The Stovebolt Site Forums The Shop Area Engine Shop 216 with a knock under load in 4th

My 216 started to knock while under load in 4th gear. Happened suddenly after sitting a few days. Idle is a bit rough. any ideas?

Workinonit,

Main bearings can make a deep 'thunk' under load and rod bearings can make a 'knock' when not under load and wrist pins can make a light metallic clicking sound all the time. If your noise is only evident when in fourth under a load I would think main bearings.

The main bearing knock shouldn't have come on overnight though. Vibration dampers can make a clunky noise too as well as a failing generator.

If you can really only hear it under a heavy load, it tends to make one think of a internal engine component, but the 'overnight' appearance clouds that theory.

Look around, wiggle stuff and listen to the truck as it idles. You might find something loose...rotten or loose motor mounts might be letting the engine rock over under load and rattle against something.

There are all kinds of possibilities, dig around.

Stuart

Check your timing, or you may have got a load of extra low octane fuel.

Fuel is expensive enough so that some fuel truckers will pump out tanks at stations that have been closed for a while.

Nearly happened to me in Denver. Twelve cars with significant engine damage. The trucker got the fuel out of a tank from a station that had been closed for more than a year. Fortunately, I only went there for a cup of coffee.

Sheesh...good point! I might not describe a 'ping' as a engine 'knock', but it would make more sense that it could be an ignition problem as it came on suddenly.

Stuart

Some type of piston problem could exhibit these symptoms and also affect the idle. However I would expect there to be a huge increase in blowby gases.

changed all the leads, plugs, cap points. new mounts, nothing hitting. If listening really close you can barely make out a low noise at idle. A guy here thought it may be a slightly bent valve or rings?

Workinonit,

A slightly bent valve would probably 'hang' open or closed...it takes very little to do this and it wouldn't make any mechanical noise. Piston rings wouldn't make a 'knock' either as they have very little mass and are always under some type of tension.

Properly describing the sound and when it actually occurs is crucial to troubleshoot the problem. When the truck is in fourth gear being 'lugged' you are loading all the engine components to the max. A crankshaft with excessive clearances with start to pound.

If the timing is too far advanced, the engine will preignite and ping. This too happens under load. The sounds don't resemble each other. Keep us posted.

Stuart

I will try recording the sound. If a ring broke, and the engine under load, not lugging, could there be a knock.

Workinonit,

In my unprofessional opinion, you would never ever hear a sound associated with piston rings, broken or otherwise. Because their job is to seal and scrape oil, any ring problem will be visible out the tailpipe or in poor engine performance, but not noise.

You stated your noise appeared suddenly. If this is accurate it almost precludes a internal 'wear' issue and points towards the failure of some component attached to the engine.

Using a short piece of heater hose as a stethoscope to find and pinpoint noises as the engine idles in the driveway may help isolate the sound. This is a common troubleshooting procedure and can produce great results...give it a try.

Stuart

With a good oil pressure gauge you will usually see the press. drop a few lbs. when you step on the gas & then it'll raise back up if you let off the gas as you are traveling at a steady road speed in high gear IF you have loose/worn main bearings.
Doug

Thanks Stuart, I'll give it a try

I never used a heater hose but I've used a long screwdriver as a stethoscope. Eventually I bought a medical stethoscope & put a screwdriver blade on the end which works great.

I havent heard of the hose method either, but a nice 3' wooden dowel works very well. Watch out for the fan!

Sounds like the voice of experience.

I forget your situation Keith..did you rebuild this engine during the restoration?

Keith

The length of hose is a great old trick.
I use vacuum hose as it is easier to get in and around the engine.
This knock only happens in top gear ????????
No noises in any other gear ??????

The engine is from a 46, dont know all the history. Was very clean under the valve cover and outside. The plugs are a nice burn, no gunk or fouling at all. The engine runs a bit rougher than before so I put new plugs, points, leads, cap etc, need to double check the gap. Starting in second is the same, shift to 3rd, no problem, when you shift to 4th on the flat, minor thump, go up a hill and major noise. More like a thunp, rather than metalic click or detonation. The truck was sat for a few days and ran out of fuel. Put fuel in, flashed up and was a little rough at idle. Can bearings be installed in an engine with babbits?

Workinonit,

I think the mains, which would be the source of a deep thunking sound, are inserts. Have you checked the oil lately, not for quantity but for quality. It might be interesting to drain the existing oil and stick in a charge of 40 weight, just to see how it affects the 'thunk'.

Stuart

I use straight 30 weight non detergent, changed the oil and filter last month. only has about 400 miles since. Havent seen any straight 40 weight around. Sure appreciate the input. Have been thinking I might put a larger displacement, newer model engine in if it turns out the bottom end is gone.

WORKINONIT
It still has me baffled that this noise only happens in top gear.
Not a driveline problem ?????????

Clutch shuddering under load in top etc ???????????

no clutch or driveline problem, I haven't tried the dowel trick yet but listening to th engine, sounds like it comes from the bottom. Will have a closer look this weekend while I have a chance

OUCH..........sounds expensive!

can new style bearings be used on engines with babbits, if so what is needed?

I am assuming that your motor is pre 1947. The manual for the 1947/48 update talks about new precision interchangeable main bearing inserts so I am assuming that pre 1947 the mains were babbitted right onto the block and caps. I don't know of any conversion for this.

The rods will be direct babbitted rods and there is a conversion for them. The rods must be machined to take inserts and the inserts are specific to the application, they are not the inserts for the full pressure motors.

The Chevy engines used main bearing inserts from 1929 on up not poured babbit. Rods were the only poured babbit in the engine.
Denny Graham
Sandwich, IL

I just got out my 1937 repair manual to have a look at the main bearing replacement procedure. The bearings were inserts with babbitt on steel. The inserts had to be installed along with a boring bar and then they were machined to size. From the description I would call it a reaming operation. So, it looks like the 1947/48 update made it possible to install new main bearings in the more modern conventional manner.

the engine is from a 46, so if I understand, the rods are babbit and the mains are bearings

Sorry, I should have related the discussion back to your question. Yes the rods would have direct babbitted surfaces. The mains have inserts which can't simply be replaced, according to the original manual. You would need to take the block to a machine shop who could fit new main bearings.