VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Re: Engine Bottom Noise - Thread Closed

Well, as I have heard ,That what happens is that the piston is pushed up against compression, then when the mixture explodes ( say burns if you must!) the force suddenly slams back down on the piston, piston pin , connecting rod and crank, The piston rotates slightly around the axis of the piston pin, remember, the moment of force is changeing because the angle of the connecting rod is changeing due to the lower part of the rod following the offset rotation of the crankshaft......then if there is too much clearance the skirt slaps the cylinder wall...... short out the plug , there is no explosion and when there is no explosion......no slap!

The noise can be confused with a rod or main bearing knock. The best way to determine what is causing the noise is to dismantle and look and measure. The next best is to use a stethascope or other listening device. I use a very large screwdriver. Put the blade on various parts of the engine block and the handle up to your ear. As you move the blade end you will hear noises getting louder or softer. When at the loudest, you are likely near to the source. I say likely because noises are transmitted along shafts, rods and other structural parts of the engine.

If I think that I will not be damaging the engine further, I will always get out my screwdriver and check things out. Too many times I have taken off and sometimes replaced a good functional part only to find that it did not solve the problem. Listening to what the engine, transmission, water pump, distributor or other part is telling us. It sure helps fix the problem the first time.

If you try it on a good functioning part you will be amazed at the sounds that you will hear. Whirs, clicks, humms but no clunks. Clunks are bad news.

Hey teach, can we put listening to engine sounds into our curriculum?

HEY CHIPPER DIPPER, I TOOK YOUR ADVICE AND BOUGHT A STETHASCOPE, AND GUESS WHAT?

Donald, at our house I found out that what I thought was the dinner bell was really the smoke alarm! It went off every time you now who put the frying pan on the stove! good thang I like my steak, frioles , and taters well done! ( and if I want her to know I said this I will tell her!)

YA, BUT MR MACKIE WACKIE, IFS I SAY ANYTHING? SHE SAYS IF YOU DONTS LIKE MY KOOKING AND DE WAYS I DO IT, AND WHEN I CALLS YA FOR DINNER, THEN YOU DO YOUR OWN KOOKING?????

Back in the 40's & '50's When someone brought a Chevrolet into the dealership with engine noises the mechanics could identify them instantly.The most frequent was loose connecting rods ,especially on the pre 1948 cars.Then it was a matter of adjusting the rods and mains.(they always did both).The slow,short trip, city driven cars the most common.If they were up to 40,000 miles or so the wrist pins were making noise (not harmful)one or two cylinders low on copmpression and starting to burn oil so most often an overhaul job was done.The oil return holes in the rings and pistons would be plugged up due to the poor oils.If job was started by 8 AM it would be done by 5 AM.The price with normal parts in 1950 was $77.00.The most often required extra parts would be a couple of exhaust valves.The car was returned after 500 miles to have the oil changed,valves readjusted and head retorqued.The head was torqued on new cars before delivery, at 1000 mile inspection plus was to be done with every tune up.The replacement rings used for an overhaul were of the expander type and would last longer han the original one piece cast iron rings (cast irons were eaiser on the cyl. walls ).The overhaul would usually last for the rest of life of the car because very few made it past 100,000 miles in those days.

Yes, Donald..... Unhuh Dear is my favorite expression, But I don't think either of us have missed too many meals from pictures I have seen, or brewskis either, My wife is a fine cook, I can even remember when she used to cook ........instead of popping Chef Schaffler in the Zapper! ( That was when we had four kiddos at home.)
I guess I better change the batterys in the dinner bell, we haven't heard it for a while.

Hey thanks for the noise input. I do have a noise under a load but I need to go listen to it again. I have been out under the knife for a while and am just getting back in shape. I will take a listen again and see what is what. I saw a lot of talk about new engines overheating and am here to say that mine never did. I had mine out on a hill in 98 deg weather and it never got in the red. I have a Filling station honeycomb radiator and a JUNK YARD DOG restored water pump so I know I couldn't go wrong. :) :) :) There you go Skip, a little advertising. I am running a four bladed fan.

Hey Matt! You're my man!!!

Mat, Don't want to get into piston panic but you can listen to it in the pre 1936 engines like Chip said.By holding a long screw driver against the cylinder barrels on the left side of the engine.Because the lower two-thirds are not water cooled on these years the noise is easy to detect ,just hold listening devise agianst each cyl. barrel while it making the noise.Another way to hear a lot of strange noises is to run the engine without a fan.It sounds really scary.The fan blends all engine noises together

Well even if it was 102 deg in Oroville today I was fealing good so I started her up for the first time in about a month. I found my pesky exhaust noise is back. The exaust pipe to the manifold has given me some trouble. Stone cold and warmed up there is no noise except a little valve train chatter. I had the wife race her up a few times while I listened. That will cost me dinner at least. Like I said the noise is when it is pulling at higher RPM's. If I lug it down I don't hear it. I will have to take it for a drive again to discribe it better. Next weekend will have to do. Also it only has 258 miles on the rebuild. I had inserts put in and the center main is modified with a thrust bearing pinned in the block. Egge pistons and balanced. She does 53 on a stock rearend and I could have gone faster but didn't want to push it. I am not sure the noise I hear is even bad. Is the 194 loud at higher RPM's? Also it is from the rear of the engine I think, so It could be a transmission noise even though I don't think so. :confused:

Ok, is was a nice 85 in Oroville today so we took her out for a 50 mile drive to and around town. I find that every time I put more miles on it she sounds better. Today was no exception. I listened very close at all speeds and power. The noise I hear is most heard just as you put power to the drive train. At a coast you do not hear it, and at even power you do not hear it. As you add power it starts and gets less as the load increases. It is not a knock although the first time hearing it you may think so. It is much lighter. It is definitely at crankshaft RPM not camshaft RPM. From what you have all said I think it is piston slap. I did hear it a few times when I started it this morning but it was ramdon and went right away. She also had a little more power today because it pulled the last hill at 38 MPH with both the wife and myself. It use to only do 35 MPH. I am going to change the oil again now that it has 300 miles on it and check for metal. She is still a little tight if you try and start it right after turning it off warm. A 30 minute wait is best. :) :) :) Any other ideas? :confused: :confused: :confused:

It is hard to tell as you said, but from what you described, it sure sounds like a piston slap as you mentioned. With the Egge pistons installed, it probably is a good chance that you do have a piston slap, since the input that I have been getting over the past decade or so, from other Chevy owners with similar problems, have all been related to Egge pistons. One fellow even changed out his Egge pistons twice (Egge pistons the second time as well) and still had the same problem. Finally, he put in another brand of piston and his piston slap went away. To be honest, I can't remember if he finally installed new old replacement stock aluminum pistons or new old stock cast iron pistons, but definitely changing the brand of piston solved his problem. Your noise sounds about the same as Donald's noise as well. :( :eek:

HI MATT, SURE WOULD LIKE TO HAVE YOU COME BACK TO SEATTLE AND ATTEND SOME MORE OF OUR CLUB MEETINGS. MATT, I HAVE ABOUT THE SAME AMOUNT OF MILES ON MY ENGINE AS YOU HAVE. WHEN MY ENGINE IS COLD, I GET A NOCKING NOISE IN NUMBER TWO AND NUMBER SIX CYLINDER, NUMBER TWO A LITTLE LESS THAN NUMBER SIX.AFTER THE ENGINE WARMS UP THE NOISE GOES AWAY. PISTON SLAP? I ALSO HAVE EGGE PISTONS AND FROM ALL THE THINGS I HEAR ABOUT THEM, WELL MAYBE WE SHOULD OF HAD ANOTHER BRAND. EARLS MACHINE ALSO BUILT YOUR ENGINE, AND I REMEMBER MARK ASKING ME WHERE I BOUGHT MY PISTONS AND WHEN I TOLD HIM EGGE, HE SAID THAT IS A BIG MISTAKE AND YOU WILL HAVE PROBLEMS WITH THEM. I GUESS HE IS RIGHT. I WILL RUN MY ENGINE WITH THE EGGE PISTONS AND GET MORE MILES ON THE CAR AND SEE HOW IT DOES. GOOD LUCK,DON :) :) :) :)

HELLO EVERYONE, I HAVE NOT DONE ANY ENGINE WORK YET, SINCE MY OTHER POSTINGS, BUT I HAVE A QUESTION ABOUT ENGINE SLAP. WHEN A ENGINE IS FIRST STARTED AND IT IS COLD, AND YOU HAVE A SLIGHT KNOCK IN A CYLINDER AND YOU TAKE A SCREWDRIVER AND SHORT THE SPARKPLUG OUT FOR THAT CYLINDER AND THE KNOCK GETS LOUDER, AND THEN THE ENGINE WARMS UP AND THE KNOCK GOES AWAY, IS ONE TO ASUME THAT IT IS PISTON SLAP. ALSO ON ALUMINUM PISTONS, WHAT CLEARANCE SHOULD THERE BE BETWEEN THE PISTON AND THE CYLINDER WALL. :) :)

Don, all I know is for the 28 with the "New" aluminum pistons it was to be set at a .002 feeler gauge no go and a .001 feeler gauge should fit freely. Seems to me around .0015

Keep in mind that data applies to the '28 piston in '28.

I GUESS WHAT IM ASKING IS,WOULDNT ALUMINUM PISTONS HAVE THE SAME PISTON TO CYLINDER WALL CLEARANCE FOR ALL ENGINES, PERTAINING TO HEAT EXPANSION OF ALUMINUM PISTONS, OR ARE THERE DIFFERENT ALLOYS USED IN THE MAKING OF ALUMINUM PISTONS THAT GIVE THEM DIFFERENT CLEARANCES IN THE CYLINDER WALLS. WHAT IS THE MAXIUM CLEARANCE YOU WOULD WANT BETWEEN ALUMINUM PISTON AND THE CYLINDER WALL. WHEN I HEAR THE COMMENT OF PISTON COLLAPSE, WHAT EXACTLY ARE WE TALKING ABOUT AS TO WHAT EXACTLY HAPPENS. WHAT IS PISTON COLLAPSE??? THANKS :confused: :confused: :confused: :confused:

Yeah, The data from the 28 repair manual says that the 28 alloy piston is different from the ordinary alloy pistons because of the special alloy insert. each manufactor would have a different alloy , hence it's own expansion curve.

All aluminum pistons will not have the same clearence.There are many designs of pistons such as Standard T slot.Cam ground out of round,and pistons with steel struts cast in to control expansion. (cam ground out of round are designed to fit tight side to side but be loose front to rear so when cold skirt is tight but will expand front to rear thus HELPING to eleminate cold piston slap)Any of these designs will usually have cold clearence from .001" to.003" specifyed.It is best to follow the piston manufactorers recomendations.It is common to hear piston noise with many pistons but most should dissappear in the first 5 min. of running.Other things being tight in an engine can also cause the pistons to slap.The two most common are wrist pins and connecting rods.(The wrist pins also get looser when piston expands and warms up) so give the engine a chance to "loosen up" before worrying too much.Also it would be my guess that pistons purchased for "old" cars are very low tech so the can be machined and adapted t many applications.

Hi Chev Nut,

Thanks, I could not have covered it any better.

There is a big distinction in Modern Pistons and New Replacement Stock (Pistons newly manufactured for old applications) (Manufacturers such as EGGE, JAHNS, ect fall in this classification).

USE THE CLEARANCE FOR THE PISTON AS SPECIFIED BY THE MANUFACTURER.!!!!!!!!!

thanks chevgene and teacher, so far I have only heard complaints from guys doing older engines with aluminum pistons. the machine shop I deal with uses egge pistons all the time on the engines he rebuilds, but shutters when someome wants to use egge pistons on the older ones. I dont know what the specks are on my aluminum pistons as I have had them for along time and never got involved with them, as they went to the guy who put my engine together. I think the bottom line is that I need to get alot more miles on the engine before any decision is made about it.

So, JYD, mrmack, and others in the know, what brand of pistons would you (do you) buy to put in your car? :confused: I know what brand to not buy. Egge

Thanks, Gator

P.S. Alum. or iron in your cars?

I would not buy by piston Manf. brand , I would have to rely on the trusted vendor to supply the correct pistons, but first I would have to find out what combo would work for the engine Rod, pin and cylinder bore. To know if the cylinders are going to have to be bored or just honed. Then after communicateing all the info to the machine shop and vendor hope that the correct parts are available.

I use new old stock GM cast iron pistons as originally came in the car from the factory.