Head stud treatment

[Bandit1200]

I'm replacing head gasket and using nickel plated studs and new bolts.
Do you recommend coating studs and/or bolts with copper grease?
Any other recommendations welcome.

Best wishes
Steve

[Motorsport Micky]

I did on mine (specifically the studs) however DON'T get any grease or lubricant on the threasd or you will remove friction and alter the clamping force which could cause stripping or failure of the component.

Micky

[DJT]

I did on mine (specifically the studs) however DON'T get any grease or lubricant on the threasd or you will remove friction and alter the clamping force which could cause stripping or failure of the component.

Micky

Sound advice.

[dasadrew]

Probably overkill, but simply to avoid having three different metals in close contact to another I used ceramic paste on mine. (Couldn't be bothered to look at galvanic corrosion tables!)

Drew

[flying farmer]

Probably overkill, but simply to avoid having three different metals in close contact to another I used ceramic paste on mine. (Couldn't be bothered to look at galvanic corrosion tables!)

Drew

I did the same on my last build as I found that after several years that copper grease had set quite hard, but the studs still came out.

Will not be able to comment on its efficacy until I next remove the heads which I hope will not be for a substantial number of years!

Neil

[Seaking]

what about this on fleabay. 320899211634.

Cheers Glenn

[robbo]

Probably overkill, but simply to avoid having three different metals in close contact to another I used ceramic paste on mine. (Couldn't be bothered to look at galvanic corrosion tables!)

Drew

+1

[LD334]

Definitely use either a ceramic or graphite grease as these are non metallic and won't contribute to galvanic corrosion.
I WOULD lubricate the threads. You will never reduce the coefficient of friction to 0 but the more you can reduce it then the higher the stud tension will be for a given torque and it is this tension (preload) which holds the head down and compresses the gasket.
Some time ago (1965) two gentlemen, Blake & Kurtz, did a statistical analysis of actual preload in bolts both lubricated and unlubricated the standard was a 1/2" UNF torqued to 800lbin - think M12 torqued to 90Nm. What they found was that the preload in the unlubricated bolts was significantly more variable than for the lubricated bolts - 15% of the mean versus 9%. In Stag terms the heads are known to warp fairly readily so the more consistent the preload in the studs & bolts the less likely the head is to warp and for this reason I would lubricate the threads.
As a side point I'm trying to stave off head removal but have noted that the near side head on my engine is secured by bolts in both rows while the offside has the standard mix of studs and bolts.

[Motorsport Micky]

As a timeserved engineer let me explain that the Triumph torque figures are specified DRY, that means they have accounted for the dry stiction (mix between sticking and friction) that the fastenings have.
If you remove that component by lubricating the threads the clamping force will be increased...but you will have no control or idea by how much. Testing shows an increase of about 15% but that doesn't mean the standard components can stand it, check out the typical torques stated as maximum for the fastenings used and you'll see what I mean. You CAN use lubricant where the fastenings are specified with it (often with ARP bolts or studs for example) but otherwise any lubrication of dry specified torque fastenings can lead to "tears before bedtime" as the bolt or stud shears with the increased torque application that goes beyond the standard fastenings thread forms and sizes.

"When all else fails, read the instructions" sound familiar.

Micky

[DJT]

Many years ago the offshore oil industry banned the use of lubricant on torqued threads for that very reason.

[LD334]

Micky,
For clarity the change in friction between dry and lubricated joints is relatively small, what the bolt is coated with has a much greater effect. However lubricant does reduce the variability of clamping force. With dry materials the variation is 15% as I noted. I've back calculated the material strength based on 55lbft and get a proof stress of 600MPa which on a 7/16" UNC thread gives a preload of 33.5kN in a stud. This assumes that the design engineers used a 0.9 factor for preload over proof load. So with a 15% variance unlubricated studs will sit somewhere between 31kN and 36kN if that variation took place across the top line of studs then you could have the back of the head held down with 5kN less force than the front - in simple terms that's 0.5Te less. If this difference happens between the studs and bolts then it's no wonder heads warp.
You note that you don't know how much effect lubrication has. I tend to use the RoyMech tables for dry and lubricated joints which show the coefficient of friction drops by about 5 & 15% when lubricated so for dry steel to steel you would be looking at 0.12 dropping to 0.10 at worst assuming a constant surface profile so there is a known range and while you will increase the clamping force a you bring the variation down to about 9%. If you hold the torque constant at 55lbft then yes the clamping force will rise by 13% so use the lower torque value in 12.29.27 of 45lbft.
What is more interesting here is that I had a quick look at the tables for plated steel, I believe the original studs may have been galvanised giving a dry coefficient range of .14 to .23, changing to cadmium or phosphated drops this to .09 - 0.14, a far greater change than adding lubricant.

[LD334]

Many years ago the offshore oil industry banned the use of lubricant on torqued threads for that very reason.

Critical lines use PTFE as a dry lubricant, the studs and nuts are factory coated. Have a look at the coefficient of friction of PTFE it's low and importantly it's static and dynamic coefficients are the same meaning that unlike a steel/steel joint no additional breakout force is required.

[PhilB]

I used Febi Bilstein Special Ceramic High Temp grease ( as suggested by some on here)
I greased the stud body and the threads that go into the block but not the top threads so they were consistent with the bolts
No mechanical engineering expertise at all after 'O'level - just a simple DIY man - just seemed a good idea.
No problems in first two years running. Still keeping fingers crossed. Seems that works best

[Bandit1200]

Thanks all for the advice.
I'll be refitting the Wards special studs with new washers and nuts, also new bolts. I have ordered ceramic grease for each end of each stud which come closest to contact with the head.
Still confused about lube on threads. The Rimmers video recommends oil on each thread.

Of more immediate concern, I've experienced difficulty, having helicoiled the IM threads in the heads. Despite having used the correct drill and tap and checked that the new bolts fitted the inserts perfectly, when inserts are in place they seem too small to accept the bolts. The size involved is 5/16 unc. I'm using a same sized tap to open up the threads determined to have easy and secure threads before I attempt to fit the IM.


Best wishes
Steve

[mole42]

Of more immediate concern, I've experienced difficulty, having helicoiled the IM threads in the heads. Despite having used the correct drill and tap and checked that the new bolts fitted the inserts perfectly, when inserts are in place they seem too small to accept the bolts. The size involved is 5/16 unc. I'm using a same sized tap to open up the threads determined to have easy and secure threads before I attempt to fit the IM.

I'm not sure quite what you mean here. Did you drill out the old threads with the correct size drill, then use the supplied tap for the Helicoil? The installed Helicoil will be a tight fit on the new bolt until you have screwed it in and out again, in my experience, but it should feel fairly free once the Helicoil is bedded in, so to speak. I did all the threads in my heads and all the ones in the inlet tract (carbs, elbows, etc) and they exhibited that tightness to start with.

I can't quite work out what you mean by "using a same sized tap to open up the threads".