11 replies to this topic

[RELF]

I have just managed to get the last stud out from the thermostat housing on my 1966 Riley Elf Mk2 (after a week of twisting and "Plus-gassing").

Should I now clean out the bolt holes with a thread chaser or a tap or am I being too fussy? As the 5/16" UNC hole is 1" deep and the stud insertion length is only 5/8" long, I presume I could clean it by screwing a 5/16" UNC bolt into the hole which would push any dirt to the bottom.

Also, I have read that a tap tends to reduce the thread in the hole whereas a chaser is less damaging - but I would need to buy these of course.

 

Finally, would you recommend copper grease or similar for the re-assembly using new stainless steel studs or bolts?

 

I would be glad to receive any comments. Thanks.

[Dan]

  Instead of buying a thread chaser just cut a couple of grooves up the threads of a 5/16 UNC screw and use that.  The grooves allow the dirt in the thread to be cleared by the screw, this is essentially what a chaser tap is.  Well done for managing to get them out clean by the way.

[Spider]

On Cast Iron, like your head, Chasers wouldn't work as designed.

 

I would recommend against using stainless fasteners here. I used steel bolts, which are just plated. I grease (just orinary grease) them every time I may have them out and never had trouble removing them, even after 20 years.

[dklawson]

However... you can use stainless following the same advice of applying grease or anti-seize compound.  It can also be beneficial to apply that coating all the way up the shank of the stud or bolt so the thermostat housing does not corrode to the fastener.

 

Do not count on a normal bolt pushing the crud down the threads.  The old rust and dirt will just get packed in the threads making future removal as difficult as it was this time.  

 

I have never owned "chasers" but I do have regular sets of taps and dies. If you already have the right tap at your disposal, by all means use it to clean the hole.  Ideally you want a bottoming tap to use in the blind tapped holes.  The modified bolt suggested by Dan has its advantages in this regard as it can clean deeper in the hole than a common tapered tap.  Regardless, clean the female threads either with a tap or the modified bolt Dan suggested.  After cleaning, a bit of anti-seize or grease applied during reassembly will greatly help with future maintenance.

[gazza82]

After cutting the slots, stick grease in to "grab" any crud that is scraped out. I do that with an old spark plugs to clean up the threads ...

[carbon]

With the last set of thermostat studs I put back in I wrapped a couple of turns of PTFE pipe sealing tape around the threads of each stud before putting them into the head with grease as well. I was fed up with struggling to get these out, don't want any hassle next time.

 

Also would stick to using the standard steel studs in the thermostat, in my experience stainless tends to be weaker and the threads have tendency to gall if not well lubricated.

[sonikk4]

There are different grades of stainless out there so you could be putting something in that is not fit for purpose. Stick to using the original studs / bolts that way plus a little bit of lube you wont go far wrong.

[RELF]

Thanks for your tips everyone. I will make up a thread chaser. Just looked on Youtube and it looks simple enough.

 

Cheers.

[Rog46]

I haven't check If there is a recommended torque for these bolts, but if there is how much should you reduce it by if the bolt is greased?

[dklawson]

Yes, you are supposed to reduce the torque applied on fasteners when the threads are lubed to achieve the same clamping force.  However, the torque on these is already fairly low compared to stressed metal-on-metal joints since you don't want to destroy the gasket.  Though I am sure there is a published spec for these fasteners... this is an area where I have never used a torque wrench.  I simply tighten until it "feels right".  

 

Sorry... I know that is not much help.   I just don't think this is an area you need to dwell on or worry about as it is not as significant as areas like main bearing caps or rod end fastener torque.

[gazza82]

8 ft/lb on all A-series engines from my manuals ...

 

11NM if living outside US and UK!

Edited by gazza82, 19 November 2014 - 03:12 PM.

[RELF]

Thanks again. All very useful information.