Underdrive Pulley Questions

[BYprodriver]

Originally Posted by DRGETZ

Considering Pedro's Underdrive Pulley Kit but read that IMS Bearing Replacement should be done before because of the need to shave down the "boss" or Top Dead Center bolt receiver/holder/whatever (not sure of technical term).

Can someone elaborate on why shaving down the "boss" may make this more difficult?

Can enough of the "hole" be left intact to use it as a TDC guide?

Any other problems experienced as a result of an Underdrive Pulley Kit?

Recommend any other kit over Pedro's and why?

Thanks in advance.

the 4" diameter pulley blocks theTDC locking hole making it difficult to lock drivetrain @ TDC which is critical for successful IMSB retrofit.

[DRGETZ]

Can't one just install the OEM pulley prior to an IMS Retrofit?

Is there an alternative to using the boss for TDC work and is it a substantially more difficult task?

[JFP in PA]

Originally Posted by DRGETZ

Can't one just install the OEM pulley prior to an IMS Retrofit?

Is there an alternative to using the boss for TDC work and is it a substantially more difficult task?

Problem isn't the pulley on many models, it is the amount of the boss you need to machine away.

[DRGETZ]

Can you recommend one requiring less shaving than others?

[JFP in PA]

Originally Posted by DRGETZ

Can you recommend one requiring less shaving than others?

We do not recommend any of them.

[Topless]

My 986 had an early RSS underdrive pulley installed in 2009 while shaving off just enough of the timing boss for clearance. When we had the IMS retrofit done a few years later we simply re-installed the stock pulley and everything held together as it should. I had very good reliability with my accessories never overheating and the PS pump never leaked with over 100 track days.

Is it a perfect solution? No. Will it work if you are careful with your installation and save your stock pulley for future engine work? Yes. Shade-tree mechanics shaving down the timing boss smooth is the bane of every engine builder.

Never had a problem with overheating the motor and some have suggested that slowing down coolant velocity may actually improve cooling with longer contact time to absorb/release heat. Ideal heat rise through a heat exchanger or motor seems to be about 40F to get maximum heat transfer. Too fast or too slow and some efficiency is lost. I have not tested this in a 986 with any objective measurement tools, just familiar with heat exchangers and flow rates in my day job. The concept is plausible and my own experience was good.

[Ben006]

Originally Posted by JFP in PA

We do not recommend any of them.

Why?
Except the old lightweight ones that broke, everyone seems to be very happy with the results.

For the cooling system, the thermostat is what regulates the flow, the pump is always spinning fast enough.

[JFP in PA]

Originally Posted by Ben006

Why?
Except the old lightweight ones that broke, everyone seems to be very happy with the results.

For the cooling system, the thermostat is what regulates the flow, the pump is always spinning fast enough.

Two reasons: Quality and the lack of a TDC boss on many of them.

A couple of the alloy versions have been prone to cracking, which makes me weak. The lack of a usable TDC boss becomes an issue in the shop when we have to add a substantial upcharge to a repair because we now have to pull the new pulley, reinstall an OEM unit, and hope to Hell there is still enough boss left to hold the TDC pin during repair procedures. And when the DIY install chewed away too much of the boss, we simply have to charge the car's owner a bunch of $ only to tell him we cannot fix his or her car.

[Xpit77]

Originally Posted by DRGETZ

Can't one just install the OEM pulley prior to an IMS Retrofit?

Is there an alternative to using the boss for TDC work and is it a substantially more difficult task?

Thats what I did. Mantis did the ims and installed one of their pulleys.

[JFP in PA]

Originally Posted by Xpit77

Thats what I did. Mantis did the ims and installed one of their pulleys.

Depends upon the pulley used, and how much of the boss was machined away to gain clearance. Some people go overboard and do not leave enough to be useful, and some pulleys require more to be removed than others.

[Xpit77]

Originally Posted by JFP in PA

Depends upon the pulley used, and how much of the boss was machined away to gain clearance. Some people go overboard and do not leave enough to be useful, and some pulleys require more to be removed than others.

Mines a DD with a bit of tricks. Not a track or club car . I really dont care about that boss. I`m living on borrowed time with 144000 kms anyway.