Spark plug blow-out!

[donaldo]

Hi folks

I have a 1974 1600cc VW Beetle that was fully restored in 2006 and fitted with a recon engine. It has since done 24k km without problems.

After changing all 4 spark plugs recently, I had the worrying experience of one plug literally 'blowing out' 1000km later with a great bang.

I was sure that I had fitted it in properly - but maybe not... The plug thread appeared undamaged, and it was re-fitted but blew out again the next day. I then fitted a brand-new plug, and this has now run for 100km. I am now left with an uncertainty as I have since learned about the 'helicoil insert' issue.

Has anyone else had a problem in this area? If so, what can you advise me about the following:

1. Will this engine have helicoils fitted?

2. If I now remove the plug in question, is it possible to examine the c/h thread area - maybe with a mirror?

3. If I find that the helicoil is partially out - what can be done, without pulling the engine?

Any information will be most helpful.

[derf]

It is common for them to have heli coils or some sort of metal insert over the years. Seems that you are doing the work yourself
If so does that plug feel any different going in than the others?
You can pull the plug out and look at the threads with a mirror.
Do you have short reach or long reach plugs? Some the the later model heads have a long reach plug now, Mexican heads?

[donaldo]

Originally Posted by derf

It is common for them to have heli coils or some sort of metal insert over the years. Seems that you are doing the work yourself

Thanks for your reply. Yes - I do basic servicing - oil, plugs, points, grease, etc

If so does that plug feel any different going in than the others?

Well, the first plug that blew out went in normally. But the brand-new plug I fitted was was tight from the beginning, and is still there.

You can pull the plug out and look at the threads with a mirror.
Do you have short reach or long reach plugs? Some the the later model heads have a long reach plug now, Mexican heads?

I'll look out for a dentist's mirror tomorrow and take out the problem plug. The plug I fitted was NGK BP6HS. Thread is about 8mm, which I guess makes it a short-reach.

[derf]

That should be short plugs. While you have the plug out try and look to see if that is the right reach,should be able to tell with the dentist mirror and flashlight. Some times with the heli-coil repair done it is hard to get the plug started correctly, I have found
Sometimes it is easy to get the plug cross threaded in the aluminum heads and it will feel OK for tightness then blow out. If it does not have a heli-coil installed ,might just need to run a tap down the hole to clean up the threads

[donaldo]

OK - that's useful advice.

Do you normally put anything on your spark plug threads before re-fitting? e.g. a dab of graphite grease?

Maybe a local VW shop has tool to clear the c/h threads if they are slightly damaged. It's a tricky area to get at, on the car...

The original plug threads look OK to me. No sign of a crossed thread.

[derf]

Originally Posted by donaldo

The original plug threads look OK to me. No sign of a crossed thread.

I meant in the head
All I have and will use is a drop of oil
Not a believer in anything else
The tap can be used in the car just a PITA tho. Which hole is it?

[donaldo]

Yes - I realized that, but I thought that if the cylinder head thread was damaged, there would some signs of it on the plug that came out. Maybe not.

Affected hole is the front on the right-hand side. Not too accessible...

[perrib]

Air cooled Spark plugs have always been installed with a bit of anti sieze.

The plug fell out because:
1. It was not torqued to spec. You can do it by hand once you know what torqueing it to spec feels like.

2. There was trash between the plug seat on the head and the spark plug gasket.

3. While not in your case, over tightened and pulled the weaken threads when it warmed up.

4. Overheated and loosened up.

If you use a tap coat the tap with grease so the chips do not get in your engine. It can be done on the car if you have good feel.

[derf]

Originally Posted by perrib

Air cooled Spark plugs have always been installed with a bit of anti sieze.

This is not a true statement Anti seize wasn't even around when the bug was first built
Some people like to use it, some don't. I have never used it and never will in my many years of working on air-cooled VW's and never had a spark plug stick on me or strip out a hole. I use a drop of oil and that's it. It is my experience that anti-seize gums up in the hole and makes it more difficult to remove the plug after being baked in by the heat of the engine.
But this is a personal choice. I know what works for me.

[perrib]

I don't know when anti sieze was invented it has been around since I started working on air cooled engines and you might be the first VW tech I have met who did not use it. When the first bug was built they also did not have ZDDP less oil, detergent oil, case and rocker stud savers, cam bearings, etc. If you look in Bentley air cooled VW manuals you'll see at some point VW thought it was a good idea. I would think if plain oil worked better VW would of used it because it was cheaper. Some where along the way VW even decided an oil filter for a T-1 engine was a good idea. When the OBD -2 cars came out is when VW stopped reccomending its use. Oil burns at a lower temp than antisieze. Do I always use it no. In my offroad and race engines I don't, but they don't get overheated either. Every customers car got it. The only real way to know which is better is get VW enginnering reports or build a couple of test engines.

[derf]

Not going to argue over this or oil,tire pressure or anything else. I am here to help people not debate. I state what works for me, it is up to the reader to decide what advice to take, but when you make a "blanket" statement I'll take exception
Happy motoring

[perrib]

Originally Posted by derf

Not going to argue over this or oil,tire pressure or anything else. I am here to help people not debate. I state what works for me, it is up to the reader to decide what advice to take, but when you make a "blanket" statement I'll take exception
Happy motoring

I'm stating a fact not arguing. Just the time line was off a generation, and you helped correct it. What's with all the smiles? A politician glossing over flawed content? I gave verifiable information, It can be looked up in a VW Factory authorized repair manual. I would think the odds are 100 to 1 VW would of reccomended it if it had been available when they made the first one. My blanket statement is all fact except for the date. If your going to help people tell what what VW reccomends first, chances are VW they spent some serious change investigating anti siezes qualities. Oil works, anti sieze works, leaving the threads dry work which one works best when the going gets tough. This a known fact Oil is used to lubricate, Anti Sieze is designed to prevent galling between soft or dissimilar metals. You may have been experiencing other peoples work who did not know/care that there are low temp, high temp, material specific anti siezes and 10-15 % less torque is required for tightening which in that case using oiled or dry threads would have been better as you have noted. If you look at each of our exceptions to the other one of our opinions one is based in fact the other in opinion. Opinion in the lack of knowledge senario just mention would trump fact and even make fact it appear fiction and opinion fact. Fact plus Z=fiction times k=opinion divided by c. We should of got the 1.5 million for the Noble Peace Prize this week. As for oil might we agree on: A VW T-1 crankcase full of any brand/ weight oil is better than being two quarts low.

[derf]

No further comments from me. I work on the older air cooled and my manuals say nothing of some things.
As some know when posting on an internet forum there is no sense of tone so hence "all" the

[donaldo]

Originally Posted by derf

No further comments from me. I work on the older air cooled and my manuals say nothing of some things.
As some know when posting on an internet forum there is no sense of tone so hence "all" the

OK guys - thanks for the interesting comments above. I've had 2 previous Beetles, but never had a plug problem before. Here's an update on the original problem from work done yesterday.

1. I plucked up courage and removed the problem plug. I estimate that it had not been fully seated (but was totally tight) as it came out after about 3 turns. The thread on the plug is definitely damaged, but not 'crossed'. More like the top of the thread 'peaks' is partially gone, so maybe the best word is partly 'stripped'.

2. Tried to examine the c/h hole with a dental (mouth) mirror but it was not very successful. A good result was using a small cosmetic mirror stolen from swmbo and a good torch! Now I could establish that:

a) no heli-coil insert is showing above the hole. In fact there is no sign of a h/c insert at all.

b) As far as I could see, the internal thread looked 'bright' here and there, suggesting minor damage.

I carefully refitted the same plug, this time achieving over 4 turns before it tightened. I know that is not fully seated, but the engine is running OK and I feel more confident now that I understand better what is going on.

I'll take the advice suggested above, and when convenient I'll get my friendly VW indy to clean out the plug hole for me. At least I now know that this is not an emergency 'engine-out' job.

[derf]

Good for you to try and see what is going on. But you need to take it in to your VW indy to see if the threads are still OK or if it needs some attention to the thread area Some times the threads can be cleaned up. If it needs some attention in that area I'd recommend an steel insert rather than a heli coil.
As always these are my opinion only, from my vast years and knowledge gained from racing and working on these air cooled car for years