Replacing cylinder head exhaust studs

[mtn500]

Does anyone have any experience with installing new exhaust studs into a cylinder head?
My question specifically is, how much resistance is normal given the threads are most likely interference threads?
I'm trying to insert new studs into a cylinder head from a 1979 Honda XL500s.
The studs start to thread in but then seem to "not fit", for lack of better terms; I've verified that I have the correct parts.
This resistance may be normal but I would like to verify so that I continue and stop worrying about stripping the threads in the cylinder head.
Link to original post if anyone is interested in more details (probably not the best way but I just copied and pasted address): http://www.advrider.com/forums/showt...=390135&page=5

Any insights or suggestions would be greatly appreciated.

Thanks

[Claytonroy]

Have you tried tightening them with an electric impact driver?

I think the vibration would help greatly and you would not risk over torquing them.

[D.T.]

Clean up the threads with a bottoming tap.

[usgser]

Originally Posted by D.T.

Clean up the threads with a bottoming tap.

x2
You're going to have old dried residual thread locker in the holes that needs to be thoroughly cleaned out.

[troidus]

Verify the pitch with a thread gauge and the diameter with a ball gauge before you bugger things up. Just because you've verified a part number doesn't mean what you're holding is that part. And if it is indeed supposed to be an interference fit, check with your local industrial supply for some liquid nitrogen and freeze the studs before trying to insert them. Heating the head may help, too.

[It'sNotTheBike]

Originally Posted by D.T.

Clean up the threads with a bottoming tap.

+1 on using a tap rather than forcing the studs to thread
in.



Using an impact is NOT a good idea !!! Don't do that !!!!


The guy above who said you need to make sure the thread size is correct
is giving you good advice. Try to thread the original exhaust nuts
onto the new studs. Those original nuts should thread onto the new
studs easily. If they do not thread on easily you need to look more closely
at the new studs which may indeed be the wrong thread size, or maybe they
are fine thread when they should be coarse thread, etc.


Use light cutting oil when you use the tap, and then make sure
the holes and threads are super clean and don't have a pool
of oil in the bottom of the hole before you install the studs. Brake
cleaning spray and compressed air would be a good way to make
sure things are clean before installing the studs.


.

[mtn500]

Thanks for the input.

I have ran a tap through the cylinder head threads, but I will do again to make sure everything is squeaky clean.

I will see what I can do about verifying the pitch and diameter with a thread gauge and ball gauge; currently all I have at my disposal is a tap and die set and a set of vernier calipers.

I don't have an impact driver at my disposal so that option is ruled out.

Unfortunately, I do not have the original exhaust studs as I purchased this engine as a spare so I could fix my burnt up head. The engine had been partially rebuilt and did not have the exhaust studs when i received it. My original head still has it's studs but I don't want to remove them as I plan on sending the head off to CA and having bearings installed so I can have a back-up.

As far as liquid N2, I contemplated freezing the head and the studs, but I wanted some practical advice before I carried on with the interference fit theory. Wouldn't heating the head expand it, resulting in slightly smaller diameter stud holes?

Thanks much for everyone input thus far.

[griffo1962]

Originally Posted by mtn500

As far as liquid N2, I contemplated freezing the head and the studs, but I wanted some practical advice before I carried on with the interference fit theory. Wouldn't heating the head expand it, resulting in slightly smaller diameter stud holes

Nope, it's counter intuitive I know but heating the head actually increases the size of the hole....

[Stan_R80/7]

Heat the head and freeze the studs. The holes will expand in the head at higher temperature and the studs will shrink with lower temperature. Double check the thread diameter and pitch before assembly. Good luck!

[emti]

Are both ends of the stud the same pitch/length? Are they bottoming out in the hole? emti

[mtn500]

Originally Posted by emti

Are both ends of the stud the same pitch/length? Are they bottoming out in the hole? emti

emti, the pitch diameter is different; the shorter thread length has a larger diameter than the longer length. The longer length will bottom out in the cylinder head but the short one will not; it gets really tight when the threads are about half way into the head.

[anotherguy]

Cleaning threads with taps/dies is a no-no. You don't want to remove metal only clean the threads. Use a proper thread chasing tool.

The stud threads that install into the head are likely a class of thread that is an interference fit. That is they are larger than a common bolt and go into the hole tight to allow the nut to be removed w/o taking the stud with it and to allow for the heat of the part in normal operating conditions i.e. HOT. Tread lightly here or face continuing problems.

I have a stud installation tool for those jobs. Makes it a lot easier.

[bomber60015]

Originally Posted by anotherguy

Cleaning threads with taps/dies is a no-no. You don't want to remove metal only clean the threads. Use a proper thread chasing tool.

The stud threads that install into the head are likely a class of thread that is an interference fit. That is they are larger than a common bolt and go into the hole tight to allow the nut to be removed w/o taking the stud with it and to allow for the heat of the part in normal operating conditions i.e. HOT. Tread lightly here or face continuing problems.

I have a stud installation tool for those jobs. Makes it a lot easier.

^ this guy knows what he's talking about . . . . . additionally, talk to the owner of any tube framed Buell . . . .they either are, or know of, experts in exhaust stud replacement.

[mtn500]

Originally Posted by bomber60015

^ this guy knows what he's talking about . . . . . additionally, talk to the owner of any tube framed Buell . . . .they either are, or know of, experts in exhaust stud replacement.

another guy, the interference thread theory is what I am leaning towards. what is this stud installation tool you speak of?

[vtwin]

I've gotten them from $nap-On when I worked as a tech. The ones I have are threaded to the common size we used and have a little ball bearing at the end to keep them from tightening on the tool when inserting into the hole. You could even torque them properly, but backs off easily and does not damage the shank like the one pictured could possibly.