jungt

Does anyone know the exact dimensions for the 2 idler rollers for the serpentine belt. I have heard around 80 mm, but I am not sure.

John

jungt

Sorry, I need to be more clear, I only need the outer diameter. Dayco have some idlers that are advertised on Ebay for the 996 TT at a price that these items should be at, and I would like to make sure that they are not too small.

John

Macster

Outside diameter of the old idler/tensioner rollers from my 03 Turbo are all 3.1535". ("3.1535" is an approx. dimension using a Bosch/Lomb dial caliper (in the shop we called these a guessing stick). The rollers could have a bit of wear say new they might measure 3.1562 or 3 and 5/32".

jungt

Thanks Macster, I went ahead and purchased a used one and measured it. It is 80 mm in diameter which corresponds to your dimension. That Dayco's are listed to fit a 996 Turboo, however they are only 70mm. They are the correct width however and would probably work. They would just spin faster, however the extra 5 mm in radius would probably not affect the tension?

Thoughts

Macster

Smaller diameter idler/tensioner rollers would spin faster. Bearing speeds then would be higher but how much higher I can't say. I have not worked the math.

Well, I just made a stab at it and the rotational speed of the 70mm rollers would be 114% of the rotational speed of the 80mm rollers. That doesn't sound like that big of an increase, but I do not know what the bearings are rated for. I'm sure they can handle more RPMs but their service life may be shorter and the decrease may not be linear.

There is the issue about slippage. Smaller rollers would have less area in contact with the belt and these could slip rather than spin. Maybe not all the time but upon hard acceleration/de-acceleration of the engine which could shorten belt life.

Also a big concern would be the affect of smaller diameters on the tensioner's tension on the belt. This would be less and that would really worry me.

Why not just buy the standard idler/tensioner rollers? There are several parts suppliers (Pelican, Suncoast come to mind) that you can use and probably get the factory parts for a good price. With just a PCA membership I get these at 15% discount. (My Boxster has never needed these in over 286K miles while the Turbo has required two sets in 125K miles.) Why risk running smaller parts and dealing with incorrect belt tension?

jungt

Thanks again, I was able to source 2 OEM roller for $25.00 apiece surplus, so I am good for now. The price for the Dayco's was $28 delivered on Ebay. It was tempting from a troubleshooting standpoint since I have some noise that seems to be coming form something driven by the belt. It appears to be the steering pump, but I plant to check all of the other belt driven parts as well.

BTW, the cheapest I could get new rollers was from EStuning at $98.