My 4.6 V8 Rebuild Thread

[bee utey]

Helicoils are supplied in 1x D, 1.5D and 2D lengths so a 20mm helicoil is about twice the nominal thread diameter of 11.1mm (7/16 UNC) . This is normally quite enough for threads in alloy, as a bolt under high tension deforms enough to only load the upper end of the threaded hole anyway. A helicoil will distort under load to share the load more evenly and also doesn't turn during installation. And it is a bigger OD too. So it should be OK so long as the head stud engages it fully. TTY bolts need the extra thread length because of all the extra shearing that goes on during tightening.

For the cost of an insert ($2) I would have just put two in the same hole, possibly two 1.5D types, if only because I could. Not really necessary.

[101RRS]

Helicoils are supplied in 1x D, 1.5D and 2D lengths so a 20mm helicoil is about twice the nominal thread diameter of 11.1mm (7/16 UNC) . This is normally quite enough for threads in alloy, as a bolt under high tension deforms enough to only load the upper end of the threaded hole anyway.

For the cost of an insert ($2) I would have just put two in the same hole, possibly two 1.5D types, if only because I could. Not really necessary.

Your point about the top of the threaded hole taking the load is spot on as that is where the original cracks appeared.

I would have thought that putting in two inserts would have been the smart move but if your satisfied that the 20mm of alloy thread that the helicoil is in will hold the 65-75 ft/ibs torque when the head nut is tightened up on the head stud then that is great.

Cheers

Garry

[bee utey]

The helicoil will hold the load no problems. What about the block though? How deep in the hole is the insert? If it passes right through the repair zone into original block metal I would have no issues with it. Helicoils themselves are really strong compared to original alloy threads as they distribute force over a much bigger surface area.

[clubagreenie]

I would have fitted the 2 or more (to fill the hole) coils. Ground/filled down to deck level. Have they broken the tang out of the bottom of the coil? If not you could turn it in and ask them for a couple more to fit. Only issue I see is that the second coiil will stop at the first but when the tang is broken out they will not be against each other, but the threads should still line up, yes?

On the gaskets, have you considered copper? They are available in different thicknesses and reusable and will not blow out as long as they are sealed correctly. A spray with hylomar both sides does the job.

[Hoges]

FWIW: I used the API head studs ...which came with a recommended torque of 90 ft lbs I got a fair bit of advice and settled on 65 ft lbs... cheers

[101RRS]

What about the block though? How deep in the hole is the insert? If it passes right through the repair zone into original block metal I would have no issues with it. Helicoils themselves are really strong compared to original alloy threads as they distribute force over a much bigger surface are.

The helicoil is about 3mm down from the top of the hole - it is cut into a mix of original metal and filler that would have formed a molten pool in the welding process. A ARP stud will be going in.

Garry

[101RRS]

On the gaskets, have you considered copper? They are available in different thicknesses and reusable and will not blow out as long as they are sealed correctly. A spray with hylomar both sides does the job.

The recommendation up to now was composite so that is what I have got - so not I did not consider copper. The supplier indicated that the correct inlet manifold gasket is a composite of cardboard over tin and did not recommend using them so I went for the older tin style.

Garry

[101RRS]

FWIW: I used the API head studs ...which came with a recommended torque of 90 ft lbs I got a fair bit of advice and settled on 65 ft lbs... cheers

I agree and has been discussed earlier in the thread - 65 to 70 seemed to be the number - I just need to get an accurate tension wrench - $40 at Aldi vs $400 at a good tool shop - didn't seem to find much in between - used to have one like the Aldi one and is crap and is now a good 1/2" short breaker bar.

Garry

[Nick S]

Garry, check out the LR4X4 site as it has a MS forum.
Nick

[clubagreenie]

Generally I use (and for ARP studs they recommend) a stepped torqueing method. Tension, in sequence, to each tension. ARP's max is 80 by memory.

In race engines I will helicoil all holes after block strip down and initial clean. Cheap insurance and never had a failure from ham fisted operators during race seasons.