Flywheel Measurements and Pins

Switching to a aftermarket flywheel? Or perhaps you have acquired a flywheel with missing or removed "grub screws". I have taken a few measurements off the factory 87 flywheel which should assist in setting the screws to the correct height. This is important because the screw is what the factory sensor reads to determine engine position. If it is not set to the correct height you can get problems from erratic starting behavior to no starts. When setting the pins to the final height use some Loctite thread locker to ensure they stay at the desired height.

 

As a side note the stock flywheel has 3 screws, 2 on the same plane and 1 further back on a different plane. Most aftermarket wheels only have 1 screw. The stock Motronic engine managements uses a 132+1 setup. The 132 is the number of teeth on the ring gear mounted to the outside of the pressure plate, the 1 is the grub screw on the flywheel. So as it turns out 1 screw is all that is required as the other 2 are not used by the stock Motronic (I believe they were for a TDC sensor which was never implemented).

 

 

 

The SPEC scallop steel flywheel that will be replacing the stock wheel is pictured below. I set the pin tip to inside lip (a) to 119mm by adjusting the grub screw. Use some type of Loctite thread locker on the grub screw (I used the medium strength blue variety). The (b) measure was the same which it should be. The SPEC wheel overall has a slightly larger OD then the stock wheel, this results in the pin tip to outside lip measure being less than the stock wheel. If you had only taken the pin measure (c) from stock and set it for the new wheel the pin would have been 1.25mm too high.

 

 

To SPECs credit the new wheel comes with TDC markings already on it which is great. The upper mark where the factory OT and line would be is a little faint and I figured in a dark engine bay through the bell housing inspection port it might be difficult to see. I used a bit of pink nail polish to highlight the area.

 

Camera had a hard time picking up the engraved line for TDC mark but it is there.

 I also thought it would be worth mentioning here that SPEC flywheels made prior to May 2017 are the ones affected the increased diameter sizing issue. A secondary problem created by the increased size is in some cases it will create interference with the square wave signal the crankshaft flywheel sensor uses. Lindsey Racing has documented the issue here and offers a simple solution.