Bad Helicoiling (written by Baz Hartech)
Discussion
Baz Hartech asked me to post this as he can't host the images:
'A 996 - recently bought from a garage by the new owner - came in running badly – making horrible noises and in need of investigation.
We found many problems – needing some further strip down resulting in us finding out that the exhaust manifold bolts on one side were so seized they broke upon removal (a common problem) and so we fitted our “made in house” 2 stage drill jig to accurately drill out the holes and helicoil them – so far – so good. This jig is perfectly aligned and allows a smaller pilot drill to go in first followed by the helicoil size drill. We had to remove the manifold from the other side – finding that someone had got there before us and made a right mess of drilling out the old broken bolts freehand.
I mentioned this on a previous posting – that it is more difficult than people imagine. The helicoil drill is the same size as the diameter of the original bolt – so you have to drill with the same sized drill. The old bolts are actually very hard (like allen bolts) and difficult to drill needing a lot of pressure to make progress. Without a jig - if the drill is even slightly off centre then it will wander towards the softer aluminium casting and keep going in that direction until the hole is no where near the original position.
Ok you may say – make sure you start out in the centre. This is not easy because if you can see a round broken piece of bolt flush with the head face - the centre of the circle - is not the centre of the bolt (because the thread spirals around the centre as it moves along the bolt and you don’t know where the centre is). Without a jig it can therefore be impossible to accurately drill the holes.
However I never expected to find anything as bad as this result (see photos). It looks like the drill wandered off and the driller kept pushing as the angle changed until the holes were many degrees out of square. They were all at different angles as well.
This must be the best example of how not to drill out studs I have ever seen. But it presented a problem because they were so far off centre that there was not enough metal left to open out the holes true again and fit home made oversized inserts (which would have to be – cylinder head off first - and done on a mill anyway). So with the customer reluctant to spend too much at this stage - we managed to bend some studs and screw them in so the part sticking out was perfectly true again (and fitted the manifold) and we then used nuts to secure the manifold OK.
I post these pictures and info to demonstrate how difficult simply helicoiling a thread can be for those without proper equipment and experience and also how hard the task of diagnosis and repair can be for garages working on customer cars they have not seen before that have clearly been worked on in such a way that you never can rely on anything being done right and anything could be disguised and about to jump out as a major fault!
This car had many other faults including miss timed cams etc – but that’s another story.'
Baz Hartech.
'A 996 - recently bought from a garage by the new owner - came in running badly – making horrible noises and in need of investigation.
We found many problems – needing some further strip down resulting in us finding out that the exhaust manifold bolts on one side were so seized they broke upon removal (a common problem) and so we fitted our “made in house” 2 stage drill jig to accurately drill out the holes and helicoil them – so far – so good. This jig is perfectly aligned and allows a smaller pilot drill to go in first followed by the helicoil size drill. We had to remove the manifold from the other side – finding that someone had got there before us and made a right mess of drilling out the old broken bolts freehand.
I mentioned this on a previous posting – that it is more difficult than people imagine. The helicoil drill is the same size as the diameter of the original bolt – so you have to drill with the same sized drill. The old bolts are actually very hard (like allen bolts) and difficult to drill needing a lot of pressure to make progress. Without a jig - if the drill is even slightly off centre then it will wander towards the softer aluminium casting and keep going in that direction until the hole is no where near the original position.
Ok you may say – make sure you start out in the centre. This is not easy because if you can see a round broken piece of bolt flush with the head face - the centre of the circle - is not the centre of the bolt (because the thread spirals around the centre as it moves along the bolt and you don’t know where the centre is). Without a jig it can therefore be impossible to accurately drill the holes.
However I never expected to find anything as bad as this result (see photos). It looks like the drill wandered off and the driller kept pushing as the angle changed until the holes were many degrees out of square. They were all at different angles as well.
This must be the best example of how not to drill out studs I have ever seen. But it presented a problem because they were so far off centre that there was not enough metal left to open out the holes true again and fit home made oversized inserts (which would have to be – cylinder head off first - and done on a mill anyway). So with the customer reluctant to spend too much at this stage - we managed to bend some studs and screw them in so the part sticking out was perfectly true again (and fitted the manifold) and we then used nuts to secure the manifold OK.
I post these pictures and info to demonstrate how difficult simply helicoiling a thread can be for those without proper equipment and experience and also how hard the task of diagnosis and repair can be for garages working on customer cars they have not seen before that have clearly been worked on in such a way that you never can rely on anything being done right and anything could be disguised and about to jump out as a major fault!
This car had many other faults including miss timed cams etc – but that’s another story.'
Baz Hartech.
Merritt said:
Christ thats awful!
Was it purely the exhaust manifold mating causing the rough running or was that unrelated??
Steve
Was it purely the exhaust manifold mating causing the rough running or was that unrelated??
Steve
Baz from Hartech said:
This car had many other faults including miss timed cams etc – but that’s another story.'
Would tend to be the cause of rough running I'd think.
Amazing and frightening to think there are people out there capable (should that read ignorant enough) to carry out such butchery on mechanical components.
I drilled out several broken bolts and studs on my 993 (please note Sleep Envy
) exhaust system. It takes a bit of know how and a lot of patience.................
I am a little bit reluctant to say too much about the other faults on this particular car because we are not really sure what else may have been done wrong or indeed put right.
There was some sludge in the coolant (not a lot) but clearly someone has probably taken off the head on one side and on both sides the cams were not timed correctly and had paint on the sprockets to enable someone without setting tools to try and re-align the cam timing by lining up the paint marks.
Yes the manifolds were leaking on the badly repaired side shown in the photos and on the other side where they were original but rusted almost away.
Sludge in the coolant (as apposed to coolant in the oil) is usually a crack in a head - and we often advise this to callers on the phone. The problem for us is to know if the head has been changed already - so the sludge is just what is left over from before and therefore the reason the manifold was drilled and the timing was out is because the crack fault has been repaired or did they give up and put it back together and sell it?
With the only way to find out being an expensive full strip check and rebuild - for something that may now be OK -we have advised that the best answer is to run it a bit longer and see if the sludge gets worse (now that the other faults that we are aware of - have been repaired).
However this is not a nice problem for a business like ours to have. It is a bit like when you rebuild and engine that has blown something and had metal bits going everywhere - you are trying to help the customer reduce his costs but can never really be absolutely sure there is not a minute crack or a fatigue crack initiation that will cause something you didn't change to fail in the future and reflect badly on the work you did for them. New engines are obviously a safer option - but so much more expensive and in most cases unneccessary.
Fortunately such an occurence is extremely rare (indeed I cannot remember it ever happening ) but it must happen one day and then your good reputation can be harmed when all you did was try and help someone in difficulties - to get out of them.
When someone has worked on such a car in the manner of the photographic evidence - it is difficult to have any confidence that there is not something else they have interferred with that will cause a problem elsewhere - that you have not found yet.
So I intend to show some photos on this site now and again when relevant to demonstrate problems (they say a picture is worth a thousand words) and perhaps these may prove interesting and demonstrate how difficult some of the indepemdent's work can be.
Thanks to Paul by the way for taking the time to sort out the photo's for you to see - I could not manage it!
Baz Hartech
There was some sludge in the coolant (not a lot) but clearly someone has probably taken off the head on one side and on both sides the cams were not timed correctly and had paint on the sprockets to enable someone without setting tools to try and re-align the cam timing by lining up the paint marks.
Yes the manifolds were leaking on the badly repaired side shown in the photos and on the other side where they were original but rusted almost away.
Sludge in the coolant (as apposed to coolant in the oil) is usually a crack in a head - and we often advise this to callers on the phone. The problem for us is to know if the head has been changed already - so the sludge is just what is left over from before and therefore the reason the manifold was drilled and the timing was out is because the crack fault has been repaired or did they give up and put it back together and sell it?
With the only way to find out being an expensive full strip check and rebuild - for something that may now be OK -we have advised that the best answer is to run it a bit longer and see if the sludge gets worse (now that the other faults that we are aware of - have been repaired).
However this is not a nice problem for a business like ours to have. It is a bit like when you rebuild and engine that has blown something and had metal bits going everywhere - you are trying to help the customer reduce his costs but can never really be absolutely sure there is not a minute crack or a fatigue crack initiation that will cause something you didn't change to fail in the future and reflect badly on the work you did for them. New engines are obviously a safer option - but so much more expensive and in most cases unneccessary.
Fortunately such an occurence is extremely rare (indeed I cannot remember it ever happening ) but it must happen one day and then your good reputation can be harmed when all you did was try and help someone in difficulties - to get out of them.
When someone has worked on such a car in the manner of the photographic evidence - it is difficult to have any confidence that there is not something else they have interferred with that will cause a problem elsewhere - that you have not found yet.
So I intend to show some photos on this site now and again when relevant to demonstrate problems (they say a picture is worth a thousand words) and perhaps these may prove interesting and demonstrate how difficult some of the indepemdent's work can be.
Thanks to Paul by the way for taking the time to sort out the photo's for you to see - I could not manage it!
Baz Hartech
hartech said:
So I intend to show some photos on this site now and again when relevant to demonstrate problems (they say a picture is worth a thousand words) and perhaps these may prove interesting and demonstrate how difficult some of the indepemdent's work can be.
Thanks Baz -
Please do keep posting photos
I find it very scarey how much of a minefield this sort of thing could be. I assume that very little of this would be noticeable on a pre-purchase inspection?
Steve
hartech said:
Hi Merrit - the sludge and the poor running should have been picked up but the helicoiling would not - you would only see the bad angles upon removal of the bolts because you only see the heads when they are bolted up.
Baz Hartech
Baz Hartech
Baz, posting pictures is eeeeasy compared with the inner workings of a 996 engine.
Try this : -
Go to www.tinypic.com (No need to register/login or any such nonsense)
Click the "Browse" button, this will allow you to view the photos in your picture file.
When you've found the picture you wish to upload highlight it by right clicking on it.
Then press "Open" followed by the "Upload Image" button.
(depending on file size the upload may take between 10 seconds and 2 minutes !)
When it has uploaded the three choices of URL appear in boxes. Cut and paste from the middle box titled "IMG Link: for forums and bulletin boards" into this reply box (ie the one you normally type your text into) and submit as normal.
It sounds contrived at first, but once you've got the hang of it, it's easy !
Good luck !
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