964 Pulleys - stock vs aftermarket
 

When I had my engine re-rebuilt, I bought the Patrick Motorsports alternator pulley conversion kit, which ties the two shafts together. On an impulse, I also bought the lower single pulley, which replaces the big triple pulley with a single lightweight aluminum one. It looks cool, but...

I don't like it.

When I ordered it, I asked if it affected cooling and charging at all - from the pic, it appeared to be smaller than the original. I was assured that it didn't, and they were running them on lots of cars down in Arizona with no problems.

Bullsh*t.

Here in Sacramento, with the ambient temps in the mid-50's, my car runs a lot warmer than it did back in October with the stock pulley, especially when I drive agressively, when the temps will climb up close to 200.

For fun, I disassembled the old pulley. It consists of a 'base', a collar (which actually attaches to the crank) and what I'm assuming is a dampening device, which is a super-heavy outer pulley (for the A/C) which is isolated from the other 2 with a layer of heavy-duty rubber.

Was there a single pulley available from the factory, if so, does anyone have a part #? Or how about one that just has the alt & fan pathways, not the A/C one? If not, does anyone have a spare 964 non-tip pulley laying around? Mine has a big dent in it, looks like it ran that way for quite a while, but I'd rather not re-use it in that condition.

Is it possible to change the pulley with the engine in the car?

Thanks!

Porsche did make a special pulley for the 3.8 RSR part number 964.102.150.20 but it takes around 15 other different parts to install it. It uses a different fan pulley since the belt is a special wider part. A special tensioner unit is required as well. $$$$'s galore for not much gain. The vibration dampener is a vital "designed in" part of the crankshaft unit that dampens harmonic vibrations within the crank assembly and shouldn't be changed without assurance the new part will do the same.

Cupcar;

There have been many theories as to why the damper is needed. The obvious is to remove the harmonics, however earlier 911 engines and the later ones do not have the damper. The rods are the same as 930 to 3.2ltrs. One thing that I have observed, my last 964 engine rebuild that I did, for kicks I checked the crank for straightness. The crank was slightly bent from the middle back. Prior to straightening we put the crank on a Schenk balancer, it was horrible. After straightening, everything was balance within a half a gram, the harmonics disappeared. I have since run that motor without the damper, I am running a Clewett Engineering pully.

Can you give me any details on that pulley?

Also, is it possible to replace the crank pulley with the engine in the car?

Thom;

It is a cnc'd two belt pulley anodized in black, with a smaller than stock diameter, which measures 4.970 inches, compared to the stock 6.125" pulley (second belt). You can replace the pulley in the car, however you need to drop the mount off, which requires lowering the engine, a little.

Kevin- To my knowledge no 911 Porsche other than the 964 has a vibration dampener. This is I think because the light crank in the 964 is comparitively not as ridgid given the reciprocating load it carries. The 993 on the other hand has no vibration dampener and Porsche redesigned the entire crank/rod/piston assembly to accomplish this. The crankshaft webs are increased from 7.9 to 9.4mm to stiffen the crank and it weighs 1 kg more than a 964 crank. The connecting rods in 993 are 112 gm lighter than 964, 993 pistons are 45 gms lighter than 964. The 993 crank pulley weighs in at 429 gm compared to the 964 dampener at 1161 gms. The net reduction is 818 gms for entire assembly without dampener. Point is that Porsche designed in the dampener for 964 and I wouldn't remove unless I were running 993 crank.

Cupcar;

I am aware of the weight reductions on the 993 rotating assembly and the fact that the cranks was strengthened, and with that point, the 964 crank, is weaker than other models and causing a harmonic vibration, There are many racers that have balance the complete rotating assembly and have installed lighter rods and pistons, thus changing the weight. Properly straightning the crank, with reducing the weight of it reciprocating and a thorough balance job, one can omit the damper. Most people have gotten rid of the dual mass situation at this extent of an engine rebuild, which would reduce alot of stress on the 964 crankshaft. I would agree with you that it would not be wise to delete the damper in a stock configuration.

Kevin-I think you are right, if assembly is lightened up, things are probably ok. Wish I really understood what was going on with these harmonic oscillations.

Well, this is a very old thread, but for me it is very timely...

My car is with my wrench right now for some unrelated service, and he called to say that it appears that the vibration dampener is no longer round and true. I don't recall the run-out measurement he gave me (18/1000ths maybe??) but he said he is very concerned that this will eventually fail, and that I should relace it ASAP.

He did have a couple 3.6 motors in his shop, but nether pulley was much better than mine to justify the effort. He said that there is a workshop manual procedure to literally hammer back to true, but he felt that this was false economy.

The bad news is, this is about $800 just for the part. Ouch!

So, is there anything anyone can tell me about this? Do I really need to replace it? I did a quick look through Adrian's book, but did not find anything in the index about this part.

Thanks for any info you might have!

Brian

The maximum permissible lateral runout is 19/1000ths so for $800 I would try the factory approach first (beat it with a hammer) and check it again with a dial-indicator ($20) a short while later. If the rubber chord of the vibration damper is busted the runout will go out of spec real quick and then you can drop/lower the engine and replace the pulley. Your not out-of-spec yet and Porsche does have a fix-it procedure.

Thanks Jason.

He did say that the pulley he had on his spare 3.6 was somewhere around 13/1000ths, so it would certainly be an improvement, but in his view, even that was more than he would like to see.

BTW, I am no way a wrench, and would not be able to identify the pulley even if someone had pitched it up side my head! FTR, he is a pretty honest guy, and I am sure he is not trying to hose me.

BGL

You're at the outer limit of what Porsche considers permissible but your still within spec. Using the repair procedure you could be closer to the median of Porsche's tolerance for runout and you won't have to drop the engine ($1000) and replace what could be a perfectly fine pulley ($800). The non-Bosch hammer approach given in the workshop manuals requires maybe ten minutes so there is no reason not to try it first. If it doesn't help then spend $1800 and replace the pulley.
http://members.rennlist.com/jandreas/Pulley.jpg

Dear Cupcar,
The 993 Carrera RS Clubsport has the vibration damper fitted as does the 993 Carrera Cup.
The 964 Carrera RS has a single pulley assembly as does the 993 Carrera RS and the GT-2.
I write about this in my 964 book actually and have continued the story with the 993 book.
The conversion to a single pulley for the 964 and 993 using the Carrera RS versions only requires a couple of changes.
If you go to www.p-car.com I think you will find the 993TT conversion to single pulley.
Ciao,
Adrian.

Thanks for the Photo Jason, now I know what the hell I need to be looking at.

And thanks also Adrian....I went back to your book, and found the discussion you mentioned (page 513), right?

I will be picking up the car tonight, with the pulley as is. Wether or not we are able to improve it with the use of a hammer, it appears that there is not a new pulley on the shelf anywhere in the US. I did find that Sunshine Porsche will sell it at a bit below $700, should I go that route, but its 4 to 6 weeks delivery from the elves at Porsche in Germany, unless I want to pay a 10% premium for 1 to 2 weeks delivery.

One more question...

My wrench insists that he he can change the pulley w/o removing the motor (a mount has to come off, along with some exhaust bits). Does that square with reality????

BGL

You do not need to remove the engine to replace the pulleys.
Ciao,
Adrian.