Cylinder Head Stud-TR4a

[AndrewMAshton]

Hello, now 16 months into my 3 month project and the latest drama, torqueing down the head after checking, re-checking and checking TDC again, the r/h second from the front stud 'slipped' as I approached 105 ft/lbs, and as the thread on the stud is a little shiny, otherwise undamaged, it can only mean one thing, the threads at the bottom of the stud hole are b*ggered.  I found 2 threads on here with information, however, for me, the important one wasn't answered. My plan is as follows, bearing in mind the stud hole is 140mm deep.

Firstly obtain a long 1/2" unc bolt, groove the thread end and see if I can clean up what threads are left, clean out the hole and try to fit the head again, if I struggle to 'clean' the threads with the bolt use the second hand 1/2" unc tap on its way from ebay.  I can fit a 1/4" drive 9mm socket down the hole and if I can securely attach the socket by butchering the end of the tap I can then run that down the thread, if either of these work have another go at fitting the head.

If that doesn't work it Helicoil gets the thumbs up in the previous threads, and as it is unlikely the drill bit supplied will reach the bottom of the hole is there any reason I can't fit the helicoil to the top of the hole, and fit two coils as per Rogers earlier post using a modified stud, alternatively fit the coil to the extent of the drill bit, and again, modify the stud to suit. So the question is, is there a difference in the clamping force from a stud at the top of the block or one buried in the body of the block?,

As always, grateful thanks for any response, cheers, Andrew

 

[Lebro]

Can you remove the stud which has "slipped" ? if so you will find that it already has a groove passing across the threads, If you are lucky it will be the bottom thread of the stud which is stripping, or have you already eliminated that (not clear from your description). Over to others for suggestions on how to fix stripped thread in the block  !

Bob

[Charlie D]

Andrew,

The Standard Vanguard block is basically the same as the TR block, but the head studs do not go down as far as the TR ones. I have read that the change was done because of the higher power of the TR spec. which could, in tuned engines, cause the top of the block to pull away from the bottom of the block. Somewhere I read that someone had this happen when they put a TR head onto a Vanguard block and fitted all the tuning bits he could find, so it has actually happened in real life.

I once had a Vanguard engine fitted with a TR head, but did not tune it and didn’t drive very fast or furious and never had any problems.

 

I guess “Motorsport Micky” would be the best person to give advice on this and hopefully he will be along soon to help you out.

 

Charlie.

 

[RogerH]

Hi Andrew

how can the bottom (or any single part of the thread )  slip and not all the rest of the thread length???

Have you fitted the correct washers under the stud nut. These are special hard washers.

As for the helicoils. I think the stud hole is deeper than any one helicoil. So you can fit one to go deep then another to give full length.

Ca you get a boroscope into the stud hole to see what is going on.

 

Roger

[BlueTR3A-5EKT]

What does ‘slipped’ mean?  
Did the nut go loose so you could undo it without using a spanner/socket?   If so that sounds like a block thread or a broken stud.

 If it just went ‘soft’ as you tightened that might point toward the nut or the fine thread stripping, or an unhardened washer collapsing, (as Roger mentioned) or horror of horrors the cylinder head collapsing.( the racing boys know of that one after extensive machining)

 

Are you using dry threads, with new nuts and studs?

[AndrewMAshton]

Hello thanks for the responses, the stud is out, it took some grunt to remove it, I locked two nuts on the top and screwed it out, with difficulty, by 'slipped' I mean as I was putting weight on the cylinder head nut , probably up to 100lbs, I had already gone all round at 80 foot/lbs, the wrench momentarily slackened off and moved probably 1/8th of a turn, at that point the cold sweat broke out and I started to take it apart.  I am using the hardened steel washers, with the difficulty in removing the stud and the fact I can't wind it back in points to the thread low down in the block.  The easiest thing would be to helicoil the top of the hole (sorry - I don't know holes proper name) and use a short stud, it is not a racing engine although the engine has been rebuilt and CR is 10:1, when I had the engine work done I noticed the thread in that 'hole' was tighter, I asked the machine to check it as I did not have the kit to do the deep holes, the response was that it was fine, cheers, Andrew

[Motorsport Mickey]

Hi Andrew,

It sounds like somethings amiss at the bottom of the stud length (been there, had that). Rogers camera suggestion is good and can give you some further idea of what is needed.

Somewhat lost in the mists of time now (1988), but on my problem long stud thread where I decided to try and keep it original, I drilled out the stud hole down it's depth with the Helicoil tapping drill dia welded onto a 3/8 th dia rod ( by hand, with a trusty Black and decker,).

Because the original hole is so deep and the Helicoil opening up is minor the drill feeds itself in and doesn't wander too badly, and then drilled a further thread clearance hole with a drill welded upon a 3/8 dia rod on the helicoil tap OD, make sure you leave an amount to take two Helicoils. Afterwards I welded a Helicoil tap to a 3/8th dia rod and I tapped the hole in the material at the bottom and fitted 2 x Helicoil inserts one on top the other, cleaned out the hole (you have to do this regularly when Helicoiling to ensure it does "gall" and damage the thread form). The stud wound in easily by hand until it's thread depth was reached and then torqueing the head down was carried out as a normal operation. I haven't the altered taps now, I loaned them to a TR owner and they never came  back, and I can't remember who it was, if you read this and think " I have those", please return, no hard feelings.

There is more material available within the depths of the block than you may think, following a "non standard" block mod in racing causing a stripped thread, I drilled out a deep stud hole to a 16mm tapping dia and tapped and fitted a hand made 16mm silver steel stud in place of one. After drilling the head with a clearance hole for the stud, the head was successfully raced and the car then sold (after engine removal and pistons and rings checked and new crank bearings fitted, and again it raced the following season and still is I believe.

The Standard Vanguard with weedy 7/16 Dia studs all short did have problems with lifting of the block surface around the studs, this was likely caused because the were no physical fastenings between the top and bottom of the block. When the liners are removed there is little between the front and rear bridges of the block other than the centre bridge which often cracks in use. The revised stud dias to 1/2" and the inner studs on the second row being doubled in depth to connect to the lower liner bed gave the necessary stressing of the block turning it from "jelly" into a relatively strong edifice.       

Mick Richards

Edited July 17, 2022 by Motorsport Mickey

[ianc]

To add to Mick's information, the text below is from my article on the derivation of the TR's 4-pot engine, which was printed in TR Actions 241 & 242 (March & May 2010).

Ian Cornish

1.                  Head Gasket: to cope with the higher compression ratio, a considerably greater torque (increased from 60-65 lbf.ft to 100-105 lbf.ft) had to be applied to the head nuts.  This caused the upper surface of the block to lift around the studs and, as a consequence, the head gaskets blew.  Solution (see Figure 2): the block casting was modified so that the studs screwed into the base of the block (i.e. the upper part of the crankcase chamber), thereby putting the water jacket into compression rather than tension.  In addition, the extra torque on the head nuts squashed the figure of 8 seals at the base of the liners to such an extent that the small upstand of the liners above the block was lost, which caused the head gasket to blow!  A change of the figure of 8 seals, from a soft material to copper, solved the problem.  As a further precaution (remember that the liners should sit only a few thousands of an inch above the top of the block), production tolerances on the various components were reduced.

[AndrewMAshton]

Hello, for once, and believe it has been a journey I have no wish to repeat, a bit of good news.  1/2" UNC plug tap arrived and miraculously the square end of the tap was a good fit in a 1/4" drive 8mm socket which only just fitted in the stud hole, after putting some cutting oil on the tap, lowered it gingerly into the hole and after very carefully tapping the damaged threads, and there was some resistance so it was clearing a path, the tap broke through and carried on easily to the end of the thread.  I think the stud was not fully screwed in hence the slip, I used my magnetic picker upper and got very little swarf out, after running the tap up and down the thread, and all the other threads, the studs all screwed in very easily, I am confident now that I have managed to salvage the thread.  Anyone want to buy an unused 1/2" UNC Helicoil set?  Thank you for your help with this,  Cheers, Andrew

[BlueTR3A-5EKT]

Good result

Peter W

[ianc]

Make sure that the stud(s) are of the correct quality steel - Pete Cox told me that the studs from Moss are good, but any old studding from AN Other might not withstand the 105 lb.ft torque applied when tightening the head nuts.

Ian Cornish

[Motorsport Mickey]

14 hours ago, ianc said:

Make sure that the stud(s) are of the correct quality steel - Pete Cox told me that the studs from Moss are good, but any old studding from AN Other might not withstand the 105 lb.ft torque applied when tightening the head nuts.

Ian Cornish

Or as an alternative to new,...clean and check your existing studs.

Triumph spent money specifying high quality fastenings and amongst them good cylinder head studs and nuts. I've built 23 x 4 cylinder engines and apart from 3 where the owners specified ARP studs and nuts, I've reused the existing studs. In that time I've had to replace...3 Triumph studs, a couple with "galling" (damage to the thread surface, normally caused by swarf contamination in the past when being rebuilt) and one caused by "necking" from overtorquing (likely badly maintained torque wrench).

Clean the stud threads (top and bottom) by washing and soaking in thinners and then run a scriber or sharp pointed instrument down the thread (about mid point of the thread profile, from from top to bottom). If there is dragging or galling which has damaged the thread, the scriber point will snag in the damage and warn you, takes about 15 seconds a thread rolling it in your hands, and then the other end and thread. Rotate the stud and check the other stud surface the same way. I allow about 2 hours to check the 10 studs, then dry and spray with WD and wipe dry. Enough WD remains on the stud surface to ease fitment without contaminating the torqueing regime numbers (105 lbs ft) which should be completed dry with no lubrication unless you are using ARP studs. The ARP studs need torqueing about 20% less ( I use 90 lb ft) because lubeing the threads removes stiction (sticking friction) from the equation and increases the actual clamping torque imposed to 108 lb ft). I know the Triumph studs nuts and block are good for 110 lb ft dry having used that previously.

Mick Richards  

Edited July 28, 2022 by Motorsport Mickey

[BlueTR3A-5EKT]

35 minutes ago, Motorsport Mickey said:

Or as an alternative to new,...clean and check your existing studs.

Triumph spent money specifying high quality fastenings and amongst them good cylinder head studs and nuts. I've built 23 x 4 cylinder engines and apart from 3 where the owners specified ARP studs and nuts, I've reused the existing studs. In that time I've had to replace...3 Triumph studs, a couple with "galling" (damage to the thread surface, normally caused by swarf contamination in the past when being rebuilt) and one caused by "necking" from overtorquing (likely badly maintained torque wrench).

Clean the stud threads (top and bottom) by washing and soaking in thinners and then run a scriber or sharp pointed instrument down the thread (about mid point of the thread profile, from from top to bottom). If there is dragging or galling which has damaged the thread, the scriber point will snag in the damage and warn you, takes about 15 seconds a thread rolling it in your hands, and then the other end and thread. Rotate the stud and check the other stud surface the same way. I allow about 2 hours to check the 10 studs, then dry and spray with WD and wipe dry. Enough WD remains on the stud surface to ease fitment without contaminating the torqueing regime numbers (105 lbs ft) which should be completed dry with no lubrication unless you are using ARP studs. The ARP studs need torqueing about 20% less ( I use 90 lb ft) because it removes stiction (sticking friction) from the equation and increases the actual clamping torque imposed to 108 lb ft). I know the Triumph studs nuts and block are good for 110 lb ft dry having used that previously.

Mick Richards  

Nearly all the studs I have rejected for reuse were corroded on their shanks.  I still have a small selection, but I wonder why I have kept them.

[AndrewMAshton]

Hello All, to close the thread, head now back on and torque down to 105 ft/lbs, I cleaned up the studs as instructed, they were in decent nick, all studs screwed in finger tight and got little extra with the double nut method so I am confident all is now well, thanks again for all your help and advice, cheers, Andrew