Threaded head bolt hole

[DaveL485]

I've just taken apart a Renault J-Series lump and the reason it failed in the first place it seems is that the idiot that assembled it thought it would 'be OK' if one of the head bolts was loose. The reason for that being the thread in the block that receives the bolt has given up.

What are my options? As I see it:
1)New block with the associated complexities of changing everything over (uprated parts)
2)Helicoil current block (if possible as its quite deep)

I know that the hole for the bolt goes right through the block and the Main Bearing cap goes in from the bottom into the same hole. Not only that but the setting torque is the same for final stage head bolt and main cap (70lb/ft). So, how plausible is....
3)Get a super long bolt in from the bottom all the way out the top and effectively 'stud & nut' the head?

Opinions appreciated

[stevieturbo]

I guess it's possible. But surely cant be that hard to helicoil ?

And if it's the same bolt hole...maybe helicoil from the bottom up ? drilling out the main cap hole and dropping a helicoil for the head stud in deep, then helicoiling the main cap.

[ian_uk1975]

Hmm, trying to picture this... I'm assuming the hole is threaded at each end? Bottom side for the main cap and top side for the head bolt? If so, just helicoil from the top and job done? Just be very careful when you drill and tap the hole that you keep the drill and the tap as perpendicular as possible to the block deck. I've done this in the past without the aid of any fixtures, but it would be a good idea to drill a block of aluminium on a drill press, for example, and use this as a guide for the drill when you drill the bolt hole for the helicoil.

I definitely wouldn't use a long bolt all the way from the main cap to the top side of the head to act as a combined main cap bolt and head stud (if I'm understanding you correctly). You'd have to be very careful about the bolt specification in terms of tensile strength and yield and, ultimately, you'd be venturing into the unknown which isn't something you want to do when it comes to high stress areas where the clamping load is critical.

[Old Merc]

I`ve just had the same problem on a 1972 Peugeot with a cast iron block.we called out www.threaddoctorservicesltd.co.uk who inserted a helecoil with the engine still in the car.I have to admit I was skeptical if this would work out.They have proved me wrong,the head is on and fully torqued up.He charged us £50!!.

[DaveL485]

ian_uk1975 said:

Hmm, trying to picture this... I'm assuming the hole is threaded at each end?

No- Its one long thread at the bottom, the head bolts are quite long.

ian_uk1975 said:

I definitely wouldn't use a long bolt all the way from the main cap to the top side of the head to act as a combined main cap bolt and head stud (if I'm understanding you correctly). You'd have to be very careful about the bolt specification in terms of tensile strength and yield and, ultimately, you'd be venturing into the unknown which isn't something you want to do when it comes to high stress areas where the clamping load is critical.

I was looking at a 12.9 threaded bar online, but yes I share your concerns! Hoping as the thread is common between the 2 bolts it'd reduce the chances of it being an issue.

Old Merc said:

I`ve just had the same problem on a 1972 Peugeot with a cast iron block.we called out www.threaddoctorservicesltd.co.uk who inserted a helecoil with the engine still in the car.I have to admit I was skeptical if this would work out.They have proved me wrong,the head is on and fully torqued up.He charged us £50!!.

Thanks for the link! I'll look them up