Ever Had Distributor Gear Failure?

Well wow is all i can say. Timing cover off retaining bolt tight cam gear all good. But the distributor drive gear has worn to a knife edge and several teeth failed[emoji848]lots of oil present and gear was on correct way with groove facing the spacer. Nil wear or damage on distributor gear. When fitting distributor drops in easily engages gear as it goes in. When running distributor runs smooth. Lower photo is of genuine drive gear which had done 2000km I'd replaced it as there was small wear evident. This new one lasted less than 1000kms. The Cloyes cam gear set is original I brought in 1988 with new chain only fitted. So - was gear faulty/crap metal? Is cam moving forward and using distributor as thrust washer (but figure if it was that would induce some vibration). Or is shoulder of cam machined wrong and cam gear isn't sitting far enough back along the nose causing misalignment?Attachment 167214
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I have had this happen to me twice, well I caught it the second time.

With the ordeal I had a couple of years back with my 89 not running when it should, I thought I had it fixed when it did random things, stripping the gear was one of them. The odd thing was it was only worn or stripped on one side. I pulled the front off and replaced it. While in there I had a look to see if anything was causing it to do it. Beutey suggested that sometimes the gear gets fitted incorrectly and the washer doesn't allow the oil, supplied through a gallery in the camshaft, to splash outwards - lubricating the gears. I made sure everything was as per the book and threw the front back on.

Well all was good, drove from Katherine back down here to Adelaide.

While waiting at the lights one day I started to hear this grinding sort of sound. Sounded like the water pump bearing had failed. Got home and did all the checks, water pump and all tensioners were fine, alternator, etc.. no idea. Noise hung around didn't get any worse.

In the lead up to Christmas 2019 I had an opportunity to change the cam. The engine was down on power, torque was non-existent, but the compression was still very good. When I pulled the front off again, the drive gear had started to wear pretty bad in the same or similar spot to last time. I was actually probably lucky to catch it when I did as I am not sure it would last another 6months.

I worked it out and it was less than 5000km when it was changed.

What I thought might of happened was the cam moving forward into the timing cover. But there was not sign of it on the cover or the bolt that secures the gear/chain gear.

On reflection, it's possible it was moving forward at a point lining up with the lobes for Cyl 7. While I didn't think to check it at the time, those lobes were more than a mil worn down and had a taper leading across the lobe. The cam might have been pushed at that point causing the extra wear.

New cam, new gear and it has been pretty good. Although I haven't surpassed 5k yet, overall it's a different engine.

Of note - I always add a drop of oil down the centre of the dizzy drive shaft and the shaft spins very freely, so I wrote this off as being a cause for the gear damage.

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What I thought might of happened was the cam moving forward into the timing cover. But there was not sign of it on the cover or the bolt that secures the gear/chain gear.

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Yes the cam lobes are sloped to push the cam backwards and rotate the lifters and excess wear on the cam lobes will enable it to move forward a bit.

The timing chain will also tend to hold it in place.

I wonder if aftermarket cams have the same slope.

At one stage LR used to sell cam buttons to hold the cam back , when someone complained of a noise. **** of a thing to set up though as you have to wind the button in, check that the timing cover can go on and so forth.

I had a similar hassle when putting a dual row timing chain on my 3.9. I had to grind a lot out of the dizzy tunnel in the timing cover.
Regards PhilipA

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Originally Posted by PhilipA

Yes the cam lobes are sloped to push the cam backwards and rotate the lifters and excess wear on the cam lobes will enable it to move forward a bit.

The timing chain will also tend to hold it in place.

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Yeah I did see that on the new cam. I went with a genuine LR 3.9 standard cam.

The lobes on the old cam did seem to have a pretty even amount of wear and weren't square at the top of the lobe. Just on number 7, more so inlet than exhaust, they were sloped really bad on one edge, which would cause a forward movement rather than a rearward or neutral movement.

Oddly though, the followers weren't worn any more or less than the others.

The new chain I fitted didn't measure as being too much tighter either. Nor were the teeth hugely worn.

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The new chain I fitted didn't measure as being too much tighter either. Nor were the teeth hugely worn.

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Yes , because it is so short you don't see much length increase.

However hold it edgeways and you will see that it bends more sideways due to the slop in the chain pins.
Regards PhilipA

Ok, so + does the groove in the distributor drive gear face inwards towards cam or outwards towards bolt/ washer? My LR workshop manual is not at all clear on that.

I want to say it faces the cam..

There is a spacer between the chain gear and dizzy gear, when lined up properly there will be a minute gap between the spacer and drive gear. I have it on the Rave CD, but no computer to check it for you.

I reckon if you search this site it will pop up under a post from Beutey.

Yeah thats how i had it installed. Just checking thanks

How old is the cam?

Cam new. Think we've found the problem. The drive gear on the distributor was fitted at shop - upside down with the short part to dizzy. So the gear has only been half engaged in cam gear. With a close look wear marks on dizzy gear show this - it was only 50% engaged.
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