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Old 12-03-2020, 07:20 PM   #1
kawagumby
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Default Help with an engine noise...

Hi all,
I recently acquired a 1931 Model A roadster deluxe that has had a frame-up restoration a few decades ago. The odometer reads about 2500 miles which seems about right based on the car's condition.
There is a subtle knock that occurs sometimes during cruising between acceleration and deceleration, but is very obvious when coming to a stop with the clutch in. The knock (rap) is tied to engine RPMs and does not sound like any kind of drive train noise. I'm familiar with piston slap and piston pin noises, and that's not it. It definitely gains noise during braking with the clutch in.



When I first heard it, the thought that crossed my mind it was a camshaft with too much end play, but reading about the noise model A camshafts make, this seems like a long shot. There is no noise a idle, no noise when the car is stopped and I rev up the engine...so that makes me wonder if something other than a camshaft or too much rod clearance is in play. There is no knock when I start the cold engine. If it is a rod issue, shouldn't I be able to hear it when I rev the engine?



I read somewhere that the '31's have a different oil pan baffle setup...can that be a factor?

Any ideas would be appreciated.


Tom
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Old 12-03-2020, 08:38 PM   #2
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Default Re: Help with an engine noise...

If it happens with the clutch in.....could it be a bad throwout bearing??
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Old 12-03-2020, 08:46 PM   #3
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Default Re: Help with an engine noise...

Maybe too much end play in the crankshaft?
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Old 12-03-2020, 09:46 PM   #4
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Default Re: Help with an engine noise...

I forgot to include that engine timing affects the intensity of the rapping noise...louder with more advance. Sorry 'bout that.

So, it isn't drive train related and really acts like a rod bearing with too much clearance, but why won't it sound off enough to hear it during rev-up-down or idle? And why does it get so increasingly loud when braking in neutral only to fall back to quiet once the car stops?

Crank bearing sounds (in my experience) are duller and of a lower tone that this noise...which is rod-bearingish. I wonder if I'll just have to pull the pan and feel for excessive up-down rod-play or plasti-gauge each one. Can oil flowing to the front of the pan under braking be a reason for a looser rear rod to get louder?

Last edited by kawagumby; 12-03-2020 at 09:56 PM.
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Old 12-03-2020, 09:58 PM   #5
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Default Re: Help with an engine noise...

sure sounds like excessive crank play to me. Had the same noise and issues. Corrected most of it with engine mount adjustment (float a motor). Crank the motor, push in the clutch and see if the front pulley moves forward. Mine did, still does, but no oil leaks and engine runs fine.
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Old 12-03-2020, 10:14 PM   #6
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Default Re: Help with an engine noise...

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In my opinion, engine knock that is affected by timing advance would indicate main bearings. Engine knock affected by depressing the clutch pedal would indicate crank endplay. In either case, pulling the pan might reveal worn or broken babbit on the thrust faces.

You might want to edit your profile and add your location. You might find some experienced help close to you to help diagnose the problem.
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Old 12-03-2020, 10:20 PM   #7
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Default Re: Help with an engine noise...

If you suspect a rod or main bearing pull the oil pan and check the bearing clearances.
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Old 12-03-2020, 10:21 PM   #8
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Default Re: Help with an engine noise...

Quote:
Originally Posted by TMarsh View Post
sure sounds like excessive crank play to me. Had the same noise and issues. Corrected most of it with engine mount adjustment (float a motor). Crank the motor, push in the clutch and see if the front pulley moves forward. Mine did, still does, but no oil leaks and engine runs fine.
That's interesting...I'll do that check. I recently installed the float-a-motor engine mounts to correct a half-inch misalignment of the hand-crank hole with the crank...the engine front was high.

Out of curiosity, did you use the float-a-motor upper rear mount in your installation?



I'll be looking at crank end-play as the number one suspect.
Thanks for all your help, folks.
Tom
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Old 12-04-2020, 08:36 AM   #9
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Default Re: Help with an engine noise...

Just replaced original rear mounts with float a motor. Front mount original. Parts were with basket case when I acquired it some 20 years ago. Check for babbit in oil when changing, possibly damaged thrust on rear. I am just living with mine. Only knocks on hard stops. Quit sure it is rear thrust broken.
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Old 12-04-2020, 10:12 AM   #10
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Unhappy Re: Help with an engine noise...

Thanks. I plan to live with mine too as I don't have a big enough shop to pull engines and I'm getting too old to deal with such an issue. I am using thinner oil than normal as I changed it to check for particles when I first got the car, no metal found. I will put heavier oil in now with additives to see if that helps. Very disappointed at this point, I've gone though just about everything over the last couple of months; carb, distributor, motor mounts, steering, electrical, cooling system, and thought I had a solid machine. The engine runs perfectly other than the noise coming up to a stop. Bummer.
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Old 12-04-2020, 10:37 AM   #11
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Default Re: Help with an engine noise...

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Originally Posted by kawagumby View Post
That's interesting...I'll do that check. I recently installed the float-a-motor engine mounts to correct a half-inch misalignment of the hand-crank hole with the crank...the engine front was high.

Out of curiosity, did you use the float-a-motor upper rear mount in your installation?



I'll be looking at crank end-play as the number one suspect.
Thanks for all your help, folks.
Tom
Did you notice the noise before the float a motor installation?
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Old 12-04-2020, 10:53 AM   #12
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Default Re: Help with an engine noise...

Id run 20/50 wt engine oil as a band aid...even pour a little STP to quiet it down some if living with it is your only option. Unfortunately the clock is ticking for both of you, thrust wear or failure, it wont be long before a bearing goes, in layman's terms the thrusting crankshaft 'pushes' the oil out of the bearing speeding up wear.
They do make replaceable bronze thrust bearings if your main babbit is good, you still have to deal with pulling the engine but you don't have to pay for new babbit or machining for inserts.

Good luck
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Old 12-04-2020, 10:55 AM   #13
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Default Re: Help with an engine noise...

Dave could be on to something, it could be a ujoint..
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Old 12-04-2020, 10:59 AM   #14
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Default Re: Help with an engine noise...

Just drive it, if'n it's serious it'll get worse.
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Old 12-04-2020, 11:26 AM   #15
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Default Re: Help with an engine noise...

Quote:
Originally Posted by 1crosscut View Post
Did you notice the noise before the float a motor installation?

Yes...
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Old 12-04-2020, 11:28 AM   #16
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Default Re: Help with an engine noise...

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Originally Posted by Jack Shaft View Post
... Unfortunately the clock is ticking for both of you, ...
Good luck

LOL, isn't that the truth. I just had 3 stents put in my heart two months ago. Maybe I bought the "A" because I relate to it....
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Old 12-04-2020, 11:32 AM   #17
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Default Re: Help with an engine noise...

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Originally Posted by Jack Shaft View Post
Dave could be on to something, it could be a ujoint..

The u-joint wouldn't be affected by spark advance, and it is tied to engine rpm. I wish it was that simple, tho'.


This forum has a good crew.
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Old 12-06-2020, 11:27 AM   #18
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Default Re: Help with an engine noise...

Quote:
Originally Posted by Synchro909 View Post
Maybe too much end play in the crankshaft?
i can measure the end play in my crankshaft with a tape measure
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Old 01-16-2021, 09:12 PM   #19
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Default Re: Help with an engine noise...

Hi all,
Just to update:

I pulled the engine and went through the rods and mains...the problem was the two rear con rods had too much clearance. As a matter of fact, the number 4 rod didn't even compress the plastigauge! In spite of all that, the bearing surfaces and journals look almost new, the engine clearly has very low hours since it was rebuilt...it just needs some tweaking. As far as the rear main thrust surfaces go, both top and bottom look new and I could fit a .002 feeler gauge with light resistance, so all is good.


If I ever work on the bottom end again I WILL order shim packs first , trying to work with the fused-together rod shims was a chore - I lucked out being able to swap shims that were pulled from looser rods to get all into spec. Heating didn't work, and even when I was able to get some separation, nature's welding would not let the leaves come completely apart.

Pulling the engine let me see several issues that needed attention that working under a car would not...such as the clutch (looked like new too) had a finger way out of spec causing uneven wear on the fingers/throw out bearing, and it was apparent it came that way from the factory (the nut/stud staking was factory). I could see where oil leaks were happening at the engine rear, etc.



Regarding the way the knocking presented itself, I believe the issue was caused by the rear rod bearing clearance being too large to hold an oil film when the #4 splash pan was emptied during braking (flowing to the front of the engine). The clutch being depressed during that time was coincidental. When the splash pan was full, as when cruising and start-up, there was sufficient oil accessible to muffle the sound.




IMG_3459.JPG

engine2.jpg
Kind of a fun project, this car...


PS.. I had purchased an aftermarket main bearing bolt kit that uses standard bolts. I didn't use it as the hex head bolts don't provide enough room to properly set a socket. I'd recommend buying the stock type bolts (if available) as there was a good reason for Ford going to the square style. I did, however use some of the sealing washers that came with the kit.



Tom

Last edited by kawagumby; 01-18-2021 at 09:08 AM. Reason: discussion of cause of intermittent knocking
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Old 01-16-2021, 10:24 PM   #20
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Default Re: Help with an engine noise...

Tom,
Thanks for the follow up. Might check the U joint while it is apart and change it out if there is any play. Let us know when you are back together and running. Would like to know exactly how you fixed your rod bearing issue.
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