My Willys 3A and 3B Community
TECH FAQ SECTIONS => Engine compartment => Topic started by: PercyUK on June 05, 2023, 12:20:36 PM
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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?
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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.
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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?
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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.
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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.
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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.
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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.
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I have a similar rule and have already tried other coils, plugs and condensers without result
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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.
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Any luck?
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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.
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This thread is a real "mystery". Thanks for sharing.
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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.
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Three more questions.
What is the timing set at?
What is the octane rating of the fuel?
Is the fuel laced with Ethanol?
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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.
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And all of the valves are set correctly and seating correctly?
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Yes, did some valve and guide replacement when I fitted new pistons.
I have 130lbs compression in each pot.
I lapped each valve seat at the time and used my shop vac to pressure test them to check the seal.
As part of the diagnosis I checked the valve clearances last week and only had to adjust one. I could see no indication that any where sticking.
I don't want to do it but I am thinking about taking the front off to check the timing marks on the crank and cam pulls however in my heart I think that if they were misaligned then I would expect to see a problem all the time even at idle and all the time instead of randomly as it does at the moment.
Flumoxed is my current word for it.
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When you tune up the motor are you using either a timing light or a vacuum gauge along with a Dwell/Tachometer?
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Hiya, I have used all three at various points. The vacuum is well within spec but does have a slight flutter however dwell is fine and the strobe is used more to check and set the timing as I try to diagnose the issue.
I can't believe that I am having so much trouble with a seemingly simple engine.
I have over 40 years driving and fixing old motors some of which were so worn out it wasn't funny but none ever had a misfire like this....... They smoked or leaked oil or lacked performance but they all ran 😁
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To what setting did you adjust the valves?
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Hiya, 0.016 a cross the board
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Not that you can really do anything about it but 95 octane (depending on research or motor method) is way to high for these engines. The fuel is burning very slow compared to what this should have. I run 12° with 7.2-1 Static compression and 87 Octane E-10 fuel.
Is the miss regular or intermittent? if regular its more likely electrical or valve if intermittent then fuel comes to mind variations on the feed.
I would also look at Distributor condition how are the bushings how are the advance springs and of course the condenser.
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May I suggest .015?
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Hi Mark, the miss is irregular. I tested the fuel supply and it reads 3.5lbs well within spec. Under load things may change of course but I have also witnessed the miss in the flash of the strobe light when idling.
The dizzy is new, replaced as part of the process to eliminate the fault, and I recently changed the condenser twice just incase without result.
Scout, I will have a look at using. 015 if you think it could help.
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The original spec was for a .14 setting. Owners complained about the occasional putt-putt from the exhaust. Willys came up with .16 to solve the issue. But at .15, I've never had the putt-putt.
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Hi, I always thought the difference between 0.014 and 0.016 was because one was chain driven and ours or later ones gear driven.
I will definitely have a go..... I guess the fenders coming off for the third time in as many weeks 😁
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Percy have you had any success getting your issue solved?
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Hiya, no luck yet. The tappet adjustment didn't resolve it. I have walked away from it for a few weeks to calm down and will have another go soon.
If I find the culprit I will definitely let everyone know.
Cheers
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Please do!
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Percy it’s not ‘if I find the culprit’ it’s ‘when I find the culprit’. Good luck and keep on sleuthing!
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Good greif with 95 octane your going to need like 15° BTDC timing thats way to slow of a fuel for our engines. With 87 Octane I run 12°