CIS Air Injection Plugs - all are not created equally.

[RarlyL8]

As probably many of you have done, I removed the air injection lines that go into the heads of my '78 engine. They were plugged with M10-1 bolts. Apparently these bolts are not all created equally.

A couple of weeks ago I was tooling down the road when BLAAAAAAAAA!!! It sounded like I blew out an exhaust gasket. Real nasty. Well I had to go out of town the very next day and would be gone a week. No-one works on this car but me. If I need help I'll be right there in the bowels of the problem with whatever mechanic I choose to help me. Well this time I was stuck. I live in a new state 400 miles away from a trusted mechanic. So hastily I drop the car off at a local Porsche shop that I know very little about. Tell the guy I have no time to look at my baby but I think I've either blown an exhaust gastket or cracked an exhaust manifold.

Long story short, I had blown out one of those M10-1 bolts. I called my trusted mechanic back in Indy and told him the story. Apparently the only readily available studs that he recommends are those from a 914 rear brake bleeder valve. These same studs are also found performing duty as the drain plug on a 450SEL Mercedes tranny converter. These are female allen head studs. He tells me they are the correct length and also have a specific taper that allow them to stay put. Using any other type is not optimal.

To end the story, I called the mechanic and told him what bolt to get, where to get it, and what to do with it. I also asked that he go ahead and check the valve adjustment and change the oil sinse he already had the exhaust system tore apart. He pulled a lower valve cover and said the valves were just fine.

THIS TINY LITTLE BOLT ENDED UP COSTING ME OVER $300. PLEASE LEARN FROM MY MISTAKE.

[Jim Sims]

The air injector holes holes have straight v-threads; not tapered. The air injectors were sealed with copper sealing rings as should be the plugs or screws. Putting a steel tapered plug or screw into these aluminum threads will likely permanently deform the threads. The tapered plug or screw will probably not come out without damaging the threads. This will likely only matter if you have to reinstall the air injectors in the future to pass an emissions inspection/test. Cheers, Jim

[Jeff Alton]

I had this same problem years ago on an SC. Driving down the roas an all hell breaks loose!! I had just used some allen head set screws as plugs. When I got home I just put a little thread locker on them and never had another problem.

Jeff

[RarlyL8]

Jim - the "specific taper" that my mechanic called out may vary well be no taper at all. I do not know the taper qualities of the different studs. The point he made to me, and you are as well, is that these particular studs are the only ones you should use.
And yes, I can say with hat in hand, you are right about the incorrectly tapered studs damaging the threads in the head. They damaged mine. Fortunately not enough to warrent a thread repair.

[jay72]

Can somebody post a picture of what the proper screws look like.

Sloane

[RoninLB]

plug, copper ring, red loctite.

[carmad]

I got mine from Ted Robinson at German Precision in CA, no issues so far.

[beepbeep]

I've been using makeshift 10x1 bolts and blew them out many times before I bought correct emission plugs and fitted them with some Loctite.

Threads are not tapered. It's just a simple 10mm plug with 1mm thread pitch.

Correct blanks can be bought from www.type911.co.uk

This is how they look like:

[justesen]

Here's a picture of the plug and copper seal rings.



The din 908 plug in the center is preferred but the 910 plug will work as well just as long as you use the copper seal. The taper that is referred to is not in the threads but in the shaft of the plug, just under the plug head. It is there to "center" the copper gasket.

I got mine from Maryland Metrics.

Jay

77 911S 37,000 ORIGINAL miles

[jay72]

Thanks. I purchased a 930 with the air injectors removed. It looks like it has the same plug as the first one pictured. I cant see if there was a copper seal used. I may have to put the air injection back on and I want to make sure there is no damage if it doesnt have the copper washer.

Sloane

[john walker's workshop]

the first plug with the hex head is available from pelican for use in the 914 rear caliper adjustment holes. the second one looks like the stock 914 adjustment hole plug which tends to round out the allen socket hole because they get real tight. personally, i go down to the local auto parts store and get some 1/8" brass pipe plugs with a hex head. they are tapered, yes, but they fit well, don't screw up the threads and don't fall out. pretty much the same thread pitch. and who ever reinstalls the emission stuff anyway?

[David]

While I had my heads off I tapped the hole all the way through and made aluminum plugs to fit. Then I contoured the end of the plug to match the port. After reading this post, I will be safety wiring the plugs to an exhaust stud.

[89turbocabmike]

Nice David! That's taking it to the next level