Tom M'Guinn

So, on an 86 951, when setting the speed sensor gap to .8mm, do you set the gap with the little spacer ring installed under the sensor or not? I presume yes, but want to check...

Zero10

That is correct, one sensor should have the spacer under it, and since that is how they will be installed in the end, that is how you want to gap them

TRP951

Yup you got it, I notched my bellhousing so you can gap the sensors with just a normal feeler gauge

Tom M'Guinn

Where did you find a .8mm feeler gauge?

hosrom_951

Sharky makes a special tool for gapping the reference sensors......

Same gentleman who did those SS hex driven studs for exhaust headers and those SS rear hatch pins

Don't have his site with me at the moment.

Tom M'Guinn

Yes, I have it.

TRP951

Its a combination of a couple of feeler gauges to add up to .8 dont remember exactly which ones since the last time I touched the sensors adjustment was over a year ago.

theedge

A dime is the correct thickness as well.

jns

I cut off the round end on a crimp-on electrical connector. It was pretty close and fits the end of the sensor good.

F18Rep

Our you could just make a tool if ya have weldnut in that old junk drawer...Bruce

PS: a dime would be about twice as thick as you want.

xsboost90

a dime is twice as thick really? ive set a few of them w/ a dime w/ no problems. Guess i'll be calling sharky!

Tom M'Guinn

So, I'll install the spacer ring when I set the gap...

F18Rep

OK, if a dime works fine by me. I don't really know how thick a dime is but .8mm is .0315 inch which is within and RCH of 1/32 inch. A dime looks like it's pretty close to a 1/16th. I think (potential memory malfunction likely) the book say .8 mm. is what we want. You can see how my rickity thinking works, huh?

Related, someone here made an offhand statement a few months back about the sensor space affecting timing. I guess that could be true. All I know is that I just want a fat signal to kick the enable for the fuel pump. bruce

xsboost90

i have a custom modified dime that is shaved to .8mm specially made for porsche applications just like they had at the factory!!! Ok maybe not.

Zero10

Over-gapping the sensors will not affect timing, it will simply make the signal for the DME a little bit weaker. There is quite a bit of a margin for error when you gap the sensors, really any gap up to 3-4mm works. If you use a dime, great, if you use feeler gauges and set it to exactly 0.8mm you're picky, but great. The sensors simply generate a voltage from the changing magnetic field of flywheel teeth and little steel pegs going by them. The closer they are the stronger the field the higher the voltage. Also, the faster they go by the higher the voltage (and the frequency). IIRC at redline the voltage (peak to peak) on the speed sensor is something like 100-150V. When cranking I usually show 7-9VAC on the speed sensor with my voltmeter (which doesn't read square wave very well, so maybe it's more like 8-12V? or 5-7V?), that's how I double check my sensor gaps.