Damaged spark plug threads

[foggyjames]

Just a quick reference document on some research I've done lately.

I bought my 1980 345 with a few problems which needed sorting out, one of them being a damaged thread on the #3 (which would be #2 on a non-French engine...!) spark plug hole. This is a common problem on heads where access to the plug(s) is restricted - in the case of early B14s, by the bulky "weights" distributor. I thought I'd do what I've done before, and just fit one of these...

http://www.google.co.uk/products?hl=en& ... &scoring=p
Specifically, this:
http://www.ecrater.co.uk/p/4046312/spar ... -kit-78237
...they're also on eBay, but the link will expire quite soon, so I won't bother!

These are an M14x1.25 internal thread and an M16(x1.25 also...I'm not sure...) external thread. I'm not quite sure exactly what kind of metal they're made of, but it's a rather odd material. It feels a bit 'gritty', and they're a bit prone to cracking / tearing in half. One even melted (as did its plug...oops!). Sadly in this case, the hole was too badly damaged, and there was insufficient metal available to allow the M16 thread to bite. After several attempts at re-installation, we gave up and pursued a better solution.

We soon decided that a larger insert was the way forward. I toyed with getting one made, until I found these - an off-the-shelf product with an M18 outer thread...

http://fulltorque.com/sparkplug.htm

These look like a great product, but I had a bit of a mis-communication with the Norwegian company who are the distributor for Europe, and he quoted me in USD, when the figure he actually mentioned was in GBP. This was still several hundred pounds (including the installation kit), but he directed me to a machine shop on the south coast who are a stockist, and I'm sure I could have pursued this option with great success. However, by the time he realised his mistake and the pricing was put right, I'd already made other arrangements...

Someone on Turbobricks suggested I look at this product...

http://www.timesert.com/html/bigsert_sp ... minum.html

There was a company on eBay in the US selling the correct size, length and material (aluminium) for about $30 for three. I contacted a distributor in the UK who were advertising other TimeSert products on eBay, asking if they could supply the full range. They could...and here is their website...

http://www.simmiperformance.co.uk/contact.html

...Helen at Simmi couldn't really have been more helpful if she tried. The only slight fly in the ointment was that the UK and US TimeSert catalogues appear to use different part codes (never a dull moment...!), and at the last minute she said she couldn't get aluminium ones at all...so I ordered steel, hoped for the best. By the time she announced this, I didn't have the heard to tell her no...she'd been so helpful. They were £7 each, shipped. Bargain!

I then had to worry about installation. Both "higher end" insert "systems" have an installation procedure (the cheap ones you just screw in with Loctite!). The Full Torque ones use a pin (almost like a Woodruff key - I imagine Chris will correct me if there's a proper name for such a thing in this application) installed in a small hole centred over the joining line between the insert and the head (grab a mug of tea and settle down for epic YouTube engineering instructional video! http://www.youtube.com/watch?v=9XfTORBtcSE). The TimeSert product uses a kind of compression arrangement on the end of the insert, rather like a pop rivet (at least that's how the guy at the machine shop described it).

I took the head down to my local friendly (and often expensive...) machine shop, and asked them for advice. While I was here, I noticed a "TimeSert stockist" logo, and found that I'd struck gold - they know all about them! They charged me £20 to tap the hole out to M18x1.5 and compress the insert.

There are pictures of the finished result, but I'm too lazy to sort them out right now.

It's early days to be drawing firm conclusions just yet, but we installed the head today, and it's got promise. It appears to be made of 'normal' mild steel, and doesn't feel as 'delicate' as the cheapo ones I've used in the past. I'll report back when we know whether or not it's been a complete success...but fingers crossed, eh? Just thought this might come in handy if you get stuck one day...!

cheers

James

[volvosneverdie]

nice work dude.
good informative read.

and highly articulate for half one in the morning.

[foggyjames]

It's when I do my best work, dude! Simmi are just down the road from you...small world!

cheers

James

[Chris_C]

The Full Torque ones use a pin (almost like a Woodruff key - I imagine Chris will correct me if there's a proper name for such a thing in this application) installed in a small hole centred over the joining line between the insert and the head (grab a mug of tea and settle down for epic YouTube engineering instructional video! http://www.youtube.com/watch?v=9XfTORBtcSE).

It's just called a key here bud, Woodruff refers to the specific shape of that kind of key. Great video, some really really cool usage of jigs as I was wondering how they were going to pull that off without a mill.

Glad you've finally got it sorted, even better that I didn't have to lathe you an insert up too

[foggyjames]

Not as pleased as I am! Snow drifting was a suitable reward for our hard work, I think!

Just needs a pair of half shafts, a rack gaiter (in the post), the exhaust sealing up (temporary repair back when the car was running was only half finished...it got to 9:30pm, and I didn't want to anger the neighbours!) and maybe a small corrosion repair on one of the front outriggers...then it's MOT time!

cheers

James