Oil pump and distributer

[PercyUK]

This is one for the experts amongst you.
Is there any way that the oil pump could conceivably affect the performance of a distributer and impose any hesitation resulting in a random misfire.
I have exhausted every angle trying to diagnose a misfire on my engine and am now thinking out of the box because I have nothing left to check, adjust or replace.
Thoughts?

[scoutpilot]

Only in as much as relocating the firing points for the plugs. A random misfire (at idle? or top speed?) is generally associated with bad connections, grounds especially, corroded, brittle wiring (including spark plug wires), carbon trails in the distributor cap, a crack in the distributor cap, or a failing condenser.

[BillT]

Just a guess on my part.... what about excessive wear where the distributor shaft key slides into the oil pump shaft? Couldn’t slop in the fitting cause  issues with the points performance? Like I say just a wag. Maybe the tensioner spring on the end of the shaft went missing?

[PercyUK]

Hi, the only reason I was thinking about it is because I have replaced and tested everything I can.
New coil, dizzy, condenser, points, plugs, leads. The solex was swapped for a new Carter.
The valves checked and adjusted where required and a compression test gives me 130lbs on each pot.
I added two further earth straps, isolated the alternator incase it was sending a spike and even supplied power to the coil directly removing the harness from the equation and I still have the problem which predates all the work.
In the absence of anything else I started to wonder about the oil pump given that it is directly responsible for the rotation of the dizzy and if it could be randomly slipping in some way.
Frankly it's a mystery.

[scoutpilot]

Percy is this "random misfire" a gentle, yet disconcerting puff from the exhaust or does it seriously affect performance? It is not unusual for an occasional minor interruption to occur in these old motors. When was the motor overhauled? It may be a worn valve guide. The valves themselves rotate a few degrees with each rise and fall. A worn valve stem in a worn guide can be an annoyance.

[PercyUK]

Hi, it's a proper misfire, most noticeable when driving along on a flat road and it feels like you're hitting bumps in the tarmac except there aren't any. Definitely affects performance.
I checked the guides when I replaced the pistons replacing a number as well as some valves at the same time.

[scoutpilot]

I have a very old rule of thumb. If one of a set is bad, replace the entire set. That has saved me many extra excursions into a motor to replace the next one that went bad.

[PercyUK]

I have a similar rule and have already tried other coils, plugs and condensers without result

[PercyUK]

Hi BillT, in the absence of any other options I am going to inspect the oil pump. I know it was replaced in the past as the distributer won't allow number 1 plug lead to be at 5 o'clock so I can use it as an excuse to rectify that.
Updates to follow.

[BillT]

Any luck?

[PercyUK]

Hi, so I dropped the pump and it looks fine. There appeared to be a bit of binding as I turned it by hand but I can't imagine the engine having trouble with it. I cleaned it and measured it to find that it is well within tolerance.
After cleaning there was no binding.
I am waiting for some gaskets to arrive and then it will be refitted.
I'm not holding my breath but you never know.
Further updates to follow.

[SteveKfl]

This thread is a real "mystery".  Thanks for sharing.

[PercyUK]

Well, that didn't fix the misfire. Pumps oil like a champ and my distributer is now oriented the correct way so it's not all bad.
Back to square one.

[scoutpilot]

Three more questions.

What is the timing set at?

What is the octane rating of the fuel?

Is the fuel laced with Ethanol?

[PercyUK]

Hi,, the ignition timing has been varied in an attempt to resolve it from the original 5 btdc to as much as 15 but is currently about 10 degrees btdc.
According to our government website our fuel is 95 octane and is E10 so has 10% ethenol in it.
It runs quite weak at 5 degrees and advancing it always improves smoothness but never gets rid of the misfire which always remains when just cruising regardless of speed.