350i distributor the saga sort of continues

[KKson]

Well tonight I refitted the rebuild original distributor with new o ring seals, new rotor arm, new cap and new and functioning ignition amp. Car started first turn of the key and purred like a kitten, for about 2 minutes and then a misfire started which got worse and worse. Stopped the car, popped the dissy cap and found the new rotor arm had virtually melted, as has the internal centre of the dissy cap. Is was this issue that caused all the problems previously with the dissy cap dancing around after the rotor arm distorted.

Anyway put the new Powerspark dissy back in, with it's ignition amp removed off the old dissy. All started up and after a few runs I've got the timing around 3 degrees BTDC with no pinking and all behaving. If I advance it any further it still pinks a bit on load.

Not a bloody clue what would cause the issue? Cap and rotor arm were off the new dissy that came with the 390SE I've bought.

Good news is the Wedge is running so out for a blast this weekend, come rain, hail or shine.

[gmw9666]

Now that's weird

[The Hatter]

Wow that's impressive damage! Looks to me like you've got two problems; you've got mechanical wear on the rotor arm tip (so it's hitting something), and it's melting (so extreme heat = large gap = too far away from the dizzy cap internal contacts). I'd say either the dizzy cap doesn't fit the distributer housing or the rotor arm is too long.

[Rockettvr]

Poor contact between the rotor arm and centre contact in the dizzy. Poor contact=high electrical resistance=heat
Damage on tip of rotor arm is either its hitting the contacts on the edge of the dizzy cap (too long?) or the high temp has melted the rotor arm allowing the brass section to move and hit on contacts.
Possibly the centre pin in the dizzy is stuck or you've got mis matched parts ???
Either way that rotar arm is fubar and the cap is probably too

[Wedg1e]

Aye, there have been at least three variants of the V8's dissie cap.

[KKson]

I measured both with a vernier gauge to double check they were the same dimensions as the origins, which had been fine for over a year and then decided to over heat and distort which I put down to the enthusiastic driving at Millbrook coupled with it being a very hot day. So it's happened twice with the same distributor. It could be that when thrashing around there's enough movement in the bearings to increase the gap and cause the over heating. I think scrap bin for the old dissy.

[B@man]

Flog it on ebay - even knackered RV8 dizzies are worth a few quid for converting into "dumpy dizzy" needed to drive the oil pump after switching to coil packs !

[mrzigazaga]

I know you are not that silly but was the cap settled in its position before you locked it down?...I done it once with Delilah and completely smashed a rotor arm into several pieces...If possible as i don't know about dismantling a dizzy can the shaft be removed and rolled on a flat surface, This would tell you if the shaft is warped...If the answer is yes to these questions then as Simon say's....

Now get out there and enjoy yourself....

[KKson]

mrzigazaga said:

I know you are not that silly but was the cap settled in its position before you locked it down?...I done it once with Delilah and completely smashed a rotor arm into several pieces...If possible as i don't know about dismantling a dizzy can the shaft be removed and rolled on a flat surface, This would tell you if the shaft is warped...If the answer is yes to these questions then as Simon say's....

Now get out there and enjoy yourself....

Yes cap was properly centred and in position with no movement on it. Shaft itself does not appear to be bent and with hand pressure no obvious signs of lateral movement. Either way it seems to be the issue.

Was further investigating the Powerspark pinking issue. With the old dissy with vacuum attached, when full throttle is applied the timing advances by about 6 degrees. With new Powerspark unit and same throttle position timing advances almost 12 degrees. To me it seems the vacuum advance is just a bit too enthusiastic. I was going to give Simon at Powerspark a call this morning to see if a different vacuum advance unit is available or the existing unit can be adjusted.

[mrzigazaga]

Not sure what the vacuum advance should be?....But if you had movement in the bearings then they were probably worn....What you need to do is remove the bearings...Carefully open up a shotgun cartridge ..Remove shot and replace with dizzy bearings....Close and seal the cartridge end...Place into shotgun chamber..Safety on......Find a nice piece of wood..Take aim...Safety off and Blam!....Sorted....

Oh and pictures of the uses of reconstitution of old parts is always nice...

This may help people like me....
https://www.google.co.uk/url?sa=t&rct=j&q=...

[KKson]

Spoke to Powerspark. They have confirmed that the vacuum advance on their unit is the correct figure and the reduced advance on my old unit is worn. They say that if need be the old vacuum advance will fit the new dissy or alternatively just retart the timing a little, or use higher octane fuel. I know the tank contents are a mix of standard and super unleaded at the moment so I'll ensure only the higher octane is used from now on.

Anyway it runs fine, it doesn't misfire and the forecast for the weekend is...... pants!

[KKson]

Okay, I mean full throttle in the confines of the garage at 9.30pm at night without waking the neighbours kids and poisoning myself with fumes so in reality probably 2/3 throttle!

I've got a total of four different rotor arms to play with, all the same depth and length, including the original one that ran for a year without issue before then distorting.

[mrzigazaga]

KKson said:

Spoke to Powerspark. They have confirmed that the vacuum advance on their unit is the correct figure and the reduced advance on my old unit is worn. They say that if need be the old vacuum advance will fit the new dissy or alternatively just retart the timing a little, or use higher octane fuel. I know the tank contents are a mix of standard and super unleaded at the moment so I'll ensure only the higher octane is used from now on.

Anyway it runs fine, it doesn't misfire and the forecast for the weekend is...... pants!

All sorted then.....

@ Bobby: Fair point about the vacuum advance...

I run mine on 97-98ron all the time and my timing will only run at 3 degrees static idle...Pinks on 4-5-6-7-8-9-10...This is with an old dizzy...Although the amp has been replaced cos the paste is newish...

Good news on the Wedge Keith even if the weather will be shyte.....

[KKson]

Hi all, just thought I'd update this topic. I still wasn't happy running the timing at 2/3 degrees BTDC rather than the 8 so last night I removed the old but functioning vacuum advance unit off the old dissy and fitted it to the new Powerspark dissy that is in the engine. It's a straight swap. This evening I've re-timed it to the correct 8 BTDC and I've been out to give it a spanking and NO pinking and it goes like stink!

So happy with it I've given it a wash and polish also. The love is back......

[Campbell]

Glad your getting to the end of your distributor issues.
Its because of the dizy this is why i went wasted spark.

[adam quantrill]

That melted rotor arm is made of the wrong sort of plastic. The old Lucas ones are more like Bakelite and resist the heat properly.

You should be able to take a hot soldering iron to it and not make a dent!