Help: Advice needed on 911 crankshaft

john_colasante · 01-08-2003, 09:39 AM

OK, I got a real problem here.

A few months ago I reported here that the crank pulley on my '85 911 had loosened up and started wobbling. The bolt that secures it to the crank had loosened up.

So, I removed the muffler, engine mount and sheet metal from the rear of the engine and I removed the pulley. There is a dowel that aligns the pully to the crank, and when the pulley loosened it gouged out the pulley which is made of relatively soft sheet metal. So I got a new pulley. The biggest problem I reported was that the dowel had "ovaled" it's mating hole in the crankshaft which is a very hard metal.

Upon reassembly I put some JB Weld into the crank hole so the dowel was straight, and then when everything was set I cleaned the internal threads in the crank carefully and bolted the pulley back on with the proper torque. I used some Blue Loctite on the thread too.

Just the other day when I went to start the car the alternator light came on and I heard a familiar rumble. I looked at the pulley and it was loose again! I have not removed it yet so I don't know what's going on with the dowel, but I suspect it's worked its way out again.

So, what are my options now? Do I need to redrill an oversized hole in the crank? There isn't much room for an oversize dowel in there because the threaded center is about 1-2mm away from the original hole. Can I drill into the crank with the engine in the car? Can I use a hand drill to drill into the hardened crank? Any ideas greatly appreciated on a more permanent fix. I know the dowel is necessary to index the pulley to the crank so the timing marks line up, but I wonder how important it is to keeping the pulley from "walking" and loosening. This seems to be important, and the JB Weld did nothing to keep the dowel from moving again.

john_colasante · 01-08-2003, 09:41 AM

Here is the ovaled hole.

David W · 01-08-2003, 09:50 AM

Idea:

remove the rear seal

weld up the over size hole. Go in spurts to keep the heat down

reinstall new rear seal

take a crank pulley to a drill press and remove the pin. (this pully will be scraficed (all pulleys the same, use a early single (used) pulley,) drill entirely through the pulley This pulley will be used as a template.

Install the pulley and align the hole to the welded up area. Tigten bolt enough to keep pulley from moving

drill new hole in crank (in weld area)

reinstall orginal pulley

Well, an idea

911pcars · 01-08-2003, 10:19 AM

John,
What is the crank pulley driving? Fan, alternator, air pump, A/C compressor? There's going to be less load on the pulley with fewer accessories to drive which may determine the ultimate fix.

Anyway, here's an idea; just an idea as I haven't validated it: Use larger dowell rod to fit the next oversized hole you drill into the crank. Dowell rod must fit tightly into the oversize hole; so use the correct size drill/reamer. The pin only indexes the pulley to the TDC mark. If it's off, you can determine TDC through other means.

Sherwood Lee
http://members.rennlist.org/911pcars

HawgRyder · HawgRyder's Garage

If it were up to me...I would simply use a stepped pin.
Drill the crank out to the next metric size....use a carbide bit...and then press a stepped pin (small side to pulley..large side to crank) and there you are.
Because you are drilling on the same centre...you should be right on for timing marks.
Bob

john_colasante · 01-08-2003, 11:33 AM

So you guys seem to think I can drill into the crank with the engine in the car with a hand drill? OK, I'll give it a try...

David W · 01-08-2003, 11:35 AM

I would still try to make a fixture to keep the drill straight. I like the strepped pin idea. have local machine shop make one

john_colasante · 01-08-2003, 11:54 AM

Wow, take a look at the photo. There is not much room there to make a bigger hole. It's paper thin.

Maybe I'll make the new hole 180 degrees away, and then drill a new hole in the pulley. The pin is removable from both the crank and the pulley by the way...

David W · 01-08-2003, 11:57 AM

yes, that is why I suggested removing the pin and drilling all teh way through to use as a template

john_colasante · 01-08-2003, 12:15 PM

David,

Thanks for the ideas. First, the hole already goes through the pulley. No need to drill it through. Also, it comes out with a tap as it's pressfit.

Once the pulley is on and the center bolt fitted, the bolt head covers the dowel.

I want to avoid welding on the crank. I don't think I can do that well enough. I can only envision making a big weld blob there. Which is why I'm thinking maybe a new hole at 180 degrees offset from the original of the same size.

My only question is can I really drill that crank straight with the engine in the car?

David W · 01-08-2003, 12:39 PM

without a fixture i don't think it will be perfect.

I like the 180 rotation. in fact the good thing about a 3.2, the timing is fixed so if teh pulley is off, no big deal (expect when cam timing).

Since it will be off anyway I might go 90 and try a hole using a used pulley (you have the risk of opening up the hole on yours). If it works great, if not, no great loss. use a 90 degree air drill

you could simply mark the drill spot with a punch but that would be harder than having a pulley as a template.

PS I forgot that the hole went through, I have driven out several as I have several early single pulleys I was plannig to use on my 3.2 race engine before i went crank fire

gregk1 · 01-08-2003, 12:44 PM

John can you drill the hole just enough to make it round and then have a pin made to press in the hole? even if it was an SAE size, then drill the hole in the pully to fit And maby you can just drop the engine down enough to get a stright shot at the crank You might have to take the rear bumper off,Just another thought Good Luck to you>>>>>Greg