helicoil? back-tap? stripped spark plug hole

[Amybirds]

This is not good:

One of the spark plugs (#5) on our 1994 Q45 worked it's way loose (or was left loose by the last shop we went to) and subsequently rammed itself into the ignition coil, breaking some of the ceramic on the plug and rubber on the coil in the process.

The threads on the plug looked fine. Obviously we need to replace the plug and coil, however we tried another plug in the hole and it won't start threading, so we think the initial threads on the hole itself are damaged.

Anyone have any thoughts on helicoil kits or back-tapping tools? I know the ideal thing would be to remove the head, etc, but that's not a financial option right now...

Thanks!-Amy

PS: In case anyone wonders what our symptoms were that led us to look at the spark plugs: it started as a light ticking noise from the driver's side engine compartment that increased with rpms, then it became a popping sound with a very strong fuel smell reeking from the area.

[maxnix]

Sue that shop.

Helicoil might work, I don't know about the heat.

Rebuilding a head would be expensive, but more of a sure thing.

[bullittandy]

I think there are specialty tools for just this sort of repair. Call a local (not chain) auto parts store and ask, or search online.

If you can access the plug hole easily then you should be able to repair it relatively easily.

Worst case would be to tap the threads again with a tap covered in grease and then vacuum the cylinder to remove any shavings.

Worst-worst case would be to thread the new plug in (regardless of whether it wants to go or not) and hope for the best. (Don't try this one though)

[Q45tech]

Spark knock [preignition] from inferior gasoline quality can cause some severe pressures......................how does the piston top look [fiber optic bore scope]?

Was it a oem NGK plug?

[Amybirds]

Thanks Maxnix and Bullittandy. We can access the plug relatively easily. I'm thinking a back-tap tool http://www.back-tap.com/ would be better than a helicoil IF it works... (less risk of dropping shavings into the head).

Has anyone used a helicoil on a Q45 or a back-tap? Surely there must be someone that has cross-threaded their spark plug and had to fix it??

Q45Tech: It was an OEM NGK plug. Not really sure what the piston top looks like - is there a way to check that without an expensive tool? What would this tell us (in layman's terms)?

Also, what does preignition sound/feel/look like? We did have what we think was dirty fuel a while back -- some isoHeet, a new fuel filter and BG445 seemed to fix the problem, or so we thought...

[Q45tech]

I've never seen or heard of a Q45 spit a NGK plug.

[carfrk666]

ok here u go, i do this kinda thing at work, what we do for stripped sparkplug holes is we drill, tap and helicoil, its a special coil, special tools and everything that alone is expencive, u can find it at your local engine machine shop, when you do that make sure the piston is at the top of the stroke and that when u do it u use lots of heavy grease on the drill and taps, and change it frequently to not get any shavings in the engine, then use a vaccum often to suck out the shaving, however what i would do first is to use a regular tap or thread chaser of that thread and very very gently try and clean the threads out, do not try to force a sparkplug into it if it doesnt want to go, try the thread chaser or tap first but do it very very gently, good luck, and let us know how it goes

[Black stallion]

Also when you use the back tap or any tap turn it abou 1/4 turn at a time, back it out and vacuum, then turn a little more.

I would strongly advise against a helicoil due to the heat/pressure in this area (temp/cheap/emerg. fix only)

Find yourself an industrial screw and bolt place. they have all kinds of tools for this type scenario and by all means take your time. Sometimes if you just get past the first one or two threads you're home free.

[maxnix]

I think BS is correct. Run a tap first, and if that doesn't clear it up, I would go with another head that you clean up after pulling it off a wreck.

I would suspect the shop either cross threaded it initially and did not seat it sufficiently, or just didn't torque it down and left it to loose so that it became dislodged. Shame on them in either case.

[Amybirds]

Update -- we bought a special back-tap tool and then looked more closely and discovered that the head/hole is stripped clean -- no threads at all! So, just realigning the threads isn't going to work...

I agree that replacing the head would be best, but since I really need to get the car up and working with minimal cost and time, I think a helicoil-type fix is what we're going to have to try next. I'm not brave enough to attempt it ourselves though, nor do we have the equipment, so it's time to tow it somewhere.

We'll keep you posted. And I'll get photos up of the damaged injector coil and NGK spark plug -- not a pretty sight!

[Q45tech]

Be HAPPY!

At least it didn't catch on fire like the numerous Furd V8 Pickups that spit plugs regularly.

Find out who did the 60 or 120k plugs and bring it to them.

Of course if these were never done and the plugs stayed in too long?

[Amybirds]

The person that did the 120K plugs is the one we bought the car from two years ago. We had no problems till we brought the car to a shop that "checked the plugs and they look fine" when we were having some stalling issues...Of course, we can't prove they were the last ones to touch the plugs, so they basically (but nicely) said we're out of luck in that department. :-(

[maxnix]

Of course, we can't prove they were the last ones to touch the plugs, so they basically (but nicely) said we're out of luck in that department. :-(

No one can prove a negative! Don't let them off the hook. Tell them if someone else had touched the plugs since they had, you would be at their door.

You have proof that they did touch the plugs. They do not have proof that someone else did. Call an attorney or at least the better business bureau.

They are at fault and know it.

[Black stallion]

I agree, don't let them slam the door in your face (nice or not). They specifically checked your spark plugs and said they were fine so they are liable for any damage as a result of their diagnostic.

Take pictures and document everything; stay professional, but don't settle.

You have rights as a paying customer so stick to your guns.

[maxnix]

They specifically checked your spark plugs and said they were fine so they are liable for any damage as a result of their diagnostic.

Or more specifically, didn't reinstall at least that one correctly.

[elwesso]

Ouch!! Thats one thign you have to be SUPER careful with. Whenever I do plugs on Q I always spray it down really well with lubricant and anti-seize. The key is when you loosen them to do it by hand (of course no air tools here) and do it slowly.

What about a time-sert kit. Similar to the helicoil, but they they use them on the cadillac northstar's. on the northstars the head bolts pull out of the block and this fixes them fairly permanently.

[StarPD]

Years ago when aluminum heads weren't common, I had them on my high-performance Corvettes. I did all of my own work.

I've always been of the mind like others have mentioned here that once you pull the head, the motor is never the same. For that reason, changing plugs on aluminum heads always made me nervous. The soft aluminum makes it difficult to get the threads started unless the plug is perfectly straight and the starting threads are lined up correctly.

I used a well greased thread chaser and VERY carefully cleaned the threads in the head, then carefully cleaned the plug seat to make sure the plug gasket seated fully and cleanly against the head. After putting a thin film of Anti-Seize on the plug threads, holding the plug in perfect alignment with the hole, and gently turning it counter-clockwise enabled me to feel and hear the slight "click" when the threads dropped into the starting position. (Do NOT push on the plug, the starting threads in aluminum heads are very thin and delicate, and can be bent if the plug is pushed on too hard, causing cross-threading.) Then I VERY carefully screwed the plug in by hand, feeling for any resistance. Once the plug seated and bottomed out by hand, I used a micrometer click-stop inch-lb torque wrench to snug the plug down to spec.

My ex-wife used to call me the world champion of thread strippers, even in cast iron, so I got to where I ALWAYS used a torque wrench, even if I didn't have OEM torque specs and had to use standard specs for the fastener. The old "Snug it down, then give it another 1/2 turn, and finally just a little more" was my undoing, and that feeling when the fastener suddenly became easier to turn made my stomach rise up into my throat.

Likewise, I buggered starting threads and cross-threaded enough fasteners to teach me the technique of carefully lining the fastener up and turning it backwards until I heard and felt the little "click" before screwing the fastener in or on by hand until it bottomed. Cross threading can really ruin your day, especially on expensive parts.

I always used new plug gaskets. Re-using plug gaskets that are already crushed can lead to over-torquing the plug, resulting in stripped threads. Today, many motors don't even use spark plug gaskets. Not sure about VH 45 or VK 45, but if they do use spark plug gaskets, that may have been how your plug threads got stripped.

If you take your car to a pro, which is now probably your best bet, I suggest that you make sure it's a place that has a good reputation for doing near miracles, or at least has a lot of experience rehabilitating spark plug holes in aluminum heads. There ARE shops like that. You don't want someone to just helicoil the plug hole and leave debris in the cylinder, or to not get the helicoil inserted and seated properly.

Good luck.

Let us know how you make out.

[elwesso]

good post!

I dont understand why people say that if you take the heads off the motor is never the same. I suppose that begs the question of WHY you took the head off in the first place, but if you followed the specs in the FSM to the T I dont see why it would be a big deal.

[StarPD]

good post!

I dont understand why people say that if you take the heads off the motor is never the same. I suppose that begs the question of WHY you took the head off in the first place, but if you followed the specs in the FSM to the T I dont see why it would be a big deal.

Once the block and heads are assembled new, then run, the repeated heating and cooling of the major components stress relieves them, and they change shape. Also the heating distorts the shape if the components. But as long as they remain assembled, they distort and move together almost as one part. Once they are disassembled however, no longer beng clamped together, they move into a different shape and usually will not mate together properly like they did when new.

That's why a highly qualified race engine shop builds an engine, they align bore the main bearing seats, then clamp fixtures to the bare block and align bore the cylinders and resurface the decks, and finally, lock a fixture to the heads and resurface them. Only then will they assemble the engine using all new parts. The motor is then run, cooled and all fasteners re-torqued to ensure that the major components have seated into each other and stay that way.

Further, removing cylinder heads frequently allows debris and grit to enter the inside of the motor, eventually causing wear or even damage. Very few places have the sterile conditions required to keep exterior grit from getting into exposed internals, and even those that do have a hard time ensuring that no dissassembly debris gets inside.

Generally speaking, a motor that has hade the head(s) removed for any purpose will not have the same life it might have if it had not been opened up.