Is my Crank Sensor in the right spot? (Pics included)

[apocalight]

Hey all,

I am working on a Smallblock Chevy, aiming to use sequential spark and fuel via a 36-1 crank wheel, and a 1x cam position distributor from EFI connection.

I fabbed up a bracket for the crank hall effect sensor, but not sure if it is in the right spot, or needs to move up slightly. Also, it's currently spaced about .039 from the wheel. Is that appropriate as a good final spacing, or does it need to be closer?

It's pretty rigid. I can move it ever so slightly by hand with a good amount of effort, however I'm not sure how completely rigid it needs to be. I took some pics of the structure in case anyone has some suggestions. It's not pretty, but I think it will be functional. Any help is appreciated.

[billr]

That position and gap should work fine, although a bit tighter air gap certainly won't hurt. Actually the position doesn't matter, as it is set by you in software, and it all depends on where the missing tooth is relative to TDC, which you also set. Did you see in the manual that you want that missing tooth to line up with the sensor about (I was too lazy to look it up!) 45-60 degrees BTDC? That's kind of where crank speed is most stable with a V-8, away from variations due to compression and power stroke loads.

Edit: I would suggest a stiffer bracket. Even if that is steel, I think there is a chance it could start fluttering at certain vibration harmonics.

[kjones6039]

Hey all,

I am working on a Smallblock Chevy, aiming to use sequential spark and fuel via a 36-1 crank wheel, and a 1x cam position distributor from EFI connection.

I fabbed up a bracket for the crank hall effect sensor, but not sure if it is in the right spot, or needs to move up slightly. Also, it's currently spaced about .039 from the wheel. Is that appropriate as a good final spacing, or does it need to be closer?

It's pretty rigid. I can move it ever so slightly by hand with a good amount of effort, however I'm not sure how completely rigid it needs to be. I took some pics of the structure in case anyone has some suggestions. It's not pretty, but I think it will be functional. Any help is appreciated.

I use a very similar setup on my own sbc (ie. same location etc). Your bracket, as pictured, appears to be rigid enough although you may want to add a gusset if you are concerned about it flexing.

Assuming that you are using MS control, (ei. not EDIS), you should not need to move the sensor from it's current location. You can simply make an adjustment in TS/MS to compensate for the fact that the sensor is not perfectly aligned with the tooth.

Ken

[billr]

I also just noticed that it is slightly below crank center, so the sensor is not pointing exactly at the teeth. I do not think that slight off-angle is going to be a problem.

[apocalight]

Thanks guys! My main concern was about it being slightly below center, but if you don't think it'll be an issue then I'll try it like that.

I'll add some more bar stock to the bracket to stiffen it up. Originally it didn't have any and flexed a good bit, but adding that piece to the part against the block certainly helped. A few more pieces probably can't hurt.

[billr]

I just mentioned the bracket because a rock-steady crank trigger signal is such a fundamental necessity for all other operations. We see so many threads here related to people struggling with "lost sync" that I suggested eliminating any possibility of problem there. Your bracket may be OK as-is, but I would play safe there.

[apocalight]

Sounds good. I'd rather the bracket end up weighting 5 lbs than to be stranded or have it run poorly to save on weight.

[kjones6039]

My main concern was about it being slightly below center, but if you don't think it'll be an issue then I'll try it like that.

I will chime in here just one more time to reenforce Bill's point. I doubt that being just a bit above/below the crank center line would create a problem as a result of load on the crank. If the sensor were mounted at the 12 or 6 o'clock position, it might be another matter altogether.

FWIW, I think it's worth a try (in it's present location).

Ken

[apocalight]

My main concern was about it being slightly below center, but if you don't think it'll be an issue then I'll try it like that.

I will chime in here just one more time to reenforce Bill's point. I doubt that being just a bit above/below the crank center line would create a problem as a result of load on the crank. If the sensor were mounted at the 12 or 6 o'clock position, it might be another matter altogether.

FWIW, I think it's worth a try (in it's present location).

Ken

Can you elaborate on how a 12 or 6 position would affect it more (or perhaps less). Push come to shove, I can slot the bolt holes for the block and move the entire thing up a few mm. Just trying to avoid that at the moment.

[kjones6039]

Can you elaborate on how a 12 or 6 position would affect it more (or perhaps less). Push come to shove, I can slot the bolt holes for the block and move the entire thing up a few mm. Just trying to avoid that at the moment.

First, let me clear! I am not suggesting that you need to change your sensor location. Quite the opposite! In fact, I would not move it if it were mine!

It is my belief/understanding that, due to crankshaft flex and bearing clearances, the crankshaft may move a very small distance, under heavy load. This movement would generally be more in the vertical axis rather than horizontal (unless of course, you have one of those funny looking horizontally opposed motors! ). Furthermore, I seriously doubt that such a small movement would have any effect on sensor clearance.

From my earlier post:

If the sensor were mounted at the 12 or 6 o'clock position, it might be another matter altogether.

FWIW, I think it's worth a try (in it's present location).

In my case, my sensor is located ~15* below the crankshaft center line (9 o'clock). and has never suffered any ill effects from being installed in that location.

My suggestion........ quit worrying about it!

Ken

[billr]

Ken, I think the OP's concern is not the "clocking" of the sensor but that its axis is not on a true radial pointing toward the center of the crank; the sensor face is not truly tangent to (a circle concentric to) the wheel teeth sweep.

[kjones6039]

Ahhhh....... Got it, Bill!

In looking at the pics again, I doubt that the small angle I see there is likely to create any issues for him.

I couldn't swear that mine is aligned any better!

Your thoughts?

Ken

EDIT: I am thinking that it might be possible to just tweak the bracket and then reenforce it, without having to move/refab the bracket.........

[billr]

I agree with Ken: the bracket could probably be tweaked, it probably doesn't matter, and mine may be no better! I'm glad Ken was able to understand my awkward explanation of the alignment concern...

[omniserv2]

My concern would be the vibrations that might cause the "U" shape bracket to break or come loose. It might be better if a flat square were welded on top of the "U". This would stiffen up the bracket without making it weigh 5 Lbs.

You need to keep the weight down on a bracket like this as much as you can. Unless you use a larger gauge of metal.

[velyse]

Hello gentlemen, not to thread-jack but I do have a somewhat related question. Just going through first firing stuff on our mk2 gti and was wondering a little bit about the toothed wheel.
We have a 36 tooth wheel with a single missing, is tooth #1 (for setting degrees BTDC) the missing tooth, or the first tooth after the missing tooth?

Thanks all

[kaeman]

I like the bracket, I don't think ou will have any problems with the signal generation from the little bit of offset you have from the centerline of the crankshaft. I would box in the top to stop any chance of vibration due to harmonics and call it good.