Piston Slap: Bustin' a Nut in a Big Six

TTAC Commentator Modest Holdings writes:

Sajeev may have once read the primer on my truck but for everyone else, here’s the brief: short-box, regular cab 1994 Ford F-150, 300-six, Mazda hand-shaker. Four wheel drive, 133K, yadda yadda yadda.

Some time ago – it must have been before last winter, because my toes still haven’t recovered – the radiator fan clutch seized and the engine has consistently run cold. Fuel economy has sufered – three recent 1,600 mile interstate runs averaged 12.2, 11.5 and 11.9 mpg on a combination of hi-altitude 85 straight gas and what I suspect was E-10 87 octane through Nebraska and Iowa.

I was going to replace the damn thing back in…January?… but couldn’t get the nut busted free and gave up. It did nothing for my ambition when I changed a friend’s water pump for her on the 3.9l in her Dakota and needed both acetylene and eventually a plasma cutter to get the fan off her old pump. So, what suggest ye to bust nut free? I’ve tried the obvious things: heat, thrice-a-day WD-40 applications, cheater bars, swear words. Many bloody knuckles resulted. I briefly considered dynamite.

If necessary, I’ll drain the whole system and pull the water pump. And get the plasma fired up. I don’t intend to replace the fan: I’ve got an electric and I hear they’re good for a few horsepower. (The big six needs all the help it can get. Heading up some mountains here in Wyoming, I’m sure I’ll have to get out and push.) I’ve heard tell the water pump should be replaced whenever the fan is replaced or removed because it will change the load on the pump’s internal bearings, but that sounds iffy to me. Thoughts?

And finally: I love the truck and bought it for the stick. But that was before I learned of the Mazda’s sometime habit of nastiness. A friend had one that blew up and simultaneously locked up the drive wheels and the engine, at 60 mph. It’s a testament to the durability of the old sixes that the engine survived the encounter, it’s a testament to my buddy that he didn’t kill himself or someone else. Question: how much trouble is a swap to a more hearty tranny? I’ve posted and browsed the forums, but there isn’t agreement. Some say it’s an easy swap. Others warn that the 4×4 transfer case will need to be moved back and new driveshafts will need to be fabricated. If so, that’s too much work and I’ll find another truck. Or wait for catastrophe.

And one final hint, since some wrench will want to know: the computer isn’t throwing any codes.

Sajeev Answers:

I shouldn’t wax nostalgically over an I-6 powered, 1994 F-150 that I truly loved (and was tempted to buy) but I will. These are real trucks: an open cockpit with great visibility, reasonable ride height and an intelligently designed bed that doesn’t need “man steps” for access. And that six-cylinder with port EFI towed like a far bigger truck: pulling other trucks, 27-ft boats, tons of mulch, etc after a swap to quicker 3.55 gears. Ultimately it was all for naught, this lovely American workhorse ran 330,000 miles only to be killed by a Cash for Clunkers rebate on a Buick Enclave. Tragic.

So let’s set your F-150 straight. Give up on the wrench, you have an obligation to make it easy with said plasma cutter. Cut off the fan at the shaft, replace the water pump (past it’s prime anyway) and do the electric fan you mentioned. The Lincoln Mark VIII electric fan is a common, affordable and very effective upgrade on the hot rod scene, if you didn’t already know.

But your story and mine have a common point: switch the stock gear to something more aggressive. I’m gonna assume you have 3.08 or 3.27 rear gears, so do yourself a solid and get a complete junkyard axle assembly with a 3.55 or 3.73 gear, do the switcheroo and return your “slow” axle as a core. You will see increased performance and almost no change in fuel economy, especially when towing on the highways. I understand the Mazda transmission is junk, but worry about that later: these big sixes go from zero to hero with the right final drive. Trust me on that.

Send your queries to mehta@ttac.com. Spare no details and ask for a speedy resolution if you’re in a hurry.