Spark-plug helicoil question

They don't fail without reason. A competant engineer can do it on the car. You put the piston at TDC, jam a rag on top of the piston and use plenty of grease on the helicoil tap so that minimal swarf falls off. Be very careful and use an air line to clear the top of the piston and it should be fine.

First port of call would be to the garage who carried out the service for you. It is too much of a coincidence that this has happened so soon after a service. If they noticed that the threads were in poor condition at the time of the service then the should have let you know.

HTH

Anthony Remove eight from email to reply.

Lass at work got her Mazda MX done with the head on. All depends if the guy doing it can successfully retrieve the swarf - he stuck a vacuum pipe down the inlet manifold with the valve open and sucked it out as he generated it. About £250 but that includes front brakes and pads, full service and a little scratch removal so it's not very useful...:-( If you are close to Warwick then I can get the number of the garage for you.

Calling at the garage tomorrow. Trouble is, I can't imagine them admitting they did any damage, and we couldn't prove otherwise, obviously. We've given them a lot of business over the last few years, so perhaps that will have some bearing on their charge for fixing this. If not, I'm not sure we'd use them again.

Thanks all for the replies.

A very simple operation, done with the cylinder head in place. As others have said the Helicoil tap is greased to reduce the amount of swarf dropping into the combustion chamber. As long as the Helicoil drive tang is removed with snipe nosed pliers or similar, IME the little swarf that does fall into the bore can be ignored. It goes straight out of the exhaust port, as soon as the engine is started. Leaving a small anount of ally swarf in the bore is harmless. It's is not abrasive, and before someone says it can get caught in the valve seat, in practice it doesn't.

Shouldn't take more than half an hour at most, and the Helicoil insert cost about a quid.

Not cross threaded. More likely it was siezed, and it's removal tore the thread in the head. You can ask, but my guess is the garage will plead ignorance. You'll never be able to prove they were responsible. Mike.

I wouldn't chance it, years ago I had a Honda 250 m/cycle that needed a helicoil in the plug hole, I asked the same question and the guy said no problem. The engine locked up solid, I had to get it trailered home and strip it down. Should have done that in the first place.

Trevor Smith

The message from "Mike G" contains these words:

Or left loose and tore the threads out as it vibrated.

For what it would cost them to fix it and keep a good customer, it would pay them to fit a Helicoil FOC as a goodwill gesture. Accepting it might have occured when it was being serviced without their knowiedge. Not an unlikely scenario if they had the 'shopboy' change the plugs. To prvent a reoccurence, when you get it back, make sure the plugs are fitted with a light coating of Copper slip or ease and are not overtightened. Mike.

I've heard of there being the possibility of the helicoil tap dislodging a valve seat if it's close to the hole on some engines. However, a decent engineering workshop should know which this applies to.

Wouldn't this only effect the top few threads? OP said it was smooth.

I'd go for gross overtightening - perhaps more than once.

The message from "Dave Plowman (News)" contains these words:

That'd depend on whether the plug's threads were longer or shorter than those in the head. I've had it happen on of all things a lawnmower. The plug's threads would have protruded about half a turn beyond the head's threads. I couldn't hear anything wrong over the racket from the tatty old engine. Anyway, it popped out so I fixed it by tapping the head out to a much larger size, screwing in an alloy bar with a thread cut to suit, then drilled and tapped again to take the plug again.

Being a 2-stroke helped!

I successfully did this, I moved the piston approaching tdc and then filled the combustion chamber with grease, moving the piston up until grease was just entering the spark plug hole. Used the reamer tap and inserted the helicoil, carefully removing the tang. When finished expelled the grease and swarf by bringing piston to tdc. Then spin the engine over on the starter to eject the remaining grease.

If it was seized they will know what they did, more likely as Guy said, they left a spark plug loose and it rattled out, though I would expect some good threads to be left at the bottom of the hole if this were the case.

AJH

I don't doubt that, but I haven't come across any personally. I've fitted a few spark plug Helicoils to different engines over the years, but haven't fitted any to newer engines, so it may be more common with later multi valve ones. I'm aware though of the possibility of the tap fouling a valve or valves if they're open and the tap is run through too far. Mike.

If you tried hard you could apparently do it on old Fiat heads, never caused me a problem though. Easiset solution to the swarf is set the piston below TDC & pack with grease, then when you rotate it to TDC any small swarf you've missed comes out with excess. (All normal provisos about common sense & not hydraulic locking the engine apply)

Or Sods law, I've had an old Cavalier pop a plug 1500miles after I'd changed them & there wasn't anything at the time to suggest owt was wrong

So how do you get all the grease out afterwards? I don't see how it's easily removed, and if most of it isn't, the compression ratio could be significantly raised. You could run the engine without a plug for a while. How messy would that be? IMO the small amount of swarf that drops in the bore after using a greased tap is quite harmless, and safer than grease in the combustion chamber IMO. It's never had any adverse effects on the running of those engines I've Helicoiled. Mike.

You don't need to pack the engine with grease, just fill the area below the hole. & it dissapears out the exhaust valve, but I'd agree that the swarf won't make a blind bit of difference to the engine, unless you where spectacularly unlucky, the greases main plus point is it avoids a lot of swearing if you bugger up breaking the tang off.

I had a steel cage that retained a captive nut on a P6 3500 airfilter housing come off and make its way through the engine. Mighty bang and it dropped onto 7 cylinders. On removing the spark plug, found the end smashed. Fished about down the plughole with a magnet and recovered this crunched up lump of steel sheet. Engine ran fine after a new plug. ;-) Never did find out where the bits of plug ended up.

The post I was replying to said this:-.

"Easiset solution to the swarf is set the piston below TDC & pack with grease, then when you rotate it to TDC any small swarf you've missed comes out with excess."

At first I thaught it was quite a good idea to ensure no swarf is left in the bore until I thaught about it. Giving it more thaught, I don't think just filling the area below the hole with grease would prevent swarf being left in the bore either. When tapping, the end of the tap needs to fully enter the bore, to ensure a full thread all the way. Anything less could cause the Helicoiled thread to be tight at the end. Chances are that the grease will either fall off the end of the tap, or remain behind whe the tap is removed. The latter more likely.

Grease may work when the Helicoil is inserted to retain the tang if it's dropped, but I have my doubts about that as well. Personally I'd still prefer to rely on a good set of snipe nosed pliers. Ones that close fully at the end. Not a knackered set with bent jaws, which seem quite common in w/shops :-) Mike.