MG Sports Cars

Hi, my baby started first time, an unknown engine with a complete rebuild and a 35DLM8 distributor that that was a complete mess originally. I was stunned....However, and there always seems to be a however, it only ran 5 short times before the brand new Amplifier Module failed. The car had no bonnet and there was a healthy cold breeze blowing through my garage.

I had expected the Amplifier to fail as they are affected by heat (so I had read), but I had hoped at least to have driven the car and for a few thousand miles.

So as I see it I can either : 1. just by in a lot of spare Amplifiers. 2. change to the 35DM8 Remote Amplifier 3. change to a different electronic gizmo. or 4. go to a Mallory points system.

Option 2 is my first choice as it it the second cheapest. Does anyone know if it is a straight fit onto the 35DLM8 or do I have to make wires and plugs or even get the 35DM8 base plate.

Option 3 is looks ok but I have no idea which is the better electronic system and I want to stick with the 35DLM8 as the base ditributor and would prefer to use its magnetic pulse system.

Option4 is expensive, although I had read that someone had had an intermittent problem with one and then returned to electronic.

I like the idea of real points as at least you can tell what is wrong when they fail.

Any help will be gratefuly recieved.


Regards Ian

I vote for option 1 ;-)

No really, how about a Pertronics module?

Jim

I would look into Petronics and stay away from the Mallory dual points.

I'm not knowledgeable about the differences between amplifiers. For that sort of question, I contact Jeff Schlemmer at "Advanced Distributors". You'll find him to be extremely helpful.

Pertronix Ignitor systems are extremely popular in North America, but I believe most UK users choose Lumenition instead. Those two options should be fairly comparable.

Thanks for the feedback. Looks like it will be a Petronix and I will keep the Rover Amplifier just in case.

Ian,

What make of amplifier did you have? Reason I ask is I had a brand-new aftermarket amp fail after about 600 kms on my RV8 (same set-up you have). I switched to a Lucas unit and although a good unit, there was still some minor running issues to deal with.

I installed the remote ignition module kit which uses a Rover amp. This has proven to be the best one yet.

You do get what you pay for especially with ignition amps.

Simon, I assume it was an aftermarket amp as it did not have Lucas written on it....and it only cost £24. It can't have been the heat as there was no bonnet, the doors were wide open and it was blowing a hooley.

I looked into buying the remote one but again didn't know where it would have been made, so I have gone for a Petronix and a spare aftermarket Rover and a very old (1995 at least) genuine Rover amplifier. The second aftermarket one, which was to be my spare, gave a great spark compared to the old Rover amplifier. I got my aftermarket from Rimmers and I believe that Clive Weatleys are the proper ones.

On my previous Roadster I took out the Lumination ignition as it occasionaly misfired and put back points which I changed every 2000 miles or less. On removing the Lumination I found that the previous owner had knicked the wire in the distributer which shorted occasionaly, hence the misfire.

As you rightly say you get what you pay for and it pays to be careful.

Regards Ian

I'd agree Clive's modules would be Rover units. Can't imagine him selling anything else.

Simon, as I am struggling to get correct Petronix unit I may go the same route you have.

You sent me the jet and metering sizes that you changed to. Was this for your RV8 or your V8 and is the V8 a 3500 or larger ?

The jets and needles are for the V8, Ian. It has a 1980 SD1 3.5 with the Edelbrock 500 carb.

The RV8 uses the14CUX FI system on a 3.9.

Simon, many thanks. I have a 1995 3947 and the 500 carb and will buy the .083 and the .080 and try them both.

Hey Ian,
not sure how common it is in the UK. But over here, one of the cheapest options for a magnetically triggered module is the old GM HEI unit.
Mounted to a suitable heat sink, it will fire most hi or low impedance coils very reliably.
They are small, cheap, reliable and tolerate abuse well.
Lots of upgraged designs are also available if a hotter ignition is wanted, but the stock setup will fire just about anything that you can think up.
Hope that's helpful.
Cheers
Fred

Fred, many thanks for the info. I have just got the right Petronix kit. They sent me the wrong one twice.
I will keep your suggestion in mind if this kit is as successful as my last option.

My problem now is that I am going to fix something that is not broken....yet

I fixed what wasn't broke and it broke. Having carefully dismantled my Lucas 35dlm8 distributor I fitted the Petronix....and it ran like a dog missing and spluttering and stopping. It ran as though I swapped 2 or 4 leads. I turned the distributor in retard and advance and nothing changed. Checked everything and nothing got better. So I reverted to the original Lucas amplifier and without touching anything else baby just started and ran beautifully.
Clearly I have done something wrong but I have no idea what. Either the spark was too weak or at the wrong time.

Any suggestions will be very gratefully received.

Disappointed and disallusioned of Ashbourne.

Dear disappointed in Ashbourne,
sometimes women are just like that.
What you need to do is..........................OOPS!.......... Responding to the wrong thing.

Most likely the Pertronics pickup is out of phase with the distributor cap. This causes it to fire between cylinders.
The most common cause is getting the magnetic ring that fits onto the distributor shaft turned to one side or the other.
The other is having the wrong kit.
An easy way to tell is to check your current timing and then reinstall the pertroics without moving the distributor.
Re check the timing. If it changes by more than a couple of degrees then you will have a phasing issue.
The hard way but most accurate and visual, is to drill a large hole in the distributor cap so that you can see any one of the plug terminals.
Run the engine, you should be able to see the spark going directly to the terminal from the rotor tip. If it doesn't you need to do some re aligning.
If your kit doesn't use the magnetic ring (new style) then the clearance to the pickup becomes critical and can cause problems as well.
Hope that's helpful
Cheers
Fred

Fred, again many thanks.
I will carefully strip the distributor, again, and re-instal the Petronix making sure the magnetic/black ring is correctly aligned with its locating teeth.

The kit came with two rings the second was a spacer ring which I originally fitted, as per the instructions, but it caused the magnetic ring to foul the rotor arm. Maybe it requires the spacer ring and I had not seated them both correctly, which would give a vertical alignment problem and maybe not give a good enough impulse.

The other thing I noticed was that the rev counter seemed to wildly under read.

I suppose the good news is that I am getting quite good at stripping distributors and getting top dead centre.

Regards Ian

Just another thought based upon the tach reading low.
Possibly you have a magnetic ring for a 4 cyl.
Get a thin steel rod (small screwdriver etc.) and check the ring.
You should be able to detect 8 distinct magnets around it's circumference.
Cheers
Fred

Fred gave up on the Petronix as I was in danger of wrecking my Lucas bits which a t the moment work OK. I will however look into the GM option plus I read somewhere that there is a similar Bosch unit.

I think as I have a new spare Lucas module I will continue to run as is until it goes wrong again. At least I can swap the Lucas bits in a few minutes.

Any suggestion as to what spark plug gaps should be. Engine is a 3947 running an Edelbrock 500 which I have jetted down and now gives all 8 plugs the same nice pale brown/grey colour.

Regards Ian

With a carb and the stock ign. I would run somewhere around .028" to .030" plug gap.
The spec for the FI. engine is .033-.038" but with a carb and the stock setup you will probably run into cold start problems at this size gap.
Plus the small gap is a little less stressful on the ign. system.
Cheers
Fred

Fred, again many thanks. I had guessed that my plug gap was a little too wide as they came at 35 thou which I suspect suits a better ignition system and EFI. So I will go down to 30thou and see what happens.

Reason for my question was that I seem to sorted out the carb jets in that I have reasonable plug colours and all 8 look the same, however, at low revs I get a slight hunting and very occasionally it runs on for 1-2 seconds which is why I looked at my plugs and whether they were to hot a plug.

When you have a non standard set up information is hard to find. But it is fun sorting it out.

Regards Ian