Have I Broken It?

[Marvel]

Did a 250 mile round trip in the Bonito today. 10 miles from home the rotor arm broke the lug which locates it on the shaft. The RAC man had a spare which lasted about 1/2 mile before that one sheared too. I don't think the cap was located poperly which broke the replacment. I managed to wedge the orginal one back and drove home without further incident. I put a new one on at home now the engine is making a scraping noise at speeds above tickover. At tickover it still sounds sweet as normal.

Tried it with the fan belt off and it's definitely engine noise rather than alternater/fan. Seems to tickover smoother with more advance than I would expect too. Not sure if it's linked.

Still seems to run smooth and quiet at tickover but starts making the scraping noise at about 2000 rpm.
Changed the whole dizzy and no difference. Sounds like it's inside the crankcases.
I'll drain the oil next and have a look but the pressure and temps were ok.

Dropped the oil and no horrers there. What next?

Ok, a few more clues. The noise is coming from the distributor drive area of the engine. The distributor shaft seems to have more back lash than my spare engine. When I time it to 10degrees BTDC it runs fine. When I increase the revs the timing advances to 50+ degrees and the noise starts. I've tried three distributor and they all do it. It's got the anti chatter spring fitted but I suspect the drive shaft or crankshaft gear or both have worn. There wasn't any brass in the oil but it's got a remote filter so it may be in there. Any ideas before it comes out?

[Marc]

40°+ is a HUGE advance curve, is that with an SVDA?

The distributor shaft seems to have more back lash than my spare engine

...as in, the drive pinion has excess slop, so damage to the brass gear is suspected? It can be a bit tricky removing the pinion - I generally try to yank it with some external-circlip pliers, but if you don't have those a wooden dowel (or a pencil) whittled down so it'll pound snugly into the spring-hole will usually do the trick. The fuel pump and its drive rod must be removed first, and the pinion needs to rotate slightly CCW as it's extracted; a little wriggling is often needed. In the case of an engine that's got many miles on it, you may need to polish the walls of the bore with some emery cloth or fine sandpaper, and/or use some kind of light lubricant, to coax the pinion out. Avoid rotating the crankshaft any time the pinion isn't fully "down", since that's a sure way to damage the brass gear (if it isn't already toasted).
Once you get the pinion out you can inspect the brass gear for damage. Fingers crossed

[Marvel]

I've tried it with 009 and SVDA distributors and they all over advance now. Before the rotor arm sheared it would time up as normal. Not sure if the sheared rotor arm and noise are linked but I suspect they are.
When I wiggle the distributor drive shaft there is more back lash on the noisy engine than on my spare one which makes me think the brass gear is damaged.
If I can get the distributor drive shaft out am I likely to be able to see any damage to the brass gear?

[buildabiggerboxer]

Guys, I can't see damaged dizzy gears over advancing unless the static timing is advanced to begin with, any gear wear would mean less advance, if it has a stock fuel pump, as to the noise, i would suspect that is worn or running dry, sometimes a grove gets worn in the foot of the operating lever and can squeak bigtime, drop it of the pedestal and fire it up to check if the noise goes away, I can only see excessive crankshaft end float advancing the ignition timing beyond specs, hope the fly isn't loose,,,,,,
Tho they don't squeak so much as clunk and brrrrt brrrrt, odd about the rotor locating lug tho, one would expect the dizzy cap to be damaged at a contact if the rotor hit with enough force to break the rotor locator, it would sure show some damage I would guess, if so, that one is solved..

[Marvel]

No fuel pump fitted and no excessive end float.
Ive tried three different distributors and they all time up ok at 10 degrees BTDC at tickover and the timing is stable. It's not until I increase the revs to set the full advance it starts to make the noise and over advances. All three distributors do the same thing.
The inside of the cap did show some marking where the rotor arm hit it.

[FJCamper]

Hi,

Possible loosening cam gear.

Pull the oil pump and look.

FJC

[Marvel]

Hi FJ,
Would that cause the erratic timing?

[FJCamper]

Hi,

A cam gear with oblonged bolt holes allows the cam timing to move dramatically as the cam shaft and cam gear are no longer in synch.

Two things happen with wobbly cam gears, too much advance or too much retard once the engine is running. As the wear increases, the timing will be so far out you will finally not be able to start the engine.

You have to drop your exhaust, remove your oil pump cover plate, and you can see the cam bolts as your rotate the engine.

A really serious wear or loosening condition is when you can rock or mover the cam gear with your fingers!

I hope this has not happened to you, but I can't think of anything else timing related you havn't checked.

FJC

[Marc]

On many engines, the distributor is driven by the camshaft. On the ACVW, however, they are both driven independently by the crank and DO NOT interract. A loose camshaft gear would be a bad thing because it would cause erratic VALVE timing, but it would/could not cause ignition timing fluctuations.

[FJCamper]

Hi Marc,

I may be describing this poorly.

On an aluminum cam gear with loosening bolts, with oblonging of the bolt holes beginning, the cam shaft will shift relative to the gear and either advance or retard the timing just like the adjustable cam gears where we compensate for error. I don't mean that the timing curve changes. I'm talking about stating with 10 degrees advance and watch it change to some crazy extreme in advance or retard.

I did this to myself once on a race engine back in 1976-77, at Sebring. My first clue was I could set initial timing, rev the engine, and on a recheck with my timing light, see that my timing was now way out.

Once I wore the gear so that it was about the equal of two teeth off, and I was having to unnaturally twist the distributor toward advance or retard (I don't remember which way now) just to get it to fire.

It was a long tow from Sebring back to Birmingham on account of (one time) not using bolt lock tabs.

FJC

[Marvel]

Hi FJ,
It's the ignition timing which is erratic not the valve timing. I can't see how a loose cam gear can affect the ignition timing as the distributor is driven off different gear on the crank.
I agree a loose cam gear could make noise from that area of the motor but I would expect it to do it all the time whereas mine only does it above tickover.
I'll remove the distributor and drive and have a look to see what's going on.

[Marvel]

Just had a thought. As I'm using an electric pump and the mechanical pump has been removed there will be less axial load keeping the distributor drive shaft in mesh with the crankshaft gear. Could this allow it to ride up and cause the noise?

[Piledriver]

Just had a thought. As I'm using an electric pump and the mechanical pump has been removed there will be less axial load keeping the distributor drive shaft in mesh with the crankshaft gear. Could this allow it to ride up and cause the noise?

Only if you omit the spring, or perhaps if the distributor is a major pile...
Or if the clamp was ever loose and the distributor rode up and down a lot, damaging the brass gear.

It can still run with that damaged to some extent, but it would teent to be geenerally erratic, not as you have described.
That sounds to me more like a gimpy advance timing light.

[Marvel]

I think I've eliminated the distributor as I've tried all the ones I've got and it makes the noise and has erratic timing with all of them. I did wonder about the timing light but its always been ok before and it doesn't explain the new noise.
I'll try fitting a slave fuel pump just to put a bit of load on the shaft to hold it in mesh.

[Piledriver]

bamboo tomato stakes/supports work well for removing the drive gear.
they compress well and don't crumble/snap off.

I have used the same 6" bit of bamboo for 20 years.