Erratic dwell angle

Dave3066

Dave3066

Well-Known Member
Gents

Having today fitted my reconditioned dizzy I set the dwell angle and timing as per the book. ie rpm to 600 - 650 dwell angle 26 - 28. This all works well until I rev the engine. When it settles to idle again the dwell angle has changed. It takes quite a few turns of the adjuster to bring it back into limits and when I rev it again, after settling to idle the dwell has changed again. For example, I set the dwell, rev the engine, allow it to settle and the dwell is 33. Adjust it back to limits rev it again, let it settle and the dwell is 18. Adjust it back in.....etc etc. Each time the adjuster requires a few turns before anything happens. Any ideas?

cheers

Dave
 
Hello Dave,

Can you feel lateral movement in the distributor shaft by holding the rotor and moving side to side?

I am assming that your distributor is fitted with points?

Ron.
 
Hi Ron

Yes points fitted.

No lateral movement of shaft. The dizzy was completely stripped down and reconditioned by H&H Ignition over here in the UK.

Dave
 
The first thing I'd look at is the nylon that the dwell adjusting screw is threaded into, if the thread on that has stripped or is loose then it can jump a thread or two as you rev the engine. If that's the problem a points nut will screw on the end, and the nylon wil hold it in position so you can still adjust the dwell in the normal way. Another thing could be that the points pivot is stiff.
 
Hello Dave,

Hmmm, with your distributor fully reconditioned and with no lateral play in the shaft.....

I know that wear in both the timing chain and timing gears and the camshaft-distributor skew gears can lead to erratic ignition timing, which you can see using a timing light when you rev the engine, but I don't think it has any effect on dwell angle.

It is my understanding that variations in dwell angle are a direct result of either lateral movment in the distributor shaft or wear over time of the heel on the points.

Now if there is no lateral movement, and obviously no wear is taking place on the heel in a few seconds, then the cause must be elsewhere. (I know stating the obvious).

If you set the dwell, take off the earth lead on your dwell tachometer, rev the engine then re attach the earth lead, has the dwell changed? If it has, then the meter is not the problem.

Ron.
 
pilkie said:
Sticky or stiff mechanism as its new!
Click to expand...

Now that makes sense! Particularly as it seems to take a few turns of the adjuster before having any effect on the dwell angle. I've managed to get the dwell stable at 22 degrees which is close enough for now and the car runs fine. I'll try it with another meter too and see what happens. Perhaps exercising the adjuster a few times over the extent of travel will remove any stiffness.

cheers

Dave
 
as you are all talking about the dwell it is the correct dwell for the v8 i am not sure it my dwell has got 8 cyclinders on there can any 1 help me out on this please
 
pilkie said:
Sticky or stiff mechanism as its new!
Click to expand...


If that is the case then it won't take long to strip the thread out of the little nylon/plastic bit that the adjuster screws into.
 
garethp6 said:
as you are all talking about the dwell it is the correct dwell for the v8 i am not sure it my dwell has got 8 cyclinders on there can any 1 help me out on this please
Click to expand...


If you haven't got an 8 cyl dwell scale IIRC (because I've got the correct one so have never had to do it) you use the 4 cyl scale and set the dwell to double the V8 setting, so 26-28 becomes 52-56.

Anyone who has a dwell meter with both 4 and 8 cyl settings could try and see whether I'm correct, or I just dreamt it after eating cheese too close to going to bed..........
 
It does sound like the nylon bit the dwell adjusting screw goes into has stripped ,But surely that should have been replaced on a recon unit ?
 
harveyp6 said:
pilkie said:
Sticky or stiff mechanism as its new!
Click to expand...


If that is the case then it won't take long to strip the thread out of the little nylon/plastic bit that the adjuster screws into.
Click to expand...

Hmmmmmmm that's a bit worrying then. I'll check it next chance I get and watch for a smooth (or not) movement of the points plate as I turn the adjuster. If it is that then I'll get back to the company who recond'd it and see what they have to say.

I wonder if Brian Humphreys had any problems with his when he got it back? Brian if you're out there..... :)

Cheers

Dave
 
Hi Dave,

I had no problem whatsoever. Mind you, the 4 cylinder dizzy is very different. I change my points (if I had any) with a screw and a screwdriver acting as a lever!

Give Lee Hull a ring and talk him through your issue, he'll be accomodating I believe.

Brian.
 
Cheers Brian

I've emailed Lee the symptoms, but I'll ring him tomorrow and have a chat.

Next move is to fit my Pertronix Ignitor once I get one of those that works. Not had much luck with ignition parts lately. The ignitor is going back because I reckon it's knackered. Tested it across a 12V supply with a bulb in series. The bulb should light when you swipe the magnetic collar past the module but it doesn't. I've been in touch with the guy I bought it from (formerly Carolina Classics) and it is guaranteed for a year so he'll take it back and test it. If it is duff he'll send me a new one.

I'll get there eventually.

Dave
 
Thought I'd post some pics of my new dizzy.

It seems to have settled down now and the erratic dwell is now more. Steady at 27.5 degrees :)
 

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Looks like they've dispensed with the nylon and threaded the adjuster screw directly into the bracket. Those points, although obscured by the rotor arm would appear to be the very early (small) type.

That will make the rest of the engine look all dirty now.........
 
Harvey

Yes they are the small type early ones. I've got a set of the later, beefier ones on the old dizzy which I'll keep as a spare set.

The rest of the engine bay does look a bit scruffy now. I need to fix an oil leak before tackling that. I think it's coming from the timing cover.....

cheers

Dave
 
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