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Old 07-26-2020, 07:30 AM   #1
31ASlant
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Default Engine Misfire Knock

I'm looking for a few suggestions on where to start with my engine issue.
I recently noticed a knock has developed in my engine.
At idle there is a misfire almost like a stumble every few seconds in rhythm.
I have tried grounding out wires with no change to knock.
The knock goes away under light acceleration , but is present at high speed if you really listen for it. Especially if the timing is fully advanced. I usually run at 9:00 or so.
It's a fast knock at idle faster than the engine is turning at. I believe it has something to do with the misfire.
All ignition and fuel items are in perfect working order.
The car drives great and has plenty of power, does not burn oil or smoke.
Runs cool as a cucumber.
The knock is present on start up and through warm up with little change in its audible sound.

I just want to make sure that it's not ready to explode.
Any suggestions I would greatly appreciate.

Last edited by 31ASlant; 07-26-2020 at 08:01 AM.
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Old 07-26-2020, 07:46 AM   #2
30 Closed Cab PU
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Default Re: Engine Misfire Knock

Sticky valve? Add Marvel Mystery Oil in the gas, perhaps in the oil. With the motor running some use a misting bottle and spray into the carb intake, some spray into the intake manifold fitting used for Vacuum Windshield Wipers.
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Old 07-26-2020, 08:40 AM   #3
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Default Re: Engine Misfire Knock

Quote:
Originally Posted by 31ASlant View Post
It's a fast knock at idle faster than the engine is turning at.
There isn't many things that can knock faster than the RPM. valves would have to be more than one (more than two actually since they cycle at half RPM speed) and they tend to tap more than knock. The only thing I can think of that could knock at >RPM speed would maybe be a bad rod bearing that is knocking every time the rod changes direction (twice per revolution). It would have to be pounded out pretty bad I would think. If it were mine i would be dropping the pan ASAP and checking the rotating assembly. Only cost is an oil change and a pan gasket.
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Old 07-26-2020, 09:49 AM   #4
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Default Re: Engine Misfire Knock

Try to locate the noise. If it seems to come from the front I'd look at the timing gear. If it seems to come from the valve cover then look at the distributor drive, valve guides. If it seems to come from the lower part or lower center then I'd look at a main bearing.
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Old 07-26-2020, 10:00 AM   #5
31ASlant
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Default Re: Engine Misfire Knock

Ok. I got out the old stethoscope. Probably should have done that first.
Definitely not coming from the bottom. I located the noise to the distributor. It seems to make sense given that there is a slight misfire and the distributor is making noise. I believe it's the original one. Still has the old style points.
Can anyone suggest a good replacement and if this makes sense?
Thank you again
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Old 07-26-2020, 10:12 AM   #6
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Default Re: Engine Misfire Knock

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Send it to the fella that advertises "rebuilt" distributors for sale on this site - he rebuilt mine & I had it back in a week !
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Old 07-26-2020, 10:18 AM   #7
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Default Re: Engine Misfire Knock

I won’t be to quick to start taking things apart.

First thing I would do is add the Marvel Mystery Oil to your gas. Than I would pull the plugs and check them. If old or if there age is unknown, I would replace. Than check you points and clean or replace, reset the gap. Clean the rotor and clean the contact points on your distributor cap. Re time the engine. Lube your distributor and check for shaft issues. Two piece or one piece shaft.

Check the water pump. Remove fan belt and run engine.

What weight and type of engine oil are you using. I would recommend 20w-50 HD oil with one 16oz blue bottle of STP if your engine has some mileage on it. If you don’t know how many miles, than try it to see what happens. Not expensive.

Model A engines can at any time start making funny sounds that sometimes just go away. You would to at 90 years old.

I have used the above recommendations a number times on noisy Model A engines that I did not really have a good history on. In every case I have seen good results.

I would not get overly excited. If it’s running good, I would think it very well could be something that can be easily fixed.

Enjoy.
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Old 07-26-2020, 11:01 AM   #8
31ASlant
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Default Re: Engine Misfire Knock

The water pump is new-leakless type.
I replaced all fluids straight 30 weight
1/2 stp and 600 in trans and diff. Definitely loved that change.
I did set points and greased distributor. I did not grease the shaft.
I'm going to pull the distributor and check the shaft and such before rebuilding it or a new type. Definately has a slight miss. I owned a 30 4 door in the past, so I'm aware how well it should run. I've already rebuilt the steering box and adjusted brakes. Greased almost everything. It's much better but I want this thing to run like it should.
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Old 07-26-2020, 11:11 AM   #9
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Default Re: Engine Misfire Knock

Quote:
Originally Posted by 31ASlant View Post
The water pump is new-leakless type.
I replaced all fluids straight 30 weight
1/2 stp and 600 in trans and diff. Definitely loved that change.
I did set points and greased distributor. I did not grease the shaft.
I'm going to pull the distributor and check the shaft and such before rebuilding it or a new type. Definately has a slight miss. I owned a 30 4 door in the past, so I'm aware how well it should run. I've already rebuilt the steering box and adjusted brakes. Greased almost everything. It's much better but I want this thing to run like it should.
I would try the 20w-50 High Detergent Oil and the Marvel in your gas.

The miss firing could very well be several sticking valves. That might also be a big part of the sounds your hearing.

The heavier oil will also help if the engine has some mileage on it. I think 30 weight oil is to light for summer use.
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Old 07-26-2020, 11:32 AM   #10
31ASlant
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Default Re: Engine Misfire Knock

I added a quart of lucas to it. should be good. Didn't make any difference with the noise
I do run MMO in my gas too.
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Old 07-26-2020, 01:08 PM   #11
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Default Re: Engine Misfire Knock

I rebuilt my distributor recently. Replaced the one piece shaft back to original two piece shaft. A noise that I had went away, also the high speed miss went away!
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Old 07-26-2020, 01:18 PM   #12
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Default Re: Engine Misfire Knock

Do not get sucked into modern points conversions, if you do, keep your original breaker plate so when you un-convert you have something to use that works. Also a misfire is generally not associated with a knock. I would like to see how you position the spark lever when driving. Is there a secondary fuel filter? Have you tried to isolate the knock by shorting cylinders under load? I agree wit others, go through the dist. and check the oil pump/ dist, drive gear tooth wear and slots on drive shafts. These are the small things outside of the mechanical insides of the engine. Divide and conquer one at a time, fix correctly what you find.
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Old 07-26-2020, 01:49 PM   #13
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Default Re: Engine Misfire Knock

If you think the problem is with the distributer, don't replace it yet. Remove it and take a look. Check the bushings and make sure it has the 2 piece shaft.

Many were changed to the 'new and improved' one piece shaft. That wasn't an improvement ! The distributor drive could also be worn, its fairly easy to replace.
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Old 07-26-2020, 02:51 PM   #14
31ASlant
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Default Re: Engine Misfire Knock

I removed the distributor and it has a one piece shaft.
If you move the shaft up and down, there is over an 1/8 of shaft endplay.
I believe this is the sound I'm hearing. click clacking away.
So the dizzy needs a replacement or rebuild
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Old 07-26-2020, 03:06 PM   #15
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Default Re: Engine Misfire Knock

Quote:
Originally Posted by 31ASlant View Post
I removed the distributor and it has a one piece shaft.
If you move the shaft up and down, there is over an 1/8 of shaft endplay.
I believe this is the sound I'm hearing. click clacking away.
So the dizzy needs a replacement or rebuild
I would go with two piece shaft and rebuilt distributor.

Enjoy.
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Old 08-06-2020, 09:09 AM   #16
31ASlant
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Default Re: Engine Misfire Knock

Finally got the new distributor in the car. What a difference in power now.
My old distributor had a worn shaft and cam gear and didn't have a good snap on the lobe for opening the points and closing them. I went with new style points system.
Took a few tries to get the timing exactly where it was happy. At first I set it with too much advance and it was pinging. Now it's dialed in. I've never timed a model a. I bought one of those Nu wrenches and wasn't very happy with the results. So I made a test light and did it the right way. I believe I can set up an A in under 5 minutes now. LOL.
So thank you for all your suggestions.
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Old 08-06-2020, 09:11 AM   #17
31ASlant
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Default Re: Engine Misfire Knock

So after all that it was pre ignition spark knock from incorrect timing and worn distributor.
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Old 08-06-2020, 09:33 AM   #18
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Default Re: Engine Misfire Knock

Thanks for the update - glad you were able to figure out. In this case you may have been able to narrow things down quickly by 1st disconnecting the fan belt, would have ruled out the generator and water pump. Then use a stethoscope, or a very large screwdriver, or a broom handle to listen for the noise. Many are not fond of nurex wrench. Personally, it is not as accurate, but is handy to have on the road, if done correctly gets you close enough (have to remember in timing to set the spark lever at full retard).



Get the timing set correctly with the official method, and just for kicks use the wrench to check where the wrench is in relation to the #4 distributor lead post., I suspect that you will only be off by a very small amount, if any.
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