I've been working on an 8BA, got it running pretty well, but it's got this clattering sound that kind of sounds like two or three marbles are getting bounced around in the cylinders.

Sometimes the sound stops but then it returns. It's there more often than not.

It's very rhythmic, not repetitive, but in sync with the engine beat. Kind of like someone was playing castanets or spoons in time with the engine.

I can't isolate the location using a stethoscope - it could be anywhere in the upper cylinder/manifold area. It could even be in the generator, I can't tell.

The engine runs pretty good, with compression about 110 lbs. in all cylinders. I've recently replaced every part of the ignition system and rebuilt the carb. But this sound is pretty loud and it takes away from the otherwise great sound of a flathead running smoothly.

Can anyone tell me what the sound is?

...chico

 

Hate to say it but it sounds like a spun rod bearing. Did the flatties use shell bearings on the rods? Does it get louder at higher RPMs? Could also be piston slap?

 

Have you driven the vehicle? Does the sound get worse under load? Sounds like it could be detonation. Was the engine running before you made the ingnition/carb changes? If so was the sound present then?

Mike

 

No, it stays about the same volume as it revs up. Kinda hard to tell, though, because one of the mufflers is shot and it's noisy in the cab. Is piston slap different than knocking?

Just a few miles on my own property.

I don't think so, but I'll go back and check to be sure.

Yes, I got the truck this summer and I've spent the last couple months trying to fix plug fouling and misfiring issues, but the whole time it's had this sound.

It is a little like knocking, but louder. It doesn't change when I adjust the timing. Sometimes the sound just stops, and then it returns a minute later. But the engine doesn't change RPM or anything else whether the sound is there or not.

Any tests I can do to verify your guesses?

 

It almost sounds like possibly the valve lash is off on more than one valve. Instead of one valve going tap tap tap tap maybe it's more than one of them doing so, which would explain not being able to isolate it to a single cylinder. Although I'd think that it wouldn't come and go as you've said, it would probably do it constant.

You can eliminate the generator/fan/water pumps from the equation by taking the belts off and starting it for a minute and see if it still does it.

 

Diagnosing engine noise is more an art than a science, and most of the time even experienced mechanics get it wrong. It is even harder when you do not hear the noise yourself but try to use someone's description.

I have seen a few old-time mechanics who could do it - isolate a knock to one lifter or one rod bearing, and go in and replace that one item to get the engine to run quite. Mostly they hung around cheap used car lots. Now days most mechanics just recommend a complete rebuild (more $ to them) and likely a more satisfied customer.

The old Motors Manual used to have an involved procedure on diagnosing knocks (I don't know if the newer ones do) that worked. I looked for it this morning but did not find it. If you can't come up with anything else I will try to find it and send you a copy.

I did do a search on the internet - using google and the terms "engine knocks" and found this site: http://remanufactured-engines.com/page4.htm that matches my thoughts on knocks.

Please read it, follow his suggestions, and then post the results. It is likely we can help you find the problem once everybody gets on the same page and understands what you are hearing.

 

Piston slap occurs when the piston rocks in the bore, usually when changing direction or firing, and the skirt of the piston hits the cylinder wall. Today a lot of pistons have extended skirts to stop the rocking. Have you had the engine apart at all?

 

I had a noise like that when I first fired up my Flathead 6 in my 51 F1, turned out to be the flywheel. The lock wires had been left off and the spacer that goes under the bolts was missing. It had lasted on the 6V circuit, but the 12V was just too much for it. The bolts were broken and one was stripped out.

 

Stock flathead pistons have 4 rings (including a bottom one) so it isn't likely piston slap with 110 psi. The 8BA does have shell rod bearings. It could be bearings, but the most likely source of tapping noise in a flathead is valve train - probably from valves hanging up slightly allowing the lifter to smack into the stem which could account for the "sometimes quiet".

Also it could have adjustable lifters that have loosened up. Pull the intake and use a liberal application of Marvel Mystery Oil on the valve stems. Check clearances with a feeler gauge .012/.015 (intake/exhaust)

It is also possible for broken piston/ring pieces (top edge) to be bouncing around inside the cylinder or even a hardened seat that let go. In any of these cases, you want to pull the heads and figure out what it is before doing any more damage.

This is a stock engine and heads/block haven't been machined/shaved have they? Piston clearance on the head can be an issue, but not likely in your case.

My own truck has a ticking noise now - it started after I installed a new valve and needed to grind it to fit. Ground it to fit and it started ticking. Checked again and found I had ground it to about .020!! Turns out the lifter was hanging up in its bore causing a too-tight reading on the feeler gauge. 'Bout time to overhaul anyway so I'm driving it as it and putting up with the ticking noise.

 

Thanks for all the suggestions. The info at remanufactured-engines.com is great.

Today I removed the belts to eliminate generator and water pumps as noisemakers. For a couple of minutes I thought I'd pinpointed the problem, but then the sound started up again. Definitely a metallic chattering/clattering, like something is loose inside. The rhythm sounds like a percussionist playing along with the engine.

Every so often the sound goes away for 10-20 seconds. Ahhhhh! But then it starts up again.

Revving the engine doesn't seem to increase the volume or change the rhythm.

Other slight clues: when the chattering stops, it seems the engine idle speed seems to drop a very little bit, then picks up again when the chattering stops (could be my imagination...) Plus I've been struggling with ongoing plug fouling problems, completely redoing the ignition and fuel systems over the last couple of months.

Please tell me if this is a crazy thought: this truck sat in a barn for the last 15 years with the air cleaner off. Any chance something's bouncing around in the intake manifold?

This could also be part of why I'm having fouling/missing problems, right?

Any way to check this through the plug holes? Using a scope or a tiny video cam? (which I've used to scope out my septic system...that's way cool!)

Don't think so. The engine was once used for vineyard anti-freeze fans. Supposedly only had about 250 hours of use. The PO had it torn down 20 years ago before he put it in the truck. The mechanic told him he'd just wasted his money because everything looked like it had just been rebuilt. For having sat 15 years now, it sure seems clean and tight, excepting the fouling and clattering.

I guess my next step is to pull the intake. I'll be back with lots more questions, I'm sure.

Thanks all.

 

How many hours have you operated the engine? Have you run it enough to loosen things up?

I am not so sure I wouldn't put a few hours on the engine before I did anything else - it may just need to be run.

 

The fact that the sound comes and goes is the biggest clue. It wouldn't likely be bearings or piston-related stuff. So I'm wondering, especially since your last post where you say it was opened up by the PO and put right back together, if there isn't a head gasket leak that is letting water into some cylinders, some of the time (like pressure builds up, some squirts into the cylinders, pressure is briefly relieved).

Is there a difference, hot to cold? (i.e., better cold, more frequent hot)

I would check torque on the head bolts right away. Sometimes 3 or 4 re-tightenings are needed after a new gasket is placed.

Are you seeing excessive water vapor out the exhaust?

Is the radiator level dropping?

What does the oil look like? What is your oil pressure at idle?

My only other guess would be along MT's lines, valve train sticky combined with bad cam bearings.

 

51Ford Fan, I don't get the connection. How can changing the battery system to 12 volts change the flywheel mounting? I must be missing something!

 

Actually, not many hours. First I got the engine running roughly, next worked on brakes and other mechanicals, now I'm back to the engine. I have a 1/2 mile private road I've buzzed a few times, the rest has just been idling while I fiddle with stuff.

Boy, that would be the best possible remedy...just run the engine until it fixes itself!

Seriously, does it require high rev operation under load, or can I run it at a high idle for an extended period, or what? It's not licensed or insured, and it's not mechanically ready for the road yet.

Sorry, I guess I wasn't clear. The PO had the engine opened up by a "good" mechanic before the engine was installed in the truck, and he then drove the truck occasionally over the next 5 years. Claims it ran great. He finally parked it in the barn, and I rescued it 15 years later.

Oil pressure at idle: 30 lbs. Radiator water ok, oil ok, no water vapor in exhaust. The sound seems to be indifferent to engine temp.

I'll try the Mystery Oil/Sea Foam in the oil+gas+carb options to see if things start to free up. I want to check the cylinders (without removing the heads) to assure that there's nothing loose inside. I've never pulled an intake manifold before but I think I may do so to check that nothing has gotten through the carb down there. Any suggestions as to how to help free up the valves when the manifold comes off?

 

The PO was in the process of installing the 12V system when he quit working on it, I finished the conversion and twisted the flywheel off the crank. The PO told me the Flathead 6 had last been rebuilt in the 70's, so I assume it was holding with the 6V system. But when I hit it with the 12V it was too much torque for that loose flywheel, sorry for not making that more clear. It didn't change the mounting the spacer that goes under the flywheel bolts, and the locking wire was missing. I assume they were never put back on after the rebuild.