Building a turbo engine

[turbobaja]

Glad to hear air cooled engines run deep in your blood klatin. And thanks for sharing some of your personal expereince with us. In case nobody else mentioned it, welcome to the forum!

What are you using for a fan shroud? All stock '71 hardware? Have you thought about the DTM shroud?

[klatin]

Glad to hear air cooled engines run deep in your blood klatin. And thanks for sharing some of your personal expereince with us. In case nobody else mentioned it, welcome to the forum!

Thanks

What are you using for a fan shroud? All stock '71 hardware? Have you thought about the DTM shroud?

I'm using a "fat" 36hp shroud (for the doghouse fan), but without the doghouse oil cooler (using an external oil cooler instead) and without heater connections. I looked at the DTM, but unfortunately it's top air connector is exactly where my plenum is located.

[klatin]

Some progress at last.
I got my trigger wheel and machined pulley back from the water jet cutter and machine shop.

Here are some pics:


The 36-1 trigger wheel is waterjet cut from 1/8" mild steel. A local waterjet shop charged me 50 bucks cash for 2 wheels. If somebody is interrested, drop me a PM. I have the drawing as dxf file that you can email to your local waterjet shop.
On the back side of the SCAT pulley a rabbet was bored on a lathe to a depth of 1/8" so the trigger wheel sits flush and with a slight interference fit. The trigger wheel is attached to the pulley with high-temp epoxy (JB-Weld would work also).

Not that it matters much, but notice that the "rim" in the missing tooth area is slightly wider than everywhere else. This additional thickness balances the weight of the missing tooth.


Trigger wheel installed in the pulley.


Side view of the pulley with the trigger wheel installed. Note that there is no additional depth requirement behind the pulley.


Here's the sensor and bracket. The sensor is the crank position sensor from a 96-97 Miata. It is a VR sensor just like the more common Ford sensor, but smaller. AFAIK Mazda 626s from the mid 90s also used a similar looking sensor. Note the Quarter for size comparison.
The bracket is cut and drilled from 1.5" x 1.5" x 1/8" aluminum angle stock. If somebody is interrested, I have a Visio drawing for it. Shoot me a PM.


Sensor installed in the bracket.


And mounted in its location on the engine.


And here with the behind-the-pulleye tin installed.
The sensor cable comes up through a little hole in that tin. Installed, the only thing visible is the cable next to the dip-stick.

I prefer this installation of the sensor, because even when the V-belt lets go, it cannot shred the sensor cable, as could happen when the sensor has to reach a trigger wheel on the front side of the pulley with the cables through the belt loop.

[miniman82]

Yeah, but it's also a PITA the swap the sensor. Well, a lot harder than mine is, anyway.

[ToRy 70]

Cool! your pulley reminds me of mine a lot...

[klatin]

Yeah, but it's also a PITA the swap the sensor. Well, a lot harder than mine is, anyway.

But why would you? A VR sensor is basically just a solenoid with the plunger replaced by a permanent magnet and the whole thing cast in some kind of plastic. If they are not mechanically destroyed, they outlast ANY engine. No moving parts, and no high voltage like an ign. coil that can cause internal arcover. The weakest part is the connector, which is top-accessible.
I usually carry a replacement belt when I'm driving a VW. I usually don't carry a spare sensor set.

BTW, the sensor CAN be replaced without even taking the pulley off or any tin. The bolt that holds the bracket is accessible from underneath the engine, and the whole sensor with bracket can be installed and taken out that way.

[WickedWagens]

That is a very clean setup. I was looking to hide my sensor, but just want to get the car running first then after all the kinks are worked out I can go back and move sensors around etc. Thanks for the ideas. I like the stealth.

[fastback]

very nice setup , indeed

[Humpty]

I really like this klatin.... The current location of the FORD sensor on my car is of great concern... If you could please send me you dxf files I'd truly appreciate it... Looking forward to hearing how it works out....

[MarioVelotta]

Great thinking outside the box, Any drawbacks of running inverted teeth or the sensor off axis to them? Have you been able to test that at all? Also how are you going about adjustment? Or are you just placing it and making final adjustment with the trigger wizard? I would love to see your files also!

[klatin]

Great thinking outside the box, Any drawbacks of running inverted teeth or the sensor off axis to them? Have you been able to test that at all? Also how are you going about adjustment? Or are you just placing it and making final adjustment with the trigger wizard? I would love to see your files also!
Great thinking outside the box, Any drawbacks of running inverted teeth or the sensor off axis to them? Have you been able to test that at all? Also how are you going about adjustment? Or are you just placing it and making final adjustment with the trigger wizard? I would love to see your files also!

There should not be any drawbacks with the inverted teeth and sensing them from the side. Just the opposite. The output of a VR sensor is proportional to the change rate of the magnetic flux. Because the "rim" of the trigger wheel is always close to the outside of the sensor, it always "conducts" magnetic flux. The "teeth" themselves basically open and close the magnetic circuit. Therefore the change in magnetic flux should be large.
This is different than a regular tooth wheel with the sensor radial, where only a tooth can be close, but the rest of the magnetic "circuit" has high resistance. There the change rate in magnetic flux should be less. Which is why the Ford sensor uses a very strong magnet, while the Miata Sensor is comparatively weak.

I will test it actually in the next 2 days. As always, the concern is that at cranking rpms the signal is large enough.

The sensor "tip" with the bracket I have is 138 degrees clockwise from TDC. You have to install the trigger wheel into the pulley such that the center of the 9th tooth after the missing tooth sits at that 138 degrees (meaning between 4 and 5o'clock position when looking at the front of the pulley). Which means the missing tooth must be about between the 7 and 8 o-clock position.
Tip for glueing in the Trigger wheel:
You can use JB-Weld, but thin it a little with acetone to the consistence of honey. Use very little brushed on the rim of the trigger wheel, as evenly as possible.
I used a piece of melamin coated particle board with a hole cut out for the pulley hub to press the trigger wheel in while the epoxy hardens. Then melamin was coated with mold release so it does not stick on.
Press it in first with the melamin, wait 5 minutes, take the melamin off and clean up any epoxy that squezes out with acetone or mineral spirits. Clean the melamin too and recoat with mold release. Then clamp it together again and wait for a day for the expoxy to harden.

For initial positioning I took an old aluminum degree pulley I had and drilled a 1/8 inch hole to where I want the sensor tip to be (~ 4mm in from the tip of a tooth). Then installed that pulley on the engine and stuck the drill bit through and rotated the crank so it marked the bracket where I wanted to drill the sensor hole. Same for the hole in the tin. I could then also read how much offset I had to set the trigger wheel to.
You should get to within 1 degree or better that way.
Distance adjustment can be done by elongating the hole where the bracket attaches to the case. Fine adjustment can be done by "tilting" the bracket toward the trigger wheel.

Unfortunately the STF moderators do not allow attachment of .dxf or .vsd (Microsoft Visio) files to posts. If somebody knows the moderators, could you please ask them to enable that so I can attach them here?

I got quite a few requests for the drawings, and I don't want to answer each and every one as email.

[miniman82]

Why not upload them elsewhere, then link to them?

[klatin]

Why not upload them elsewhere, then link to them?

Do you know of a public ftp site where I can upload them?

[Humpty]

Why not upload them elsewhere, then link to them?

Do you know of a public ftp site where I can upload them?

http://www.yousendit.com

[miniman82]

There ya go.