Guessing RPM of Ticking Noise

[Digger1]

I've been chasing an engine noise in my car (see my signature) for quite some time:

http://www.toyotanation.com/forum/t114374.html

I'm interested in discerning whether the noise is originating in the valve train or the piston/rod/crank area. To do this, I need to be able to estimate the rpm of the knock.

My ears are bad (something about having over 4500 hours in fighter-type jets) and I have a hard time gauging the rpm of the knock. I have an osciloscope lying around and I've been toying with the idea of hooking a microphone up to it to determine the frequency of the knock when the engine is idling at 750 rpm. If the frequency is about 325 rpm, then I'll know that the noise is from the valve train. If the frequency is about 750 rpm, them I'll suspect a source from further down.

Any ideas?

TIA.

[toyomoho]

Use a length of hose as a stethoscope and attempt to narrow down the location of the noise. A piezoelectric pickup device may work better then a microphone. Something to pickup the major vibration and not all the background noise.

[Digger1]

Toyo,

Thnx for the reply. Actually, I have no problems hearing the tick, I just need to determine the RPM of the tick. At idle, I want to know is if it is ticking at 375 or 750 rpm when the engine itself is idling at 750 rpm. (I'm probably confusing you.)

Any ideas on how to do that?

[toyomoho]

If you had a timing light this could provide a timed source to compare the sound with. First check to see if the ignition is the type that fires each plug once per two crank revolutions or once per rev (one spark is wasted). 375 RPM is not that fast, about 6 taps per second you can almost mimic that by tapping you hand.

If the noise is an engine knock noise like a bearing, this are usually limited to one cylinder. This would make the tap at around 187 RPM.

The piezoelectric pickup would filter out all the noise a microphone would other wise pick up.

[tamago]

i have a squeaking type tic and believe it to be my throwout bearing..

just as a thought.. not sure if you have a manual or not, but i'd say listen to the tick and touch the clutch to see if it goes away. damn throwout bearings suck in some toyotas.

[Digger1]

Originally Posted by toyomoho

If you had a timing light this could provide a timed source to compare the sound with. First check to see if the ignition is the type that fires each plug once per two crank revolutions or once per rev (one spark is wasted). 375 RPM is not that fast, about 6 taps per second you can almost mimic that by tapping you hand.

If the noise is an engine knock noise like a bearing, this are usually limited to one cylinder. This would make the tap at around 187 RPM.

The piezoelectric pickup would filter out all the noise a microphone would other wise pick up.

Toyo,

Thanks for the reply.

Well, now I'm gettin' confused as to what rpm various engine noises will occur at.

Let's say my engine is idling at 750 rpm.

What will be the frequency of the noise caused by:

1. Piston slap?

2. Loose camshaft journal?

3. Wrist pin bearing?

4. Big end rod bearing?

5. Crank bearing?

6. One valve with excessive clearance?

TIA!

[Digger1]

Originally Posted by tamago

i have a squeaking type tic and believe it to be my throwout bearing..

just as a thought.. not sure if you have a manual or not, but i'd say listen to the tick and touch the clutch to see if it goes away. damn throwout bearings suck in some toyotas.

Tamago,

Thanks for the input. However, I have an automatic (see my signature).

[timebuilder]

4500 in fighters? You must an old F4 guy! When I left the auto shop environment, I went off and flew the Lear 35 and 55. One our 35's was an old C21 type used to fly air force staff officers around. I'm still kicking myself for turning down an appointment to one of the academies, where my "uncle" would have covered the cost of my flight training.

If I were trying to determine the source of a noise, I might mull over the frequency of the sound, as you are, but my first instinct would be to first try and decide which cylinder bank (on a V-type motor) or which area (generally) of a inline motor is making the noise, and see if the noise responds to whether or not the cylinder is firing.

Bottom end noises are affected by whether or not the components are being loaded by combustion pressures. One way to make this test is to short out the cylinders one at a time, as explained on the page linked to below.

Noises I have characterized as "taps" are almost always upper end problems. Bottom end noises are more of a "knock" type sound.

See if this page helps:

http://remanufactured-engines.com/page4.htm

I'm not as cynical about repairing engines with rod or crank knocks as this one author is. Then again, you have to remember that the company in question would like to sell you a remanufactured engine!

Let us know what you find.

[Digger1]

Originally Posted by timebuilder

4500 in fighters? You must an old F4 guy! When I left the auto shop environment, I went off and flew the Lear 35 and 55. One our 35's was an old C21 type used to fly air force staff officers around. I'm still kicking myself for turning down an appointment to one of the academies, where my "uncle" would have covered the cost of my flight training.

If I were trying to determine the source of a noise, I might mull over the frequency of the sound, as you are, but my first instinct would be to first try and decide which cylinder bank (on a V-type motor) or which area (generally) of a inline motor is making the noise, and see if the noise responds to whether or not the cylinder is firing.

Bottom end noises are affected by whether or not the components are being loaded by combustion pressures. One way to make this test is to short out the cylinders one at a time, as explained on the page linked to below.

Noises I have characterized as "taps" are almost always upper end problems. Bottom end noises are more of a "knock" type sound.

See if this page helps:

http://remanufactured-engines.com/page4.htm

I'm not as cynical about repairing engines with rod or crank knocks as this one author is. Then again, you have to remember that the company in question would like to sell you a remanufactured engine!

Let us know what you find.

Time,

I've stethed this engine everywhere and I can't seem to narrow the location of the noise down.

Thanks for the link. It looks like good stuff.

BTW, most of my time is in A-10s, F-16s and T-38, with some Shuttle time thrown in there (you talk about your noisy environments!). Yeah, my ears pretty much suck these days and I'm not even 50 yet!

[timebuilder]

Ah, I see. When you said 4500 I figured you were older than I was. In 1970, places at the academies were going wanting, and our class at VFMA looked pretty attractive to them. Wish I'd been smart enough to take the hint.

Seems like a lot of guys in the space program have recent T-38 time. A-10 and F-16 is some pretty diverse experience, too, so you must have done this for a long time. Did you make 0-6?

Your hearing loss must be significant. Has the FAA issued you a SODA, or are you not flying these days? If you have friends who want to keep flying, here is a link:

http://flightphysical.com/part67/67sube.htm

As for the car, maybe it's time to ask someone to take a listen for you. And look on the bright side. At least we don't have to feed a toyota jet A at these prices!

[Digger1]

Time,

Yep, Pilot Astronauts fly T-38s to maintain their flight proficiency. It is an extremely honest little jet, very enjoyable. I spent over 22 years in the USAF and never had a "desk job." I tell kids that if they have to work for a living, being a pilot is not a bad way to go. I've had a good time over the years.

I got out before making O-6. SWIMBO and I promised ourselves years ago that we would try something different after the kids were grown up and gone. So, I quit NASA and the Air Force a few years ago and we are in the process of prepping for a motorcycle trip around the world.

Thanks for the link, but no more flying for me. My motorcycles feed my Jones, no regrets!

As for the car.....I'll get 'er figured out one of these days! I'll let everyone know what the problem was, too.

[timebuilder]

I figured it had to be a proficiency issue. Never had a chance to fly one, myself.

The motorcycle trip seems like a wild ride. Let me know if you make it to Penna.

Write back about the car, and keep the dirty side down.

[Digger1]

Due to a great post in the Gen 3/4 forum, I've determined that my noise seems to occur at about 1/2 engine rpm. The obvious suspect would be something in the valve train, perhaps a sloppy camshaft journal or something. However, does piston slap make a noise at 1/2 engine rpm? I'm thinkin' that the piston would only make noise during a cylinder combustion event, which happens in any given cylinder at 1/2 engine rpm.

Thoughts?

[timebuilder]

Here is what piston slap sounds like on many GM motors.

http://www.pistonslap.com/photos.htm

I would agree that slap occurs under the pressure of combustion, and the piston moves from one side of the cylinder to the other because it is being forced down the cylinder. Of course, a very worn piston can rattle in the cylinder like a castenette.

If you suspect the valve train, it might be a good idea to check the clearance between the cam lobes and the follower shims.

[timebuilder]

Oh, and here is the second page of the site I posted before. He has a piston slap test.

http://remanufactured-engines.com/page5.htm