2f Head Bolt Question (1 Viewer)

[Freeborn]

I'm exercising demons from my '78 2f with low compression in one cylinder. When I was pulling off the head, I noticed a couple of things:
1. It took very little effort to break the head bolts loose. Like shockingly little torque. And I know that they were torqued to spec on installation.
2. I have carbon on the head gasket between a couple of cylinders, one of which is the problem child.

The question is this:
Is it possible that the head bolts stretched enough that they are the cause of my head gasket not sealing?

Everything I've read leads me to believe that the bolts are re-usable. Is that 100% true? Or is it possible that after 46 years they gave up?

 

[Malleus]

Anything's possible. Did you use a Toyota head gasket?

Those bolts are supposed to have around 90-lb·ft of torque at installation. It should have taken more than that to loosen them, given that static torque is by definition greater than dynamic torque. I'd believe the gasket crushed at installation, lessening the clamping force of the head bolts, before I believed the bolts stretched.

The engine service manual says nothing about reusing or replacing head bolts. Anything you've read is tribal knowledge, take it for what it's worth.

 

[Green Bean]

Did you clean out the threads prior to installing? I was thinking that dirty threads can cause a bolt to bottom out too soon leading to a false sense of torque.

 

[charliemeyer007]

+1 for chasing the threads. Put them in by 1/3 in sequence. After it has heated up and cooled retorque them at 100%. If the gasket has any sort of fiber I soak it in warm water for like 1/2 hour. I try and put it together quickly and fire it up.

 

[Freeborn]

Anything's possible. Did you use a Toyota head gasket?

It was a Felpro gasket. Ordered the Toyota for this round.

 

[Freeborn]

Closing the loop here...It seems like what I have will continue to do the trick. I just measured the height of the block + head gasket. It comes in right at 97mm. I threaded all the head bolts back into the block without the head as far as they could go and measured the distance from the deck to bottom of the head of the bolt. All were well south of 95mm. It seems all the holes are clean. Had a couple of bolts with a little rust on the threads that I cleaned up with a brush and worked just fine. Unless those M13 bolts are going to stretch more than 3mm I'm fairly confident that they're going to work just fine. I will definitely be re-torquing them after initial start-up. Thanks for all the input!

 

[Malleus]

You can check the threads with a pitch gauge if you want to know if they've stretched. If they have, the pitch gauge won't fit consistently down the length.

 

[serenity]

You can check the threads with a pitch gauge if you want to know if they've stretched. If they have, the pitch gauge won't fit consistently down the length.

Stretch will also show up as narrowing on the shank of the bolt, and can easily be checked with calipers.

 

[serenity]

Closing the loop here...It seems like what I have will continue to do the trick. I just measured the height of the block + head gasket. It comes in right at 97mm. I threaded all the head bolts back into the block without the head as far as they could go and measured the distance from the deck to bottom of the head of the bolt. All were well south of 95mm. It seems all the holes are clean. Had a couple of bolts with a little rust on the threads that I cleaned up with a brush and worked just fine. Unless those M13 bolts are going to stretch more than 3mm I'm fairly confident that they're going to work just fine. I will definitely be re-torquing them after initial start-up. Thanks for all the input!

Excess anti-seize/oil on the threads could cause premature bottoming. Also insufficient lubrication or a rough surface under the head of the bolt can reduce clamp force.

 

[andrewbridges1]

Majority of cars have TTY head bolts and can only be used 1 time. After having a issue and being 46 years old chances are they probably need to be replaced. Just avoid any issues in the future and slap some new bolts in. Also check for head/block warp

I'm exercising demons from my '78 2f with low compression in one cylinder. When I was pulling off the head, I noticed a couple of things:
1. It took very little effort to break the head bolts loose. Like shockingly little torque. And I know that they were torqued to spec on installation.
2. I have carbon on the head gasket between a couple of cylinders, one of which is the problem child.

The question is this:
Is it possible that the head bolts stretched enough that they are the cause of my head gasket not sealing?

Everything I've read leads me to believe that the bolts are re-usable. Is that 100% true? Or is it possible that after 46 years they gave

 

[Malleus]

...except this is a 46 year old engine with 46 year old parts. Torque to yield wasn't used back then. At least not in the 2F engine.