Engine Issues

Superman · 04-10-2002, 01:27 PM

I may have an e-mail at home from Warren, but I'll describe my concerns here for everyone's consideration and benefit. There is a rhythmic noise in my engine that was present before the rebuild and is still there. It's a thunk or knock noise, or exhaust noise or something. At 85+ mph it's kind of nice because it sounds like an engine working hard. But at low RPMs it seems like roughness I don't like and perhaps a little vibration.

It is a very subtle noise and is harder to hear when the engine is not warmed up. Ignition wires check out okay, and I've been meaning to check injector spray pattern and volume. In the right conditions, it sounds a bit like a gentle rod knock (scary), but usually just sounds like exhaust pulse or something.

At any rate, it bugs me because I expect this engine to be pretty darned smooth. Then again, it's so subtle I think many folks would not even be able to hear it if I tried to point it out.

Porcupine · 04-10-2002, 11:18 PM

Get a set of mechanics ears.
Sears snapon pepboys etc
Who what where and when?
Or crank/flywheel out of balance variances in rod/piston weight
chain slap, to tight valve adjust transaxle issues axles etc.
Martin

Superman · 04-11-2002, 12:03 AM

Good idea. I have a mechanics' stethoscope. I mean a real one, besides my long screwdriver, which probably works just as well. but here is out second clue: The noise happens only under load. And as near as I can tell, the noise is loudest under load, loudest between 2000 and 3000 rpm and loudest when the engine is fully warmed up.

Tim L · 04-11-2002, 06:21 AM

Superman,

When you rebuilt you motor did you change the rod bearings?
I tried to track down a sound like that and only found it when one rod Bering was completely gone.

Tim

Jandrews · 04-11-2002, 06:50 AM

Supe,

My motor makes a very similar noise... I call it a "buffeting" noise that I believe is coming through the exhaust. It is similar, yet more subtle than driving around in a sedan with only one rear window down.

In my case, I have low compression in cylinder number two due to a poorly repaired bent valve. On my car, I am certain that this noise is the result of a valve not seating properly during combustion and the resulting hammering is exhaust being forced past a partially seated valve. I plan to address this shortly.

I know you have a fresh motor, so I am pretty sure our problems are different. However, I felt compelled to post because of the similar description of such an elusive "noise".

JA

makaio · 04-11-2002, 06:57 AM

Super,

I had a very similar sound that was coming from a cracked weld on my muffler. Only happened around 3000-3700 rpms. When the power started coming on, it just made this sound that didn't sound right.

Just a thought.

HawgRyder · HawgRyder's Garage

I have had the same type of noise from a racing engine years ago....turned out to be too much end play on the crankshaft.
Very difficult to find....but in my case..I used the old pry it back and push it forward method.
Bob

Superman · 04-11-2002, 09:26 AM

Thanks for the ideas. The noise sounds like an ordinary exhaust/engine noise except at 2000- 3300 rpm when it has a sharper knocking tone, sounding like a quiet rod knock. Again, mostly when it is all warmed up. It is certainly not deep enough for a main bearig noise, but is deeper than a valve lash "tick." The main bearings and rod bearings were replaced. I did not put a micrometer on the crankshaft or rod big-ends, and probably should have. The rod bearing journals all looked EXACTLY the same. Beautiful, high'lustre finish with no lines going around any journals. Inspection with a magifying glass revealed a polish that is not quite mirror-fine, but almost. Again, all rod bearings appeared identical. I'd like someone to tell me that there is no possible way I could have a loose rod. That's what I think.

Again, the noise is a non-scary exhaust -type noise below 2000 rpm and seems to be an exhaust growl above 3300. The noise is basically always there, but the scary noise happens mostly after complete warmup, only between 2000 and 3300 rpm and only under load (3/4 throttle or better). It is not intermittent, but is in rhythm with the engine and there is an associated vibration. Both the vibration and the noise are not fast enough (in my opinion) to be an out-of-balance problem, but rather it is a noise and vibration synchronized with every OTHER revolution of the engine. In other words, it only happens on the power stroke of one of the cylinders. Valves, rings and ignition are okay. Unless I'm hearing a loose rod bearing, my first vote is exhaust leak and my second vote is a poor injector.

Leland Pate · 04-11-2002, 10:11 AM

Jim,
I can't help diagnos the problem, but I may be able to offer a tool that may be able to help you find out what's wrong.
I bought one of those Fiber optic scopes that you see for sale....

If you think it'd help, I could send it to you... you can inspect the combustion chamber through the spark plug holes, and the interior of the case through the sump plate or oil return lines...

If you think it would help, let me know and I'll send it to you.

I was able to look at my piston crowns though the spark plug holes.... my #4 piston top looks darker and wetter than the others, and I can see a small puddle of fuel or oil (or a mix) at the bottom.
The other cylinders are a lighter brown color than #4.

I would never have known that without the borescope.

Just email me.

Superman · 04-11-2002, 10:20 AM

I'd be a danger to society with a tool like that. Just kidding. I'll keep that in mind, Leland, and let you know if I want to use it. To save mailing costs, perhaps I would just come and get it.

Superman · 04-11-2002, 10:22 AM

Actually, the tool I'd like to play with is one of those infrared temperature sensor gun things. Point it at stuff and see the surface temperature. I wonder what the temperatures of my six heads, and their exhaust manifolds are.

Early_S_Man · 04-11-2002, 11:04 AM

Jim ... you mean like this one:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1719754747

Superman · 04-11-2002, 11:14 AM

Yes, thanks, Warren. These devices are generally available for around $100 new, though the Fluke would likely be a bit more. I am also intrigued by your earlier report that good analog VOMs can be had for a song. I think I'll look for that. I'm about to post a Voltage Regulator question.

Porcupine · 04-11-2002, 11:23 AM

Raytech is the brand.
Tool trucks have them, sears maybe napa carquest etc.
Or online tool dealers
Or plumb your exhaust for pyrometers 2 will be needed
Plumb 1" from port on cylinders 2 and 5 and should read no higher than 1340* under load.
Did you measure the big end on the rod that had the crank damage to make sure it was still round and able to provide the correct bearing crush?
What kind of clearances did you get for the rods and did they fall with in spec.
Also do you get this noise when you slowly accelerate through the rpm band?
You could be running into advance curve/cam spec spark knock issues.
Lots of things.
Martin

Superman · 04-11-2002, 11:45 AM

The noise was present with SC cams, and is still present with the new 20/21 cams. It sounds like you may be recalling my concern about one of the rod bearing journals. My concern was about a blemish or stain. It was quite small and polished out nicely. The rest of the journal looked EXACTLY like all the others. I thought, and still think, that if there were any wear on rod journals, then the micropolish finish would have been changed. That polished finish (a couple of microns thick) was present, and exactly the same on all rod and main bearing journals. So I made a decision (mistake perhaps but I still don't think so) to not worry about measuring them or the rod big-ends.

Hey, if I get the feeling that a rod may be loose, and they should be measured/looked-at, then I'll be happy to remove and disassemble this engine again. Well, "happy" is probably not the right word here, but it would not be that difficult now that I've done it once. But I really still think I was justified in having this degree of confidence in those parts. I think this noise is something else, and it sounds like something else, except for a subtle rod noise-like noise under certain narrow conditions.

Jim T · 04-11-2002, 11:51 AM

How many miles in the I-shaft bearings?

Bill Douglas · 04-11-2002, 12:46 PM

Super, I get a noise like what you describe from my gearbox. I'm sure it's my gearbox and it is always when the revs are a bit low (under 2,500) and I'm giving it a bit of gas. Maybe have someone else drive the car, and get the noise to re-occur while you crawl around in the back. Although gearboxes are a pain in the ass, it would be a blessing if it's not the engine.

Superman · 04-11-2002, 01:12 PM

Bill, this seems to be an engine noise, but of course with noises anything is possible. Also, the tranny input shaft is just an extension of the crank, so it may be a tranny noise.

Jim the intermediate shaft bearings are about 1000 miles old! Same with the main and rod bearings.

I think some of you know what this noise sounds like, based on the posts above. Hard to describe. I will admit I have head other healthy P-cars make this noise, like on the tarmac at Bremerton autocrosses. Superman often worries WAY too much about stuff like this. I'll show it to some friends and they'll roll theri eyes and tell me to turn the radio up if it bothers me. At 4500 rpm, it's a pretty cool noise.

Again, my vote is either exhaust leak, or colliding exhaust pulses in the crazy stock exhaust system.

Early_S_Man · 04-11-2002, 02:37 PM

Here's a nice one ...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1718814511

Superman · 04-11-2002, 02:58 PM

Thanks again, Warren. That looks like a nice one, nicer than any I have ever used, and at a price I can barely believe, knowing what they used to go for. I guess the digital revolution has made them seem obsolete to some folks. Until now, they seemed obsolete to me. If you see another one of these excellent deals in the future, send me an e-mail. At these prices I think I'd like to have one.