The Stovebolt Site Forums The Shop Area Engine Shop Engine has rap when not idle

1953 chevy 3100 has a 216 in it. Has not ran for over 15 years. I have been able to start it up and it idles nicely, but when the rpm go up it has a rather noticeable rap.

You can hear it here

Do you think a rebuild is needed?

I cant play the video due to me and my equally stupid dialup system here in the dead spot of Texas. I was wanting to hear it first, but from the description, of rapping (meaning ?popping?) Could it comming from the carb? If so I would tend to think that you would have an Exhaust valve that is not opening. And when the explosion goes off, it cant excape when the exhaust valve opens ('cause it wont open) so whats left of the explosion's burnt gas and sound will come out the only place it can, which would be the Intake valve (when it next opens), then through the intake manifold and finally out the carb/aircleaner as a "rap", "pop", or some similar noise, At idle it may not seem to be there, but with some revs it will be very noticible- especially if you could load it in gear. If this is the problem then find out why the exhaust valve wont open. Worn out exhaust cam lobe or lifter, exhaust valve rocker arm set too tight, etc. Wish I could have heard it-this post could then have had more worth. Just find out where the "rap" noise is coming from-maybe a big crack or hole in the exhaust manifold.

Maybe this is why it sat 15 years before you got there?

Sure has a knock. With it running pull then reconnect one plug wire at a time & see if/how the knock changes. If it stops when one particular plug wire is pulled you've found the cylinder with the problem. There are folks here with MUCH more knowledge than I about how the fix the problem. It should be possible to fix a rod without overhauling the whole engine if the compression is good and it's not burning oil. It could be as simple as removing a shim or two from the rod cap. Keep in mind that a vehicle that was parked is usually parked for a reason, usually a mechanical issue. Good luck.

So I can see all the valves opening. It sounds more like it is in rhythm to the crankshaft or cam. Not intermittent like one particular lifter. Hard to distinguish at idle more pronounced at more rpm.

I am trying some mystery oil on the rods,valves and in the cylinders, in case I need to free up something

If you can't determine which cyl/rod is knocking by the 'plug' test... Chuck that video into a edit program, separate out the sound track and 'zoom in' to the timeline till you can see the 'Knock' sound and it's pattern, then look closely at the video track to locate what position everything is in, in relation to the knock.
That and the plug test should get you closer to determining which cyl it is....

I can tell there is carbon deposits on the first plug. It is pretty much dusty black.

I bet start with the simple stuff. Like timing. I rough set it. Would that cause a rap?

When pulling the plugs not much changes but the number four, seemed to make it run much less smooth than any other plug.

With the "rap" as you call it (I'd call it a knock like Tiny said) and the stated history I'd guess someone knew they were throwing a rod and parked it 15 years ago. It's starting to sound like a rebuild they didn't want to do to me... They could still say "It ran when I parked it" and your video is proof it still runs... But it still needs the same attention now as it did then.

I'd be dropping the pan and getting personal with the bottom end at this point... if I wanted to keep the engine, otherwise I'd drive it till something broke just to hear it go bang.


ps: I should have said earlier that a close up of the rockers from a tripod would be better to zoom/expand the timeline in the video editor with... but its just a diversion from dropping the pan and finding out.

There is the rare occasion where a chunk of carbon breaks loose from one area and gets caught between the top of the piston and where the head is close to that piston. This can cause quite a knock.

Usually with a bad rod bearing the knock will go away when the fire is shut off to that particular cylinder by pulling the plug wire. No spark means no explosion and no slamming the too loose rod onto the crank. If the knock didn't change there are a lot of things it could be that are difficult to diagnose long distance. It could still be a rod but you'll need to buy a manual, pull the pan and do some diagnosing. You can do some things with the rods without having to pull the engine. Mainly removing shims on affected rods.

things do get crowded on the exhaust side of the chamber-fleas hafta crawl in that area.

I have noticed the valves/rods are well worn and no where near .006 ..lots to do ...getting busy

Can you just pull the pan and check things from the bottom?

Yup will be doing that tonight. what am I looking for? Besides the obvious? Wear on the crank? loose stuff?

Move the rods side to side & see how they move. The procedure on an early 216.

OMG!! So I should never trust the Previous Owners work. One of the bolts on the number 5 cylinder that holds the connecting rod to the crank was in the pan?

I hope I can just put it back and there is little damage. I will check the tourque on the rest.
oil pump is new with all new hoses - all gaskets are new so I know he went over the engine - a bit.

Might want to check the bearings for clearance. Have you used a plasti-gauge before? They are cheap and work. Any FLAPS should have them. $2 or so???

Yes none of the other bearings have any up an down play at all - but damage is worse than thought - The connecting rod is damaged- the bolt must have ridden on it a bit a tore up the bolt and rod where the bolt goes in.

Is it possible to replace the rod without pulling the engine?

I have never replaced a rod without removing the head but have heard of it being done. From what I have heard you can get the piston down low enough to slide the wrist pin out enough to change the rod. I would really take a close look at things and see what else needs attention. Especially if it had a rod bolt laying in the pan and it had been run that way. I would check the clearance for the rest of the bearings at a minimum. The end results of patching a patch job usually end up with a bigger mess.
Good Luck Don

I agree with Don. Might be easiest to just pull the engine, tear it apart and see what you have. Sounds like new parts were installed along with new gaskets. Take it all apart, lay out what you have and have the block, head and crank inspected by a reputable machine shop.

yup I hear you. I see no sign of the lock nut - it could have been NOT put on and that is why the bolt came undone. Or it is hiding somewhere in that engine. The bolt definatly came unthreaded.

pic of connecting rod damage

pic of bolt that came out

I may just pull er out and get it on a stand.

At this point I would want to pull the head and look at the top end as well, just on general principles... I'd want to look at everything top and bottom. If this wasn't his first rodeo I'd say maybe try the leave the head on route but I advocate for an end to short cuts on this one...
Bite the bullet or it will bite you.

in deed - that is what I am going to do. Would never feel comfortable taking it for a ride in the country with just my wife and 45 knowing I am riding on some shabby work.

I have been scrutinized at times for taking the harder path. But it does give peace of mind knowing, lack of effort will never be my down fall.

I know I will need a Babbit Connecting rod - what year did that Babbiting end?

Lucky you, you got the last one

I remember many years ago I bought a rebuilt short block (Buick V-6) for my Jeep Commando. Just for curiosity I took the pan off and checked torque etc. Found 11 rod nuts perfect, 1 finger tight. Don't trust anybody, recheck what ever you can.

1948-53 rods interchange.
PM me if you can't find any.

So my rods on the truck all have this silver (lock nut) on far right of this pic

rod with nuts

I found a babbit connecting rod - but not with that second bolt. Can I just use a hardened steel one from hardware store?

that is just a tin lock nut - I should be able to find that

Are you looking for the bolt or the pal nuts?
Pal nuts.

pal nuts - thanks for that link

Somewhere there is a long thread discussing palnuts. There were quite a few opinions stating that they were not needed. Personally I use them. I think that fastening the rod cap with the nut against the thin dipper material does not give the same security as when there is no dipper.

I also like the extra security when a dipper is used.

Well the one bolt that did not have the pal nut was the one that loosened and caused me issues. Now it is possible the previous owner did put one on and he just did not tourque the nut correctly and the palnut vaporized - I found no trace of it nor metal in the pan.

So I removed the head and replaced the rod - it appears I am very lucky no damage except the connecting rod and bolts - both bolts where not tourqued - the second bolt spun. He must have forgotten a cylinder -

anyway - while I have the top torn down - anything extra I could be doing?

All rods are nice and straight.
Getting all the gaskets in the AM.

If you have the time and the inclination it wouldn't hurt to check the valves & lap them if necessary. If you don't have the valve spring compressor most parts houses have a loaner.

Wow, looks like you have dodged a bullet! Get 'er done and take a ride in a time machine-this is what the pickup world was like a half century ago-that truck was the way Americans knew trucks, the way farmers when to market, pulled their cows, and crops to market-this was the America's mechanical workhorse!

Although I do not want to rebuild this engine - it looks real clean- I am sending the head out to get rebuilt seeing it is off. ...but already I then say... a new Cam would be easy, hey give em the block too - Lifters are cheap and right there...look at the carbon on those pistons...

I rather get the 216 running well - drive the Truck- get a 1955 or 57 235 on a stand and start rebuilding that...so I will stop at the head.

Not going to get the head rebuilt- too pricey- I want a 235 to rebuild later. So upon examining the head bolts the two up front have a bit of oil build up on them. No others do.

Is that a concern?

So I have it all back together. Rapping is gone. But still seems a bit clickity clickity will post a video.

Need to adjust the timing. Much better though, starting to like this simple little 216...grows on ya