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Besides the cool factor and simplicity (which are totally fine reasons for wanting stuff) can someone help me understand actual failure points for a road car that lead people away from stock?
belt tension gauge fails
fan bearing fails
others?
Coming from earlier 911s I am just used to eyeing the belt and temp gauge regularly as part of life and getting reasonably quick at belt changes / tension checks. Yes I realize there are now two belts but unlike other such things such as changing a dual dizzy belt, the two belt setup is very not scary to me from a maintenance standpoint.
I don’t have the Clewett Belt but removed my large harmonic balance pulley 4 years ago and replaced with a smaller crank single belt pulley system. I have had no issues with engine at all. DE and AX car, engine idles smooth and rev’s very fast ( I think duhttps://rennlist.com/forums/964-foru...l#post12172584e to the LWFW and the light weight smaller pulley.)
Great feedback, thank you for responding Gus.
Originally Posted by r-mm
Besides the cool factor and simplicity (which are totally fine reasons for wanting stuff) can someone help me understand actual failure points for a road car that lead people away from stock?
belt tension gauge fails
fan bearing fails
others?
Coming from earlier 911s I am just used to eyeing the belt and temp gauge regularly as part of life and getting reasonably quick at belt changes / tension checks. Yes I realize there are now two belts but unlike other such things such as changing a dual dizzy belt, the two belt setup is very not scary to me from a maintenance standpoint.
Failed bearings (I’ve suffered two, and run with RS fan hubs which are awesome, and stock)
Failed belt sensors (there’s no tension),
Fan belt failure (and cutting A/C belt to get there)
Weight savings
The Clewett system reduces the risk of a belt failure, and replacing the belt takes minutes instead of an hour. Belt failure can be catastrophic if not addressed in time. I’m fine with carrying a bunch of tools and spare belts around, but why risk losing an hour at the track or an autocross event, or worse...
Engines pulse and aren't as smooth running as we think. That is why when switching to the RS LWF we use a springed clutch setup vs a solid disc. This absorbs those pulsations. If you don't use the springed clutch the pulsations move down the line to the transmission and I have seen the bearings go prematurely.
There are many differences between the 964 and 993 engines. The crank, rods, heads etc are all different. Porsche reduced the tolerance from (Don't hold me to exact numbers) something like +/- 9 grams per side to something like +/- 3 grams per side and all this makes a difference. Even with my 993 engine I had everything balanced through to the flywheel as not to have any issues. You can try removing it if you drive lightly around the street but I am constantly pushing my cars and I want longevity as much as performance.
Engines pulse and aren't as smooth running as we think. That is why when switching to the RS LWF we use a clutch setup vs a solid disc. This absorbs those pulsations. If you don't use the springed clutch the pulsations move down the line to the transmission and I have seen the bearings go prematurely.
There are many differences between the 964 and 993 engines. The crank, rods, heads etc are all different. Porsche reduced the tolerance from (Don't hold me to exact numbers) something like +/- 9 grams per side to something like +/- 3 grams per side and all this makes a difference. Even with my 993 engine I had everything balanced through to the flywheel as not to have any issues. You can try removing it if you drive lightly around the street but I am constantly pushing my cars and I want longevity as much as performance.
Hearing concerns from knowledgeable folks like you Cobalt, certainly has my attention. But my harmonic balancer is beat to hell and it’s clearly out of balance now. And the prospect of losing 6 lbs, 5 oz. where it matters most is enticing.
I drive lightly on the street, but I also drive the snot out of the car at several DE and AX events each summer. But as taught in DE, I try to be light on the car especially with regard to shifting. I will be more careful now based on your comments about the 964 drive train. Thanks for the feedback.
Originally Posted by Peteinjp
I think Clewett should make a version that used the harmonic balancer and just replaces the double pulley with a toothed one. Best of both worlds.
pete
Given the condition and the weight of my 30 year old harmonic balancer, I’m kinda glad that Clewett has a nice lightweight pulley. At 6 1/3 lbs., the weight of the harmonic balancer is staggering, and it’s in the absolute worst location behind the engine.
I contacted ATI racing to buy one of the harmonic balancers. They told me that Gamroth buys directly from them and machines his own pullys to interface with the balancer. I called Gamroth and he does not offer the product. I called ATI back and they said they had no one to distribute their balancer for Porsche specifically fo the 964 and that they currently had no plans to offer a specific pulley balancer configuration for us. Sucks, I now, but such is life. I have a Clewett system ready to mount and contacted Gamroth for the balancer pulley option form ATi. No go was the answer. Gamroth builds only for his specific engine projects. I bought my Clewett system used from Rothsport (Gamroth) hoping that I could also source the harmonic balancer and pulley from him.
The stock balancer is a 3 part affair: the hub that bolts to the crank, the harmonic balancer which doubles as the a/c pulley and finally the double pulley (fan/alt) that is sandwiched between the hub and the balancer. What I'm saying is what about the possibility of machining the clewett pulley to bolt between the stock hub and the balancer in place of the dual row pulley? For those of us that want the serp belt with a harmonic balancer this would be a possible solution. In Jim's case he'd be throwing out the bent part of his pulley. The unknown is whether or not the offset will line up and if not between the lower and upper bullies -if not then maybe Clewett would be willing to produce a pulley with the proper offset and bored to fit the stock hub. Needless to say the unit should balanced after assembly.
All I have to say is that I have installed this kit on both my 993 engines in the past and will be installing a THIRD kit on my current car soon. This kit is refined, functional, reliable and what I believe is to be the only ''care-free'' single belt pulley conversion.
Based on the 993 RSR system which is not available to buy, the design is one that is proven to be the most modern aircooled pulley setup that Porsche had used before changing to watercooled engines. The conversion makes most sense when AC has been deleted and no other belt is needed in my opinion.
Price is the only real bummer as the kit is basically a Gates belt and tensioner from some other automobile application along with the pulleys and small bracket Clewett makes (which no doubt required R&D).
Based on the 993 RSR system which is not available to buy, the design is one that is proven to be the most modern aircooled pulley setup that Porsche had used before changing to watercooled engines.
The pre-MY97 993RSR that used the 964 crankshaft required the harmonic balancer from the 964 Turbo.
All I have to say is that I have installed this kit on both my 993 engines in the past and will be installing a THIRD kit on my current car soon. This kit is refined, functional, reliable and what I believe is to be the only ''care-free'' single belt pulley conversion.
You were one of the reasons I finally decided to install the setup in my 993 5 years ago. Love it.
Since then, I’ve installed five other Clewett setups for nearby Rennlisters.
03-14-2020, 10:25 AM
