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Buick 1940 bottom engine sound, i want to check


Robby120113
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After a few setbacks since i got the car there is still 1 sound i dont trust. After trying to pinpoint the location it looks like the inside of bottom engine. I do have nice oil pressure at low and high rpm.  To be sure i want to remove the oil pan to check if there is play somewhere. So started to read on this forum. But ive read two thing. Babbit and shims. Is it possible to check from the underside for play in the connecting rod? Are there shims i can check? I will go crazy if i already need an engine rebuild after owning the car for 5 months. hope i will get some reaction since i cant sleep due to worrying
 

here you here the sound while driving

 

 

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I am having a hard time hearing the sound you hear. I do think I may hear a low volume, steady tapping sound. Now for the thoughts...  It does not seem loud enough or low (think bass drum) enough to be a crank related sound. It could be a lifter/valve noise. Check valve adjustment. It could be a fuel pump rod tap. Check with a stethoscope or dowel rod to see if you can localize the noise to the fuel pump area. The last thought is a rod/wrist pin tap or possibly a piston skirt slap.  You can check rod bearing and crank main bearing clearance with plastigauge with the oil pan removed. When removing the rod caps be sure to keep the shims in place with the caps. If you find a loose measurement you remove shims and recheck for proper clearance. If there are no shims and the measurement is loose there are different ways to approach this. Some people say to lightly file the rod cap to tighten the clearance. I am against this idea because once filed there is no turning back. You can also get the babbitt bearings repoured and scrape them in and my choice... have the rods machined for insert bearings and not have babbitt issues in the future. Babbitt bearings are perfectly fine and original, but inserts are easy and newer technology. Your choice.  The crank main bearings are checked the same way, but they are insert bearings from the factory. Now for the rod/wrist pin tap and piston skirt slap I am not really sure how to check with the engine assembled. There may be a way and I am sure others will chime in with suggestions and thoughts.  Also, what engine do you have 248 or 320?

Hope this helps.

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Engine noises can be tricky to pin point, even with experienced ears. Valve train tends to be more common than other sources. Accessories including fuel pump can be a cause. Excessive play in components operated by the camshaft can affect camshaft life. The constant hammering can eventually take its toll.

Piston slap / wrist pin noise. Sounds produced by this is not good but the engine can probably be babied and used with caution for a fairly long period of time.

Main bearings can be noisy at times but these old engines can limp by for a long time as long as oil pressure remains strong.

Rod bearings may fail quickly and put a connecting rod through the block.  Use caution here. If concerned drop the oil pan. Inspect and measure the connecting rod journals and check bearing surfaces as well as check clearances.

You may purchase an older Chilton or other manual which may aid in diagnosing various engine noises.

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Sounds like a rod to me (ugh!), like a rod on my 1936 Pierce 24 yrs ago.  Do you hear any of that noise at idle?  If so, with engine idling, use an insulated-handle screwdriver to short out one spark plug at a time.  When the noise goes away, that's the problem cylinder.

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Goodmorning. 
 

thanks for the tips so far. Some additional info. The fuelpump is replaced for and electric version. The location of the mechanical fuelpump has a cap on it. So thats not the issue. The engine is a 248. And with a stethoscope it was clearly from the bottom end. 
 

@37_Roadmaster_C dobyou have a picture of how a shim looks like on the connecting rod? So it is possible if there are still shims to remove 1 and no rebuild is needed? As for the wrist pin the garage said maybe we can put in a small camera through the sparkplug hole and turn the crank to see if the piston moves. 
 

@Grimy yes. You can hear it. See video clip below. Only at higher speeds its gone. Probably because of additional sounds. I will see if we have a big glove to remove each sprakplug cable to see which piston. 


 

in this video you might hear it better. Its not the valve sound but the hollow thicking sound. 

 

 

 

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4 minutes ago, Morgan Wright said:

You asked about shims and babbitt. You can check the rod bearings for play with plastigauge it's only around $7 for a package.

 

Good luck getting the oil pan off that car, the front bolts are hard to get to.

Is there a picture how the shims look like on the babbit? So i know what to look for?

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Robby, although the noise sounded like a rod bearing in your first video (on the road), after the last video I'm not sure.  For your peace of mind, check for a rod bearing issue by pulling one spark plug wire at a time, engine idling, using insulated pliers.  As I mentioned, if the noise goes away that's your problem cylinder.  If there is no change in noise level from that test, I'd try to eliminate many other possibilities before doing all the work of pan removal.

 

Other possibilities include fan belt and/or pulley(s), water pump.  Remove fan belt and run engine for not more than one minute.  If there is no noise, something driven by the fan belt is the problem and you have saved yourself a lot of effort.

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12 minutes ago, Grimy said:

Robby, although the noise sounded like a rod bearing in your first video (on the road), after the last video I'm not sure.  For your peace of mind, check for a rod bearing issue by pulling one spark plug wire at a time, engine idling, using insulated pliers.  As I mentioned, if the noise goes away that's your problem cylinder.  If there is no change in noise level from that test, I'd try to eliminate many other possibilities before doing all the work of pan removal.

 

Other possibilities include fan belt and/or pulley(s), water pump.  Remove fan belt and run engine for not more than one minute.  If there is no noise, something driven by the fan belt is the problem and you have saved yourself a lot of effort.

The waterpump and fan belt are just last week replaced. The sound is also clearly coming from lower in the engine and not front. I will do the check with cancel the spark per cilinder

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7 hours ago, Robby120113 said:

Is there a picture how the shims look like on the babbit? So i know what to look for?

 

I don't know about your year, but on mine the shims are not "on the babbitt" they are on the bolt that tightens the caps to the rods, remove a shim and the bolt gets tighter. The shims don't touch the babbitt. The shims are thin metal washers between the nut and the bolt. Or I should say, between the cap and the rod at the nut and bolt.

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1 hour ago, Morgan Wright said:

 

I don't know about your year, but on mine the shims are not "on the babbitt" they are on the bolt that tightens the caps to the rods, remove a shim and the bolt gets tighter. The shims don't touch the babbitt. The shims are thin metal washers between the nut and the bolt. Or I should say, between the cap and the rod at the nut and bolt.

I have a early 1940 special. I found a picture of the rod. I marked it with 2 red lines. Is that the location of the shim?

85EB3CA7-5D59-47FA-9254-21558F8D6E95.jpeg

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8 hours ago, Robby120113 said:

The waterpump and fan belt are just last week replaced.

Was the noise present before the water pump and fan belt were replaced?  If not, I'd suspect one or the other.  By all means, short out each spark plug first, before checking anything else.  Do the easy checks first!  🙂

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I spent quite a while chasing noises on my '41 Limited that sounded like wrist pin knock. I thought it was the water pump so I replaced it and it turned out to be the fan belt. Replaced the belt and it only got worse. Replacing the water pump proved that the old water pump was good and the rebuilt replacement was bad, so I'll be doing that job again this winter. Then I had a strange thumping noise that sure sounded like a wrist pin, but turned out to be the fuel pump. Replaced the fuel pump with a rebuilt unit and the noise just got worse. Verified it was the fuel pump by removing the mechanical pump and running the engine on the electric pump. Process of elimination.

 

So it can be a lot of things and new parts don't necessarily guarantee that you've solved the problem. It's always possible that it's a rod knock, but if so, it should be pretty pronounced at idle. I agree with the advice above to remove the fan belt to cut down extraneous noise and determine whether you still hear it. Do the spark plug test, too--that's effective if it is a rod knock. Either remove one plug wire at a time or simply short it to ground ad Grimy suggests--just touch the screwdriver between the spark plug terminal and the block to kill the spark.

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1 hour ago, Matt Harwood said:

I spent quite a while chasing noises on my '41 Limited that sounded like wrist pin knock. I thought it was the water pump so I replaced it and it turned out to be the fan belt. Replaced the belt and it only got worse. Replacing the water pump proved that the old water pump was good and the rebuilt replacement was bad, so I'll be doing that job again this winter. Then I had a strange thumping noise that sure sounded like a wrist pin, but turned out to be the fuel pump. Replaced the fuel pump with a rebuilt unit and the noise just got worse. Verified it was the fuel pump by removing the mechanical pump and running the engine on the electric pump. Process of elimination.

 

So it can be a lot of things and new parts don't necessarily guarantee that you've solved the problem. It's always possible that it's a rod knock, but if so, it should be pretty pronounced at idle. I agree with the advice above to remove the fan belt to cut down extraneous noise and determine whether you still hear it. Do the spark plug test, too--that's effective if it is a rod knock. Either remove one plug wire at a time or simply short it to ground ad Grimy suggests--just touch the screwdriver between the spark plug terminal and the block to kill the spark.

Thanks all for the help. At this moment im still leaning towards lower block. Reason is indeed that the sound is still there without fan belt and fuelpump. Also hard to tell by a video but standing by the open hood it realy comes from the lower parts. The sparkplug test will be the first next week and then the plastigauge hopefully on a cilinders thats quiet after missing its spark. Is a oilpan from a 1940 special model41 removable without any crossmembers in the way?

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Hi Robby,

I do not have any pictures as I went for the machined and insert bearings right away. As said above the shims are between your red lines in the picture. You are on the right track to figure this out. You have eliminated fuel pump, water pump, generator and belt. Great start!! Next do the cylinder by cylinder test as outlined above.  My Buick is a 320 Roadmaster so I do not know what kind of issues you will bump into if you need to remove the oil pan. There are several 1940ish Special owners on this forum. If you get to the "remove the oil pan" step you might want to start a new thread asking just that in the title. They will jump in and give you their input on the subject. Your last video makes the sound much clearer and I also am leaning toward a crank end rod bearing. Don't panic, continue troubleshooting and move forward from there. One recommendation, do not drive the car until you know what is causing the problem. Right now it is a noise needing repair. If it throws a rod it easily could be new block time. These old straight 8 engines are relatively long stroke motors and with that they have a very high torque rating. High torque means higher power at lower RPM and therefore easier to do damage if the bearings are failing.  Keep us posted!

Edited by 37_Roadmaster_C
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I have a 1940 Buick Special model 41 that I just dropped the oil pan on. I didn't find it difficult at all. I had read a few posts that lead me to believe it was a real tight fit, but mine came right off with no issues. I had the front end up on ramps and the splash pans were already off. It was just break all 32 bolts loose and then spin them out. I left two on either side mid-way along the engine to hold it up until I was ready to lower it so the weight of the whole pan wasn't on either of the short ends. A couple whacks with a soft mallet freed the pan as the gasket was sticking. The front bolts (4 if I remember) are accessible with a swivel on the end of the socket. Good luck on tracing the noise down. 

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Thanks. Iately i still drove the car because i just love it. Now it is more clear it is a rod bearing maybe i will take it more easy. Wednesday i have to drive it 20 miles to the garage who are specialized in these kind of repairs. Will post here what the outcome is. For my knowlegde, can the camshaft also cause this kind of noise (since it also on the noise side of the engine). 
 

to be continued 

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It is possible that the cam could cause the noise, but not likely. The noise could be coming from a lifter but the normal result of that type of problem is rocker noise from a loosely adjusted valve. These engines have solid lifters so any misadjustment of the valves could transfer noise lower in the block, but it is not a normal event.  Now you said something in your last post that may be very relevant...  

3 hours ago, Robby120113 said:

For my knowlegde, can the camshaft also cause this kind of noise (since it also on the noise side of the engine).

 

You imply that the noise is more prominent on the cam side of the engine. This makes me rethink things a bit. I would think that a rod knock would be virtually the same from both sides of the engine. I am not sure about this as I have only heard rod knock on a few engines and all have been newer V8's. Hopefully others will chime in with their experience.

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I'll throw in my 2 cents here only because I've had a few burned out rods in my life.

Usually... The tapping will increase if you lightly accelerate, then go quiet when you take your foot off it.  should be loudest under the car.

Grounding the plugs in turn should identify the cylinder.  Now a loose wrist pin will sound almost exactly the same but more to the middle of the engine than underneath.  If the tap is consistent under load or no load changes it likely Isn't crank related.  Piston slap will typically be louder when the engine is cold and get less as it heats up. Diagnosing noise in an engine is an inexact science, but always go for the easy stuff first . We have a tendency to always jump to the crankshaft when there is a noise.  A cam can make erratic knocks if the bearings are loose. Distributor drives, fuel pumps and belts can all make noise 

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The wrist pin is maybe to see with a camera through the sparkplug hole. Turning the crankshaft and see what the piston does. The sound is more present on acceleration and half throttle like in the interior video. Less on deaccelaration. Wednesday hopefully i will have conclusion. 

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On 11/26/2020 at 9:59 AM, Robby120113 said:

Is a oil pan from a 1940 special model41 removable without any crossmembers in the way?

 

Robby, if you end up dropping the oil pan, here's a good tutorial that Dave Stovall posted on a thread I started when I needed advice on dropping the pan.  The front crossmember is in the way, but the front four bolts are accessible through holes in the crossmember.  The next four bolts (two on each side) going back are the most difficult to reach, but you can get them with a swivel socket.

 

 

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Hi all. 
 

so today i had the time to take off the oil pan. Which was very easy. All the bolts were accessible. The inside was very clean and nice. We took of the caps and did the plastigauge as seennin the picture. We measured 0,025mm or for you 0,001” after further inspection we might found the problem. When turning the crankshaft it took a small moment before the camshaft turned. When we peaked to the front of the crank we could see the chain. And we think the chain is overstretched and causing the noise. So to be sure. I will look around for a new chain and sprocket. Checking the the crank has given me some reassurance. Thanks all for the help. Now wait for the the parts and will let you know

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