Rick's Free Auto Repair Advice

TTY bolts

What is a TTY bolt?

TTY stands for torque-to-yield. All bolts stretch a certain amount as they’re torqued and then spring TTY head boltsback a bit as they relax; kind of like a bungee cord. That’s just the nature of what happens when you apply torque to steel. A TTY bolt is designed to stretch by a certain amount and then spring back to provide a precise pre-determined amount of clamping force. The amount of stretch allowed is called yield zone and it requires following torque instructions to the letter. If you over-torque and exceed the yield zone, you can permanently damage the TTY bolt.

Why newer engines need TTY bolts

Metal expands and contracts. When engine blocks and cylinder heads were made from cast iron, both expanded and contracted at the same rate. But newer engines are made with aluminum alloys that expand and contract at different rates. When you install a new gasket, it will relax over time as it “sets” and compresses. If you simply rely on torque during installation, the connection will loosen as the gasket relaxes. For example, it’s common for a composition head gasket to relax by up to 25%, causing a 0.011 loss of spacing.

But a TTY bolt is more like a spring or bungee cord that has a certain window of “spring-y-ness” to allow for expansion and contraction while still applying enough holding power.

The TTY torqueing procedure is a multi-step process

Torqueing a TTY bolt requires both a torque wrench and a torque angle gauge. You cannot torque these bolts without both or you risk damaging the bolt. Worse yet, you’ll screw up the head gasket and have to do the job all over again.

Step 1: Torque the bolt to a specified torque.
Step 2: Attach a torque angle gauge and turn the bolt the prescribed number of degrees.
Steps 3 & 4: This step may involve another torque step or another rotation.

Once TTY head bolts have been torqued they generally cannot be re-used. However, some car makers do allow re-use. If you don’t know for sure whether your head bolts can be re-used, don’t risk it, use new head bolts. If you attempt to reuse a TTY head bolt that can’t be reused, you will either break the bolt or screw up the head gasket job. Don’t risk it. Buy new head bolts.

How to torque a non-TTY head bolt

Non TTY head bolt torque is shown without an angle measurement. For example, this torque listing “1st 22, 2nd 48” is for a non TTY bolt. It means you torque the bolt to 22-ft/lbs. Then reset your torque wrench to 48-ft/lbs and torque to that amount.

How to torque a TTY head bolt

Here’s an example of the torque procedure for a TTY head bolt: “1st 29, 2nd turn 90 degrees, 3rd turn 90 degrees, NOTE: New bolts turn additional 90 degrees.

Here’s what that means:

1) Torque the bolt to 29 ft/lbs.
2) Attach a torque angle gauge and turn the bolt 90°
3) Then turn the bolt another 90°
4) If you’re using a brand new bolt, turn the bolt an additional 90° after step 3

Other torque specs may say something like; 56 in three steps.
Here’s what that means. Set your torque wrench to 56 ft/lbs and tighten the bolt to that spec. Remove the torque wrench for a moment, then torque again to the same 56-ft/lbs. Repeat for a third time. What you’re doing here is allowing the head bolt to stretch slightly between each torque attempt

Loosing and tightening pattern

Loosening the old head bolts randomly can CAUSE the cylinder head to warp. Likewise, tightening the head bolts in the wrong pattern can also warp the cylinder head. Always follow the numbered patter shown here.

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat


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