heli-arc plug hole???

j.hall · 07-03-2006, 09:52 AM

A past owner installed a helicoil on #4 cylinder. When I was changing plugs a while ago it backed out. I installed a thread insert and had enjoyed 700+ miles without trouble.........until last night! The hole is now too big for an insert.
I would like some input on heliarcing the plug hole and retapping. The head will be removed (of course). Will this warp the head?
Any thoughts would be great.
Thanks, joe

69-912-swt · 05:32 PM

All late model 356's and 912's had helicol spark plug holes from the factory. It probably needs to be welded and drilled. You will need to check both heads for cracks while the motor is out. Also might as well get the valves done with new valve guides. No telling what else needs cleaning up IE. valve tubes seals, gaskets, rubber hoses, exhaust gaskets, clutch and more. Its a slippery slope once the motor gets pulled you never can stop.............................Make sure who ever does the heads KNOWS HOW TO WELD PORSCHE HEADS (only a handful of shops know how) or you will end up with a paperweight!!!!!!!

Bill

j.hall · 07-04-2006, 02:14 AM

Thanks for the tips and enlightening me on the factory installed helicoils. You REALLY emphasized having a Porsche shop weld the heads......what ARE the inherent dangers??? Also are the factory helicoils known for backing out?
I've done a TON of work to this car (theres not enough space to type it all in!!)........luckily I can do most of it myself. I'd never be able to afford it or drive it if I had to make an appointment and wait for each fix!
joe
'68 912
'64 356C Outlaw

lep · 07-07-2006, 08:06 PM

For welding, yes the head would likely need to be annealed (heated up) significantly and then welded. Welding any engine part, especially a head, without heating it up appropriately in an annealing oven will result in significant warping -- GUARANTEED. If this is not done carefully with annealing, you will almost certainly be asking yourself "now what am I going to do with a head that is warped?"

The downside is that if you didn't get it welded correctly you could put the head on, and won't seal correctly -- sounding like you have a blown gasket or something.

I learned the hard way - trust me - you have to really get it welded by someone who goes through all the detailed steps of ramping up the temp in an oven, taking it out of the oven and welding it, then bringing the temp down slowly.

Don't take any shortcuts on engine part welding, because it will actually cost you more time and money if not done correctly the first time.

It's been several years since I was in contact with a group in California who did this type of working on all kinds of older Porsche engine parts. If you want to pursue them, then reply -- even if you want to talk with them it would be better than letting some Joe weld your head.

Just tyring to help and save headaches -- hope you understand.

lep

j.hall · 07-09-2006, 02:20 AM

Thanks for your very sound advice. I used a product called EZLOK, they're an insert with micro-encapsulated epoxy resins on the threads. They start to set up right after installation and completely cure over night. www.ezlok.com
They have a heavy wall (3/4X16 external thread) and are head and shoulders above any over the counter thread insert. I put 300 miles on them yesterday...... time will tell.
Are the factory helicoils known for backing out? I can't be the only person who encountered this.

lep · 07-09-2006, 06:26 AM

Never used a heli-coil (never stripped a plug threading) but understand they have a long history of doing a good job. With the time and costs associated with pulling a head and having it welded/repaired in order to retool the spark plug threads, you should probably just stay with the heli-coil.

Remember, this is just a suggestion based on personal experience related to ways to keep workloads and costs down. If something works well, then leave it, otherwise if it breaks, fix it.