Jon Kaase Fixes 429 & 460 Rear Main Seal Leaks

Front and rear views of the Kaase 1-piece rear main seal for Ford 429-460 engines.

Two-piece rear main seals leaking in Ford 429ci and 460ci engines is hardly an uncommon problem these days. Numerous Internet forums confirm this habitual engine bleeding and the resulting frustration to the owner. There’s very little flexibility in correcting the situation. The engine usually has to come out since many vehicle applications deny access to the pan.

Jon Kaase, arguably the most accomplished engine maestro with the Ford 385 Series platform, appears to have a solution. He had to go across the pond to find it, but this unique 1-piece seal fits perfectly when installed and is constructed from materials that may withstand heat better.

Here’s a comparison of the standard 2-piece seal, left, and the new 1-piece seal from Kaase. Photos by Moore Good Ink.

Here’s how the traditional 2-piece is installed. Even offsetting the tips of the seals won’t guarantee complete sealing.

“We never would have done this if you could buy a seal like for Chevy,” says Kaase, whose shop is located in Winder, Georgia. “A regular 2-piece Rat motor seal, they’re never bad.”

Kaase admits he can’t pinpoint the problem with current replacement seals on the market but acknowledges that there is no consistency in the results.

“Any seals we can buy now, about half of them leak like hell,” says Kaase. “You try to figure out what’s wrong with them, and it doesn’t make any sense.”

About five years ago, Kaase sourced a few hundred NOS seals and didn’t have a single problem.

To install the Kaase 1-piece seal, make a cut with a sharp razor blade on the dot, then wrap the seal around the flywheel flange.

“We paid triple price for them but finally ran through that supply,” adds Kaase. “Then we started getting desperate.”

Kaase teamed up with a British supplier well known for manufacturing seals for NASCAR teams. He reviewed and modified proposed dimensions until arriving at a part that would work in stock iron as well as aftermarket aluminum blocks. Kaase didn’t request a 1-piece design but rather worked with the company’s strengths.

When positioned properly, the ends of the seal are joined with a daub of silicone.

“If they would have had a 2-piece, it would have been okay with us,” says Kaase. “But this is the way they make them, and it was made to our exact blueprint.”

Obviously a 1-piece seal won’t fit over the flywheel flange, so the Kaase seal is designed to be severed at a specific point with a sharp razor blade. The seal is then wrapped around the crank behind the bearing surface and mated with a small daub of silicone sealer.

“Everything we’ve run them in so far has done just fine,” sums up Kaase.

About the author

Mike Magda

Mike Magda is a veteran automotive writer with credits in publications such as Racecar Engineering, Hot Rod, Engine Technology International, Motor Trend, Automobile, Automotive Testing Technology and Professional Motorsport World.
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