Disaster strikes again..

[2cams70]

Stop - don't go any further! Take the head off. Take it somewhere where they have a vertical drill press so it can be drilled accurately right on centre. Usually they can still save the existing threads without using a Helicoil.

[alan.barker]

Jon,
as i suggested make a steel Drill Jig that just slides over to centralise on the broken screw shank.
Clamp in position and when you are drilling your tapping drill is centralised and cannot move off centre.
With a broken off screw like that it is imposible to centre punch in the centre and the drill will always move off centre into the soft alloy head.
At least that's what i learned during my apprenticeship.
I would suggest if you hit it with a hammer be very very careful not to crack the cylinder head.
If you are lucky and drill out the broken part you can clean up the thread with a n?3/plug tap.
Then you can use a longer bolt than original as most holes are threaded deeper.
I would also make sure the thermostat housing cover is flat and lap it on some wet and dry paper.
Alan

[JonB]

Stop - don't go any further! Take the head off. Take it somewhere where they have a vertical drill press so it can be drilled accurately right on centre. Usually they can still save the existing threads without using a Helicoil.

That was my thinking. I've already damaged the head by drilling off centre. I have a drill press that would drill it out perpendicular but it won't fit in the engine bay of course. Anyway, I needed to pull the head off at some point to resolve the timing chest oil leaks.

I might try a jig of sorts to hold the drill square. Could use a flat iron bar bolted to the other side with a hole as a guide, but not sure how to stop it moving side to side:

Daughter's prom at end of June and this is the car she wants to go in. Better get my skates on.

[MarkDa]

I'm sorry to read about your woes and I hope you can resolve it.
I'd say the car is driveable a short distance if you find someone to do it in situ.
Use RTV as a seal, pull down on the one stud and then dont put a pressure cap on the rad and it should hold.

I know this is too late but this sort of extractor is pretty good. Easy to use, no reduction in section area and no risk of leaving anything superhard in the way of drilling out if they don't work. Good on rounded nuts/heads as well.

https://www.machinemart.co.uk/p/5-piece ... nsion-set/

Or as previously mentioned drill to bottom of the stud and use splined extractor.
This sort of kit centres and aligns the drill.
Metric thread of course nowadays but still adaptable.

https://rover.ebay.com/rover/0/0/0?mpre ... 3601363424

[alan.barker]

On second thoughts maybe 2cams70 is correct.
Remove head and take to machine shop. Best not to take any risks
Better to be safe than sorry
Good luck
Alan

[William2]

If you go down the drilling route it is essential that you use very good quality drill bits especially as you are going to be using small diameter ones to start off. You can't beat a brand new drill to help start the hole off. I have had to drill the odd broken stud over the years and had success. Beware that there's an awful lot of crappy chinese quality drill bits around. Good luck.

[Bigbaldybloke]

I agree, head off and off to a good machine shop. They?ll probably use an end mill rather than a drill as they don?t ?wander? like a drill can do. Looks like the thermostat housing could do with a very light skim too while it?s there to ensure you get a good seal when it?s replaced. Check the cover is flat too as they are often overtightened to try to cure a leak and this can bow them and make it worse.
Good luck, at least you won?t need a transporter this time !

[JonB]

I did a search and found this: lotus-twincam-f39/head-removal-replacement-for-dummies-what-avoid-t30023.html

Basically what I need, I think. At this time I want the minimum effort to remove and reinstall the head. As I understand it the cams do not need to be removed, is that correct? I was planning on aligning it all to TDC then ziptie the cam sprockets to the chain to keep them on the right teeth, but I am not sure how to stop the chain slipping on the lower sprocket. Don't want to dismantle anything else at this time, but hopefully will cure the oil leaks with new gaskets.

I have Miles' book but it describes the head removal work in the context of a full engine strip down which I am not doing now.

[2cams70]

Dare I say it - If you are under time pressure it might be worth considering a temporary bodge. Silicone sealant and it may be possible to rig up a temporary clamping arrangement using 2 bolts and 2 steel flats either side of the thermostat housing. You might even be able to use some fencing wire!

Don't leave it there though. Head off straight away after the event.

[JonB]

I considered that. Maybe I should do a tryout before pulling the head, but can it really take 8 weeks to sort it properly? I'm not doing any other work "while I'm in there" as the engine is (maybe I should say "seems"?) really healthy otherwise.

Thing is, if I do a temp repair, I'm going to want to drive it - perhaps 50 miles a week. Would be a shame for the temp repair to pop while away from home and strand me somewhere. I do have breakdown recovery but it takes forever for the service to get to you.

Do you think a G clamp would suffice, with a plate to spread the load under the housing? The other end of the cover can be bolted properly.

I guess I will try it. Wouldn't hurt, that's for sure.

[rgh0]

Keep drilling. it does not matter if its off centre just drill all the way through and then use progressively larger drills until you reach the thread on the nearest side. The remains of the bolt will normally collapse and come free at that time. if not get a rat tail file or suitable dremel bit to remove the rest of the bolt until it collapses.

Its probably good you did not manage to remove the bolt as it probably would have stripped out the thread in the head. This way you have a chance to save the head thread and not need to helicoil it.

Remove the temp sender underneath to ensure you dont drill into it by accident.

I use hex socket cap head unc bolts with nickel antisieze in these rather than the original studs the same as I use on the exhaust manifold

cheers
Rohan

[Foxie]

I was planning on aligning it all to TDC then ziptie the cam sprockets to the chain to keep them on the right teeth, but I am not sure how to stop the chain slipping on the lower sprocket.

You are right there, set it to TDC before removing the head. You will have to remove one sprocket (Inlet) to free the chain. There is no point in zip tying the chain to the cams sprockets, as you will have to start from scratch when putting it all together and timing it again. Just tie the chain over the side of the timing cover to prevent it falling down, but it's easy to fish it out if it does !

[JonB]

Keep drilling. it does not matter if its off centre just drill all the way through and then use progressively larger drills until you reach the thread on the nearest side. The remains of the bolt will normally collapse and come free at that time. if not get a rat tail file or suitable dremel bit to remove the rest of the bolt until it collapses.

Its probably good you did not manage to remove the bolt as it probably would have stripped out the thread in the head. This way you have a chance to save the head thread and not need to helicoil it.

Remove the temp sender underneath to ensure you dont drill into it by accident.

I use hex socket cap head unc bolts with nickel antisieze in these rather than the original studs the same as I use on the exhaust manifold

cheers
Rohan

Thanks Rohan. Problem here is that it's drilled off centre and I might already have gone into the cylinder head. I need to get some new drill bits and have another go perhaps. I'd be delighted if I managed this and did not need to take the head off at this time.

[rgh0]

Start with a small drill as near the centre of the bolt as you can get and drill all the way through. A centre punch will help create a start in the approximate middle of the bolt and to the inner side of the hole you already have. Once you have that hole slowly expand it keeping it as close to vertical as possible until you get to the bolt threads and the bolt collapses in and can be freed up.

It does not matter if you accidentally take a little off the head thread just go slow and watch carefully and stop if you see any of the head threads appear in the hole as you expand it. In the end if the head thread is no good then you can helicoil it back to be better and stronger than original.

Should be no need to remove the head.

cheers
Rohan

[JonB]

OK Rohan. New drills, then. I'll get some this evening and try again, but there isn't much left of the centre of the bolt:

Drill hole off centre and possibly cutting into the threads in the aluminium.

From a different angle it looks like the head is damaged.

I'm not sure I can drill it any more with the hole so offset as it is. I'll try with a really small bit.

Thanks to all for the advice so far.