What thread is a knock sensor?
 

Got a new Dart gen 6 block and its not drilled for the knock sensor,anybody know what size thread it is?

I'm guessing it 1/4 npt?

Thanks

Yes, it fits in the water drain hole in the side of the block.

I noticed it did screw in,just want to make sure before I go to drilling on a new block

Rob

are you saying it goes in the water drain hole,i dont think so.

Some people put them there, I wouldn't, I just said it would screw in and it's the same size. Could make a bushing for the hole that is used for a clutch set up in a car.

on every ski boat with efi that I have worked on the knock sensor was screwed into the drain hole on the side of the block. they all came that way from the engine builders.

We put them in the drain holes on just about every engine we do. Nothing wrong with putting them there.
Eddie

Thanks for the replies

I really dont want to put it in the drain,Every time I rebuild the engine I remove the knock sensor and the built in nut spins and rounds off, have to use channel locks it remove,maybe im screwing it in to tight,but I assume its bad after it spins.

There is 2 blank boss's on the side of the block I could drill and tap,also the clutch pilot hole I could inlarge and install it there.

Rob

fixx
 

their should be a 1/2''or 9/16'' hex on the under side of the knock sensor,,thats where i tighten from..ya its a stupid place for it,,then they get all rusty and throw a service code..

I dont recall one under the head,I allways got it from Merc, maybe a non merc is diff? Ill look again

Rob

fixx
 

how come you didn't get the steel main caps?

Knock sensors are very sensitive, It is very important that the knock sensor be torqued to the exact specification. Incorrect torquing will result in unsatisfactory performance.
Do not use sealer on threads.
Install knock sensor in engine block. Torque to 12-16 lb. ft. (16.3-21.7 N·m).

Depending on the old engine application the knock system came off of, You might be able to install the knock sensor in the upper location on a Y-fitting to use as a block drain as well for winter time.
Merc part number 22-8067051, Item #12,
http://www.mercruiserparts.com/Show_...rs+and+Sensors

See page 4B-22 for the idea,
http://www.boatfix.com/merc/Servmanl/16/16B4R2.PDF

well i stand corrected,you learn something every day on oso.

The last engine I built, I retapped the threads on the knock sensor to 1/2x13 and screwed it in the hole for the clutch pivot ball. I was not sure if it would work or not, but while dyno tuning we could see it working fine.

retapping the threads might work ok.

lakematdude ive been over tighting them then,never knew the spec's,thanks

this is the one that came out,and it is a merc part

Rob,
I understand it’s difficult to photograph machined surfaces due to shadowing, however, does picture two accurately represent the surface finish of the deck?

Bob

Here is one other option Rob. I have run into a few situations where we couldn't put the knock sensor in a pipe plug hole. I made an adapter to mount it in a bolt hole. This particular one is 1/4"-20 thread. I've done them in 5/16 and 3/8 thread as well. It's made from 1" aluminum bar stock. I just turned it down on the lathe, cut the threads and then drilled and tapped the 1/4"NPT for the sensor.
Eddie

as far as I know this is the only gen 6 block they make,price was close to the same as a new GM gen 6,this weighed alot more than the GM and looks like higher grade materal.The stock block was holding up good and still had a good leak down.Im having to buy new Whipples and the new ones will have 1 psi more, so Im going to turn it down some .really didnt have to have it.Im building it back just like it was,just all new guts.:drink:

Rob


Eddie would the aluminum change the frequency of the detination to the knock sensor?



heres a pick of the 2 blank bosses,

It doesn't change the frequency of the sensor, but it will effect it's sensitivity. The GM knock sensor that Merc commonly uses has a frequency of 10.5kHz. Different block locations can change it's sensitivity, putting them in brass y-blocks, etc. If your EFI system isn't capable of fine tuning the sensitivity then sometimes you have to move them around or use adapters to avoid detecting false knock. The block will drill and tap pretty easy, I'd put it there if you don't want to use the drain hole.

Yes I am having to have it redone:(

I think im going to put it in that boss,try to drill it and tap it the same as the factory other block,Figured Id start there .that should be the closest to factory as I can get. Only difference is the block is a denser better material,its diffidently heavier than the GM block,

thanks for all the help

Rob:drink:

I drilled the boss, it drilled real easy,tap bottomed so it doesn't thread all the way,but its enough.

just need to figure were to put the oil sensors now

Thanks
Rob

Bringing up an old post....
I have a 94 454 mag efi I am replacing my knock sensor. could I use a knock sensor from a 94 454 chevy 3500 truck or will the frequency detection be different or not read properly to a merc knock sensor? Would it work the same and be a lot cheaper?