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View Full Version : Sugestions on crankshaft harmonics (over machined)



A.K. Boomer
05-27-2008, 12:16 PM
When I bought my car it had a spun rod bearing, I rebuilt the engine --- the crank did clean up but at its smallest OD sizing, Small journals are efficient and I dont mind that but here's the thing --- I cant set the cars idle to normal or it will eventually self destruct -- the crank sings like a tuning fork and bad -- really bad, I have the stock harmonic dampener/front pulley, it looks fine, never owned the car before so dont know what it was like but im guessing it was OK and its the small diameter mains and really small rods that are setting it off, Any gains I make in efficiencies from the small journals are being gobbled up at stop lights by having to set the idle so high, I can help it out a little by running tighter serpentine belts but I wont do that either as Iv always ran my belts (except timing) as loose as I can get bye without them squealing - for both efficiency and component bearing life,
My Questions to you Catz is where else can I turn? what can I do to bring the Idle back down to normal without the crank Ringing its guts out (and eventually snapping in half), Its that loud, every time you shut the engine off it will ring as it coasts down, If I use high beams with brake lights and the rear window defrost all at the same time it drags it into this living hell...
Im not pulling the trans to do anything with the flywheel, should I experiment will a little harmonic adapter that I can put as an extra add on onto the main crank bolt or what?

Mark Hockett
05-27-2008, 12:34 PM
A.K.
What are the specifics on the vehicle like make, model, year & engine? When you say clean up the crank did you have the crank reground or just polish the journal?

A.K. Boomer
05-27-2008, 12:42 PM
Mark, its a 92 toyota tercel 1.5 liter, I had the crank ground by one of the best crank grinders in the area, I cant remember if the rods are .030" or .040" under, anyways they are at the smallest diameter you can go with this crank as they dont sell bearings any smaller...

jimmstruk
05-27-2008, 12:43 PM
A K , Does the original damper have a rubber insert? If so possibly the rubber has deteriorated over the years and the damper should be replaced. Also most machine shops will not guarantee their work unless the crank damper is replaced anyway. JIM

A.K. Boomer
05-27-2008, 12:48 PM
First thing I checked Jim, the rubber "looks" perfect, who knows whats underneath though, have you seen them look great and still give Probs?
Maybe the rubbers getting hard? Could be worth a shot.

Rich Carlstedt
05-27-2008, 01:10 PM
I would suspect, that the "vibration" caused the turned insert !
My thoughts are that the mains are not alligned , or one is loose.
Any bolts bottoming out BEFORE tightening the parts ?
Rich

jimmstruk
05-27-2008, 01:50 PM
A K, Looks dont count for too much in these instances, as the good looking rubber may no longer be "live". My recent experience has been with larger diesel engines, but for example the cummins shop manual states that the damper MUST be replaced at time of engine overhaul. Just my thoughts and experience. JIM

torker
05-27-2008, 02:47 PM
This whole thing sounds weird to me.
I have had a couple of outer rings on balancers "slip" due to old rubber. First thing I check if I'm having oddball timing issues. Pull the balancer and put it overtop of a known good one to see if the timing marks and the keyway line up.
Don't forget... proper oil pressure should cushion the crank bearings somewhat.
Also a serpintine belt should soak up some harmonics as well.
The big blown alky motors I've run don't even use a balancer... we rely on the blower belt to soak up the vibrations.
The problem you are having reeks of timing problems to me. I'd be checking cam sprocket/chain position, timing etc.
Russ

aboard_epsilon
05-27-2008, 03:31 PM
never heard a crankshaft ring before ...and would not know one if i heard one ...

but if that noise was on mine ...first thing i would check is the starter pinion is retracting

all the best...markj

DICKEYBIRD
05-29-2008, 04:06 PM
I've diagnosed and repaired a lot of engine noises in my career but have never heard a crankshaft ring unless it was out of the engine, standing on end and whacked with a hammer.

I suspect what you're hearing is an alternator resonance. I think the engineers call it "heterodyne." Do you hear it with the belt removed? Some alternators will really sing at a certain rpm & load.

rantbot
05-29-2008, 04:21 PM
This is weird. I doubt it's a crankshaft resonance.

Crankshaft resonance problems are just about always at much higher frequencies. Auto engines notorious for resonances have trouble in the 5000 RPM range and up. That implies a resonance frequency around 80-100 Hz, which you're probably not going to hear as a ring. It wouldn't be excited at idling speeds (down around 15 Hz) in any case.

Removing 40 mils from a journal won't have much effect on the stiffness. Torsional stiffness varies with the fourth power of the diameter, but even so .040 under will only decrease stiffness at each journal by something on the order of 10%, and will have an even smaller effect on the crank's resonant frequencies.

The only time I ever ran into something similar was a funny tinkling ring I'd get at idle on a BMC B-series engine. That turned out to be the crankshaft pulley sheave, which was working loose from the rivets holding it to its hub. The pulley on that engine was just a pulley, not a damper. I replaced it with another one, and goddamn if it didn't do the same thing after a couple of months. These were both old pulleys which hadn't played any such tricks when new in the 1950s. Weird. The permanent fix was to weld the sheave to the hub, but I still don't know what caused the failure.

The whole engine can go through a large-amplitude resonance near idle speed if one or more of the rubber engine mounts has failed.

Mark Hockett
05-29-2008, 05:14 PM
A.K.,
I have never been a big fan of reground cranks in Toyota's. The factory crank uses selective rod and main bearings so the end result is a blueprinted engine with clearance specs within a .0003" tolerance. With a regrind you get one size bearing choice and what you get is what you get. With that said I doubt your problem is related to the bearing clearance.
You said that you like to run your accessory belt loose and your timing belt tight. This is the opposite of what you really want to do. It is very easy to over tighten the timing belt and that can cause all kinds of strange noises. The proper procedure for adjusting the timing belt tension is to loosen the tensioner bolt and rotate the crank pulley clockwise to take up the slack in the timing belt. The spring in the tensioner will set the proper tension, then tighten the bolt to 13 ft-lb. Never pry on the tensioner to set the tension.
I would start by removing the accessory belts to eliminate the alternator or other components and then try adjusting the T-belt.

I also forgot to mention that we have had a lot of problems with aftermarket timing belts making strange noises.

Not being able to hear it, a noise can be very hard to diagnose over a computer.

A.K. Boomer
05-29-2008, 10:27 PM
A.K.,

You said that you like to run your accessory belt loose and your timing belt tight. This is the opposite of what you really want to do. .


Mark, for the record i said nothing of the sort -- what I stated was; "I can help it out a little by running tighter serpentine belts but I wont do that either as Iv always ran my belts (except timing) as loose as I can get bye without them squealing - for both efficiency and component bearing life,"

This is a big diff, I run the timing belt at the recommended factory tension from the tensioner OR the recommended factory tension from the automatic tensioner spring. As far as the ancillary components I have found over the last 35 years that I can extend both the component and the belts life by using just enough tension to get by, i have also found that belt overtightening is one of the most common mistakes in the repair industry --- So no, its not exactly the opposite of what you want to do, its right on the money esp. for a personal vehicle, if its a mountain customer that I know I wont be seeing for awhile I may snug a componentry belt a little extra.

I also never stated that I thought my problem was from any kind of bearing clearance, I rebuilt this engine myself --- every thing has been gone through and spec'd out, what I believe happened was that the crank is "thinned out" --- its extra skinny journals are allowing it to chime like a church bell.

Also for the record --- I appreciate all the reply's but let me spare you guys all the firing in the dark, This is a crank harmonic problem, believe me -- in know way is it an alternator or anything else, Its been checked out and verified, Now --- how do I fix it? I believe im going with Jimsstruks suggestion, but first im going to play with jamming some rubber into the crank pulley just for ****ts and giggles. Thanks.

TRX
05-29-2008, 10:51 PM
A.K.,
I have never been a big fan of reground cranks in Toyota's. The factory crank uses selective rod and main bearings

So does Chevrolet in all their V8s. I have a 454 on the stand at the moment; a handful of .0006 and .0003 undersize bearings went into the trash can.

Turning the crank undersize isn't going to affect its resonant frequency enough to notice without specialized instruments. Back before cheap Chinese import cranks flooded the market, I used to start a 5.0 Ford stroker by putting a 351 Cleveland crank in the grinder and taking half and inch off the mains and three eights off the rod throws...

A.K. Boomer
05-30-2008, 12:19 AM
This is a crank harmonic problem, believe me -- in know way is it an alternator or anything else, Its been checked out and verified,



All my years of wrenching and I never would have guessed because I never ever heard anything like this, I brought my old post up to eat some crow, at the very least you catz will know I dont do the "cover up" thing, But believe me -- if you could have heard this thing when I put the idle down youd swear it was a big heavy item going through a frequency/harmonic phase, i thought I verified things when I tightened the belts and it made it better, I then deduced that I put more pressure on the crank pulley and it dampened the noise,
Wrong answer as it also dampens whatever component your working against,
The grand prize, the "my hat is off to you sir" and please except my sincere apology -------- there is someone on the board who did indeed get it right,
Dickybird and his heterodyne theory, I still cant believe it, perfect throughout all other RPM ranges -- get it into idle and you could hear this loud loud sound -- like when you super scrub a finger and get it wet with distilled water and then circle a wine glass with it until you get it to whir like crazy and are worried about breaking the glass --- like that except you could hear it 5 blocks away... Congrats Dickybird and thank you ----------- Now -- how do I fix this?:p

I might also add that I had my stethoscope on every component many times(but the free floating spinning crank) Not a wimper out of the alternator case when whirring was extreme, must not convert the frequency very good.

quadrod
05-30-2008, 12:50 AM
i would still remove the accessory belts and even remove the timing covers to try and isolate the noise. also have seen distributors make horrendous noises at low rpm's. just my 2 cents worth.

DICKEYBIRD
05-30-2008, 07:59 AM
Cool A.K.! Like my Pappy used to say..."A blind hog gets an acorn once in a while."

I've heard that a loose alt. stator can cause the noise but I've never seen it personally.

A.K. Boomer
05-30-2008, 08:46 AM
DB My dad said the same thing in situations like this, "even a blind pig finds an acorn once in awhile fella's" he'd mutter, "better than a hit in the head with a dull Axe" was another one of his favorites --------
I hate to burst the heterodyne theory but I think it has to be pitched, Im not excluding the alternator and am glad you mentioned loose stator as you could still be on track with it, BUT, I always sleep on something and then awake with idea's ---- it cannot be the heterodyne resonance because as I previously mentioned in this thread It happens every single time I shut the car off and the engine has to coast through this low RPM mode, so with no power to the fields of the alt. their cannot be this anomaly --- I should clarify It happens every time the car is shut off after the engine is warm, it wont do it when cold --- this was just another factor that was steering me towards crank res. --- thinner oil = less cushioning = more resonance --------
Im kinda back to square one but with armed info, by removing the belts and having it completely stop its going to really help me pin-point it today, The crankshaft is not "off the hook" yet, Maybe the rubber dampening material is too soft, perhaps at a higher RPM it does not have time to conform (from belts side loading it) and keeps the pulley's metal to metal contact away then at low idle it rears its head -------- this also could go hand and hand with the relationship to heat, cold rubber is harder --- warm rubber gooshi and more compliant.

Edit; The more I think about it the more and more its tougher for me to accept the alternator even if it was a loose stator, as we know stators get loaded when charging, even if its a mechanical resonance there should be either be a difference in RPM's or a different sound from when the alt is being excited to just free running (power cut), there's not. Hmmm

wierdscience
05-30-2008, 09:17 AM
Could it be coming from the tranny or flexplate?

A.K. Boomer
05-30-2008, 10:06 AM
When You say "flex plate" im assuming your talking automatic, this is a 5 speed manual, Pretty much ruled out anything to do with trans as it will do it with the clutch in, also resonance does seem to be coming from pulley side of engine, Little extra tidbit of info I always took note of --- resonance does not change when clutch pedal is depressed, this is one area that if it was the crank humming you would think it would have an effect as the pressure plate is forcing the crank into the main thrust, BUT --- this only eliminates half of the crank as thrusts are located between #2 and #3 and could leave the nose to still go through its changes, something else to consider is that the alternator fan would be unaffected by electrical loads if it indeed was a mechanical resonance, I will find out today.

bighammer
05-30-2008, 10:22 AM
Just a thought i had a similar sound in a Ford 300 six,turned out to be the idealer pully bearing. Happened only when at idle, could hear it a block away. You have probably have checked this, i have also had alternator bearings do same at idle speed only. Cookie

A.K. Boomer
05-30-2008, 01:24 PM
I still cant believe it, perfect throughout all other RPM ranges -- get it into idle and you could hear this loud loud sound -- like when you super scrub a finger and get it wet with distilled water and then circle a wine glass with it until you get it to whir like crazy and are worried about breaking the glass --- like that except you could hear it 5 blocks away... .



It was in my very description that I should have paid more attention too...
I found it --- but I got lucky finding it as it has to be pretty warm for it to happen --- I got it good and warm this morning, I quickly disassembled all drive belts and was rotating the alternator back and forth, I removed the crank pulley and was ohms testing between the two rubber isolated pulley and hub surfaces -- i put wood blocks in the vise and clamped 120 degree's around and squeazed the pulley to the hub and then again ohms tested --- nothing, totally isolated ----- I quickly went back under the hood and was checking out the other components (again) This time when I rotated the water pump I heard it ---- WHIRRRRR go back the other direction WHIRRRR --- UUHHHGGGG (that last noise was me), I checked this before but I guess it wasnt warm enough -- I also had the stethoscope on it when the noise was going off - many many times, nothing,,,

The water pump bearings are perfect. What i believe is going on is what I described earlier -------- the wet finger on the crystal wine glass,,,, except this is a loose ceramic seal thats being vibrated by its mating surface.