Tapping block for 11mm headbolts

[Vigo]

I have an 85 block in my 89 Spirit with the older 10mm headbolts. Anyone who's listened to me talk over the last 10 years i've been here shouldn't be surprised to hear i RARELY buy new headbolts. I've reused the 11mm headbolts over and over with success. Recently i've been setting the torque wrench to 90ftlb and checking that it clicks during the last 90 degree turn on the headbolt. Over time i've noticed the 10mm seem to 'feel' as if they've failed far more often than with used 11mm bolts. Since i started doing the 90ftlb check, I dont think any of them have clicked the wrench during the final turn. This is all pretty vague but over time i've become more and more uncomfortable with them.

I had to take my spirit engine apart because i cracked a piston running the engine with no coolant (long story involving being parked over winter and forgetting something i did several months ago) and when i took it apart i was a little miffed by how easily the 10mm headbolts broke loose by hand (long handle 1/2" ratchet, but still..), so i decided i would just tap the block for 11mm headbolts while it was apart.

This turned out to be way easier than i for some reason imagined. The 10mm headbolts are a 10x1.5 thread, while the 11mm are 11x1.5. This is very convenient for tapping purposes. I think my tap chart called for a 9.8mm drill bit to tap for 11x1.5. Well, the closest thing i had was 3/8 which is ~9.55mm. Drilling a hole with 10mm threads with a 9.5mm drill bit leaves you some thread left, and since it's the same thread pitch as the larger 11mm headbolt, this makes it very easy for the tap to 'thread' into what's left of the 10mm threads and tap a perfectly straight hole.

I was able to do all of the headbolt holes with the ac bracket and passenger mount brackets on just fine, in about an hour.



Can't wait to go back together with USED 11mm headbolts.

[cordes]

How do you go about cleaning the bolt holes in the block?

[black86glhs]

I agree it wasn't that hard to do, but my tap was not the greatest. Plus I should have used cutting fluid. Other than my screw ups, it was quite easy.
Cordes, I blew mine out with brake cleaner and then shop air. Definitely put a rag over the holes.

[Vigo]

How do you go about cleaning the bolt holes in the block?

I just run the tap through the hole and blow it out with compressed air and brake cleaner until stuff stops coming out.

I agree it wasn't that hard to do, but my tap was not the greatest. Plus I should have used cutting fluid.

I think my tap was just fine, but i could tell a huge difference in effort when i added the cutting fluid. I used a long handled ratchet and tap socket for leverage once i knew it was going in straight, so it was more tedious than strenuous.

[83scamp]

I upgraded the motor in the Scamp when I rebuilt it to 11mm bolts. But since I was having the block milled anyways, I just let the machine shop do it...

But, I agree, it's not a hard job to do...

[ajakeski]

I've done them before, just run the shop vac hose next to the thread bore and then clean as described above.
If you screw up a hole, you'll have to buy these:

http://www.timesert.com

[DodgeZ]

I have an 85 block in my 89 Spirit with the older 10mm headbolts. Anyone who's listened to me talk over the last 10 years i've been here shouldn't be surprised to hear i RARELY buy new headbolts. I've reused the 11mm headbolts over and over with success. Recently i've been setting the torque wrench to 90ftlb and checking that it clicks during the last 90 degree turn on the headbolt. Over time i've noticed the 10mm seem to 'feel' as if they've failed far more often than with used 11mm bolts. Since i started doing the 90ftlb check, I dont think any of them have clicked the wrench during the final turn. This is all pretty vague but over time i've become more and more uncomfortable with them.

I had to take my spirit engine apart because i cracked a piston running the engine with no coolant (long story involving being parked over winter and forgetting something i did several months ago) and when i took it apart i was a little miffed by how easily the 10mm headbolts broke loose by hand (long handle 1/2" ratchet, but still..), so i decided i would just tap the block for 11mm headbolts while it was apart.

This turned out to be way easier than i for some reason imagined. The 10mm headbolts are a 10x1.5 thread, while the 11mm are 11x1.5. This is very convenient for tapping purposes. I think my tap chart called for a 9.8mm drill bit to tap for 11x1.5. Well, the closest thing i had was 3/8 which is ~9.55mm. Drilling a hole with 10mm threads with a 9.5mm drill bit leaves you some thread left, and since it's the same thread pitch as the larger 11mm headbolt, this makes it very easy for the tap to 'thread' into what's left of the 10mm threads and tap a perfectly straight hole.

I was able to do all of the headbolt holes with the ac bracket and passenger mount brackets on just fine, in about an hour.



Can't wait to go back together with USED 11mm headbolts.

Damn, you should have drove up. This rampage has 10mm, I want want to upgrade to 11mm but didn't have time.

[wheming]

Vigo- if you are coming to SDAC i'll donate to you a box of 11mm headbolts that i torqued once, but never even heat cycled when i bolted the wrong headgasket in Slug.
They will likely be the freshest headbolts you've ever used!

[black86glhs]

I've done them before, just run the shop vac hose next to the thread bore and then clean as described above.
If you screw up a hole, you'll have to buy these:

http://www.timesert.com

I know all about that....lol. Because I didn't have cutting oil and tried to use a penetrant spray for lube, a few of the holes had nasty looking threads. So I got the baby northstar kit and did all the holes in my block.

*Note to self: Patience.....it is a good thing.