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Advance Weight Springs

coolbop
Posts: 8
Joined: Sat Jul 13, 2019 10:10 am
Location: Woodbridge, Suffolk

Re: Advance Weight Springs

Post by coolbop » Mon Jul 15, 2019 10:56 am

I guess what's happening below 460 crank rpm is kind of academic as the engine never runs at that speed. By the time we get to an idle speed, going on your figures Christopher, the engine should be advanced by a couple of degrees, by which time the spring is probably under tension.

Ian

coolbop
Posts: 8
Joined: Sat Jul 13, 2019 10:10 am
Location: Woodbridge, Suffolk

Re: Advance Weight Springs

Post by coolbop » Fri Jul 19, 2019 12:53 pm

I thought people might be interested in the advance I was getting once I ran the distributor on the car.
advance_original_springs.png
These are actual advance figures, measured against the 10 degree static advance marker.

At first I thought I was way too advanced, then I remembered that I forgot to disconnect the vacuum! Disconnected showed much better figures so at least I know vacuum advance is working.

Looks like I'm around 2 degrees too advanced in the mid rev range and about 5 or 6 degrees in the lower range which suggests that weaker spring is indeed a bit slack. However, I might leave it alone for now and look out for any pinking or hesitation at low revs when I'm driving.

Main thing is, all the gunk is cleared out and the whole thing is running totally freely now.

Ian

Petelang
Posts: 213
Joined: Sat Feb 13, 2016 10:23 am
Location: Nottingham
Contact:

Re: Advance Weight Springs

Post by Petelang » Sat Jul 20, 2019 9:25 am

Would it be right to say, that with modern ethanol fuels, the greater advance would suit better?
Peter
Peter Langridge
Cloud Nine Classic Weddings, Nottingham.

coolbop
Posts: 8
Joined: Sat Jul 13, 2019 10:10 am
Location: Woodbridge, Suffolk

Re: Advance Weight Springs

Post by coolbop » Sat Jul 20, 2019 11:30 am

Hi Peter,

My understanding is that it's the other way round - today's lower octane fuels have a greater propensity to knock and so need to run more retarded than with older higher octane fuels.

I'm lucky enough to also own a Lotus Elan and it's really sensitive to timing. I assume Lotus set it as advanced as possible to obtain the maximum power from the engine. They were also timed to run high octane five star fuel available at the time. It's therefore to common to retard them from spec to avoid knocking.

I sense that the Daimler engine was never timed so aggressively and so might not suffer so much from being more advanced than spec. I can't drive it at the moment but when I do I'll keep a close ear out for any signs of knocking.

Ian

fredeuce
Posts: 47
Joined: Mon Feb 29, 2016 10:56 am
Location: South Australia

Re: Advance Weight Springs

Post by fredeuce » Wed Jul 24, 2019 5:12 am

Coolbop,
Something you should look out for whilst examining the mechanical advance mechanism is to check for wear on the pins that the weights are anchored to. Also where the weights engage with the distributor cam base this area can wear as well together with the main shaft bushes. I had to replace pins and bushes on my distributor to tighten everything up. Prior to this the rotor arm was firm but was able to oscillate back and forth causing misfiring at higher rpms.

Ian Slade
Posts: 456
Joined: Sat Feb 13, 2016 9:54 am
Location: Akrotiri Cyprus

Re: Advance Weight Springs

Post by Ian Slade » Wed Jul 24, 2019 6:50 am

When I timed the engine I set the timing statically as in the manual, this requires it to be checked on a number of revolutions as there is a slight difference of position every time the distributor is moved, once set at least 2 revolutions by hand is needed to ensure accuracy, I then fired up the engine and marked the crankshaft static mark against the the timing bracket on the timing cover. Back in those days the RPM setting was from the rev counter in the dash, a 10rpm increase or decrease can cause the dynamic timing to be off by a couple of degrees, today with clip on digital rev counters this can be set more accurately.
Owner since the 70's, Genghis is slightly to my left.

coolbop
Posts: 8
Joined: Sat Jul 13, 2019 10:10 am
Location: Woodbridge, Suffolk

Re: Advance Weight Springs

Post by coolbop » Wed Jul 24, 2019 8:32 am

Thanks guys.

A misfire at higher revs is actually something I was suffering from and hence the strip down. I'm hoping the fact the mechanism is no longer gummed up will resolve it but if not, next stop will be to look again for the kind of wear you describe fredeuce. When timing with the light I'm seeing almost no scatter which I read as a good sign :D

I had a similar experience Ian - I went round multiple times just to make sure everything was consistent - as I suspected, doing everything in the proper direction of rotation seems really important.

Looking forward to getting my steering rack back so I can go for a drive!

Ian

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