silent running

One of the threads for the head bolts in my block is very tight and I can't get more than 3 or 4 turns into it. Being as I'm guessing my ARP head studs are much tougher than the aluminium of the block, I don't want to wind it in by force.

Where can I get an M11x1.25 thread chaser/tap to clean the thread out, that is long enough to get all the way down there? Could I use an old head bolt to cut in there somehow? I threw mine all away only last week!

adzer

iTrader: (13)

you not get one from the likes of halfrauds or somewhere similar?

NUTTYNICK

Are you sure they are the right thread pitch as 3 or 4 turns is about all you will get if they are out?

Not saying they are wrong but it isn't unheard of.

As for the tap, I guess a cheapish set will do and on the square drive, you can fit a small quarter inch bi hex socket (most good socket sets) with extension and ratchet to give extra length, worked for me before.

silent running

Yes, the other 15 studs go in fine, the whole way down, smooth as butter. This one last hole won't have any of it. I'll have a hunt around tomorrow and see if I can turn anything up.

NUTTYNICK

Ah good, just thought I'd suggest it

I expect you've tried swapping this stud with one that deffo screws in to ensure it's not a rogue.

As you are simply wanting to clear a thread out, I reckon the cheapest tap set you can find will do with some lubrication.

Hope all works out

silent running

Yes, it's definitely the thread in the block that's at fault. Problem is the size is really unusual and M11x1.25 doesn't even come in most of the decent quality sets let alone the cheapies. I have a cheap set that has M10 and M12 but not M11. I've tried the M10x1.25 and the pitch is right but obviously it's not a close enough fit to do much good.

I think what I need is someone who's got an old head bolt knocking around that I could 'mod' to work as a tap. I just threw out dozens of the things that were lying around my garage!

cookstar

iTrader: (6)

Im sure someone like API will send you one, must have millions of old ones, doesn't really help on a bank holiday weekend though.

172sport

iTrader: (6)

I've ground a flat on both sides of a bolt to clear threads before with success, although nothing as potentially expensive......................!

NUTTYNICK

See what you mean, I should have read the thread properly, didn't realise you were after an M11.

They are available but not too cheap for the amount of times you will use it

Single Tap

This guy lists all sorts apart from the one you're after but may be able to source one if you're stuck

Ebay Link

silent running

Good link to that tap, that's the cheapest so far, but still £30 once VAT and delivery are on top... I just knew there was a good reason for keeping spare head bolts around!

The weird thing is, looking down the hole, I can't see any blockage at all. I don't know whether it had some water in there before and the threads got coated in that chalky hard white stuff?

silent running

Disaster has struck! Just to see if it might work, I sprayed some PlusGas in there to clear it out, then wound in the stud a few turns, as it had gone in 4-5 threads before. Within seconds it started to feel like it was tightening so I quickly started backing it out, but not quick enough! The thing seized rock solid, I've never known anything like it...at this point I was bricking it thinking I'd written off my block so using brute force it came out. I figured it was better to wreck my brand new 3/16" allen key and ARP head stud than to leave the block with this thing sticking out of it! Here are the results:



Here's the best photo I can do of the head stud hole, it looks the same as it always did, i.e. the same as all the rest but really tight for some reason, but now the first bit of the thread is chewed up, so I drilled a little of it out with a 10mm bit figuring there's no way the correct sized tap will run through it now anyway. That thing that seems to be there at the bottom doesn't stick out or anything, the length of the hole is the same as all the rest so it must be just a machining mark or something?



WHat the hell do I do next? A tap/thread chaser now seems out of the question. I've never helicoiled before, do I need to do that? Should I just carefully remove the first few chewed up threads with a drill the same size as the actual hole and then use the bottom half of the thread which I think might be OK - this is at least the 'no cost' option? Can I overbore it and retap for a bigger size stud? HELP!!!

Of course, with hindsight, what must have happened was that the moly lube was the only thing allowing the stud to go in by 4 or 5 threads at all. With the plusgas sloshing around in there, it washed away the lube as the stud went in and it locked in position. I still can't think what the original cause of the tightness was. It definitely didn't feel like a crossed or weak thread.

NUTTYNICK

The lube is there primarily for when you torque load the bolts, it reduces the shear stress between materials. For it to sieze so early on, the thread must be damaged or have swarf in there. You'll be suprised at how little you need for things to go wrong.

Avoid the drill for as long as you can, I've tried that and it still makes it very difficult to get the bolt to catch the initial thread right without crossing. You would have effectively removed the lead in thread.

The tap is still the best option you have and now potentially the cheapest. You must ensure that it is straight as you initially wind it in though.

A problem you have now, is that the tap itself might not catch the original thread correctly and try to cut a new thread, which means removing the old thread making the whole thing weak.

Helicoils might work, they are designed to have an existing thread there in the first place strong enough to use. Threadserts are what I have used before, it uses a solid insert and are ideal when you have totally lost the original thread. The hole is oversized, tapped and then the smaller insert screwed in restoring the original thread size. That would be an engineering shop job though as the kits are too expensive for one job.

As much as I hate to admit defeat, I think if the tap doesn't feel like it's going to work, then it's an engine builder/engineering shop visit as they will have the right kit. Not saying you can't do it, but the cost of the tools may be prohibitive.

NUTTYNICK

Just thought, the thread in the block, does it go right through so you can get to the other side? I don't think it does, just making sure.

You don't want any fluid in there at all, that plus gas stuff you've been using needs to come out. Only a small amount of lube is necessary.

Reason being, you don't want to create a hydraulic lock which in some cases, when the bolt is wound all the way down, it punches a hole through the other side especially on alloy blocks.

silent running

The thing is, I don't think there's any way now that the tap will catch the original thread and lead into it because the top part of the thread is scrap now. The threadsert thing you mention is I think what I've found - a kit for £60 (!) with the correct drill, helicoil insert, tools etc, so you drill down into it, tap it and insert the new coil, job done, restoring it back to the original thread size.

They are blind holes and when the other 15 studs went in, you could hear the air bubbles popping through the lube as they went down. So no way of getting through to the other side.

taffy with ppp

Buy a re-thread tool for the pitch of thread that you require, it is like a narrow hacksaw blade with grooves machined along it's length to match your pitch thread, put this down the bore so it alignes with the good thread and follow the thread backwards applying pressure to the damaged threads, this should roll your damaged threads back close to their correct position, you will be able to then see where the thread cuts the metal at the start (Top). Run a start tap down the bore, then a secondary and finally a plug tap, this has the largest diameter and should then match up with the good threads further down the bore.

NUTTYNICK

That's what I was thinking but it can still be done with a 'set' of taps like taffy suggests.

You've been luckier than me then with the air bubbles/fluid escaping

taffy with ppp

As long as you can establish where the thread started at the top of the bore by using a re-thread tool, then run the taps through in order, if you dont start at exactly the same point you will encounter mismatch at where the good thread exists part way down the bore if this happens you are in trouble. The only way out of this then short of a Helicoil or Insert is to run the taps 100% all the way down, re-forming the good threads but weakening them then apply a high temperature high strength threadlocker to the first 30mm of the head bolt when you insert it. This should then lock the bolt down but not reccomended.

silent running

Well I can't find a 1.25 pitch rethreading tool anywhere so that rules that out for the time being. Meaning I can't re-establish the lead-in point of the thread at the top.

I think I may try drilling down carefully to remove the top part of the thread entirely, I'm sure it's only 2 or 3 threads, then hopefully that will 'clear the decks' and reveal a new lead-in point and a decent thread to work a tap or home-made chaser through... I'm sure if I try any other way I'm going to wreck the rest of the hole somehow.

Why they didn't use M12 or M10 I don't know.

bandit1216red

ok ya said you had a M10 x 1.25mm tap???
try that and "wobble" it as u go down use tapping fluid or grease / oil etc as a lube
pity u havent an old bolt you could harden n make into a tap???
also remove all damaged threads on the new stud with a file
stainless will pick up in other materials very easy hence the damage
if you know the tapping size drill im not at work so no tables here you could tryit in the hole with ya fingers turning it again use lube

silent running

Yes I've got an M10 but I'll have to rig up some sort of attachment to make it longer reach. I'm gonna take the damaged threads on the stud off now. For the helicoil kit to restore an M11 thread the drill bit is 11.4mm. How that corresponds to a normal tap though, I don't know.

I'm definitely going to drill the top couple of threads out of the block, they're done for and won't be any good to run a tap through.

jayb1970

I am not an engine specialist or anything bu I am a maintenance engineer with 20 years experience and for what it is worth do not panic ! You will be able to rescue that thread with a tap no problem. I would say do not try drilling out the top couple of threads as there is more than a good chance the drill will catch and drive all the way to the bottom of the hole, ie. no threads left !
Just buy yourself a tap and carefully tap the the hole out, as for hydraulic pressure that won't happen as the tap has flutes cut into it to allow the swarf and lube to come back out again. If there is still some left in the hole afterwards then just soak it up wth a peice of rag.
As I said before don't panic just be careful. W e do this stuff all the time at work and so long as you take your time you will be fine.

Good luck.

hixxys STI

hi mate being a mechanical engineer (toolmaker) i would'nt use helecoil cuz you will have to redrill and tap to suit the helecoil making sure you drill and tap square ideal if you have a HURCO vmx60 cnc miller or any miller, but anyway personally i would try running a tap bk down the hole (you can get long seri ones) and running a die nut down the thread of the arp bolt BUT dont hold the die nut tight in a vice as it will remove matirial from the thread you just want it to clean up



p.s how far down the block do you have to go cuz i have metric taps that are long seris, about 2.500" long
cheers matthew

hixxys STI

also matey if its defo m11 x 1.25 thread it has to be a fine pitch not std
STD M11 is 1.5 pitch

StickyMicky

lots of advice here, and i will chip in with some of my own, remember folks, this is not just a thread that "bolts something on" like a piece if machinery (bear with me)

this is holding down the heads on a car and taking up vast pressures in use, hot or cold, the head bolts take quite a bit more abuse then a simple or average "retap" job would entail

if it were me, i would try a tap, but would also try and speek to an engine builder just to confirm its going to be ok

would be a right PITA if the headgaskets failed at a later date due to this one thread being a little bit weaker

hixxys STI

totally agree with you there sticky

silent running

Thanks for all the advice on here, it's all welcome. The helicoil is going to be the last resort if I can't get anything else to work, because the alternative is to scrap the block which I can't afford to do after having had it bored and faced - it owes me money!

The hole is 100mm deep and only 13mm wide, and even worse the actual threaded part is the bottom 45mm so it's virtually impossible to see what's what. I still can't figure out how just running a tap through it will correct the problem, as I have no lead-in thread at the top so it's bound to cross the existing threads further down. Surely I have no choice about having to drill out the top few threads that are chewed up?

bmfcrash

iTrader: (14)

Dont drill out any threads,for the money you have invested if you are not up to the job yourself take it to a machine shop and let them correct it for you.

If it was me, I would beg / buy or borrow a set of long series M11*1.25 taps.
Use the taper tap first and if you cant feel the start of the thread turn it backwards 90 degrees and try again. You will be suprised at how a taper tap will pick up the original thread even when you think its foobared.
Get a feel for it before diving in and trying to cut a new thread all the way down to full depth.

Once the thread seems cleared you can use a plug tap if you wanted, but there should be no need for this as the bottom threads are ok anyway. Make sure you use cutting compound on the taps and not just wd40 ect.

As for the stud either use a Die or a thread file to clean up the damaged threads.

Wouldnt worry about the strain the stud/thread sees, There is a tolerence on thread length and a margin of safty in the design, if the first couple of turns are iffy cant see a problem there. Most errors come from studs
'streching' not ripping the threads out of the block itself.

Hope this helps, PM me if you need any help and I can have a look at work for a Tap if you like.

silent running

Well last night I went out and used a flat 12mm bit, measured carefully, and drilled down to the depth of the wrecked stud threads and no further. So now I had a flat shoulder half way down the hole with good thread below it, and to my great delight, there was a clear lead-in thread sitting right there. I'd filed off the damaged threads of the stud but to avoid any extra problems I wound out one of the good studs that I'd put in one of the other holes, and tried that in the drilled out hole - bingo! It went straight in nice and true, only a couple of turns in but I could feel it was good thread. Then it hit the problem area that had been the original cause of the whole problem, but I'm not so worried now because I know that a tap will run through that and correct it properly.

So no need for helicoil now that I've got a good lead-in at the top of the thread in the block! THe only remaining problem will be getting a long enough tap that will reach to the bottom so needs to be 100mm at least, and make sure it's a taper and not a plug ('bottom' tap?) What should I use for cutting fluid if not WD40? I read somewhere that 3-in-1 oil is good for aluminium?

bmfcrash

iTrader: (14)

If you now have a reasonable thread and are not actually 'cutting' much material then any lube should do the job, I would stay away from any to thin though eg wd40, 3in1 should be fine.
Once you get a tap remember to wind it in a turn and back it off a 1/4 to break any swarf, and repeat untill full depth required.

silent running

Will do - cheers for the advice!