Distributor advance stuff

Post by **cumbriankeith** » 15 Feb 2006, 20:52

CU engine - all standard.
Was checking the timing and sorted it at idling - 5ish degs ATDC@800-900rpm as per book.
Thought I'd check the centrifugal advance and was shocked to find that it jumped to about 32 degs by about 2000rpm and was 38@3000 and I think went over 40 at top revs. I think it should be max 30 at around 3000 - so it seems that my dizzy springs are beluga'd.

What sort of issues happen with this condition? I'm thinking poor performance and running hot - anything else??

Can springs be renewed?

Anyone got a goodun going beggin?

Post by **redstar** » 16 Feb 2006, 10:25

same with mine!!!!!
could do with one also...

Post by **HarryMann** » 16 Feb 2006, 10:38

Potentially, catastrophic failure through high-speed detonation, that's what - overheating in the sense that local chamber temps and pressures are higher, but not the engine as whole. Don't rely on temp gauges to predict this sort of detonation, on a hot day (high intake temps) and at high throttle, high rpm, it can all be over in a fraction of a second! Been there, done that, usually on higher performance engines, bits come off spark plugs and pistons can be eaten.... usually motorway driving, into wind or up hills. Does it ever hesitate or 'kick' at times like that? Might even be going extremely well at the time, but that cough or splutter is a BIG warning sign, you won't necessarily hear hsd, unlike lsp (low speed pinking), too much racket going on usually at high speed.

Obviously I'm trying to worry you, but that's what can happen. Worth sorting asp and putting some 98 octanne in now and again till you do, lay off the high speed and high load stuff. Anything funny happen when you lift off at high rpm?
You might also back the static off a bit till then (retard), as long as it starts and runs OK low down.

5ish degs ATDC@800-900rpm - is that right, 5 after?

Post by **cumbriankeith** » 16 Feb 2006, 17:01

Yeah that's what I was fearing - I have a spare diz which I will try to see if it is any better - and also look to getting another when I can - anyone got any spare, going to DF??

5 AFTER is what the book and the timing scale says (ie where the red dot is)

Post by **HarryMann** » 16 Feb 2006, 19:58

Do these ere, CUs have a vacuum advance Keith?

Post by **cumbriankeith** » 16 Feb 2006, 20:20

Yes - they have 2 pipes to the capsule thingy and look like this:

Post by **HarryMann** » 16 Feb 2006, 21:50

... and the vac was disconnected doing the centrigugal swing?

and what was the datum point for those figures you gave, that is, for say 32 degrees, is that the TOTAL advance

'cos we really ought to plot them out to see where the kink is, it's usually quite low, 1500 rpm (presuming there's two sets of srpings of different rates) - guessinga bit here.

Just thinking has the stiffer rate spring jumped off it's hook... (still guessing)

Post by **cumbriankeith** » 17 Feb 2006, 12:16

I'll do a few more tests tomorrow...

Post by **toolsntat** » 18 Feb 2006, 21:00

Hi Keith, do you use the idle stab..ing unit or do you leave the 2 plugs connected to each other?

Post by **cumbriankeith** » 18 Feb 2006, 21:05

No I don't use it - even tho it did still work I took it off on the advice of Steve Shaw and Simon Baxter.

Post by **toolsntat** » 18 Feb 2006, 21:16

You say you are setting to 5 after but I thought it should be 7 before!! Could this be where things are going wrong??
Been trying to sort out the same problem today but had no luck!!

Post by **cumbriankeith** » 18 Feb 2006, 21:57

Haynes says 4 to 6 after TDC and that corresponds with the red dot on the timing scale...

Post by **cumbriankeith** » 22 Feb 2006, 23:31

Just been looking at the Haynes again and puzzlement continues - I also have a printout of a web-page Simon Baxter did a few years ago which differentiates between the timing setup using the idle-stabilising-unit and not using it - that is, it seems to be 7 btdc if you intend to leave the unit out and 5 atdc if you intend to reconnect. Maybe Simon or Steve S will confirm or clarify - or I might give Steve a ring and report back...

Post by **TimL** » 23 Feb 2006, 17:34

did you find anymore info as im about to swop the dizzy this weekend and will have to reset the timing( something ive done but not good at)

Post by **cumbriankeith** » 23 Feb 2006, 19:40

Yes - spoke to Steve who recommends it's set at 30 degs advance at 3000rpm - gets the best out of the engine (vac pipes connected as normal - ditch the idle stab unit) Can check the vac advance works by looking at the marks while opening the throttle.
I'm in the middle of stripping a couple of dizzies to make the centrifugals work...

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