Hi Folks - Just curious to see if anyone could diagnose an unusual noise I hear from the engine. I hear what sounds like a rattle when I'm above 30 MPH but it only happens when the engine is neither accelerating or decelerating. If I am on a perfectly flat road, let off the accelerator to cruise, I hear it. If I press the accelerator it goes away. If I allow the transmission to slow the truck it goes away. It's that odd in-between spot.

Thoughts?

Just found this post on another forum that describes the same thing for others: http://www.hotrodders.com/forum/engi...tle-36272.html

One user says "i have a similar noise, it only happens to me when im the engine is settling down from a high rev.. for example if im on the highway, and then i let my foot off the gas to coast, i get a rattle, or for example, if im revving the engine and take my foot off the gas to let it settle down to an idle it rattles.."

Mine is identical to that description.

 

What engine are we asking about? Y block? Loose rods, perhaps. Valve train to include timing chain? How is the oil pressure when you hear the noise?
Edit: Different engines make different noises.

 

Duh. Sorry. 272. The main and rod bearings were replaced when I had the engine out along with timing chain and sprockets. Valves adjusted too.

EDIT: 40 PSI

 

Loose wrist pins will also cause that noise, and piston "slap". Did you have the engine rebuilt? A bad universal joint will make a similar noise.

 

With the wheels blocked, parking brake set, and the truck out of gear, bring rpm up to road speed equivalent. Do you hear the noise under these conditions?
And as Bob said, was the engine rebuilt or just have some new parts installed? Was the crank turned, bearings fit and to what clearance? New pins installed?
What is the oil pressure when you hear the noise? What weight oil are you running? We are assuming the engine is at normal operating temperatures, right?

 

"Rebuilt." No. More like repaired. The engine had a bad knock when I got the truck. I yanked the engine and found bad rod bearings on cylinders 1 and 2. So I replaced the crank (after the machine shop broke the original) and did the repairs you see above.

Piston slap...kind of has that sound to it. How is that repaired? Better yet for starters how do I identify that this is my issue?

 

1) I can do that when I get home later.
2) Parts replaced. I can't recall the clearance but it was tight and well within the tolerances spec'd in the manual.
3) Rotella 15-40
4) Up to temp yes. Engine seems to like the 170-190 mark with 190 being one really hot day and with a load.

 

Some times a noise can be located by removing a spark plug wire, one at a time and running the engine. Lots of unknowns on this one.

 

What trans ? If you have an automatic the first place to look is your torque converter bolts what you are describing is exactly the noise they will make when loose

 

So you did actually use plastigauge when checking the bearing clearances?
Were the wrist pins replaced?

 

Nope I have the T98 4 speed. No auto in this beast!

The new crank's main journals were machine .010" as were the rod journals. Bearings were ordered to match.

Wrist pins are original.

 

Pilot bearing or clutch related ? does the noise persist with the clutch depressed ?

 

Okay I just ran out and got the truck started and brought it up to temp. I cannot reproduce the sound sitting still. (Which makes me very happy!) U-joint seems to be a very distinct possibility.

Clutch related? That's possible too.

I'm going to check the u-joints first!

 

U-joints very typically make noise under acceleration. Begins with 'squeak, squeak, squeak' and after a long period of negligence is followed by high speed vibration (normally not evident until 45 m.p.h. or higher) until it snaps and all heck breaks loose (depending on speed when it breaks.) Very obvious when shifting between forward and reverse, sounds like a loud 'ting' as opposed to a loud ring and pinion 'clank'.

If I remember correctly Y-blocks have pressed wrist pins - it would be odd, but not impossible, for them to create a knock. Typically a wrist pin knock on an engine with pressed pins has extremely high miles or very poor past maintenance. The 215 (and possibly the 223) have full-floating wrist pins and the bushings in the con' rods can wear and create a 'double knock' as the piston/crank changes direction. (Mine does this, someday I'll get around to fixing it but they typically can go for what seems forever before creating any real problem. I don't like hearing it but I have way too much on my plate to worry about it at this point.) Wrist pin noise will be evident at idle speed and above.

Piston slap - again, can typically make noise forever before causing any real issues. Usually caused by barrel-shaped cylinders, sometimes a broken piston skirt. Repair requires boring and new pistons. Anyone that tells you the pistons can be knurled and refitted is either extremely old or has heard stories from extremely old people. Knurling pistons is a short-lived repair (in regard to reducing the knock they make) and you'd be hard-pressed to find a machine shop that could/would do the knurling, these days. Knurling is NOT cost-effective these days. Typically the noise is more prevalent when cold and reduces as the pistons warm and expand.

Rod knock begins as a noise that you can hear when lightly decelerating from 30-35 m.p.h. Not saying this is your issue but just because you had the bearings replaced doesn't preclude that one of the rods or crank journals may be egg shaped. Plastigage (I'm guessing that's how they were checked, in-situ) is kind of a Hail-Mary, last-ditch way to measure clearance. Better than not measuring at all but definitely not anything to hang your hat on. Sounds o.k. when first replaced but shortly after returns. One rod knocking won't normally have a huge affect on oil pressure, especially on a dash gauge. Pulling plug wires to identify doesn't usually result in much help - same with wrist pins.

Main bearing noises are normally a heavy, deep thunking (all these scientific descriptions - lol) especially loud during acceleration.

Differential noises (bearing or gear clearance) typically is a continuous sound when accelerating/decelerating, usually described as a 'howl'. However, a broken tooth can create a knocking sound. Axle or wheel bearings are a droning sound, center support bearings also.

With all of that out of the way... You originally noted "...if im revving the engine and take my foot off the gas to let it settle down to an idle it rattles.."

Mine is identical to that description."
That precludes u-joints, the differential and wheel/axle bearings as the truck isn't moving. From there I would suggest removing the belts to eliminate the possibility of ancillary noises (generator, fan, etc.) If the noise persists, check to see if it changes when holding the clutch pedal down (if equipped.) If it does then your search is reduced to the clutch or transmission - unless you have a really weird thrust bearing problem in the engine.

 

Whoops, just saw your last post. Oh well, maybe my post will help someone. LOL