The Stovebolt Site Forums The Shop Area Engine Shop 216 motor knocks

the 216 knocks a little just started to do this. Knocks when you rev motor up a little , no knock at idle .Oil presure is good. Can this be fixed with motor in truck? Mains have inserts, rods have shims. Any info on this will be more than I know now. thanks Bill

If you're lucky it might not be a bad bearing.
I had a knock in a 235 that turned out to be nothing but a worn out woodruff key on the end of the crankshaft letting the crankshaft pulley cause a knock at idle.
If that's not it, start by raising the idle enough to where you hear the knock & one by one short out each spark plug one at a time. If you hear the knock go away or lessen significantly you'll have narrowed the problem down to that cylinder before removing any parts. If you find the source of the knock like this, it's caused by a bad connecting rod bearing or wrist pin bushing.
If you still haven't found the source of the knock this way it may be a main bearing.
Some folks use a stethescope or a wooden dowel with one end on the suspected site on the engine and the other end touching the outside of your ear. I hope this helps, let us know what you find,
Jacques

There are two serious knocks that I look out for. A main bearing knock has a bit of a thud to it, it is sort of heavy sounding. A main bearing will usually knock under load at low RPM. A rod knock is a harsh sound , rather metallic. It is most noticeable when you give it a quick rev. As the engine is between accelerating and decelerating a rod knock appears as a rattle. Either knock is a bad thing and shouldn't be ignored.

The rods have shims that can be adjusted down. The procedure is to remove shims on a rod a retighten until the rod hangs up and can't be moved back and forth. Then one shim is added back.

After taking off the pan, It would be a good idea to look at each rod bearing babbitt surface to see how they are. Sometimes the babbitt drops away from the iron surface and causes a bearing failure.

The main bearings had shimms too, in the original configuration.

Also make sure your valves are not too loose.

trucknix
It sounds metallic when reved up a little.
I think the main brgs are inserts ? Are there shims there also?
A friend has a service manual for his 49 chevy 3/4 ton will it be the same as a 51 chevy 3/4 ton.
I plan to drop the pan tomorrow a service manual would help. thanks for your help Bill

I would think that they would be very similar. The mains also had shims, coming from the factory.

The shims, especially the rod shims, are very delicate and it is sometimes hard to tell how many there are in a stack. You can buy new shims from places like Chevs of the 40s. I cut my own new rod shims from .001 brass stock.

Fred

OK I did what swampcat said removed one plug wire at a time with motor running . the # 1 wire closest to radiator when removed makes knock go away. Will drain pan now.
Have a 49 service manual says to remove an equal # of shims on each side untill the rod will not move by hand,but can be tapped back and forth with a light tap from an 8 pound hammer . then add shims untill it can be snaped back and forth with one hand. _
(49 manual 51 motor should be the same??)
hope I don't make this worse. thanks Bill

The service manual that they now sell as a reprint, covers those years and more. It should be exactly the same in this respect.

If you find bad rod babbitt, there are usually people selling NOS or remanufactured rods on Ebay. Sometimes it takes several months for them to turn up.

Here are some more details for you: They came from the factory with .004" of shims on each side of the rod. From what I have seen, this appeared to be one .002 brass shim and two .001 steel shims. I think that the mains were similar but I don't know the exact count on them. This can give you an idea as to hwo much work has been done on the bottom end.

Ok adjusted all the rod bearings knock is gone, thanks for all the helpfull addvice.
Thinking about adjusting the valves but I see some post here where that has not worked out well. The manual says to have motor at operating temp before adjustment ,doesn't say if you adjust with motor runing or stoped? 06 to 08 intake --013 to 015 exhaust. I read about the rocking adjustment by HOTROD LINCOLN that should work on my 216 ?
thanks for the help Bill

I would be interested to know how many shims you had to remove. You are very fortunate if an adjustment cured the knock.

There is a valve adjustment procedure in the tech section, for solid lifters, and it works perfectly. Yo do it with the engine stopped.

TRUCKERNIX
I had the motor apart last year got new shims they where thicker than the ones that came out, looked about as thick as 2 of the old shims . This time I took out one new and reused one old on each side of the #1 rod which when plug wire was removed knock was faint. This helped knock it seamed gone
now I have a couple of hunderd more milles on it I hear it a little (may be I just didn't want to here it before.) If all shims are removed the rod cap will not snap back and forth I think there where 2 shims original on #1 now just 1 original shim not sure some rods had 2 or more of the original shims? I will just run it for now. Bill

I had a motor once that had a rod bearing fail. It was a 261, and I cleaned up the crank to get the metal that had transfered to it off, and installed new bearings. After, it ran pretty well but had a faint rod knock. I eventually replaced the motor because my stomach would get in knots listening for the sound. I hope that you are not like that!