Head bolts might seem like a minor or unimportant part, but without them, combustion wouldn't be possible and your diesel engine wouldn't work. They hold your cylinder head to the engine block and help the head gasket to seal properly.
When you take apart or replace these components, you shouldn't ignore your head bolts. Doing so could increase your risk of serious failure down the road.
The initial temptation might be to just reuse your old head bolts. I mean, how bad could it really be? At times, this might be completely fine, but as we'll go on to discuss, it may not be in your engine's best interest to put old bolts back in.
So, just how do you tell when it's safe to reuse your bolts? We're taking you through when you might want to consider replacing your head bolts.
After you remove your head bolts, you'll want to give them a solid inspection before deciding whether or not to reuse them.
First, check for any obvious signs of wear or damage to your bolts. Especially pay attention to the threads. Worn or damaged bolts stand a much higher chance of failure.
Check the length of your bolts as well—if your bolts have been too stretched, they will have lengthened. They will likely display some visible distortions because of this.
You should also always check the length of new bolts, as depending on your engine model, different bolt holes require different length bolts. The wrong length bolts won't clamp down with the correct force, which affects the seal and allows for leaks.
The bolts and bolt holes need to be completely cleaned before reinstallation to ensure proper clamp and torque measurements. Lubricate the bolts in engine oil as part of the cleaning process.
Bolts with any signs of damage, no matter how slight, should never be reused. Not only will the bolts eventually fail, but when they do, there is the potential for them to cause damage to your cylinder head. This results in a much more expensive repair than simply replacing the bolts in the first place.
Bolts are designed to stretch as you torque them into place, and when you remove them, they snap back to their original position. Because of this, many standard head bolts are okay to use more than once, as long as they have not been stretched past their spring back point. Once this occurs, they should no longer be used in the engine, as they won't clamp properly.
Torque-to-Yield bolts (TTY), should not be used more than once, because, by design, they are stretched past their spring back point the first time they are installed. This allows for a more even load, and is especially useful for some of the gaskets and cylinder heads made out of less forgiving materials.
Because they are stretched out the first time, though, it's highly likely that they will fail if reinstalled, due to overstretching and improper clamping. If you're unsure whether or not you have TTY bolts in your engine, check the specifications in your engine manual, which should tell you.
An old head bolt that doesn't allow for proper clamping can lead to leaks in your engine. Coolant will be able to leak through the bolt hole and cause more issues for your engine.
One of the largest issues with reusing old head bolts that are past their prime is the risk it creates for your gasket. If a head bolt breaks or fails to maintain torque, you can blow the head gasket, which in turn leads to a whole host of other issues for your engine—and an expensive repair.
Similarly, you won't be able to install worn or damaged bolts correctly, which impacts how the gasket is installed. A poorly installed gasket leaks and can damage other engine components.
All in all, it's often best to install new head bolts when you work on your cylinder head or head gasket, unless you can be absolutely sure the age and condition of your current ones. It will save you headaches and cash in the future.
If you have any questions about reusing your head bolts, or any other cylinder head problems, give us a call! We have ASE Certified Technicians on staff who can help you diagnose your diesel engine problem and make sure you're getting the parts you need to get the job done right.
At Highway & Heavy Parts, we ensure you're getting the best quality diesel engine parts. We only source our parts from the most reputable and reliable manufacturers—in many cases, these are the same manufacturers that supply the OEM dealers.
We make buying quality diesel engine parts easy! You can call or shop online. Our large inventory of replacement parts helps us ensure you'll be getting the right fit for your engine.
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Originally Posted December 26, 2018; Edited February 11, 2021