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 Posted: 04-20-2020 05:27 pm
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Esprit2
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I've had two 907s develop a problem with "ignition scatter". Put a strobe timing light on it, and the ignition timing could be seen jumping all over the place. Careful examination showed that neither the distributor nor the electronic ignition pick-up were the cause... so what was?

I decided to dig in deeper, and remove the auxiliary housing for a more thorough 'bench' examination. But when I pulled the auxiliary pulley off, I noticed that the keyway in the bore had been 'hogged' out to about 3/4" (19mm) wide. The Woodruf key is shorter than the bore is long, so both ends looked normal. But look inside the bore, and the damage was obvious.

Even when an engine appears to be running smoothly, the power comes in pulses. In a 4-cylinder, two pulses per revolution. The pulley hadn't been mounted with Loctite. And even though the bolt had been torqued to spec, the pulley eventually over-rode the wimpy little wire circlip, releasing all the clamp load. It was loose on the shaft, and the pulsing power delivery had worked the Woodruf key back and forth in the bore enough to 'machine' a wide grove. The pulley & shaft wobbling back and forth relative to one another... and to the crank... is what was causing the ignition scatter.

I've killed two pulleys that way, mounting both without Loctite. Sometimes I can have a rather flat learning curve, but this lesson eventually sunk in. Don't forget the Loctite.

Regards,
Tim Engel

Last edited on 04-20-2020 05:28 pm by Esprit2

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 Posted: 04-23-2020 06:12 pm
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SimonD
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Thank you all for the very informative replies. I have taken it apart and the little spring between the distributor and the shaft is missing, so nothing to keep the shaft forward.
Now need to find a suitable spring.

Attachment: 1.jpg (Downloaded 43 times)

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 Posted: 04-23-2020 06:40 pm
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redracer
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Simon: if you can't find one locally, I have some :used: ones. As long as we're on the subject of woodruff keys wallowing out their sprocket slots, my experiences are somewhat different from Tim's.
Although I have never had the oil pump/distributor sprocket push past the spring washer(except for some Dave Bean aftermarket ones in the '80s; one side was chamfered and the other side flat, unlike the OEM Lotus ones; ALWAYS test torque before putting the belt on), the steel crank pulley is held "in place" by the friction of the thick washer using the 50+ psi from the main bolt. HOWEVER, if you ever remove this nut & washer, you will notice the washer has been "pulled" in by the force of the bolt, and should be turned around, reflattened, or replaced, or I guarantee you will ruin your sprocket '
best wishes, bruce

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 Posted: 04-24-2020 06:25 am
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discogodfather
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Speaking of oil returns, is there any function to the holes surrounding the head studs? I removed the old head studs, waiting on an ARP kit from Greg. I cleaned them as best I could and then started to realize- to these holes drain oil back into the pan at some point? Are they closed off at the bottom?

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 Posted: 04-30-2020 04:03 pm
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mtechwim
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Good topic

Found out that from my oil pump the outer ring was broken in 2

But a fast replacement from Kees fixed te problem I hope.

Last edited on 04-30-2020 04:05 pm by mtechwim

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 Posted: 04-30-2020 04:52 pm
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PF18602
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Disco,

I'm not sure why the diameter of the stud hole is that much bigger than the stud itself (maybe for some heat transfer or expansion so it doesn't crack the block?). But I do know that the hole for each stud just bottoms out. Mine were all filled with some impressive 40 years of gunk.

And of course from all those heat/cooling cycles, I ended up having to weld the nuts onto each stud to get the damn things out!
I ended up cleaning the threads with simple green and a pipe-cleaner type brush. Also used the old stud to chase the threads on a couple, as the ARP studs didn't want to go in easily.

Patrick

Last edited on 04-30-2020 04:53 pm by PF18602

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