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4 Cylinder Ignition Timing


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A quick question on ignition timing. I have three working distributors for my TR3A. I've had them all in the car today. Set them all to 10 Deg BTDC with the engine at 750 to 800rpm. This with the vacuum advanced connected (but should make a difference at that RPM) when each was set at 10 Deg BTDC at tick over I measured the max advance at higher rpm. I got 28 to 32 Deg BTDC dependent on the distributor. Which seemed OK. All vacuum advances work as far as I can tell (to the suction and tongue over test). However I'm.not sure they are right for the TR but take comfort that they were all similar at max. 

      My question is more about the variability of the timing. All three distributors showed an iratic timing spike. It would be consistent and then suddenly there would be one spark that was about 10 Deg retarded to the rest and the back again. I'm using an Accuspark SP8000 which also measured rpm which also jumped about at the same time. The mechanical rev counter in the car was rock steady. The reading did not feel correct and just a glitch. Is this because the distributor is not surpressed or could this be a real reading. I'm not presently believing all three distributors have the same fault but it not impossible. 

     Another quick question, are you better advancing the timing until it pinks and then take it back a bit or is 10 Deg dynamic about right and leave it alone. 

Neil

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That’ll be a worn distributor drive bush, advance weights, advance springs etc.  Points ‘scatter’ is what you are seeing.    Best solution is get it fixed by Distributor Doctor.  

Interim fix is fit a Pertronix electronic ignition set up, but not as good as a total rebuild.   My own distributor gave similar vague measurements and the Pertronix levelled things out a bit.    https://www.moss-europe.co.uk/pertronix-ignition-systems

 

Peter W

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On 6/3/2021 at 3:44 AM, NCS_TR3A said:

Another quick question, are you better advancing the timing until it pinks and then take it back a bit or is 10 Deg dynamic about right and leave it alone.

Ignition timing is most critical to performance at the maximum power load & revs, its your 'all-in' timing where the centrifugal wont go any further. Idle ignition timing has far less importance. The 10deg at idle assumes a new dizzy with proper advance curve....with an older/worn dizzy its better to set ignition at higher revs (the all-in point)...or do it 'by ear' using the just-not-pinking method.

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Should be, the points are the same. only possible difference could be the shaped grommet where the wires pass out of the distributor.

Bob.

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41 minutes ago, Lebro said:

Should be, the points are the same. only possible difference could be the shaped grommet where the wires pass out of the distributor.

Bob.

No they are not

Lucas distributor 40403 as used on TR2 has different points to all the later type distributors.

https://www.moss-europe.co.uk/shop-by-model/triumph/tr2-4a/electrical-system/ignition-system/ignition-system-tr2-4a-1953-67.html
 

Peter W

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I can confirm they are different. We took TS2 on a rolling road last week & when we tried to change the points in the DM2 distributor they were different to the 25D4 and we were not able to get any on the day.

To my mind pertronix is a good upgrade although it will not cure any other faults in the distributor.

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Interesting. I recently sent my 25D distributor to Martin Jay for refurb, & moved the Accuspark unit from it to a DM2 to keep the TR on the road. They fitted fine, so I assumed the original points would also be the same. ??

Bob

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Thanks to all that commented - I have have had my dizzy rebuilt by Dizzy Dr but I'm still on points.  I am considering going to EI but keep a baseplate with points and condenser in the tool bag.  I will have a look for a DM2 specific EI.

Laurence

 

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I keep a spare Pertronix sensor in the tool bag, much easier to swap that than re-setting points & timing on the side of the road.

Bob.

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