Read­ers’ Tech Q&A

Hot Rod - - Front Page - Mar­lan Davis

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.

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