328 rotor arm disintegrated

Has anyone seen this happen? One of my rotor arms (rear bank distributor) has just lunched itself.

I had to replace the oil seal at the distributor on the rear bank of my 328 (oil in the cap) . To do that you have to remove the rotor arm so you can remove the plate that carries the seal. Its pretty straightforward stuff.

All done & rotor arm re-fitted & running well. Drove about 15 miles & then opened it up a bit. On backing off it didn't sound right & then started backfiring + loss of power. Limped home down on power & backfiring whenever I lifted.

I think the rear bank was still firing on maybe 1 or 2 cylinders intermittently. I've had the loss of a full bank & the thing won't do much more than 40 or 50. It wasn't that bad. My initial thought was that it had just burned a plug extender.

Pulled all the leads & the extenders were all OK (on both banks) so pulled the plugs on the rear bank & they were all black. So it pointed to something affecting the whole rear bank.

Pulled the distributor cap to find bits of melted rotor arm inside. The bulk of it was still bolted in place but it was generally a mess around the base. lots of melted plastic . It wasn't loose or flapping around.

Checked the cap carefully & it looks to be OK. No damage there.

I can't see anything else going on so I've replaced it with an old one I had & it started & ran fine on all 8 again. I haven't driven it anywhere yet though.

I suppose I could have overtightened one of the three small bolts that holds it causing a bit to crack off but I've had these off several times before & besides there are brass bushings embedded in the thing.. You can't get a socket on the bolts so they are done up with a 7mm open ended wrench about 3" long, so hardly a great lever.

They were new in 2011 & they have done about 15K miles. They came from Ferrari, but they aren't Marelli parts.

 

Did you check the distributor cap carbon brush, carefully. These can get damaged very easily if the distributor cap was stiff to get off. I've found these caps can stick to the cork gasket. I broke one of these brushes a few years ago because of this, and since then have smeared the gaskets in Vaseline to aid removal.

 

Did you replace the cork gasket on installation?

 

Tom Yang had this happen and made a video about it. The distributor cap was blank on top where marked Marelli originally and he said the copy dimensions were too tight. I believe this is may be the mold shrinkage effect from casting reproductions.
Take care and only use original parts

 

I have not used those since Ferrari started using them. They achieve nothing and sometimes make the cap stick to the housing.

 

In the future there is no need to remove the rotor unless it is being replaced. The seal easily goes over it.

 

Ferrari left a few intake cams loose on the early 328s and those would break rotors. If all the same parts were used except the seal and gasket I have to assume something was incorrectly installed.

BTW, as I said, no reason whatsoever to remove the rotor to replace the seal.

 

This is what Tom Yang found; the carbon tip was ground down from extra pressure of tight dimensions of a reproduction cap. this one is 13 years old so probably very before todays repros

 

That was a result of incorrect indexing of the cap on the machine for machining the interior of the cap. The reproduction caps were then a brand new item. The problem was fixed a very long time ago.

 

Just leave the gasket out. It was a dumb fix for a problem that no longer exists.

 

Agreed, mine never had the cork material gasket since I bought my car 18 years ago without any issue.

 

And yes, this thread is worthless without pictures.

Everyone I've touched since 1984 does not have them either.

 

I'm thinking you'd probably hear it rattling around a bit if the cam was loose! I'd guess that would make a mess of the cap too. If it was loose that would be down to me because I've had those out in the past - but it isn't that.

I do have the cork gaskets (just always have) & the centre brush in the cap is fine & not stuck. I'd be reasonably confident I put it together correctly, its far from the first time I've had the caps off.

There was no damage to the cap either, just a mess of a rotor arm. I checked it all carefully & did continuity tests on the leads etc as well.

I'll take it out in the next week or so & we'll see if it repeats itself and eats another one but I can't see any reason why it should.

The rotor arm that was in there (bought from Ferrari) was unbranded. The one I have put back in now is Mag Mar branded.

There's no obvious reason for it, its pretty odd, hence asking if anyone had seen something similar. I can only think that the plastic in the rotor arm failed in some way.

 

No you cannot hear a loose camshaft and no, in 15,000 miles it destroyed 5 rotors and did not damage a single cap.

If you took it apart, changed a seal and gasket, reused the same rotor and cap I do not believe the Gremlins broke it.

Again all this is guessing based on a description with no pictures.

 

Here you go.....

On the left a used one from my tool box, on the right the offending item

A few points of note. As can be seen, it has substantially melted around the base. This was not all that was left in place, a lot of it (melted plastic) broke away when I removed it.
The upper part is in tact & there is no sign of any damage to the brass i.e. no contact with the cap.
Look at the location of the bolt hole bottom left, the base has clearly twisted in relation to the upper part - but as explained, all three bolts (and brass bushings) were still in place and tight.

Yet as can be seen in the second picture the upper part of the base is still attached to the stem. Its as if the base has delaminated in some way.

Whatever, it well & truly melted.

The only two things I can think of that would cause the necessary heat build up would be friction or possibly vibration/resonance.

The only source of friction in the locale would be the contact between the new seal and the cam & that seems unlikely. It was an easy fit over the cam with a smear of engine oil & indeed the seal pressed into the housing by hand just using my thumbs.

Which leaves vibration. The thing was still well bolted in place when I found it.

What I did not discuss before (because I didn't/couldn't see that it might be relevant) was that I have also had the cams out as part of this work to replace the (leaking) O rings on both the cam seal carriers at the front.

The cam journals/caps all looked good, I was careful to install all the caps back in the right locations and the right way round (its not the first time I've done it) and I used new conical washers under every nut & torqued them all in a sensible sequence.

The consequences of a Cam rattling around would seem to be potentially fairly horrific so I guess I better get some more gaskets & take the cam cover off again & check the caps.

So question, is it safe to remove & replace them one at a time to have a look & see of there is any evidence of damage or am I going to need to take the cam out again?

(Its also had a new cambelt on that bank into the bargain - I'm not a fan of reusing them.)



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Vibration does not generate heat, a new seal does not generate heat. Something generated heat and it was generated at the cam end, not the cap and rotor.

If that was my car or a client car Id have the valve cover off and the cams out and see whats going on before the motor broke in a very expensive way.

The only time we see heat at a cam generated like that is in cases of oil starvation to a bearing and it will not run long that way.

Id pay particular attention to the cam bearings and be sure they went on the correct way and not turned around backwards. Especially the end one right next to the rotor.

 

Noted & thanks, I will see what I find.

As above, I know about putting the caps back in the right place & the right way round, I'll be fairly pissed off if I've somehow screwed that up.

Off to Maranello Spares for more gaskets, washers & another cambelt I guess (happily its only 10 minutes down the road).

 

Might explain why the lip seal was leaking in the first place, especially if it was a nitrile seal. .....
Any obvious damage to the lip due to overheating?

 

Not that I could see. The rotor was fine when I took it out initially.

If it has got very hot the new seal also appears to be OK still as well because there was no oil in the cap after the meltdown. I will have a good look at it & take a view on whether to replace it again.

This has only happened post the work I did to reseal the top end of that bank of the engine (which included removing the cams).

We will see what there is when I take the valve cover off. It will be fairly obvious if I have put one of the caps on backwards. I'd be very surprised, but you never know maybe its a case of "idiot be me".

 

It can be that the high voltage of the coil went trough the plastic to the cam and heat up the plastic ?

 

I am going to assume that is a joke.

 

Yah, a joke. High current from coil passes through the carbon tip on the brass plate in the middle of the rotor, then to the brass tip of the rotor, going over to the 4 brass tips of the cap, trough the leads and spark plug over to the metal of the engine.
Imagen that, instead springing over to the 4 brass tips in the cap, current passes trough the plastic direct to the metal of the cam....I'm just trying to find an explanation what could cause such a heat for melting that plastic.

 

Never one to be able to resist a good mystery I have pulled the rear cam cover tonight. Happy/relieved to report that I have not been a complete eejit and all my cam journal caps are in the right place and the right way around - 10,9,8,7 & 6 & "S "to the front on all of them (same for the exhaust cam).

There is evidence of heat in the Dist seal journal though for sure, it is discolored. as can be seen. I cleaned it with a scotchbright pad before I assembled it. The distributor oil seal looks to have taken on a funny shape at the lip though as above, it was not leaking. I probably should replace it though sadly it appears to be the worlds most expensive oil seal (!)

The one I took out was a brown Viton seal - any views on one of those vs the black one?

Brian, do you think I can get away with pulling the cam caps one at a time to see if there is anything obvious before I have to pull the whole cam (remove the timing belt etc) ?

The plot thickens (a bit).

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The black coloured seals are made from Nitrile Rubber. They don't have such a high tolerance to temperature compared to the brown Viton seals. I bought some of those black seals from Maranello, a while back. They were unbranded and not great quality. The lip retaining spring came out of the lip very easily when assembling them into the heads and after a while one leaked.
When I replaced the O rings (with X rings) in the lip seal carrier at the pulley end of each cam I bought some SKF Viton seals from Bearing Boys. £11.50 + VAT & postage.
SKF CR35x47x7HMSA10V Double Lip Viton Rubber Rotary Shaft Seal.
Much better than the ones sold by Maranello and since fitting them no oil leaks into the distributor caps.
Incidentally, when I pulled the cams on mine I found one cap the wrong way around. One on an inlet cam nearest the cam pulley. There was no evidence of any damage, and it must have been like that for at least 30K miles, which is how many miles I've put on the car.

 

Thanks for that. I'm also using X rings at the front bought from the same source. I'll order a couple of those Viton seals, Maranello want about 25 quid for that black seal.