PERAs Core Corner: Ford Balance Shaft Information For Gearheads - Engine Builder Magazine

PERAs Core Corner: Ford Balance Shaft Information For Gearheads

This month’s column is going to be information about balance shaft gears and changes that have occurred in some Ford engines. But I thought before we got to that I would give a little history on balance shafts and their purpose.

The basic concept behind balance shafts has been recognized for nearly a century. Contrary to popular belief, the internal combustion engine has an inherent second-order (twice engine RPM) vibration that cannot be eliminated no matter how well the internal components are balanced.


To deal with these harmonics, engine designers often incorporate two balance shafts rotating in opposite directions at twice engine speed. Equal size eccentric weights on these shafts are sized and phased so that the inertial reaction to their counter-rotation cancels out in the horizontal plane, but adds in the vertical plane. This gives a net force equal to, but 180 degrees out of phase with, the undesired second-order vibration of the basic engine, thereby canceling it. In a “V” configuration the same may be accomplished by opposite counter weights on the same/single shaft. The ultimate result is to eliminate NVH (Noise Vibration Harshness).

Now that we have the boring – but necessary – history out of the way, let’s move on to the important stuff. The meat and potatoes, as it were, and we will skip the utensils and just eat with our hands (as men were meant to eat)! The 3.8L, 3.9L and 4.2L Ford engines in the same family configuration have had these shafts at various times and in different vehicles but that is something to talk about in the future and not the issue here. The issue at hand is recognizing change in the amount of teeth of the drive and driven gear. A similar example is the Pontiac 2.5L engine. If you ever saw one of those mis-matched entanglements it was ugly.


As best I can figure, the drive and driven gears of the balance shaft changed in August of 2003 for vans and August of 2004 in the truck. The driven gear on the balance shaft changed from 31 to 38 teeth, and as you can see in the illustrations it would not be hard to confuse the two.

The change in teeth was to further reduce the NVH of the gears that drive the balance shaft. Obviously a mix up would result in a catastrophic failure.

However, what I have found is that as long as you keep the camshaft drive gear and balance shaft gear matched it makes no difference which ones you use.

One last informational nugget: if you have not already heard, EngineDataSource.com has joined forces with Mitchell 1 and has become the ultimate information resource for professional engine enthusiasts at any level including DIY’ers.

For technical questions, contact the Production Engine Remanufacturers Association (PERA) at: [email protected]

You May Also Like

America’s Best Engine Shops 2022 | Choate Engineering Performance

This shop’s dedication to quality engine work, its growth, its machining capabilities and its impact in the diesel industry, all make Choate Engineering Performance well deserving of Engine Builder’s and Autolite’s 2022 America’s Best Diesel Engine Shop award.

Necessity is the mother of all invention, and it certainly played a role in the founding of Choate Engineering Performance. The diesel engine and machine shop was founded by shop owner, Cass Choate, after finally becoming fed up with having to rely on others for certain aspects of his work.

America’s Best Engine Shops 2022 | 4 Piston Racing

The 4 Piston Racing facility in Danville, IN houses two buildings – one is 12,000 sq.-ft. and the other is 2,500 sq.-ft. The shop is very heavily focused on Honda cylinder heads and engine work to the tune of 300+ engines and 1,000 cylinder heads annually!

Randy Bauer Shares His Experience as PERA President

We recently spoke to Randy about his PERA presidency and what some of the biggest hurdles are facing the engine remanufacturing industry right now.

Women in Motorsports: Mattie Graves

Mattie Graves competes in the Outlaw Diesel Super Series (ODSS) dragster class, and is the only female doing so in a class that already has very few competitors in general. Find out more about this up and coming diesel drag racing star.

Women in Motorsports: Johnna Dunn

She got her drag racing license before she got her regular license, and that tells you everything you need to know about Johnna Dunn. She’s a drag racer and clutch specialist for her grandfather’s NHRA Top Fuel Funny Car team, Jim Dunn Racing.

Other Posts

Women in Motorsports: Kayla Blood

A veteran of the military, a former track star, an MMA fighter, Motocross and ATV racer, and now a Monster Jam driver, Kayla Blood has packed a lot into her still growing career. Now the driver of Soldier Fortune, she strives to make a name for herself and for other women looking to make motorsports a career.

Women in Motorsports: Felicia Smith

Felicia Smith was never a huge gear head. However, following her first taste of speed at the track, she’s been living a life of cars and racing ever since. She’s taken the past six years to build up her CTS-V and her own car/engine skills in an effort to share it all with the car community.

Women in Motorsports: Jillian McLaughlin

Not all of us start out in this industry. Take Jillian McLaughlin for example. The once hairdresser is now an engine builder helping do a little bit of everything at Precision Machine Engine in California.

Women in Motorsports: Janine Shoffner

Whether it’s motorcycles, skydiving or road racing, Janine Shoffner has an addiction to adrenaline-filled activities. For the last decade, road racing has been her biggest passion as a co-founder of J2-Racing.