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Onan B48M -- What Are These Sounds? ... What Do They Mean?

onan b48m sounds case 448 valve train bearings

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#1 Case448 OFFLINE  

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Posted February 25, 2016 - 08:33 PM

Recently started work on my project tractor, a 1986 Case 448 with an Onan B48M (18HP).

 

I'm getting some strange noises... And I can't decide what to do about it...

 

Wondering if I should leave this motor as-is, and just run it, or if I should pull the motor out, take it apart and see if I can figure out what the problem might be.

 

Here are the vitals, before I describe the sounds it's making...

 

Compression:

Drivers side: 125 PSI

Passengers side: 105 PSI

 

Oil Pressure - Cold:

Bounces off 45 PSI (when relief valve kicks in)

 

Oil Pressure - Warm:

Idle: 18-21 PSI

Full Throttle: 30-34 PSI

 

Short history / whats been done so far:

 

Bought as running tractor (but barely), with plan to fix it for use in my garden (tilling and plowing), and in the fall to clean up leaves.

 

Motor was backfiring, could not get to run right. Poor compression. Found it had ingested two of the little screws from the top of carb, one per cylinder, and spit them both out. Minimal damage, however the valve seat on the passengers side had a groove across the seat.

 

Had a valve job done. Guy said he "lapped them in" (I latter read in manual this is not recommended). Did not replace anything in the valve train.

 

Eventually got motor running pretty good, motor has good power, starts easily, has a very slight miss about once every (I'm guessing) 10 revolutions.

 

SOUNDS ITS MAKING:

 

I'm trying to figure out what to do from this point...

 

Motor makes a fairly loud high pitched "clattering" noise, sounds just like valve clatter to me. Put a stethescope on the motor, high-pitched metal on metal tin-ey "clattering" noise is heard with about the same intensity from the valve area (both valves, both sides, exhaust valve a little louder), and the center back of the motor near the top (only place I can reach to listen). Also hearing a fairly loud "whirring" sound heard everywhere, sounds the same as the sound when a roller (ball) bearing is going bad.

 

To establish some kind of a "norm" I went and listened to my friends 446 (onan B43) with the same stethescope-- much quieter, valve-sound only very slight, with none of the whirring sound. his motor is definately not in great shape, and my motor is making a lot more noise than his, maybe 2-3 times as much.

 

My "valve clatter" noise is loud enough that people comment on it when they hear the tractor running.

 

WHAT TO DO?????

 

Should I RUN IT and hope for the best? Or TAKE IT APART and have a look?

 

Any thoughts and/or ideas are welcome!

 

Thanks!

 

Dave


Edited by Case448, February 26, 2016 - 10:03 AM.


#2 olcowhand ONLINE  

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Posted February 25, 2016 - 08:41 PM

If it were me, I think I'd tear it down.  Does your governor seem to be working fine?  Reason I ask is because the spider that holds the ball bearings apart could be busted up and might be causing some of the noise.


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#3 Case448 OFFLINE  

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Posted February 25, 2016 - 08:47 PM

If it were me, I think I'd tear it down.  Does your governor seem to be working fine?  Reason I ask is because the spider that holds the ball bearings apart could be busted up and might be causing some of the noise.

 

Governor seems to be working fine, however it does come down about 10 percent from full throttle on its own, so I have to hold the throttle lever wide open to make the motor run wide open. Not sure if thats governor, or a much-needed throttle cable adjustment.



#4 MH81 ONLINE  

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Posted February 26, 2016 - 12:46 AM

I agree with Daniel, it'd be worth it to know.
The noise could be bad gap on valves or the beginning of serious damage and a grenaded engine.

#5 KennyP ONLINE  

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Posted February 26, 2016 - 05:33 AM

I would be taking it apart and do some looking.



#6 crittersf1 OFFLINE  

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Posted February 26, 2016 - 08:55 AM

Tear it down before it grenades



#7 toppop52 ONLINE  

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Posted February 26, 2016 - 09:43 AM

The whirring sounds could be normal, camshaft and crankshaft spinning in bearings, car engines have that all the time, but the tapping/knocking is a problem.



#8 Case448 OFFLINE  

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Posted February 26, 2016 - 09:51 AM

I agree with Daniel, it'd be worth it to know.
The noise could be bad gap on valves or the beginning of serious damage and a grenaded engine.

 

Checked the valve lash a couple weeks ago, it was exactly to spec., just as I set it about two months ago.

 

I agree with the general consensus, so I'll tear it down and have a very good look around.

 

I believe these sounds are a warning, that if ignored will be the beginning of the end for this motor.

 

I'll tear it down over the next couple weeks.

 

I'll keep posting to this topic with further details, as they become available.

 

Thanks everyone --

 

Dave


Edited by Case448, February 26, 2016 - 09:54 AM.

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#9 Case448 OFFLINE  

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Posted March 05, 2016 - 03:48 PM

Progress Report:

 

Okay, so I started taking the motor apart today. Here's what I found so far:

 

Overall the motor looks great, except for:

 

1. Shavings in the bottom of the oil pan. Volume of shavings is about 1 to 1 1/2 teaspoons. Did not examine shavings real close, but some shavings look like they could be flashing off the block casting (not likely), some shavings have a jagged edge like you would see coming off a metal lathe.

 

Can't see any missing or damaged parts, pistons all there and look good, rods all there and look good, back crank bearing all there and looks good. So, not sure where these shavings might be coming from.

 

I haven't taken out the crank, cam, valves/springs/guides/etc, front gear off cam or crank. Will need to locate special tools to continue.

 

2. Governor cup - when I rotate it, sounds a bit loud, like a "bearing going bad" sound -- not sure if this is normal.

 

Everying else looks real good, with no visible damage anywhere, looks like not much wear, although I haven't taken any measurements yet.

 

OK -- Any ideas?

 

Thanks everyone --

 

Dave


Edited by Case448, March 05, 2016 - 03:50 PM.


#10 MH81 ONLINE  

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Posted March 05, 2016 - 04:06 PM

As you dissemble this, there will be an aha moment
Keep looking.

Are the shavings magnetic or aluminum?

I'm concerned something is in between a piston and the wall or the bearings are spinning on crank, but I suppose it could be bearing noise.
Also, be sure to investigate your oil pump and its flow.

#11 Case448 OFFLINE  

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Posted March 05, 2016 - 04:25 PM

Are the shavings magnetic or aluminum?

 

The shavings are *NOT* magnetic.


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#12 Case448 OFFLINE  

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Posted March 05, 2016 - 04:27 PM

Also, be sure to investigate your oil pump and its flow.

 

Oil pressure was real good, tested just before I took apart (see numbers in prior post).


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#13 olcowhand ONLINE  

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Posted March 05, 2016 - 05:00 PM

Look very close at the cam & crank bearings.  They sometimes spin in the case and can block off the flow of the oil passages.  The worst one about this is the cam bearing directly behind the cam gear.


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#14 Case448 OFFLINE  

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Posted March 05, 2016 - 05:29 PM

Look very close at the cam & crank bearings.  They sometimes spin in the case and can block off the flow of the oil passages.  The worst one about this is the cam bearing directly behind the cam gear.

 

Could bad cam bearings cause what sounds like "valve clatter" ? Valve lash was correct, clattering was rather loud. Have yet to figure out what is causing that noise.



#15 KennyP ONLINE  

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Posted March 05, 2016 - 05:58 PM

Might be in the governor!






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