Stripped threads in plug hole

[miked]

Guys,

I was unfortunate today to find No 4 spark plug a bit slack when I went to take it out. When I put it back it pulled the thread. Boo Hoo

I have been having a look on the net. I see normal helicoils, helicoils with serrated edge (to lock) and full inserts. I see the inserts can have high temp glue/compound. Also there is no need to drill any as the tap has a leader.

What is the collective wisdom? The inserts look better than the heicoils as they have a proper seat and flange to bottom out. I am about to pull the head off which only went down 1600 miles ago. Boo Hoo again!

I notice a few guys on the net saying that using grease to cut the threads collects most of the tapping debris. That which drops on the piston being collected with a dab of grease through the plug hole. They are saying that it is not the end of the world to leave a tiny bit of alloy debris.

Thoughts appreciated please. See insert kit.

http://www.ebay.co.uk/itm/Spark-Plug-Re ... 4832bcf27e

Mike

[Kerryt333]

Hi Mike,
The full insert ,as you've shown from eBay, is definitely the best remedy & you should be able to do it with the head left on.
I've used this form of insert with the head left on & if you use grease it should collect almost all of the swarf.The good thing about
this system is that it has a shoulder to go down to, to stop the insert going too far, whereas with a helicoil if after you've inserted it ,
you then wind a plug in with a slightly dodgy thread, what is going to stop the helicoil from winding down further & ending up on top of the piston.The tap supplied with these kits usually has the M14x 1.25 thread on the front ,which picks up on anything that is left of the old thread, & is followed by the insert thread so that it keeps it in the original place & axis.
Regards
John

[nebogipfel]

Yes Brian Buckland in his excellent book advocates that it is quite safe to fit an insert with the head in situ.

He recommends slowly does it with plently of grease on the tap. Reglarly backing the tap off and cleaning the swarf away. He also wisely suggests turning that cylinder to TDC and then any errant crumbs of swarf which find their way onto the piston can be carefully lifted out with a suitable implement with a blob of grease on the end.

The shouldered insert mentioned by John sounds like a good idea

[miked]

Thanks Guys.

I feel a lot better now I don't have to pull it all apart. It is well sealed and not showing any leaks. I will order the kit and take my time doing it.

Mike

[Sea Ranch]

Now isn't that nice . . . I just feel, sort of, all tingly inside . . .

Seriously, this is such a perfect example of the beauty of the community that has grown up through this forum.

Beautiful cars, beautiful people . . . oh, oh, I'm getting all misty-eyed again . . .

Randy

[elanner]

Mike,

I had exactly the same experience of a thread feeling slack when removing a plug way back in the early '70s. That was one night's sleep down the drain. Anyway, I limped the car to a local garage and they popped a helicoil in without a second's thought. I was mightily impressed.

I've always assumed that I mangled the thread during the previous insertion. I guess aluminium is so soft that with a slightly worn thread it's easy to do. And I probably overtightened it (a curse of mine). Anyway, the episode taught me to treat plug threads with extreme deference. I will admit to not having removed the plugs from my Elan since I purchased it last Spring. I've not needed to, so am content to let sleeping dogs lie!

Nick

[twincamman]

I dont post much here anymore but in this case----- I suggest you remove the head to repair it . I have NEVER had success using grease to hold swarf . the head takes 20 or 30 minutes to remove and costs a head gasket .otherwise you run a great chance of trashing your motor -oh and the plugs only need about 10 pounds of torque --ed

[miked]

Thanks guys.

I too am alway careful and concerned about these threads, however I have seen varying sloppyness on twincam head plug threads and figure it was better going now than when at Classic Leman. Believe it or not I do not dog them up mega tight. Have not got history as a stripper.

I have investigated a bit more into the kits and see a better USA system and also German (I think) one's with seat cutter etc. I will invest in one of the more expensive better ones. Will report back for future reference.

Ed, It sure would be easier to effect the actual repair with the head off. I have been contemplating and worrying overnight and figure I will have a go. However if I have any doubt whatsoever that it is not clean, I will lift the head. I am paranoid anyway about bits dropping in so will not let it go. Who knows sometimes you only make these calls when you start the work. A spare head kit is not expensive. If I think the grease thing is a lot of trouble and not effective, I will just pull the head.

Mike

[elangtv2000]

I've made this repair to two aluminum heads - my old Isuzu Trooper, and a buddy's Lotus Twin Cam, both in situ.
Used no grease, only light cutting oil to install the full inserts with shoulder. Piston close to TDC to reduce spread of chips. Easy-peasy.
Taped a suitably-sized plastic tube to my shop-vac 2" suction tube, and sucked out the chips through the spark plug hole, which was easy to do because they collected in a small area on the piston crown, wetted with cutting oil. Used a fiber-optic viewer to inspect the piston and cylinder, and repeated vacuuming until there were no chips. Took 45 minutes the first time, 30 minutes the second time.
Drove the Trooper another 15k miles with no troubles before selling it, and the buddy's Twink is still going strong.
Greg T.

[twincamman]

I also have an optic viewer but I doubt many of the enthusiasts here have that extensive a tool kit . I prefer not to endanger the engines I have by using short cuts as I am not on the clock and do the work for the pleasure --and I sleep better not fretting about potential damage caused by short cuts as a result one of my twin cams is approaching 200 000 miles . rebuilt every 50 000 -ed

[elangtv2000]

Yeah, I can relate. The Isuzu head was going to cost me $3k for a shop to R&R the head, but after I talked with a couple of buddies who work as chief mechanics at Ford dealers, they told me that spark plug stripping is a common problem in one of the motors (V10, maybe?), and they do this same repair without removing the head every week. Turns out there is a special kit just for the Ford motors that have this weakness. The main concern I had was getting the chips out, but it turned out there were very few chips, and they landed all on the center of the piston, so plenty of judicious vacuuming later, no chips.
The Twink was way easier than the Isuzu - plug hole in the middle, easy to see in, good size piston to catch the chips, vacuuming tube went straight down to the piston.
There are shortcuts, and then there are shortcuts...

[Elan45]

I had to repair all 4 plug holes in my Lotus Eleven's original Climax FWA in the late 80s. I borrowed a Helicoil kit and bought a set of inserts. I raced that engine for a couple more years until I built my FWE. No problems at all.

Later, on the FWE, I had to make a repair insert for the 1/8" BSP oil pressure location on its head. Try finding a repair insert in BSP!

Roger

[miked]

I did it last night! Bought the Bergen unit kit with inserts. Like the Time Cert USA one. I took my time over a couple of hours. This kit does not need a drill, it has a stepped tap. This worked great. I must have had it in and out about 9 times to clean the flutes and re grease. Cutting compound worked well. Yellow melted butter type stuff. Filling the flutes gathered about 98% of the cutting debris.
The nervy bit is the stepped seat cutter that comes with the kit. It also cuts a profile for the insert return lip. You have to get quite deep before the second blade contacts the plug washer landing. This takes a nice cleaning shave off to give good seat for the plug washer.
I used the vacuum with various size pipes and tubes to vac out. Plug hole is biggest before the insert goes in! Piston needs to stay down (not TDC) as the step tap stays in when seat cutting and acts as a guide/centre. You don?t want to hit the piston while cutting.
I got hold of an old endoscope from work and checked. Then sprayed some brake cleaner down the plug hole and did the vac again. Even opened the inlet valve and sprayed down there. At the end I opened the exhaust valve and blew compressed air thro? the plug hole and out the exhaust. Clean as whistle. Even had the lad, with better eyes than me on it. Could see nothing but clean.
I had to buy Loctite 272 (high temp, ?35 delivered) to glue the insert in. The tool put this in nice and then slacked off to leave it there. Wiped up the excess and left to go off over night. There is a finishing tap with the kit to run though incase you spill glue etc. Will do that tonight and examine for debris and vac and we are in business again. I took the camera in to Photo but the batteries had gone again. Will post some shots of the kit and the repair for future reference if you are unfortunate enough to be on this thread with a problem.

Top tips.
Work slow, use the yellow cutting compound (you can see the chips) and keep pulling the tap after about 1 turn to clean and re grease. Watch were piston is, you could hit it.
Re: Plug seat cutter, go very steady with ? of turn a time until you form a circle cut, no low spots. This is the bit that took the time.
PS the most debris was from the old plug hole threads, before I started. This was removed first with the vac. They were obviously quite large circular pieces.

Mike

[Stuart+2]

Mike many thanks for this information.
I found the thread of my no. 2 plug had all but gone on a recent plug replacement - I knew the day would come as a PO had over tightened.
I also used the Bergen kit which was excellent.
I bought an excellent bore scope to make sure I picked up the swarf with my adapted vacuum cleaner rather than grease the tap as that could make pieces that did drop in difficult to get out.
A really rewarding repair - always good to have another addition to the toolkit as well!

Cheers

[miked]

Hi Stuart,

Great, it is good to write stuff up and gather the input at the time. I agree very satisfying.

Mike.