Atomic 4 engine knocking

[ryanmohr]

After taking the carburetor apart and giving it a good cleansing I was finally able to revive my newly acquired A4 from its year and a half slumber. At anything above a low idle though I'm getting a horrible knocking sound, even after fine tuning the timing by adjusting the distributor body.

When I searched for some help, not much came up so it appears this is an uncommon problem with the A4. Originally I hoped it was just the low octane fuel I was using (initially I was running 87 since the manual said "regular" -- but later I saw they recommend 90-94), but today I swapped out the old fuel with some 92 and didn't notice a difference.

Along with the knocking I'm getting a lot of white/gray smoke out of the exhaust. I believe this is just the extra oil I added to the top of the cylinders burning off but I'm not positive (since the engine had been sitting unused for so long I put two teaspoons of oil into each cylinder and turned the engine over a couple times by hand, as recommended by the manual).

A lot of the advice I found on engine knocking said it's likely due to carbon deposits and that the best way to fix is it to take the engine out at push it hard to burn the junk out. Seems like a risky thing to do if carbon deposits don't end up being the source of the problem.

Any ideas what might be causing the knocking or how to fix it?

 

[tommays]

Well

The motor is VERY low compression at about 6.5 : 1 and has pretty conservative timing advance so even with a bunch of carbon it should not have a Pre-ignition knock which is really the pistons shaking in the bore and has a pretty distinct sound and tends to be motor load based

IF its overheating it WILL get a Pre-ignition knock BUT it would take at last 1 minute to get this HOT

Due to the way the cooling system works you can have a full flow of water out of the boat and have NOTHING going through the block

You can check this by clamping off the hose that goes from the block tee to the thermostat housing this would try and force water through the block as the thermostat can be bad or thee can be a corrosion issue

The other possibility is rod or crank bearings

 

[Ross]

With the engine running, take a long (1 1/2to2 feet) screwdriver and place the end of the blade against the block at various points and place your ear against the handle. It will serve as a stethescope and allow you here the location of the knocking. From your discription I would guess a bearing is worn and allowing some slap. Make sure that you have filled the oil sump and have good oil pressure.

 

[Benny]

Too lean of a fuel mixture or/and advance ignition timing will cause an engine knock. I would richen the mixture some and retard the ignition and also adjust the valves. It would also be a good idea to run a compression test on the engine to determine its condition since you claim it is smoking. We used to use thick oil aditives to raise the compression on old tired motors; it would also quiet worn bearings and control leaks. The good news is that there are plenty of parts for your engine and a complete rebuild is fairly inexpensive. Good luck.

 

[ryanmohr]

I'm pretty sure the cooling system is working just fine. Getting lots of water out the exhaust and the engine warms up to about 160 and then sits there.

Oil level is good and oil pressure is roughly 40 psi when cold and 20 when warm. I tried the screwdriver trick on each cylinder yesterday but honestly couldn't notice a difference between any of them. From everything I've heard it should be dead obvious which cylinder the knocking is coming from. I'll have to try it again when I have someone else there to really get the engine pinging as I poke around with the screwdriver.

Does the continuous white/gray smoke coming out of the exhaust not concern anyone? I've let the engine idle for 10-15 minutes at a time and the smoke never goes away. Could that be from the oil I added to the upper part of the cylinder or would it be from something else?

 

[Ross]

The grey/white smoke may be water vapor which may indicate a blown head gasket. You may be getting steam explosions in the cylinder. How far from the exhaust port does the smoke drift? steam will disappear rather quickly but true smoke will only disapate over distance not time.

 

[ryanmohr]

It drifts for a good 10-15 feet before vanishing completely. Thickest within 5 feet though. There is the slightest oil sheen on the water below the exhaust, and the smoke looks a little thicker than I'd imagine simple steam would look.

 

[CalebD]

Ryan,
You should also ask this question over at the Moyer Marine forums: http://www.moyermarine.com/forums/index.php

 

[ryanmohr]

Thanks Caleb. Just posted it over at moyer as well.

 

[Ross]

How hot is the exhaust water? and how is the flow rate?

 

[Alec]

I used to have an Atomic Four for many years and on two occasions it started to knock so badly that I thought it threw a rod. However, a quick dose of Marvel Mystery oil added to the gas quickly cured it. I believe that it was caused by a lifter hanging up. After that it got a steady diet of MMO in the gas and no more knocking. I believe that I heard that adding it to the crankcase oil was not recommended tho.
Don't know if that lifter hanging up is causing the smoke but I'm sure it's a possibility.

 

[ryanmohr]

I heard the same thing about MMO so I bought some today and threw it in there before giving her a go. Ran a little smoother but still not good. I took some photos / videos today though.

The only thing I picked up on was that the number 3 spark plug has a much more burnt / dry carbon look to it, while the others have an oily look.

Here are the spark plugs in numeric order:

And here are the videos:
Giving it a little gas -- sharp knocking sound
Messing with the timing
Exhaust
Idling from flywheel

 

[higgs]

This could possibly save you a lot of money and work

One spring I started my A4 and it sounded like a diesel. Had a car mechanic listen and he told me low end bearings. Pulled the engine and tore it down. The questionable bearings were in great shape. At that point I just went ahead with a rebuild which cost around 1K.

The knock, we decided, was probably a chunk of carbon that broke off the head and fell into one of the cylinders and was bouncing around in there as the engine ran. A4s are notorious for carbon buildup because their thermostats, at 140, don't let the engine burn off carbon. My head had significant build up of carbon deposits.

If suggestions given here don't solve your problem and you are ready to pull the engine and tear it down, first pull the head and see if a piece of carbon has dropped into a cylinder.

 

[Alec]

Unlikely as it seems I always found that it took quite a while to burn out my winterizing oil after sitting all winter. In your case you have to burn out two teaspoons of oil which is quite a lot. I suspect that cyl #3 didn't get quite as much.
As erratic as the knocking is I still think there is a possibility it could be a valve or lifter hanging up, especially as the engine sat for a while & sludge may have solidfied around them. It may take more time for the MMO to work or possibly disassembly is required.
Don Moyer will probably be able to provide you with the best advice, especially if he sees the excellent videos you have taken.

 

[kloudie1]

Excellent videos.. Sounds more like valve noise (Alec, I agree) because it is kind of intermittant.. ?? I would try pulling one plug wire off and replacing in turn while it is idling or running at a high idle to see if you can isolate to one cylinder.. Pull the cam covers and check the springs for broken ones, and check lifters and valves for smooth action. Set the clearance while you are there. Did ya turn the engine over a few times before putting the plugs in after putting in the oil to get out any oil that might hydraulic the engine?

 

[jimg]

I would bet you have water in the number 3 cylinder. The blown head gasket (or cracked head) suggestion is probably correct. White exhaust is probably steam and almost always means water in the combustion chamber. The A4, being a flathead, is a very simple engine on which to remove the head. Do that, take it to an auto machine shop for inspection and/or repair, and then put it back on with a torque wrench and a new head gasket. Really pretty easy.

 

[ryanmohr]

Thanks for all the suggestions guys. I'm heading back down to the boat later today and I'll keep you posted on any updates.

 

[txtowman]

I have a 1951 jeep cj2a which is essentially the same engine if my info is correct. that engine will run on 79 octane, so fuel is very unlikely to be the problem.

I also have several other similar flat heads that are basically the same but some have magnetos instead of distributors.

my jeep has had a tappet(lifter) knock for 35 years. Yes 35 not a typo. it runs great and I did rod and main bearings 25 YEARS ago. I agree its carbon or a tappet.

I would pull the head wire brush it if its dirty and then pull the side cover and check the valves and tappets.

Might also pull the plug wires one by one before you tear into it, to see if the knock stops and you have found the cylinder with the problem if it stops knocking while one is not firing.

also mkae sure the dist cap and rotor are in good shape and no carbon in it from arcing.

also check the points for arcing.

sorry this is so unorganized but I wrote as I thought of them.

hope I explained these ok if not someone else may be able to.

 

[ryanmohr]

Those are almost exactly the steps I went through today. Tried pulling the wire on each plug, but the knocking never ceased. Taking off one of the plug wires would decrease the RPMs and in that way quiet the knocking a bit, but it wasn't the isolated single cylinder knock I was hoping for. The knocking is very much RPM based. On low idle it's undetectable, and the higher I rev it the worse the knocking gets. Almost sounds like something's bouncing (if I had to describe the knock I'd say it sounds like a woodpecker).

Distributor cap and rotor look fine but they could probably be replaced since it's likely they're two or three years old (though half that time the boat was sitting unused). Installed electric ignition a few days ago so don't have to worry about the points.

I pulled the side cover today and had a look at the tappets. Didn't have any feeler gauges on me but everything looked just fine and each one was rising / falling as it was supposed to. All the valves that I could see through the spark plug holes were working just fine as well (I used the bent screwdriver trick suggested by Don).

Since I still don't have anything new to work with, next I'm going to pull the head and have a look to see if anything fell in one of the cylinder. Was hoping it wouldn't come to that because now I have to wait for replacement gaskets to arrive, but I can't think of anything else to check.

 

[ryanmohr]

I think I found the culprit. The spring retainer on the #4 intake was busted but I didn't notice it until I tried to insert a feeler gauge. Would that be enough to cause the knock I'm hearing?

I took some photos of the cylinders, valves, and head just in case I'm missing anything else. I know for sure I don't want to have to take the engine apart like this again anytime soon. Some of those nuts felt like they were set in concrete!

I appreciate any advice you can offer.