Have you tried shorting out cylinders the see if it changes on one cylinder more than the others? To me it sounds more like piston rather than a rod. You also might try using a long screw driver or broom handle to listen to the pan and side cover to narrow done the area where the noise is.
Dens Chevys 1927 Speedster 1928 coupe 1941street rod 1947Fleetline 4 door 1949 1/2 ton Pickup (sold) 1954 210 4 door 1972 Monte Carlo 2003 Corvette convt..
The first thing I would do is remove the valve cover and see if everything looks OK. Does the noise cange under load? Short out or remove one plug wire at a time and see if noise changes. Probe around with a long rod or stick held next to your ear and see if you can pin point the noise. It is NOT a wrist pin and noise is distorted when recorded. What were you doing when it first started? Sounds kinda like a burnt out rod and the top of the piston is hitting the head or it injested some metal and it is caught between the piston and head.
It has had a bit of a "tap" for a while. I had someone listen to it and poke around with the stethoscope and he said it was somewhere in the top near the middle. I readjusted the valves and it seemed to go away. Then it laid idle through the generator shemozzle. After the second ride it started doing this. I did take it up to about 55 so maybe a rod is the culprit. I'll follow the steps above and report back. At the risk of looking foolish, how does one "short" a plug?
Take an insulated screwdriver and short the spark plug lead to ground while it is still on the plug of course you have to have exposed spare plug leads connected to the plugs.
1.removed valve cover. Everything in its place. Nothing loose. No visible foreign objects. 2.Started it. Lo and behold it is quieter. Pulled each plug wire one after the other. No change. Somehow that made me feel better. 3.While it was running took the feeler gauge to the valves. A couple of tight ones at the rear. Backed them off a bit. 4.Went for a ride. It sounds pretty well like it did before. No rapping or knocking. At least not while inside the car.
Could a stuck valve had caused this noise? I'll start it up tomorrow morning to see what it says.
The ATF quieted it down some. It still rattled like a diesel after a restart several hours later. Went for a ride. Didn't hear anything bad. Seems to go away when warming up. I think that indicates an excessive clearance somewhere that closes up. I suppose I could drop the pan to have a look. Would a platigage test reveal anything?
If worse when cold it is probably a piston. If worse when hot a bearing (because the oil thins out) I would still try shortinng out a plug or removing a plug wire on at a time so as t pin point the cylinder.
So here we are almost two years later and the engine still doesn't sound right. Here's a recap: 1-Tried to isolate the noise by shorting out plugs. No noticeable difference. 2-The sharp metallic noise is still there upon startup. I suspect Gene may be right about something rattling on top of a piston. 3-the other day, I took a long (20 miles) "fast" (55 mph) ride and twice while slowing down on the overrun a rapping sound a bit like a hammer drill. 4.the few times I drove it since (abysmal weather) it seems to get worse.
So I plan to open it up.I can check for loose parts in a cylinder by removing the head. I suppose I could check bottom end clearances with plastigage (if it still exists). What about pistons? I guess they'd have to removed and miked?
What I'm looking for is a sequence of elimination starting with the easier test proceeding to a total dismantle if need be. And what should I have on hand just in case?
Would it help if I went for a ride with a passenger equipped with a recording device?
Last question....maybe....try it. If it was a piston would make noise when cold and go away when hot. Is a push rod hitting the side cover? Run some ATF throg the carb. with engine runnning at fast idle. Did you install the helper springs on top of the lifters? Is something loose in that hardware?
Plastigage is stil available but I would ude the 1934 shop manual preceedure.Rods will be quiet with the cold thick oil and noisey with hot thin oil.
If by "overrun" you mean when the engine is "unloaded" then the knock is probably a rod. I've had 2 rods knock over the years and both knocked when the engine was unloaded (not pulling). I was fortunate in both cases as I was able to adjust the rods by removing shims. I would take a quick look at the rods. You don't want to beat up your crankshaft.
Last question....maybe....try it. If it was a piston would make noise when cold and go away when hot. Is a push rod hitting the side cover? Run some ATF throg the carb. with engine runnning at fast idle. Did you install the helper springs on top of the lifters? Is something loose in that hardware?
Plastigage is stil available but I would ude the 1934 shop manual preceedure.Rods will be quiet with the cold thick oil and noisey with hot thin oil.
That would mean removing them all & testing them one by one right?
If by "overrun" you mean when the engine is "unloaded" then the knock is probably a rod. I've had 2 rods knock over the years and both knocked when the engine was unloaded (not pulling). I was fortunate in both cases as I was able to adjust the rods by removing shims. I would take a quick look at the rods. You don't want to beat up your crankshaft.
Yes that is what I meant. Slowing down from speed with the foot off the gas.How did you find the culprits?
It would mean removing the rod caps one at a time. Remove two shims, one on each side, bolt the cap back in place, and see if you can tap the rod back and forth with a little hammer. If the rod is fit correctly you sould not be able to tap it back and forth with the shims removed.
"Yes that is what I meant. Slowing down from speed with the foot off the gas.How did you find the culprits?"
I was fortunate in that I was able to find the loose rods by wriggling the rods with the pan off. It's kind of a feel thing. If you can't feel it you'll have to use Chevgene's approach. I, personally, have never had much luck with plastigauge and poured babbit rods.
I could get mine to knock when parked by racing the engine and letting off on the gas. They both would knock on the downside.
Have you tried a stethoscope just to ID the general area the knock is coming from. Top or bottom of engine.
The old general rule applies - mains knock under load and rods knock when unloaded.
I was fortunate in that I was able to find the loose rods by wriggling the rods with the pan off. It's kind of a feel thing. If you can't feel it you'll have to use Chevgene's approach. I, personally, have never had much luck with plastigauge and poured babbit rods.
I could get mine to knock when parked by racing the engine and letting off on the gas. They both would knock on the downside.
Have you tried a stethoscope just to ID the general area the knock is coming from. Top or bottom of engine.
The old general rule applies - mains knock under load and rods knock when unloaded. [/quote]
Yes we tried the stethoscope two years ago.One old time mechanic and a not so old one and both said it wasn't bottom end. Now I'm not so sure. Only one way to find out. Pity having top do that at the beginning of our short cruising season. They said summer might be on a Wednesday this year.
Although my engine experience is with a '28, I think it applies here.
When I checked the rod end cap clearances on my '28 engine, I found that the previous owner had smushed some of the shims so they were folded over in spots and therefore were falsely tight. I cut off the folded parts, cleaned up the shims, and checked each bearing clearance.
I loosened all the rod end caps and worked with one at a time, so I knew each was what it should be. I removed two shims (one from each side of the bearing), tightened it, and then spun the engine by hand to make sure it turned freely with the hand crank (spark plugs out). When I felt the crank bind, I put one shim back in. The clearance for each ended up about .0015 of an inch (as measured by plastigage).
This procedure only took a few hours. Hopefully, it'll find your problem and get you on the road again for the season.
Cheers, Dean
Dean 'Rustoholic' Meltz old and ugly is beautiful!
Looks like I'll have to take a few days off from installing my wife's new/old kitchen cabinets and concentrate on the car. As far as a few hours, at my age that would account for getting in and out from under the car. The actual work wil likely add a day or two.
Just thiught of something. what is the recommended torque value for rod cap bolts?
I am under the opinion that todays babbitt is superior to what was originally used. According to sources I have talked to the babbitt contains more tin and less lead making the end product better able to stand up to load. So from that perspective perhaps nos and nors rods are not as desirable as having them currently babbitted.
Later NORS rods or rebabbitted rods have a higher tin content as well. Originals have softer babbitt so they can capture particles and bury them in babbitt instead of scoring the shaft. Technology and much better roads resulted in less need to capture stuff.