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| Diagnosing Engine Whirr https://slantsix.org/forum/viewtopic.php?t=55844 |
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| Author: | nm9stheham [ Thu Jul 24, 2014 10:29 am ] |
| Post subject: | Diagnosing Engine Whirr |
I posted this on another forum for feedback,but this is problaby the best forum due to the focus on /6's: Engine is a 225 slant 6, original 1962, 60,700 miles. Issue is a 'whirr' or vibration in the engine that cyles on and off at 1-2 seconds intervals; it builds up and dies off and then does that over and over. It seems most pronounced when warmed up, and the intervals are somewhat erratic. The whirr is a moderate pitched sound, not a light tick like valvetrain issue, or a heavy knock like a crank issue. Using a tube or long screwdriver to listen to the block whiel idling, it seems to be towards the front. I was thinking possibly a loose pilot bushing or trannie input bearing but for this. Water pump was changed and there's no change in the sound; no impeller marks in the block or on the old impeller. It is not coming from an alternator bearing. The nature of the sound and the location makes me thing timing chain has a lot of slack and it is slinging out and rubbing on something, but I can't say I ever heard this before with several /6's in the past. The only other thing that pops into my mind is the front cam bearing but how that would do this is not making sense. Anyone have any similar experience to share on this? Thanks! |
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| Author: | emsvitil [ Thu Jul 24, 2014 1:05 pm ] |
| Post subject: | |
Alternator or water pump Take off fan belt and see what happens. |
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| Author: | nm9stheham [ Fri Jul 25, 2014 7:27 am ] |
| Post subject: | |
Thanks emsvitil. The water pump was changed for other reasons and there was no change in this noise. And the alternator bearing whirr is higher pitched and steady. I am now thinking this is a timing chain loose; the crank has 5-6 of free movemnt back and forth before the distributor gear moves. Does anyone have a /6 cam timing gear lying about form which they can give me the outside diameter? I have a service limit of 11/64" of movement at the cam gear edge with the crank gear stationary, and want to back-calculate that to crank degrees. My scaling off of drawings shows the limit to be 5.8 crank degrees but that scaling is only so accurate. Regardless, 5 degress of crank movement due to chain stretch sure feels LOOSE! |
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| Author: | oldskoolracer [ Sat Jul 26, 2014 9:47 am ] |
| Post subject: | |
That 5-6* movement isnt that much, from my understading its pretty common... What you should check is the timing with the engine running and see if its bouncing around. If the chain is stretched that bad, you will see it and more than likely feel it in the way the engine runs... However, I do suppose that if enough slack is present, and depending on the oil you run you could be hearing the chain mesh around the gears (not too common with factory chains)... I would consider looking into the belts and the grooves they ride in, and bouncing or forward/backward motion of the crank pulley, and p/s and a/c pumps if equipped... Like emsvitil said, take the belt(s) off and see if the noise stops or not... |
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| Author: | Aggressive Ted [ Sat Jul 26, 2014 2:39 pm ] |
| Post subject: | |
My power steering pump is the original and makes a slight whirr when running. |
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| Author: | nm9stheham [ Sun Jul 27, 2014 1:00 pm ] |
| Post subject: | |
I took another fellow's suggestion and took off the fan belt and ths whirr seemed to be gone. Put the belt back on and made it tight; the whirr was low but steady. Loosened the belt and it became louder and erratic. With the belt really loose and the engine off, I examined the old stock 4 blade steel fan and water pump pulley; all tight. I tapped the fan blades so see if I could find any loose blade rivets (none) but noticed that the whole fan/pulley/water pump shaft had the same dull ringing quality when tapped as this whirr. So, my conclusion is that the teenine, tiny looseness in the new water pump bearing is allowing the shaft to rapidly wobble just a tiny bit, and when that wobbles, it is exciting the dull ringing tone in the whole fan and pulley assembly. The wobble is variable with the fan belt doing its usual small amount of movement, and thus the 'whirring' comes and goes, and varies with belt tightness too. I'll visit NAPA someday when I am ready to chage the coolant again, and see if this very tiny looseness falls under the water pump warranty. I just might have to go through a couple to see if there is one with no bearing looseness. Like many things like this, it led me to know that my timing chain is getting pretty slack, so all this rigamarole will have the benefit of me deciding to put in a new chain set; that ought to make things run just a bit better by eliminating most all of what appears to be up to 5 degrees of cam retard. Attributing all of the crank-to-rotor-button slack to the timing chain assumes that the distributor gear is pretty tight on the cam, but in my case, I could easily move the crank pulley back and forth at least 5 degrees. 5 degrees seems like a LOT of timing slack and my calcs show that 5-6 degrees chain slack at the crank corresponds pretty close to the '62 FSM service limit in chain slop. (That seems like a pretty sloppy service limit.....) BTW, that actual FSM check is to block the crank for no movement with the timing cover off, and rotate the cam gear back and forth to see how much a chain link on the cam gear on the side of the gear opposite to the crank gear will move. That movement should be under 11/64". Thanks to all for your input! |
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