion of clamp length and cross sectional areas involved. Stresses work out to be almost identical in each part.

If the shank had been 11 mm dia, then the stretch would have been: 0.19 mm and 0.56mm, but stress in the thread would have been 50% higher than in the shank!