505 toothed wheel installation

robs

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A while back I answered some questions here by wadehilts on his 505 GTI fuel injection. The upshot was that he decided to convert to Megasquirt and I've been giving him some help off the forum. A side effect of this has been to convince me to move both my cars to use a toothed wheel crank position sensor in place of the distributor sensor.

I've done the 505 now and it has dramatically improved some aspects of driving. The job wasn't easy though, so I thought I would write it up in case anyone else wants to go down the same path. Pretty sure Wade will be at any rate.

New parts were a 6 3/4" 36-1 toothed wheel and sensor from DIYAutotune. That's about AU$100 worth. The trick was getting them fitted. The 505 harmonic balancer has a triple channel pulley (power steering, water pump/fan/alternator and A/C) pressed around it. There's a chance (low) that this might slip, so I preferred to bolt the wheel to the inner balancer itself.

Not very easy. The rim of it is only 6mm wide, and it's recessed relative to the pulleys, and it's not exactly on-centre (or mine wasn't at any rate). So mounting the wheel required a spacer to make up for the recess, and (I opted for) 12 5mm tapped holes in the balancer. So here we are:
twparts.jpg
That wasn't hard for you, but several weekends' careful measuring and machining for me.

Now we come to mounting the sensor. Very few suitable mounting points sprang to eye. I played with the idea of mounting it direct to the cam belt cover, but it's a flimsy thing, rubber mounted and probably prone to cracking. I ended up making a bracket going from the M10 A/C adjustment bolt on one side across to the M7 cam belt cover stud below the water pump. Made it out of 1.6mm (1/16") steel that I had lying around and braced it up so it was pretty stiff.
sm3.jpg

I was a bit worried about only having two mounting points and had a backup plan of bringing the alternator pivot bolt into action if there was too much flex. So far it seems fine with just the two mounting points. One other thing that had to be carefully considered from the outset was where the great tangle of belts were going to run and what they might lash out at if they broke. I managed to avoid the first problem. Will let you know how it goes when a belt breaks. Here it is in one of my trial mounts:
twwheel.jpg
And here are a couple of photos of it fully assembled after a few weeks running with it.
twinst1.jpgtwinst2.jpg

It's pretty busy above the pulley and the fan's pretty close too. Adjusting the air gap was no fun (ended up taking off fan and shroud). Replacing an aircon belt won't be fun either. It's also pretty hard to see the timing marks. I think, given my time over, I'd try mounting the sensor looking up up from below. A few suitable holes tapped in the A/C-power steering brace might well have done the trick.

But it's working now and, as I said, driving has been greatly improved in several areas. I fully expected it to improve under changing conditions (i.e. acceleration) and it is dramatically improved. Much smoother. The bulk of this is undoubtedly down to the more accurate spark timing, but not all of it. I drove around for a couple of weeks with wheel and sensor mounted but not used (just to be sure they weren't hitting). The extra flywheel mass of the 450g toothed wheel held the revs up during gear changes, which smoothed upshifts noticeably.

One place I didn't expect much change was in creeping along in traffic. It used to be inclined to get into bunny hop mode, with the occasional kangaroo getting in on the action. That's all gone and I can creep on nicely with all the other happy Sydney drivers. I'm sure this is entirely down to the more accurate timing.

I've skipped over any number of blind alleys and pratfalls here, but I think I've given the guts of the job. Having spent several years running a Megasquirt with distributor based tach input I have come to the conclusion that it wasn't a good idea. I should have run fuel-only with the old mechanical distributor until I was prepared to fit a decent crank position sensor.

Now I just have to summon the enthusiasm to do the same for the 604 (which, I'm glad to say, looks a good deal easier than this was).

Have fun,

Rob.
 
Good to see a 505 get a new lease of life!

Now on to the 604 , I run a PRV V6 in my rally car , and I decided that a chopper plate was to exposed and prone to damage from mud rocks water etc so started looking for a better solution.

What I found was a Nissan cam angle sensor that fits in where the original distributor was .
The sensor has two Hall effect sensors and two track rings , one ring has 360 slots the other ring has six different sized slots .
These give both crank and cam angle information to the ECU providing the ability to run sequential injection and individual coils.

Have run the sensor for 4 years in a rally car with no problems.

If you want more info please ask.
 
Thanks Rally.

I already have the wheel and sensor from DIY and fitting them doesn't look too bad, so I think I'll stick with that. Might need to get back to you if it all goes pear shaped. Will try to steer clear of the off-roading and keep to the 604's stately and refined roots.

Someone else suggested the Nissan optical distributor recently. Megasquirt firmware doesn't support it (too many pulses), but I see DIY sell a replacement plate for them to reduce the number down to something digestible.

Thanks again.

Have fun,

Rob.
 
Wadehilts came up with a better mounting for the sensor. I was convinced the moment I saw it. Thought I'd follow up to this old thread for other people wanting a toothed wheel on the Douvrin engine.

Here's the new bracket:

CAS.jpg

It's all in 30mmx10mm steel bar. The base is 5cm long, with a 10mm hole 35mm in from the outer face of the stem. The stem is 7cm long (making an overall reach of 8cm) with a 12mm hole for the sensor eyeballed to centre on the wheel. The stem is mounted 5mm in from the end of the base so I could use fillet welds for both sides. It mounts on the lower aircon adjustment bolt. Enthusiastic people might make a cross brace to the other aircon adjustment bolt so the sensor can't twist. It's not bad as it is though... even if the bolt comes loose and the bracket rotates, the sensor falls away from the wheel without touching it.

CAS2.jpg

While there was no sign of the wheel hitting the sensor with the old bracket, this one's more confidence inspiring. What's more, I can see the timing marks without being a contortionist.

Have fun,

Rob.
 
Seems to me you could use a 30 mm wide piece of 75mm x10mm mm angle iron and avoid any welding.

Which may be useful for others who want to make the same bracket. :cheers:
 
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