Spark plug port threads stripped

[Nuvo]

Yesterday when replacing my oil and plugs I found that I couldn't get the thread started on cyl #1, I have been frantically trying to source a thread restorer this morning from various "local" motor factors. No of them carry them and will need to order one. I really need to get one this weekend if at all possible.

Can anyone recommend a franchise or supplier (Halfords don't seem to do them).
In a my frustration I bought a tap and die wrench and the correct size of tapered tap, but I can't help but thinking that using this do more harm than good. Am I right to avoid using this as I'd probably destroy the remaining threads and then I'd need to remove the head to make way for timecerts or helicoils.

Even recommending a online source would be welcome.

TIA,
Nuvo.

[Bibby]

I can't see much of an alternative to removing the head. Surely if you try and cut the thread, you run the risk of dropping swarf into the cylinder if the head is still on?

[Nuvo]

Hi, I understand that you fill the flutes of the restorer with oil or thick grease to catch the swarf and besides the swarf will be minimal too.

Nuvo.

[moony]

swarf

cut the thread then put one of those small magnetic pick up tools through the hole this should pick up any swarf.

[Jas11n]

cut the thread then put one of those small magnetic pick up tools through the hole this should pick up any swarf.

Aluminium head = non magnetic

[Keeper of The Kitten]

Yes, I was just thinking the same thing!

Timesert or Keensert would be the best type of thread restoration, but these are quite expensive, helicoils would be alright too and a tad cheaper. The alternative being to go the whole hog and weld-fill the hole and remachine it to the correct spec (head off, naturally).

__MDC__

[Nuvo]

Yes, I was just thinking the same thing!__MDC__

A nice little tip, just a shame it can't be put to use in this case. Thanks all the same moony.

Timesert or Keensert would be the best type of thread restoration, but these are quite expensive, helicoils would be alright too and a tad cheaper. The alternative being to go the whole hog and weld-fill the hole and remachine it to the correct spec (head off, naturally).
__MDC__

I haven't heard of Keenserts before read up on these. If it has to be done I think I'd choose Timeserts over Helicoils based on the experiences of others on this forum.

I hadn't considered weld-filling the plug port and then remachining. I'm no expert, my understanding was that aluminium was an extremely difficult metal to weld?

Thanks for all the replies so far!

[iain1067]

I would try the tap route first with a lot of grease, just make sure you get the tap centred first, alternatively it's helicoil or insert route, i had an insert done on an ali head yeasr ago by a local eng firm did it in situ, no probs with swarf. Helicoils btw are used alot in the aircraft industry from day one, it's the only way of making a decent fixing in ali.


Iain

[Keeper of The Kitten]

Yep, helicoils are used from new in lots of cases - but they are held only on the "springing" effect of the coil. Keenserts and Timeserts are very similar to each other, and use driven-in locking pins ("Keys") to prevent insert rotation. Used a lot in motorsport for fixings in softer materials. Not sure about minimum purchase quantities but they cost about £5 or £6 each, maybe more, depending on sizes.

Welding aluminium is more difficult than steel, but not extremely difficult at all - lots of competent fabricators would be able to do it, a couple of the guys at work can do that sort of thing but there are plenty of others who can.

I would agree with Iain though - don't do it the hard way if the easy way will fix it for less, and will last just as well.

__MDC__

[Nuvo]

Some great information there guys, this is helping to convince me to try using a tap. I'm assuming that the tap I have is made from carbon steel (based on price) versus High Speed Steel: I know that the former is more brittle than he latter, will I be okay with the carbon tap given that aluminium is a relatively soft metal?

I surmise from both of your comments on helcoils and timecerts, that timecerts tend to be favoured in automotive applications.

I have a few more questions to help me approach this with confidence:
1. I know that there are three types of tap available, namely taper, second and bottoming. In you opinion what is the best suited for this work?
2. What kind of grease do you recommend, and what can I do to remove any excess grease or swarf from the port? Any tips on this?
3. Other than using ones best hand/eye judgment to align the tap 90 degrees to the cylinder is there anything else I can do to ensure accuracy?

Sorry if the questions seem a little green, I'm sure you'll undestand I don't wan to eff this up.

Nuvo.

[iain1067]

Don't use copperslip just normal white grease out of a tin will do, you should have because of the depth a good idea just by eye if it's central or not, if your tap is tapered so much the better, are you 100% sure it's the the right thread???? To clean up afterwards i would pop some lint free rag down the hole a few times to get the excess out, followed by one soaked in brake cleaner, you might end up with some tiny bits of ali in the bore but i don't reckon it will hurt anything, when i have tapped stuff before it normally goes up the tap anyway, remember when you are doing this to go slow half a turn in a quarter back out and so on, it mught be a good idea to measure firts the depth of the plug and then measure on the tap the depth you are going to, mark this with either paint or masking tape or something similar i think it would be a bad idea to go too far in.

Good luck and hope it works, if itdoesn't then it's insert time. If it's only a matter of cleaning out a few threads then you will be fine, my only worry is that if the thread is really ******ed then how secure is the spark plug gonna be??? Only you know how bad the thread is, i wouldn't want a plug being popped out by the compression of the engine, seen it once and it screwed the head, there is btw a specific torque for plugs, i think it's 30nm if memory serves which isn't a lot.

Iain

[iain1067]

Oh and the tap should be made from carbon steel not high speed, but seeing as how you are going into ali it will be more than capable of doing the job. I have just looked on the familly album but it doesn't give a thread size for the plugs.


Iain

[Nuvo]

Don't use copperslip just normal white grease out of a tin will do, you should have because of the depth a good idea just by eye if it's central or not, if your tap is tapered so much the better, are you 100% sure it's the the right thread????
Iain

I'll buy some white grease tomorrow from Halfords to tackle this. I understand the point you are making about making the judgment by eye, I was just a bit concerned due to the restricted space of the engine bay. The tap I bought today is tapered so that is good news, as for it being the correct size I got the information from the spark plug data. It is M14x1.25. It's a good job I rechecked this as it is the sales guy has given me a M1414X1.5 tap! Thankyou very much for mentioning this as I would proably not have double checked this.

To clean up afterwards i would pop some lint free rag down the hole a few times to get the excess out, followed by one soaked in brake cleaner, you might end up with some tiny bits of ali in the bore but i don't reckon it will hurt anything, when i have tapped stuff before it normally goes up the tap anyway, remember when you are doing this to go slow half a turn in a quarter back out and so on, it mught be a good idea to measure firts the depth of the plug and then measure on the tap the depth you are going to, mark this with either paint or masking tape or something similar i think it would be a bad idea to go too far in.
Iain

Some great tips there Iain. I'll print this off and have it close to hand tomorrow when I set about it.

Good luck and hope it works, if itdoesn't then it's insert time. If it's only a matter of cleaning out a few threads then you will be fine, my only worry is that if the thread is really ******ed then how secure is the spark plug gonna be??? Only you know how bad the thread is, i wouldn't want a plug being popped out by the compression of the engine, seen it once and it screwed the head, there is btw a specific torque for plugs, i think it's 30nm if memory serves which isn't a lot.
Iain

Thanks. Yes it is only the first two or three threads which are knackered. Yep I aware of the plugs having a specific torque, I'm sure the Bosch plugs quote 25Nm on the packaging. This has been an accident waiting to happen since I first got the car if I am honest as I have always had a hard time starting the thread on port #1. I think it is fair to say that the plug has been over tightened at some point in it lifetime, if anything I have been guilty of under-torquing them in the past Thankfully cyl #1 is nearest the front front of the car so I should not have to strain myself too much.

Thankyou very much for your help and insight, I really do appreciate it.

Cheers,
Rob.

[iain1067]

Pleasure just go careful and let us all know how it turns out


iain

[philS2]

I would try the tap route first with a lot of grease, just make sure you get the tap centred first, alternatively it's helicoil or insert route, i had an insert done on an ali head yeasr ago by a local eng firm did it in situ, no probs with swarf. Helicoils btw are used alot in the aircraft industry from day one, it's the only way of making a decent fixing in ali.


Iain

i did one in situ like Iain on a laguna.just let all the swarf drop in (not my car anyway).just gave it an almighty f*cking rev when i started it up from cold (again,not my car so not bothered ).only thing might be swarf going through the turbo.although it should just blow through i would have thought.