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Dr J Dr J is offline
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Join Date: Apr 2008
Location: Miami
Posts: 680
I'm a little behind on the write up (I have a deadline after all and have been out on too many trips!)

Here is the knock sensor work summary. With much appreciation for the input on knock sensors, I decided to continue with plan A of the knock sensor and keep the suggestions as plan B if I ran into any trouble. Fortunately, plan A worked.

I have received good suggestions on where to mount the knock sensors in this thread. I also read up on some old threads with recommended sensor locations. However, given how inexpensive the knock bridges were, I decided to use them.

The main problem was how to make the holes without removing the cylinder heads. Clewett says it can be done with an angle drill adapter so I went for it. The specific drill adapter I used was Amazon:

Originally I was going to get the snap on but they were taking too long.

It's nice that the kit has bits but I need a 5 mm (#9) bit to tap and thread the M6 bolt. I ordered one from:

First I ground flat the section of the cylinder where the bridge contacts the cylinder as there were raised numbers at that location in the cylinder. Then I drilled and tapped the holes. I mounted the knock sensors with no problem.

Picture of numbers that were ground off with dremel type tool.

For the bridge, the center to center distance of the bolt holes was 4.645". The lines at the center of the cylinders are pretty accurate indicators. The holes can be drilled 0.7 inch deep (I wouldn't drill deeper than 0.8"). The tap is 6mm-1.0. At 0.7" depth you should not need an end tap. The holes can be made 0.475" from the bottom of the cylinder wall, measured next to the heads. Too low and you would need a thinner angle drill to drill a horizontal hole. You can drill higher without fear of interference with the shroud. I took the drill hole guide provided by Clewett for the install of the cam sensor. I ground the edge to get the proper height for the hole. I pushed the spacer against the head to keep the drill as perpendicular to the head as possible.

Here is a picture of the angle drill adapter and the drill

This is a picture tapping the head.

Here are pictures of the finished product!

The part numbers are:
993 104 391 00 for the knock bridge (2 needed)
900 075 51801 knock sensor bolt (M8 x 30 mm) (2 needed)
900 074 015 02 knock bridge bolts (M6 x 30 mm) (6 needed)
N 011 524 27 knock bridge bolt washers (6 needed)
O 261 231 006 for the Bosch knock sensor itself

The torque spec was obtained from 993 torque specs (valid 1993-1998)

M6 bolts tightened to 7 ft-lbs
Knock sensor bolt to 15+- 4 ft-lbs

Two holes were made in the shroud with grommets to allow the wiring to pass through. I drilled two 1-1/8 in holes on the shroud near the knock sensors and used a large grommet which I slit to allow the wire to go through. This first grommet was large to cover the hole but also had a large center hole. I then used a smaller grommet, more like a rubber stopper to seal the center hole with the wire in the middle. This completing the knock sensor part of the project.

1979 SC, Slant nose wide-body cab conversion. AEM Infinity EFI. (Whipple Supercharger currently off for rebuild)
Old 08-03-2017, 01:11 PM
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