Crank Trigger guidance

[jonesb930]

(Cross posted as I did not get many responses)
So I am starting to make some forward progress on my project and need some guidance on installing a crank trigger on my 1976 930/50 motor. I currently have the factory trigger as well as the mount to use the flywheel that Patrick Motorsports sells. I plan on using the upgraded scavenge pump from Clewitt with the cam sync sensor as well.


Below is a photo with the mount installation location. My question is, how do I best locate it and make the necessary mounting holes. Does anyone have a process that they can share? Any suggestions would be appreciated.

[dannobee]

Here's what the factory case looks like. Do you need measurements?

[Speedy Squirrel]

Your engine is pre DME, so no holes. Does it have those bosses though? I get 25mm on the bolt hole spacing.

[Evan Fullerton]

My 3.2L case has the holes, 993 crank trigger and bracket (same as GT3) bolts right on.

[jonesb930]

Any measurements would be helpful. Here is a picture of what I am working with in that area. No bosses present.

[Peter M]

Bill,
Why don't you just add a trigger disc and sensor mount to the to the front pulley like most people do? Clewett and others do a simple bolt on kit like this one: https://www.clewett.com/index.php?main_page=index&cPath=3_61

[safe]

What Peter M said.

[Speedy Squirrel]

The trigger on the front pulley can work. Looks a little small block Chevy to some people.

If you have the Clewett cam position sensor, and the flywheel 60-2 target, you can machine a threaded hole in the bell housing to thread a crank sensor into. There are several varieties of Hall effect or variable reluctance sensors with threaded bodies out there.

[Peter M]

What sensor gap do you need to accurately achieve?

Trying to accurately drill and tap holes in the crankcase to mount a non adjustable factory mount or even drilling the bellhousing is frankly madness when a Clewitt front pulley set up is proven and easy.

I disagree that it "looks a little small block Chevy" as it's all pretty much hidden by bodywork and rear engine mount.

But each to their own! Looking forward to what solution you adopt.

[winders]

I use a 60-2 flywheel and use a reluctor sensor. My gap is around .040".

[jonesb930]

I have been weighing the options. I have not purchased the flywheel yet, so maybe I need to go the simple bolt on route from Clewitt and call it a day. I had the sensor and mount from some other stuff I picked up in a box of parts.

Any advice on which wheel to get? I am running a Motec M600 for an ECU. I believe the M600 will work with a variety of wheels so any advantages to a 60-2 vs a 36-1?

I was looking at the 1972-83 Serpentine belt conversion w/ crank trigger adapter since I deleted the AC.

[Peter M]

Originally Posted by jonesb930

. Any advice on which wheel to get? I am running a Motec M600 for an ECU. I believe the M600 will work with a variety of wheels so any advantages to a 60-2 vs a 36-1?

Whatever is convenient and works with your ECU is the bottom line when I investigated this for my M130 install.

For our purposes you can't go wrong with either options suggested above.

[spuggy]

Originally Posted by jonesb930

Any advice on which wheel to get? I am running a Motec M600 for an ECU. I believe the M600 will work with a variety of wheels so any advantages to a 60-2 vs a 36-1?

Pah - the motec will use just about anything, LOL...

However, IMO, you'll get a cleaner signal at high RPM with the 36-1 pulley, as the pulley is so much smaller diameter/teeth are smaller & closer together.

My wrench likes to replace the sensors Clewett supplies (GM? I seem to recall) with the Bosch ones.

With a mag pickup, I found setting the noise floor on a Motec 800 greatly improved establishing sync with the Clewett cam sensor - and thus startup was much quicker. Motec help file says to use 2/3rds of the peak value; read the actual value in the Motec ECU Manager and set the floor appropriately.

Even slightly too low can have it counting noise as teeth when cranking. And probably trip sync errors with a cam sensor. I deliberately set it too low (half of the original "not quite high enough" value), and the tach read 5000 RPM when cranking...

Originally Posted by jonesb930

I was looking at the 1972-83 Serpentine belt conversion w/ crank trigger adapter since I deleted the AC.

You don't need that. That said, I do like mine - and the CR 175A alternator doesn't appear to slip at all with that belt. Ever.

[safe]

36-1 on a crank pulley I would say. I got that on 2 cars and it works really good. I've made the trigger mounts myself , quite getto, but works perfectly. On the pulley its easy to set the right gap.

[spyerx]

So... on my build we had issues with the pulley sensor/wheel that is supplied by Rasant at high rpm. Getting breakup, etc. Computer is Motec M130. We ended up with Motec sensor (IIRC). Which works great.

[winders]

Originally Posted by spyerx

So... on my build we had issues with the pulley sensor/wheel that is supplied by Rasant at high rpm. Getting breakup, etc. Computer is Motec M130. We ended up with Motec sensor (IIRC). Which works great.

Which MoTec sensor? Reluctor or Hall Effect?

I tried the RaceGrade "M DHALL HS230" Hall Effect sensor with my 60-2 fly wheel and had issues. I switched over to the RaceGrade "M 4-APX-001" Reluctor sensor and the problems went away.

I am using a MoTec M130 ECU with a Rasant motorsport wiring harness.

[spyerx]

Originally Posted by winders

Which MoTec sensor? Reluctor or Hall Effect?

I tried the RaceGrade "M DHALL HS230" Hall Effect sensor with my 60-2 fly wheel and had issues. I switched over to the RaceGrade "M 4-APX-001" Reluctor sensor and the problems went away.

I am using a MoTec M130 ECU with a Rasant motorsport wiring harness.

I'll have to ask the shop ... invoice says "magnet sensor".

I'm also using an M130 with rasant induction + wiring harness, etc - tho we ended up completely reworking the harness after it wasn't built as we specified (including a visit to the shop to discuss at the time....).