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Engine noise 38 LaSalle

Started by Tom Beaver, January 08, 2011, 09:35:47 PM

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Tom Beaver

I am getting a strange noise from the engine at idle.  The noise is an infrequent, somewhat random metallic clacking sound which starts to occur after the engine has warmed up.  The noise is very much like someone is tapping on the inside of the block with a hammer.  They mainly come two close together and then a pause with the loudness varying as well.  It is hard to tell but with the clutch inspection plate off the noise appears to be coming from the back part of the engine.  Now if I increase the engine speed with the hand throttle about 200 to 300 rpm the noise completely goes away, at least it is no longer audible and when the engine returns to idle the noise does not seem to come back right away.  The engine has been rebuilt and the car has only about 150 miles on it.  Oil pressure at idle is about 35 psi.

Has anyone had a similar experience or any idea what might be making the noise. Thoughts that occured to me are the crank or camshaft moving fore and aft or the oil pump check valve opening and closing but I have had no experience with this type of engine noise before.

Tom Beaver 

Doug Houston

I suppose that the first  thing I'd worry about would be a loose, or oversize rod bearing. The rate of the tapping is important. If it would be a rod bearing, it willl be double the speed of the engine.

The good oil pressure contradicts this idea. It would be good to observe the oil pressure with the engine at running temperature, and see what it is.It should go down to possibly  20 PSI, if everything in the oiling system is working properly.

The other thing that could cause a rapping noise, is a valve lifter that occasionally stick, and sounds off. Its noise will be half of crankshaft speed.

Don't knoe anything else. Good luck finding it.
38-6019S
38-9039
39-9057B
41-6227D
41-6019SF
41-6229D
41-6267D
56-6267
70-DeV Conv
41-Chev 41-1167
41 Olds 41-3929

TJ Hopland

I dont know anything about that specific engine but I presume this has solid lifters?  So it requires periodic valve adjustments?

Its not something simple like a loose spark plug?   An exhaust leak close to the cylinder can sound like that.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

grumpydad

could you make a video of it running with sound
please try to make shore the sound is good
post it on you tube and give us a link
:)

buicksplus

It sounds to me like a collapsing valve lifter.  The fact that it is intermittant rules out loose rod or main bearings in my opinion.

This engine has hydraulic lifters that are very sensitive to dirt, tiny check valves can fail to hold pressure and cause the valve clearance to increase dramatically -- and that makes a pretty heavy clack-clack-clack sound at half engine speed.  Increasing rpm increases the oil flow enough to cover any leakage.  A rebuilt engine can have small bits of debris left in the oil galleries that can migrate to the valve lifters -- which are at the end of the oil circulation circuit.

If it is a valve lifter, the problem may correct itself as the dirt eventually gets flushed out of the lifter(s).  If not, you may have to carefully dismantle (don't mix up the original combinations of parts) and clean each lifter.

Suggest you play with the clutch pedal to see if it affects the noise.  If it is something on the flywheel, the clutch pressure should affect it.

Good luck!    
Bill Sullivan CLC# 12700

Tom Beaver

Thank you all for your input.  The noise doesn't seem to be associated with a rod bearing or wrist pin since the sound is not regular and much less frequent than the engine rpm would dictate and it appears to go away if the rpm is increased, at least I can't hear it.  Besides it just doesn't sound like any bad rod or wrist pin I ever heard.  When I started the engine up yesterday the car had been sitting for a couple of months and at least one of the lifters had bled down so they were quite noisy until they got pumped back up but the sound I am concerned about now is not the same as that made by the lifters and doesn't appear to be coming from the upper part of the engine.  I have had the clutch, flywheel and bell housing off to fix a transmission problem so I have verified that there is nothing wrong there. Depressing the clutch has no noticeable affect on the sound, besides this noise was present before I did that work.

I started it up again today to make another check.  The noise is indeed random, down low and to the rear of the engine and only appears after the engine is completely warmed up to operating temperature.  The noise starts out very faint and then gets louder with time.  It goes away as the rpms are slowly increased and appears to be gone after about a two to three hundred rpm increase (~1000 rpm).  As I said the frequency of the noise is fairly low but usually comes with two together (clack clack and then a few seconds pause before I hear it again).  I think I am going to drain the oil and add a higher viscosity to see what happens.  I am using 10W30 at present and maybe I should try 20W40 or something like that?

I really really don't want to take that engine out of there if the problem is something simple or if I can't identify it first because I have to disassemble the whole front of that car just to be able to get at the engine much less take it apart.

Tom Beaver   

Jim Stamper


     I would pull the oil pan before pulling the engine. I have pulled the pan on a 37. I don't recall if I had to move any steering parts or not, but I don't recall it being a big deal. Plenty of sludge when I did get into the pan. The coupe hadn't run since 1962. Hopefully the 38 is similar and removing the engine is not necessary.

     What an annoying little gremlin to have to deal with.  Good luck.    Jim Stamper CLC# 13470

buicksplus

#7
I agree that removing the pan is a good idea.  It's not a difficult job with these engines and a good idea anyway with a fresh rebuild.  This way you can recover those lost valve keepers and other debris that may have fallen into the pan!

There are various sheet metal plates down there, I wonder if one of them may be loose or vibrating and perhaps interfering with the crank under certain conditions.   The only way to tell is to take the pan off and inspect, any contact with rotating parts will probably leave some signs.

You might check the pinch bolts on the wrist pins too.  You can see them from below and check to see if they are all there and tight.  A pin moving side to side could generate the kind of heavy intermittant noise you hear. 

I really doubt if changing the oil thickess would make that much difference.  I usually use straight 30W  or 10-40 after a rebuild.  On my older engines I use 20-50W to help keep the oil pressure upon hot days.    
Bill Sullivan CLC# 12700

Bob Schuman

While the pan is off, another thing to look for is possible interference between the oil dipstick and any rotating parts, which has happened on other engines.

If oil pan removal is like the 1940 and 41 cars, no steering linkage parts need to be removed. Just rotate the crankshaft until the front counterweight clears the pan, so it can be slid back and down for removal.
Bob Schuman,CLC#254



Bob Schuman, CLC#254
2017 CT6-unsatisfactory (repurchased by GM)
2023 XT5

Tom Beaver

Thank you all again for the help.  I had considered removing the pan but was somewhat reluctant to do so since I didn't have any idea what I was going to look for once I had it off.  But I guess in this case, I will follow your suggestions and remove the pan and check to see if I can find anything at all that looks suspicious. I will play close attention to the oil pump and the windage tray to see if there are any signs of looseness or interference with the crank.  The pan will come off easy enough as there is nothing restricting it from below.  However, this would be one of those cases where a hoist would be very helpfull.

Tom Beaver