Many bolts on my XKE bind before they become fully seated. I have removed some of the head bolts and if i try to screw them in they will go less than half way before a tool is needed. Many other bolts on my car are this way. Should these be cleaned up with a tap and die before installing the bolt or is this a way Jaguar uses to shake proof some of it’s fasteners?
Some bindigs were from the PO using the wrong fastener like SAE with a UNF but i know the head bolts were not.
It seems unwise to send a tap through the block (head bolt passage).
Thanks in advance for answering, Den
You have dirt or rust on the threads. Trying to force them like ruins them. I always wipe bolts off with a file card before putting them back in. If the bolt had Loctite on it or any corrosion then it goes through a thread chasing nut first. I avoid using actual tap/dies because they remove metal. That not what you want unless you’re cutting new threads.
Clean the male threads like Erica states and use a thread restorer, not a tap, on the female threads. Blow out the hole with compressed air before and after running the thread restorer through the hole. If really gunked up using the thread restorer and compressed air will be an iterative process.
Taps/dies only remove metal that ain’t supposed to be there!
I use(d) them all the time: if the threads are damaged, it will remove the damage.
Use bottoming taps to clean up blind holes, once blown clean with compressed air: USE GOGGLES!!!
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After using thread restorers, my bolts go in wth no resistance at all. They’re as clean as they need to be. Applying a die to a munged up bolt with a lot of Loctite will end up carving metal that need not be carved off. They also remove plating very effectively.
I must be using them wrong, alll these years…
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Yup, so was I before I discovered chasing tools. 
You make a mistake, assuming I dont have those…
Ill have to go back in time, and bugger up the thousands of fasteners I should have, using the wrong tools…!!!
My understanding is a tap will tend to cut, or remove, metal from a deformed or damaged thread, while a reforming tap or thread restorer will reform the existing threads.
I have a file card and a thread restorer but I find the handiest tool for cleaning up male threads is a 6" wire wheel on a pedestal grinder motor.
For female threads, I’d probably use a good quality bottoming tap and compressed air.
Regarding the head bolts are you referring to a long stud engine? Best tool for these is a plug tap (bottoms) welded to a long shaft with a T bar welded to the top. Studs must bottom or the dome nuts over the washers will not tension. Of course, I could have the bull by the arse here. Paul.
Hello Dennis,
That’s quite OK, as U.N.F [National Fine] is exactly the same as the old S.A.E [Standard American Engineers] that existed before threads were unified.
As Erica and Doug suggest for the male part, a file card, wire brush, or better still, a wire wheel. With regards the female, if you want to be sure no metal is removed using a tap (they shouldn’t remove any, as they are made to a tolerance and standard), use a bolt of suitable length and cut 3 or 4 flutes in the Thread using the corner of a bench grinding wheel, of a cut off disk of around 3mm thick in a hand grinder. The flutes should be cut deeper that the Minor Diameter of the Thread. They provide space for the crud in the thread to accumulate and won’t remove any metal.
You don’t want the thread to be much longer that 50mm. Therefore, If you have access to a lathe, relieve the diameter of the bolt past the 50mm section that’s to be fluted. If no lathe, you can still do a satisfactory job using a grinder.
When cleaning the female thread using this type of tool, use plenty of kerosene, or some type of penetrating oil (WD40 or the like).
Regards,
Bill
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There is a lot of great information in these responses.
I never knew about thread chasers. I am researching the available ones now with little luck. I checked several tool suppliers like Granger and only found thread files and spark plug/O2 senser chasers. I was able to find some on google but information on them is not good. Can someone show a kit that is suitable for a Jaguar?
My car has the short head bolts. The treads that were exposed when I removed the studs were shiny clean and the studs only have a slight discoloration. Still the stud will only go in 3 turns by hand. I normally use a wire brush or wheel on bolts, on the female threads I usually rely on a bolt with a notch cut in it or a bore brush.
Bill, thanks for the detailed reply. I did not know SAE and UNF were the same. Your info clears a lot of fog.
Thank you all for the help. This information about tap & dies VS thread chasers will prevent a lot of dammage to this XKE and prevent future thread follies. Den
The files are okay for bolts but won’t help with nuts. UNF is a subset of SAE along with UNC. Although the vast majority of threads on Jags are fine, there are some course ones. A combined set like this works fine
A buddy recently turned me on to thread restore taps…a life saver…use these all of the time, best tool purchase in years. Seldom do I use my tap & die set.
Thanks for the lead Erica. I just ordered the Lang Tools one you showed me. Den
As Erica says there are course and fine. Course generally into aluminium alloy. Studs into the head are an example: one end course and the other fine. Enjoy! Paul.
Hello Erica,
The SAE fastener standard, was incorporated into the Unified Thread Standard and therefore, at best, would be a subset of the Unified Standard.
The Unified Thread Standard uses the term UNC (Unified Coarse) to describe a fastener that previously would have been designated USS (no longer supported) and the Unified Thread Standard uses the term UNF (Unified Fine) to describe a fastener that would have previously been designated SAE.
Regards,
Bill
Something else I probably don’t need, but really want now that I’ve seen it. Thanks a lot Erica. 
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I’ve had a set of chasers for 30 years. Fine thread only, though.