Sealing Engine Case Hardware?, To goop or not to goop? Options

[bkrantz]

In theory, sealant on all the mating surfaces for the engine case halves should contain oil and prevent leaks, and (with a couple of exceptions) the design of nuts and bolts, and where they attach, was not intended to form a seal.

But many mechanics swear by applying lots of sealant to every piece of case hardware. Is this overkill? Anyone had good luck lately with just sealant on the case halves?

[ClayPerrine]

I use a thin bead of Drei-Bond. It is the adhesive that Porsche used in the 964 and 993 motors to seal the case halves when new. It never fully cures, and is flexible, allowing slight movement between the case halves. I also put a bead on the base of the cylinders and around the base of the heads on the case through bolts and nuts.

The only leak I have on my 4.0 engine is because of a warped right magnesium timing cover. No leaks between the case halves. And I assembled the case halves with my hand wrapped in a shop towel to stem the bleeding from my cut finger. So I was not as careful as I normally would have been.

People that use a ton of orange silicone on the case halves of air cooled motors piss me off. It is ugly, messy and doesn't seal well. It was designed for use on water cooled motors and is not as flexible as it needs to be for an air cooled motor.

[Shivers]

Hi Clay. I googled Drei-Bond, haha could you post the numbers off the tube. They make a lot of sealants evidently. Never thought about it, but those case halves can move a tiny bit.

[Mark Henry]

My newest favorite is loctite si 5900, factory spec on 996/7.
Proper application it's a 1mm bead, it's RTV but a whole different class of sealant. I like because it replaces a couple different sealants I used to use and it cleans up fairly easy.


Threebond 1185 or yamabond 4 seals a case good, but it's a PITA to clean up if you ever have to take it back apart. Both are a threebond product, it too is an RTV, lately I've had a hard time sourcing it locally so I don't use it much anymore.

[Superhawk996]

But many mechanics swear by applying lots of sealant to every piece of case hardware. Is this overkill? Anyone had good luck lately with just sealant on the case halves?

Adding sealant under washers is not good fastened joint design practice. Having goop under your fasteners will result in skewed fastener torque and resulting clamp loads.

What you ideally want is a hard metal to metal joint. Adding sealing between case halves is a necessary evil and was accomodated by the OEM torque recommendations.

What isn't accounted for is adding massive amounts of RTV goop on below washers. In effect it creates a softer fastener joint. The RTV forms a sort of hydrostatic "bearing" that tends to float the washer just a minute amount. This RTV film softens the joint and prevents X amount of toruqe from achieving Y amount of clamp load.

But some will argue that the washer is compressed metal to metal and squeeezes out the excess RTV. My question is, if that is the case, what was the good of putting it there in the 1st place? If the case is sealed properly, you will not have leaks at the fastener pass-through holes.

If some RTV is indeed left under the washer, it will slowly creep over time, resulting in a loss of clamp load. Not what you wanted in the 1st place to prevent leaks.

I've always had good luck with Yamabond or Hondabond (probably same product - different tubes) on T4 and motorcycle split cases without goop under fasteners. I'll have to research Mark & Clay's other options - always looking for something better that works or cleans up better and has a proven track record of major OEM endorsement.

[ClayPerrine]

Hi Clay. I googled Drei-Bond, haha could you post the numbers off the tube. They make a lot of sealants evidently. Never thought about it, but those case halves can move a tiny bit.

It is Drei-Bond 1209. I had to switch computers to look it up.

The bird has it....

https://www.pelicanparts.com/More_Info/0000...1IaAixUEALw_wcB

And I know other vendors have it as well.

Clay

[Shivers]

Thanks Clay

[johnhora]

Have had good results with these over time...

Old School left...New School right.

[Mark Henry]

But many mechanics swear by applying lots of sealant to every piece of case hardware. Is this overkill? Anyone had good luck lately with just sealant on the case halves?

Adding sealant under washers is not good fastened joint design practice. Having goop under your fasteners will result in skewed fastener torque and resulting clamp loads.

What you ideally want is a hard metal to metal joint. Adding sealing between case halves is a necessary evil and was accomodated by the OEM torque recommendations.

What isn't accounted for is adding massive amounts of RTV goop on below washers. In effect it creates a softer fastener joint. The RTV forms a sort of hydrostatic "bearing" that tends to float the washer just a minute amount. This RTV film softens the joint and prevents X amount of toruqe from achieving Y amount of clamp load.

But some will argue that the washer is compressed metal to metal and squeeezes out the excess RTV. My question is, if that is the case, what was the good of putting it there in the 1st place? If the case is sealed properly, you will not have leaks at the fastener pass-through holes.

If some RTV is indeed left under the washer, it will slowly creep over time, resulting in a loss of clamp load. Not what you wanted in the 1st place to prevent leaks.

I've always had good luck with Yamabond or Hondabond (probably same product - different tubes) on T4 and motorcycle split cases without goop under fasteners. I'll have to research Mark & Clay's other options - always looking for something better that works or cleans up better and has a proven track record of major OEM endorsement.

No sealeant under the washers sounds great in theory, but in practice good luck with that.
Putting sealant under certian strategic fasteners, like the four lower head studs, is a necessary evil.

I always subscribe to "a little dab will do ya" philosophy. I never "goop" sealants on, to me that's the mark of a disorganised builder.

[ClayPerrine]

No sealeant under the washers sounds great in theory, but in practice good luck with that.
Putting sealant under certian strategic fasteners, like the four lower head studs, is a necessary evil.

I always subscribe to "a little dab will do ya" philosophy. I never "goop" sealants on, to me that's the mark of a disorganised builder.

(IMG:style_emoticons/default/agree.gif)

Don't over-do the sealant. A thin bead is enough. I use a 2mm wide bead on the case halves, and about the same on the cylinder bases.