Lower Fan Pully

Jeff Higgins · 08-13-2004, 05:40 AM

Is it possible for the lower, crankshaft mounted fan pully to slip on the crank? I have checked every reference I have from my Haynes manual to Wayne's engine rebuilding book, but cannot find a drawing or photo to show what indexes that pully. These books do reference a dowel pin, but none show how it is fitted. Is it possible to shear this pin, or to have it fall out, or otherwise allow the pully to slip? The reason I ask is that I went to tune the car up the other day and checked the timing before I started. I have a '72 911T with the 184-001 distributor fitted with the Pertronix ignitor. It's supposed to be timed at 5 degrees ATDC with the vacuum hose hooked up at idle, initially, then 35-38 degrees BTDC at 6000 rpm. It's not even close on either count, but it runs great. When I attempt to time it to the idle marks the timing is so retarded that it spits back through the air cleaner at idle, and will not take any throttle to even be able to check the 6000 rpm advance. Luckily I made note of where it was before I started and simply returned the timing to where it was and it runs great. Any thoughts?

chuckw951 · 08-13-2004, 06:18 AM

I can't answer your questions, but here is a pic of an 82 lower pulley. You can see the pin. Not sure if it is removeable or not (or if early/late pulleys are the same or similiar). Wish I could be more help.

Grady Clay · 08-13-2004, 06:32 AM

Jeff,

What year is your car? A/C?

Yes, that pin indexes the pulley. If everything is in good condition it is remarkable accurate (+/- ½ degree or less.) You should always check for any rotational play with the bolt just barely snug.

If you have a pulley – crank that is sloppy or somehow out of index from some PO, it is relatively easy to re-index the pulley when assembling an engine. The critical issue is to determine TDC with a dial indicator on the #1 piston and the cylinder properly secured.

If the hole in the crank is damaged, I prefer to drill a second index hole about 50 degrees from the original rather than try to repair the hole in the crank or use a larger pin. If the pulley is damaged, just replace it.

Best,
Grady

djmcmath · 08-13-2004, 06:45 AM

Just for my own edification, can anyone explain what that particular pulley has to do with timing? I thought these cars had timing chains that were driven internally, and that the pulley in question merely pulled the fan, alternator, and A/C (if installed). Maybe I'm thinking of a different pulley????

TIA,

Dan

Rot 911 · 08-13-2004, 06:47 AM

Quote:

Originally posted by djmcmath
Just for my own edification, can anyone explain what that particular pulley has to do with timing? I thought these cars had timing chains that were driven internally, and that the pulley in question merely pulled the fan, alternator, and A/C (if installed). Maybe I'm thinking of a different pulley????
TIA,
Dan

You need to have the pulley properly indexed so that when the Z1 mark is lined up you are actually at TDC!

Grady Clay · 08-13-2004, 06:58 AM

Kurt is right on.
That accurate index on the crank pulley is what you use to set cam timing, MFI pump timing, and ignition advance. If the Z1 mark is off, nothing else is timed correctly.

Best,
Grady

Jeff Higgins · 08-13-2004, 07:40 AM

The photo really helps; thanks. I kind of suspected the pin was captured under the washer when the center bolt is tightened down. Grady, the car is a '72 with no A/C. Is there a way to get to that center pully bolt without dropping the engine? I'm at work so I'm going from memory here, but when I was looking at it the other day, it did not appear that there is an easy way to get at the pully. It looks like that might be where I need to start; I suspect the pin might have sheared off. The pully itself appears to be tight, i.e. I cannot wiggle it by hand, it runs true without wobbling, and when I pull all the plugs I can rotate the crank using the fan pully bolt, indicating neither the belt nor the lower pully are slipping. So assuming I can get at the lower pully, I should be able to re-align the dowel holes and re-pin it if the holes are good or drill a new one, and it will be re-indexed. Hopefully I won't have to drop the engine to do this...

djmcmath · 08-13-2004, 08:12 AM

Quote:

Originally posted by Kurt V
You need to have the pulley properly indexed so that when the Z1 mark is lined up you are actually at TDC!

Oh right, yes, of course. I'm a dufus and I knew that. Thanks!

Dan

Grady Clay · 08-13-2004, 08:42 AM

Jeff,

Yes, it is possible to remove and replace your pulley without disturbing the engine mount. It appears you may need to remove the engine mount completely to address this problem. I would remove the pulley first for inspection and diagnosis. It might turn out to be an easy fix.

Your first mission is to go to a 25c wash and get the mount/pulley area very clean. Next, you should check your ignition timing and MFI pump timing and record what it is on the pulley. Don’t re-time anything.

If the crank-to-pulley index is damaged you will need to determine TDC on #1 or #4. This is not as easy with the heads on. I have a sparkplug body with a 10 mm bolt threaded through it. The end of the bolt is carefully rounded. It acts as a stop against the piston somewhere (45 degrees?) +&- of TDC. With a degree wheel bolted to the pulley end of the crank, you can find TDC within a few tenths of a degree. This is not a particularly elegant solution but works well with care. Always disconnect the battery and remove all the sparkplugs before this. Triple check that you have removed the stop before reconnecting the battery. Be very careful when rotating the engine forward and backwards to the stop, you do NOT want to damage the piston. Pay attention so the stop can’t contact a valve.

To rotate the engine; a useful way is to put the transmission in 5th, lift one rear tire and rotate it to move the engine. Be careful because you have lots of gear ratio there.

If you must replace the crank pulley, you might consider replacing it with the 134 mm crank pulley from a ’78-’79 SC to gain more engine cooling - if needed. This situation takes a non-standard length, but readily available fan belt.

Best,
Grady

Jeff Higgins · 08-13-2004, 09:31 AM

Thanks, Grady. That sounds pretty staight forward. My biggest worry was gaining access without dropping the engine, but it sounds like I can do that. I'll be sure to put some temporary timing marks on the pully before I remove it so I don't completely lose where it's at right now. Hopefully I don't have to go through finding TDC to finish this. Would Porsche have done something really simple and obvious like putting the index hole in the crank at TDC for #1, or at least at some known offset from TDC? From the photo above that Chuckw951 supplied, it looks like there are two timing marks (Z1 TDC and 5 degree marks) at about 1:00, with the pin at about 4:00, for a 90 degree offset. Could it be that simple?

Rot 911 · 08-13-2004, 09:38 AM

Even if you do have to drop the engine you won't have to pull it out completely. Remove the back bumper and rear valance. Remove muffler. You can now lower the engine enough to get unrestricted access to the pulley.

Jeff Higgins · 08-13-2004, 10:02 AM

Thanks for all the help everyone. I'm heading out for a four day backpacking trip with my son, so I won't be able to check this thread until next Wednesday. I'll start tearing into it when I get home and let everyone know what I find.

Grady Clay · 08-13-2004, 10:06 AM

Jeff,

I actually don’t remember. That is a good question.

Most rebuilds we also painted and dimpled the flywheel, more precise on our engine dyno. Some 911s and all 914-6s came marked. You can only see the marks through the notch in the top of the transmission.

Before you start I would be prepared for all eventualities:
How will you remove the sheared off pin from the crank?
Can you repair the pulley? How?
Can you get a new pin? Sizes?
Do you have a spare pulley available somewhere close?

Some “while you are there” might be the gasket on the jackshaft cover, new fan belt, inspect the fan pulley and hardware, etc. How long since the tensioners and chain ramps were inspected/replaced?

You will need to remove the muffler and the rear tin. Remember you can’t lower the engine much without stressing wiring harnesses, fuel lines, shift linkage and more. Depending on your tools, you may want to remove the license plate panel.

Best,
Grady

Rot 911 · 08-17-2004, 05:53 AM

Glad you came back and gave us an update. While it was a PIA at least you didn't have to modify the pulley and end of the crank!

Amac · Amac's Garage

Jeff,
I was having the same type of problem
with my track car last year.
The bolt holding the pully on would back
off making it sheer the pin and slip.
I would loosen the motor mount on each
side put a jack under the motor and remove
the center mounting bolts. Drop the motor about
4" and remove the plate covering the pully. You will
have some rear engin tin to deal with.
If the pin sheers you can usually pull it out of the crank
with a magnet.
I'm not running a muffler on a single turbo so it was
easier to get to. Now I have a hole cut in the cover
plate for fast excess without dropping the motor.
Use heavy duty loctite on the bolt, it will never happen
again.
You can get the pin at your local Dealership, PP may
carry it.