Readers’ Tech Q&A
Q:I have a 1989 Mustang that I have owned since it was two years old. I have used it for everything from transportation to Solo II racing to bracket racing. A few years ago, the engine blew up at a drifting event. The car sat for a while, then I rebuilt the engine from leftover parts and parts I found by keeping a close eye on eBay and at swap meets. I then drove it regularly back and forth to work. My daughters that have been driving for a few years have shown interest in the car (they can drive a stick, unlike other teenagers). We started to take the car to autocross and cruises. We had plans this summer to set it up for the 130- and 150-mph club at the salt flats. Abby was going to try the 130 and I was going for the 150. Last winter, one day driving home, the car developed a big noise in the engine. It sounded like the flywheel was rubbing. Crankshaft endplay was OK. I think what happened is the machinist added weight to the flywheel to make up for the lightweight pistons. It may have came out, is my guess. What do you think?
A:Even on externally balanced engines like production Ford V8s, weight is generally added or subtracted from the crank, rods, and/or pistons as needed to bring the engine into balance. That allows easily replacing a damaged flywheel or harmonic balancer with an equivalent standard unbalanced part for the application without any need to send the replacement unit out for additional balancing. Just remember, 1982-andlater Ford 302s use a 50-oz/in unbalance factor; earlier were 28 oz/in. Weights are welded on to a stock flywheel; some aftermarket performance flywheels have bolt-on weights. Assuming your engine is not internally balanced for a high-end aftermarket stroker crank designed to be internally balanced, if there’s no visible add-on weight, you’ve found the problem. If not…
Engine “noise” is a somewhat generic description. Technicians usually describe engine noise more specifically, such as a hiss, a knock, a rattle, clunking, popping, chuggling, pinging, vibration, and so on. In any event, your problem calls for careful diagnosis and a step-by-step “logic tree.” For example, does the noise occur all the time, or only under certain circumstances? If not all the time, does it happen when the car is stationary or moving, when it’s turning hard left or right, when it’s cold or warmed up, at a particular rpm, in a certain gear, or some combination of these? Does it vary in severity?
If, as you say, “it sounds like something’s rubbing,” have you checked whether the exhaust pipes are hitting the chassis, and/or the motor mounts are worn or broken? If you push the clutch pedal in, does it go away? In other words, are you sure the problem is in the engine, or could it be somewhere else in the drivetrain or suspension?
If the engine had a balance problem, the noise would be more like a vibration, and it generally varies in intensity at different engine rpm ranges. Has the base timing been jumping around? Erratic base-timing fluctuations may be caused by a delaminating harmonic balancer, which could also tie in to a vibration or noise because the production Ford harmonic balancer is also externally balanced. A worn timing chain can also cause erratic timing. Missing sprocket teeth on a slipping chain may produce a slight rubbing, whirring, or whining sound.
If the sound is more akin to knocking and the knocking gets louder as the engine warms up, this could be a sign of a bad rod bearing—oil thins out as it warms up, so it’s less able to dampen-out the knock. Obviously, if you have fluctuating/low oil pressure or blue smoke coming out of the tailpipes, it’s an internal engine issue.
If you suspect internal engine wear or damage,
Marlan Davis [ Externally balanced small-block Fords require unbalanced flywheels. This performance McLeod ’wheel has bolt-on weights, permitting it to fit early engines that need a 28-ounce unbalance ( shown), late engines like Simmons’ requiring a 50-ounce unbalance (the add-on weight would be much longer), or custom-built, internally balanced motors (no added weight).
[ Doctor of Ford Engines, Mark Sanchez, AEW, examines an ailing 5.0L Ford. If you don’t have a stethoscope, try a long screwdriver. Sounds will travel through the screwdriver just like they do with a stethoscope. A noisy valvetrain indicates a bad lifter, flat cam lobe, or other valvetrain issue.