Hi All ! Brand new here and my first post. : I have a Series 3, 4.2 engine in a Replica car. It doesn’t idle beautifully and cylinders 1 & 4 run 1-200°C hotter than the rest . I have checked the dynamic timing with a strobe ( 20° BTDC at 1700 rpm on No 6) spark plugs and leads all OK. Distributor cap no obvious problem. However whilst the leads are in the correct firing order on the cap, I’m not sure they are in the right positions i.e could be 60 or even 120° rotated from the Haynes manual illustration. My suspicions aroused as 1 & 4 are consecutive in the firing order, I don’t think fuelling would affect only 2 cylinders.Car does run and drive so any ideas please ?
Welcome to the forums.
Is the engine still running injection or has it been converted to carbs?
It’s got triple,SU HD8’s but I really can’t see fuelling being the answer.
If it had still been injection then there was the possibility of a problem with the two injectors, triple carbs nullify that concern.
Also just to confirm and please dont take any offence at this question but just so we are talking about the same cylinders, No1 is next to the firewall?
Yes, 1 at the firewall and 6 at the fan.
You are aware the firing order is153624. (Anti clockwise looking down onto the dist cap.
That’s just an indication that when somebody rebuilt the engine they didn’t align the distributor shaft correctly and its 180 deg out, it will still run that way. If you pull either 1 or 4 off when the engine id running do you notice any change in RPM?
How do the plugs look when you take out all six and compare? Do you have compression figures to compare?
OK,I removed all the plugs and turned the engine over until No6 (front cylinder was on compression then continued until the 8° BTDC mark aligned on the crankshaft pointer. As I suspected the rotor arm is pointing 180° away from the No6 position indicated in the Haynes Manual diagram above. I’m at a loss how to change it though ! The distributor shaft will only fit in one way due to the unequal size of the lugs that engage the engine driven shaft. The rotor arm will only fit one way on the other end ?
The only way to correct it would be a sump off and reposition the lower portion of the distributor shaft. Not a job you want to tackle until the engine needs a rebuild.
This is not a new problem, its been reported many times before, just position the leads so that the leads go to the correct plugs.
Could I not achieve the same result by taking the offset dog plate off the bottom of the distributor shaft and turning that 180° ?
Possibly, but it was match drilled and may not line up correctly when turned 180 degrees. It would be worth a try.
Also, If I recall correctly, isn’t the distributor drive dog off center? This would prevent it matching the distributor drive. The idea is worth a look.
Yes, the dogs are off centre rather than being different sizes. Effectively I’d be rotating the distributor shaft 180° inside the dog drive plate,so it should work ! I might see if I can get a second hand Dizzy to try it out.
Is the 180° issue a red herring though. Shouldn’t I be able to achieve the correct timing simply by reordering the HT leads on the cap ? If so I’m still no closer to solving the original problem.
The lower shaft inside the block has a gear with 20 teeth, thus it is possible to put this shaft in 20 ways, one of which is the standard factory method. Slot parallel to the crank at TDC.
If somebody else rebuilt this engine, you can confirm that they put this shaft in right by looking at the offset in the top end. It should look like this when #6 front is ready to fire.
The dog #17 at the bottom end of the shaft is off center, so you can only put it in one way. The rotor should be pointing at #6. If it is not, say it is pointing at #1, you don’t need to drop the sump to solve this problem.
The upper shaft #12 can be put on the lower shaft #14 two ways, by rotating it 180 degrees. That is what I would do.
If you really want to have the wires the way they are in the book you don’t need to do any engine disassembly. Take out the distributor, remove the points plate and unscrew the screw in the center of the shaft. Unhook the springs and lift off the top cam shaft. Rotate it 180* and put it back together again. All that is unnecessary though, since the engine will run fine with the distributor in any position, as long as the correct plug is getting spark at the correct time.