I am pulling my 1999 block with large
threaded knock sensor and going to install a 2001 block with
smaller threaded sensor.

Knock sensor
19xx to 2000 Blocks
Uses a 1 wire with a large thread in bolt around 1/2" to 5/8"

2001 forward Blocks
uses a 2 wire with a smaller threaded bolt 1/4"

I have read...
1. Can Drill & Tap smaller hole to fit 1 wire larger sensor.
2. Can Use Blue wire and ground Gray one on the sensor.
3. Use a reducer - large female size to male 1/4 and
thread into 2001 block 1/4" small hole.

Pics I have found attached with my notes.

Thanks for any input on this, I know I am not going to let
a damn 1/4 hole size change stop me from getting that 2001
block in my 1999 Blazer.

Bill

 

Anyone ??

 

I'd go with option 1. Drill and tap the hole and keep everything 1999. Option 2 is easier if you're sure it will work. Option 3 I wouldn't do because I'm too fussy. The piezoelectric crystal in the knock sensor produces electricity when shaken. Raising it's mounting point even that little bit may create a pendulum effect where it's moving farther than it would in the stock location. I don't know if they are that sensitive, but I know my luck when I try to take the easiest way.

 

Thank you... I am leaning that way as well, ..not to mention..
If option 2 didn't work it would be a mission impossible to
drill tap after motor was back in.

 

FYI


1 wire sensor is 1/4" NPT thread

2 wire sensor is supposed to be 5/16-18 thread

Option 2 will not work - don't do it - check the wiring schematic.

Drill and tap the hole in the 2001 block to 1/4 NPT if you can, and screw in the 1 wire sensor. It doesn't have to seal - just be solid.

I have also recently heard of screwing the 1-wire sensor into the 1/4 NPT coolant hole in the side of the head and extending the wiring to that location.

 

Confused Les - Did you get sizes backwards ?


Did you mean drill tap 2001 block which is 1/4 already
to 5/16-18 thread for larger knock sensor size bolt ???

And -

?? - The 1 wire sensor 5/16 size.. would not fit in coolant
hole if coolant hole is only 1/4 ?


From pictures I have seen the (1999) 1 wire sensor looks like
a big boy around 7/8 or 1/2, hope to find out tomorrow
when my guy pulls it out of 99 block.

 

1/4" NPT (national pipe - taper) is considerably larger than a 1/4-20 or other similar straight thread since it is formed into the outside of a 1/4" pipe having a nominal outside diameter of 0.405".

 

1/4 NPT is larger than 5/16-18. 1/4 NPT is the size of the threads on a the 1-wire knock sensor used in 1999.

 

Ok kool I did not know that...

I was just going off standard bolt sizes,
was wondering what NPT stood for.