Engine distributor

[Wedg1e]

Both the DM8 and the DLM8 distributor setups are electronically identical. The DM8 uses a GM HEI module. The DLM8 uses the same electronics in a Lucas made module that hangs on the side of the dizzy. DM8 stator and pickup on the left; DLM8 setup on the right. The only difference is the amplifier connector. This GM HEI type setup is fitted to huge numbers of 4, 6 and 8 cylinder non-GM 80s & 90s cars, only disappearing when conventional distributors were replaced by crank triggering and coil packs.

View attachment 228571

I've seen a couple of RV8s (including my own) that had a strange 'rev limit' effect going on - seemed to pull hard enough but would hit about 5000rpm and just stop, then pick up when the revs fell. Turned out to be that pickup coil breaking down. On mine it eventually failed open-circuit and the car just wouldn't start.
For info, the coil should measure about 3000 Ohms or less; if it's substantially higher than that then it has to be suspect.
Also on the DLM8 with the ignition amp mounted to the side of the distributor: the amp is bolted to a small add-on casting that is finned on the back to allow heat to dissipate. The amp gets its earth through its mounting screws to the casting. If the casting corrodes two things happen: first the amp doesn't see a good enough earth and secondly the heat can't conduct through to the fins to allow the amp to cool. How this manifests is usually that the car runs OK for the first few miles and then starts stuttering (the amp is overheating).
Pull the amp and casting off the dissie, polish up the back of the amp, clean up the finned casting and refit with a bit (literally a smear) of heat transfer compound behind the amp and use new mounting screws and normal service should be resumed

 

[Wedg1e]

Knew I had the pics somewhere of the last time I did this job.

I'm sure the centrifugal weights changed over the years so not sure you'd get perfect response but agree that it's feasible to interchange them.

 

[Morrisman]

Nah mate, forget the ignition; I think that insufficient carburation was your problem there

Everybody told me the tunnel ram with 2 x 600 Holleys would be carp, no bottom end, rough tick over, that it wouldn’t pull below 3000 rpm etc.

I got it to idle at 700 rpm and it would light up the tyres just by tapping the throttle when trundling along at idle in gear. Power to weight ratio was incredible.

Then I sold it when wife and I split up and I moved back to England.

 

[Morrisman]

I've seen a couple of RV8s (including my own) that had a strange 'rev limit' effect going on - seemed to pull hard enough but would hit about 5000rpm and just stop, then pick up when the revs fell. Turned out to be that pickup coil breaking down. On mine it eventually failed open-circuit and the car just wouldn't start.
For info, the coil should measure about 3000 Ohms or less; if it's substantially higher than that then it has to be suspect.
Also on the DLM8 with the ignition amp mounted to the side of the distributor: the amp is bolted to a small add-on casting that is finned on the back to allow heat to dissipate. The amp gets its earth through its mounting screws to the casting. If the casting corrodes two things happen: first the amp doesn't see a good enough earth and secondly the heat can't conduct through to the fins to allow the amp to cool. How this manifests is usually that the car runs OK for the first few miles and then starts stuttering (the amp is overheating).
Pull the amp and casting off the dissie, polish up the back of the amp, clean up the finned casting and refit with a bit (literally a smear) of heat transfer compound behind the amp and use new mounting screws and normal service should be resumed

I replaced all my ignition components bit by bit, to track down an annoying low rpm ‘fart’ from the exhaust, for want of a better word. It would miss occasionally, and splutter and fart at me. A very unpleasant sound when one is sitting at the lights looking cool.

After no end of faffing about, including fitting a new Edelbrock 4 barrel carb and manifold, to the tune of £500, it turned out to be me connecting the distributor vacuum to full time manifold vacuum port rather that the ported stub above the throttle plate.

The stock distributor can’t handle that much vacuum at low rpm, as it advances the timing far too much.

 

[Domdom]

Nah mate, forget the ignition; I think that insufficient carburation was your problem there

You owe me a keyboard, just snorted coffee all over this one.

 

[Stueeee]

I'm sure the centrifugal weights changed over the years so not sure you'd get perfect response but agree that it's feasible to interchange them.

It's only the bottom half of the distributor spindle that needs changing, so you can choose whether to use the original weights and springs or the "new" ones from the DM8 dizzy.

 

[Stueeee]

Everybody told me the tunnel ram with 2 x 600 Holleys would be carp, no bottom end, rough tick over, that it wouldn’t pull below 3000 rpm etc.

I got it to idle at 700 rpm and it would light up the tyres just by tapping the throttle when trundling along at idle in gear. Power to weight ratio was incredible.

Then I sold it when wife and I split up and I moved back to England.

Can't see from the photo whether they're vac secondary style Holleys or double pumpers. My Chevy truck had a huge double pumper on it when I bought it in the US. Would have needed to have my own oil well to drive it with that carb on there in the UK; I fitted a 650 vac secondary Holley, which still delivers brisk performance with tolerable fuel consumption on a warmed over 350 SBC. After all, we aren't buying or building this stuff because of the fuel economy are we?

 

[Morrisman]

Can't see from the photo whether they're vac secondary style Holleys or double pumpers. My Chevy truck had a huge double pumper on it when I bought it in the US. Would have needed to have my own oil well to drive it with that carb on there in the UK; I fitted a 650 vac secondary Holley, which still delivers brisk performance with tolerable fuel consumption on a warmed over 350 SBC. After all, we aren't buying or building this stuff because of the fuel economy are we?

Vacuum secondaries they were. I don't think I ever calculated the gallons per mile, but it wasn't much.

I had a single 600 Edelbrock on a stock manifold before that, that ran rubbish, always lagged or stumbled when ones foot fell heavy on the throttle, no matter how much I tweaked and adjusted and changed jets. Apparently it is quite a common failing with them.

The tunnel ram and carbs was the sharp end of £1500, with import duties etc, (this was in the Philippines)but well worth it when driving, made it far more fun.

 

[Wedg1e]

The stock distributor can’t handle that much vacuum at low rpm, as it advances the timing far too much.

On the TVR the vac advance is coupled via a delay valve to stop the advance coming on too quickly... or too soon... I forget which