Head bolt tightening procedure?

[tgraham]

On the old site there was at least one (fairly recent) thread discussing skipping the manual's lengthy and redundant angle procedure and cutting to the chase by doing an incremental torque procedure.

What were those increments?

And, for those who swear by this procedure, any problems?

Thanks!
Travis

[dmc6960]

As suggested to me by Josh Bengston, 25/50/75. So tighten them all up to 25ft/lbs in the order listed in the manual. Then bring them to 50 in order, then finally 75ft/lbs in order. I did that on my engine rebuild and so far ~10-15k miles no problems.

[tgraham]

Wonderful. Thanks, Jim!

Travis

[Delorean Industries]

In the shop manual order that is the procedure that we still use here. On turbo engines I have been torquing the final value to 85 instead of 75.

Also as always make sure that you re tap all head bolt threads in the block. They are not blind holes and have corrosion on the bottom threads. Run a 12 1.50 tap in all 16 holes. The tap needs to run down far enough so that the first actual cutting edge on the tap protrudes from the bottom of the hole. Run the tap down first with a cutting lubricant present. Then a second time with lubricant present. Finish with brake clean down each thread. Check head bolts on each one for binding after.

Finally before torquing make sure you put engine assembly lube under the bolt head. From being torqued previously the rocker bracket and head bolt have spawling marks. Lubrication helps with not having inaccurate readings.

If you have any questions feel free to call the shop line at 330 983 4737.

[tgraham]

Thanks for those tips, Josh!

Engine assembly starts this weekend. My driver car has been out of commission for too long with my little engine project. I'm really looking forward to getting it back on the road.

Travis

[David T]

It is always best to go by the factory recommendations. The reason this procedure is so important is that it is difficult to retorque the bolts so this method gets the heads tight enough so you do not have to retorque but not so tight that you stretch the bolts or rip out the threads from the block. Deviating from the factory procedures, as always, is at your own risk. As mentioned, torquing bolts is VERY dependent on the condition of the tapped hole and bolt, cleanliness, and whether it is dry or lubricated and with what lubrication. You are measuring the twisting force of the fastener and it is indirectly affecting the clamping force which is what you really care about but cannot directly measure. Also, the accuracy of your torque wrench is very important. When was the last time it was calibrated?
David Teitelbaum

[jmettee]

All good points, David. Especially the last point! I had my torque wrench calibrated at work right before I put my heads back on. Also, as Josh said, running a tap all the way THROUGH the holes (including creating freshly cut threads at the very bottom) cleans a LOT of crud out of the holes.

I even had 1 bolt bring 1 to threads from the BOTTOM of the hole all the way out of the hole. I was afraid the bolt would not take the torque on the re-install, but it did & so far, so good on the head gasket!

[content22207]

You only got away with that because our engines are made of cast aluminum. If a fastener or tap ever loads up in a piece of wrought aluminum, you will remove all the threads in the hole as it is removed. Cast aluminum actually behaves somewhat like steel as far as chipping is concerned.

I have to be very careful when tapping holes in my intake manifolds not to load the tap up.

Bill Robertson
#5939