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Discussion Starter #1
In our '86 Graduate, as the RPMs go up we encounter a nasty rattle that starts suddenly at a few thousand RPM and continues as the RPMs drop back to idle. The rattle sounds a bit like a heat shield, but that is only part of the noise we are hearing. My son noticed that the plug wires (!) began vibrating significantly when the rattle started. We thought at first it might be the start of the dreaded "motor mount sag makes fan hit shroud." But this seems not to be the case, because jacking up the engine on the sagging side (the motor mount on one side of this Bosch Spider was replaced a couple of years ago -- guess which one remains to be done) did not change the sound, and it appears not to be coming from the fan shroud.

With the damage to the dist. cap and rotor noted in post #17 of this thread on lost oil pressure a couple of weeks ago:
http://www.alfabb.com/bb/forums/showthread.php?t=44031
it might be that the dist. rotor is not tracking well. Is this common? Does it trash the distributor, or can it be re-bushed? Any input from anyone?

Thanks.

Michael (and George)
 

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Can you feel any appreciable play in the distributor's shaft? (Remove the distributor cap and grab the rotor. Some rotating wiggle due to gear lash is normal but it should not be possible to move the shaft side to side.) Anything more than barely any is probably too much.

Have you seen this thread: broken oil pump shaft ? I wonder if a misaligned distributor hold down could have caused high side loads on your distributor shaft?

Or parhaps I'm not understanding the oil pump thread and it has nothing to do with your problem...
 

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The '86 Quad that appeared recently on our driveway (around Father's Day ;)) did have a rattling downpipe heat shield. The heat shield was loose on the downpipe. I put a couple weld on it when I had the downpipe out to replace the O2 sensor. Anyway, it sounds like your rattling problem is at the distributor or near that!

Have you tried move the dist by hand, side to side and up and down, to see how much play? Check the tightness of the hold down nut and the clamp bolt. You might want to pull the dist out, check the shaft, eccentric key (both on the dist and the engine) and inspect the dist clamp (is it sitting at the correct position). I pulled mine out to play around since the dist was in an odd orientation. Mine has been turned by somebody (without loosening the position clamp bolt :eek:) and a piece of the dist next to the cap notch was broken! I replaced the "temper proof" clamp bolt with a real bolt and install/set the dist back to the usual #1 orientation position. However, I found out that #1 on this engine is actually 180 degree off (somebody installed the CAMs with the crank 1 turn off :confused:?). To get the engine running, spark plug wires were rotated 180 also! Anyway, (back to your problem) I think you might want to try to pull the dist out and have a look.
 

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Discussion Starter #5
During the panic over missing oil pressure and prospective timing chain breakage, we inspected the timing chain and cam timing prior to turning it over with the starter. The chain was properly tight and the cam timing exactly on. So that has probably not changed. But the damage to the rotor and cap might reasonably be due to unnaturally large distributor shaft play. We'll take it apart this afternoon and hope for the best. We've inquired of the local AROC chapter (MAARC -- Hampton Roads) about whether anyone has a spare Bosch Spider distributor we could swap in for a test, possibly for the duration of a distributor rebuild.

Do distributors get rebuilt by alternator shops, engine shops, or both? I might guess both could do it, but that electrical shops which pull/replace bearings, turn armatures as needed, and replace bushings in rotating electrical machinery might have tooling, expertise, and materials right on hand. Our last trip to the local Auto Electric Service shop resulted in a 2-day turnaround for the (Bosch) Alfa 164 starter and Spider alternator. (This could be either good or bad in terms of the shop still being there in a few years.)

Michael
 

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When I was rebuilding the engine in our '84 Spider I lucked out and bought a 'rebuilt' Bosch distributor on eBay for very few dollars (I made one low bid and no one else bid - wasn't even expecting I'd win...)

Anyway, the L-jet distributor is very basic. There is nothing inside except the shaft to hold the rotor. No points, no weights, no vacuum advance device, etc. It is really just a 4 positon switching device to send the coil output to the appropriate spark plug lead.

I would appear that 'rebuilding' such a distributor would entail pressing out a bushing, pressing in a new bushing and possibly reaming it to size. I don't know why they charge so much for them. Likely due to the economics of scale - supply & demand.

I do have the original distributor if you'd like that one. It would need to be cleaned but I believe it is serviceable.
 

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Source for engine rattle

I really doubt that your rattle has anything to do with the distributor. They do wear, but they don't wear that much - not enough to cause the whole engine to shake. I suspect that the sparkplug wires are just resonating at a certain frequency - the vibration is caused by something else.

If you have eliminated the timing chain (good theory), heatshields, broken off fan blade, ...., then I guess you need to keep searching. Sure, substitute another distributor if you want to, but I'll be surprised if that makes the rattle go away.

Fractured oil pump shafts are caused by misaligned oil pumps - not by the distributor. Again, your oil pump would have broken long ago if there was a misalignment significant enough to make the whole engine shake.

Good luck in tracking this down - this sort of problem can drive you nuts. Have you tried the "piece of hose, one end near your ear, the other end scanned around the engine bay" trick yet?
 

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Discussion Starter #8
Jay,

No, we haven't done the tubing stethoscope thing yet. But I'm not certain that the character of misbehavior has been made clear yet. The problem is not an always-present thing. The engine sounds just fine on run-up, until at around 3k RPM a distinct rattle sounds. It comes on with a distinct vibration in the plug wire bundle and not really in the whole engine or car (although there must be some additional vibration present there). Then as the RPMs drop, the rattle remains.

I presently suspect the dist. shaft is staying centered for some time after the engine is started, and then it grabs the side of its hole and starts rattling around in it. Possibly a good dose of lubricant would help this, at least as a temporary diagnostic aid. If lubing the shaft keeps the problem vibration from appearing, it could make the car driveable for a while until we find a workable solution (like getting Eric's distributor from nearby NC while we rebuild ours or his).

I hope that this is a useful and interesting problem for the assembled Alfanatic masses. I'd like to have a good sound recorder to go along with it. I'll probably have to get my wife's digital camera out and try to capture a short video. I don't know how to get the size of these monster files down, though, so I'll have to work on that. They come out with multi MB of file even for not many seconds of audio. I _know_ there are ways of improving upon that, but I've never had to do so as yet. Old dog, new trick, takes time.

Michael
 

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Another wild guess but our '84 Spider had an annoying rattle/buzz that I knew was coming from the right side of the engine. It was also in the 3000 rpm range. At first I thought it might somehow be the starter motor. I finally tracked it down to the plenum brace. One end is bolted near the engine mount/starter brace. The other end supports the intake plenum. The bolt near the starter/engine mount was loose.

I assume the 4 cylinder engine has some sort of harmonics in the 3000 rpm range that cause things to vibrate. Seems that is where we hear heat shields buzzing for example.

P.S. I got your email about the distributor. Check for a reply.
 

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Discussion Starter #10
We'll check the plenum brace, too. Also received your P.M. reply. Our suspicion about the distributor is because of the rotor and cap damage. It doesn't seem to be compelling, and we will continue searching for alternates. I have received no replies indicating that worn distributor shafts make an audible buzzing noise, and that makes me more inclined to search for other causes.

Eric, I'll get this sorted out today so we don't cause you too much extra effort regarding the distributor if it turns out not to be the culprit. But your offer is hugely appreciated.

Michael
 

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Have you removed the distributor? Checked the distributor shaft for excessive play? A little bit of up & down is normal but there shouldn't be any in a side to side direction. If you don't find any slop in the distributor's shaft (i.e. due to worn bushings), then I'd don't why the cap & rotor self-destructed.
 

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Discussion Starter #12
Update: turns out it was the distributor rattle. The bushing was horribly worn out. I had no luck through local auto machine shops and parts houses getting pointers to someone who could re-bush (at acceptable cost) the distributor to stabilize the center shaft. Then I remembered a shop which had re-done two Volve driveshafts with worn-out U-joint yokes fo rme several years ago.

The shop folks said they could fabricate and replace bushings and knew the right material words (including "oilite" for the porous bronze/brass material inpregnated with oil or graphite). But Eric (ghnl) was the one who _really_ came to the rescue. I wanted the car back up and running, so I took Eric up on his offer for his distributor _and_ arranged for the shop to rebush the old one. I expected Eric's unit to be a little worn and the shop's unit to be tight-like-new.

It worked out just inverted from that. The shop's tolerances were very loose or they over-drilled the bushings or the shaft is terribly worn and they didn't true it up. It has maybe only 1/3 to 1/2 of the slop it had when I delivered it to them, but this is far outside nromal limits. The unit from Eric is marvelously tight, almost no slop transverse to the shaft. The shop made the right noises and convinced me they knew what they were about. I received back a unit only slightly better than delivered, and well outside my expectations for a rebuilt unit. I have to inquire about possible problems with my distributor as delivered to them, but I am not a satisfied customer.

Eric asked for a donation to the bb in lieu of payment to him. It has been done. The car works now, very smoothly. A valve job looms in the not distant future.
 
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