lgrant

I'm assuming that the 4.0L thru 2001 did not use torque-to-yield head bolts, which are most common on engines with aluminum heads. Can anyone confirm that the bolts are not T-T-Y?

Further, if replacing a head gasket, can the head bolts be reused for this era 4.0L?

Thanks in advance.

third coast

Correct - At least on the later year 4.0's the factory manual does not call for torque to yield or what is also called torque angle method. The head bolts can be reused once. They are not that epensive so I suggest buying new. It's a fair amount of work to get that far so why take a chance with a used head bolt. You never know if corrosion is at work or if someone else was in there and did not mark the bolts with a paint stripe as you are suppose to if reused.

cruiser54

I've never used new headbolts on a 4.0 since they were introduced.

I'd be more confident in the bolts that came from the factory than some replacements that were made by WunHungLo and his comrades.

Bugout4x4

Me neither, and never had trouble reusing headbolts on anything I did reuse them on. The only bolts I ever did replace with new was on the ford V-6 models. But this was only because they are undersized for the application and designed to stretch and be "spring loaded" at torque specs, which in my opinion was an absolute mistake from the initial engineering.

third coast

At minimum I would be inclined to follow the design engineer’s recommendations, which in this case is that the 4.0 head bolts can be reused once per the FSM. I paid less than $25 for a new set of Mahle/Victor Reinz head bolts. They are a quality OE supplier that likely supplied the original bolts on your 4.0. I expect that Jeep/Chrysler had more incentive in putting out a reliable engine and repair procedures than making money by selling low cost sets of head bolts.

Bolt fatigue analysis and developing reliable bolted interfaces for the intended life of an application is a science. Any bolt has a fatigue life limit. Many factors impact the actual life including preload (torque), repetitive load, temperature, metallurgical properties, manufacturing processes, corrosion, handling damage, manufacturing defects. Head bolts have a tough job to do given combustion pressures, head temperatures and the number of load cycles. When all goes well you can likely get several engine design lifetimes out of head bolts so reusing once or even twice will probably be fine. When something goes wrong that shortens the fatigue life, such as overheating or bolt damage you risk undoing all your hard work and causing expensive damage to the head or block. For $25 it's a reasonabley good investment to just put in new quality bolts, especially if there is a chance they have been reused or abused. You can spend that about much on half a tank of gas or a couple of 6 packs of craft beer.

For a bit of information, all bolts stretch when preloading to a specified level. It is a matter if you are measuring the stretch or measuring the torque applied to the bolt during tightning. There are advantages and disadvantages to both but the stretch method usually provides more accurate results. Torque has more variations that come into play such as dry or lubricated and bolt head mating surface quality.

cruiser54

Good to know there is a respected supplier of head bolts.

I'm suspicious of most replacement parts nowadays.

XJwonders

I reused head bolts all the time U ll be fine

Bugout4x4

Of course they all have a little spring load to them under torque. But in the case I mention about the fords is they have too much stretch. The key words in this particular case are "undersized for the application." Brand new they barely hold the specified torque without snapping. Whole different ball game than these are.