Silicone Sealant - Threat or Menace?

[FJCamper]

Above: 1600 Mahle piston with broken con rod. We used too much silicone sealer and the excess got loose inside the case and clogged the oil pickup.

Silicone Sealant - Threat or Menace?

Most VW engine builders will tell you not to use silicone sealants or gasket makers on VW engines, or at least not to overuse them. A little silicone, like a little stupid, goes a long ways.


Above: Sealing up the cylinders sealed this 1600's fate.

One place many builders feel fairly safe using this type of sealant is on the cylinder-to-case fitting. This photo shows exactly how to overdo it, allowing excess silicone debris to get into the oil and in turn restrict flow at the oil pickup tube. And blow an engine. Or two. We blew two. One was our 1600 test engine for the centermount fan housing project, and the other was an 2.2 litre enduro engine we use for LeMons racing.


Above; Our dry sump tank originally had no verticle baffels to stop slosh. but amazingly had a stack of three perforated plates, deck fashion, that kept the oil from surging up and down. We fixed that after early use proved it necessary.

The 2.2 at Road Atlanta when it still had oil pressure

https://www.youtube.com/watch?v=Tng5ReSc2wY

The 2.2 litre was the first to go. It had at least 12 to 14 hours already on it, and those were all on our original non-baffled (and square) 3-gallon dry sump oil tank, which would often allow the engine to briefly starve for oil in a high-G turn. It failed at Road Atlanta on 22 April 2016, knocking when we shut it off.


Above; Example of a cross-over plate replacing the stock oil cooler. There are not block-off plates. The oil coming out of the oil cooler outlet port (closest to the pulley end) has to be routed down the inlet port (closest to the flywheel) to feed the bearings.

On disassembly, we found very little silicone in the engine, but there was enough right where it counted. The crossover plate (replacing the stock oil cooler) had beens sealed with a liberal amount of silicone, and a glob of it was partially obstructing the "cooled oil" return passage back into the case. We figured the glob had been there since the case was closed, and slowly contributed to the failed rod beaing, as if the too-frequent unbaffled dry sump sloshes were not enough.


Above: The Ghia at Barber, long telephoto shot, moments before the rod exploded through the case top.

The 1600 didn't make two full laps at Barber on 21 May 2016 before throwing a rod (#1). This engine also had the same red high-temp silicone used on the pushrod tube seals, so it suffered from a double whammy. On teardown, we found the screened oil-suction pickup was well clogged with silicone peelings.


Above: We use an O-ringed Oil Suction kit which pickup flares to about one inch in diameter, and has a nice stainless steel screen. These kits are very effective, but having the larger area of the stock oil strainer would be better.


Above: The Type 1 case oil flow is from the pump to the pressure relief valve, where very cold oil is either routed directly to the main oil gallery and bearings or hot oil is routed to the oil cooler then on to the bearings. We found a lump of silicone partially blocking the crossover plate channel, sure slow death for this one.

No one else to blame here but ourselves for ignoring a basic rule. We've never done it before and we'll never do it again.

FJC

[Piledriver]

Ouch.

That's why the red anerobic is suggested for most things, esp the case seal, it won't really ever set unless its also in intimate contact with clean metal, on both sides. If anything gets "loose" it mixes with the oil and eventually gets filtered or drained out. Its also a ~translucent red gel and it's very easy to tell how thick it is going on---a thin film is all it takes.

I imagine you could still find a way to use way too much an cause issues, but no evidence of it was found on my last tear down except exactly where it was meant to be.

As I know you know, if one feels possessed to use RTV all you want is an almost see-through smear.
The anerobic cleans off a LOT easier than RTV, if not fully cured, a shot of Brakleen will make it all curl up and fall off.

[Ol'fogasaurus]

It funny you mentioned this. After the origional engine wore out in my buggy (partly due to the intake being rusted out in a spot you couldn't see it and causing the engine to lean out ) I went through two purchased used engines in quick succession. The first one was in worse shape that it was supposed to be and the other one was a low milage engine that was put together wrong and used cheap components. It also did not like to go up and down hiills angled more than 1 or 2 degrees without getting into the oil starvation bit.

I took a bunch of heads I had to a good engine builder that was a ACVW person also. I think we threw away 3 or 4 sets of cracked heads and a bunch of other things. He then machined the block and components for me and I took it home to assemble it (this is the first VW engine I had worked on much less assembled). I was told by several people to put silicone on the case halfs when putting the case together but after having troubles getting the front bearing onto the pin correcctly I took it back to the machinist and he told me not to put anything in the case join or anywhere else; that is what straight edges are for... checking flatness. If during fit check, the parts are not fitting correctly then find out why, fix the problem then assemble it correctly. He advised me to let him reassemble the short block which I had come to figure out was probably a good idea. By-the-way, the engine is still running over 15 years later; I dd have to put a sump on it but things are seemingly still good.

Lately when watching engine builds, by those who are supposed to know, what is being done in preperation for the assembly of parts has changed a lot. Things I wondered about which were back then considered to be a no-no to do now seem to be an accepted practice but then you need to give the block/parts a second bath to make sure every thing is spic and span.

The concept of too little vs. too much is often hard to define. To some people a skim coat could be desctibed as piled on crap (I can't imagine what a thick coat would be to them) that will displace in any direction that it can; hence what has been pesented here previously.

Good subject guys.

Lee

[madmike]

I bet it didn't leak
I hate RTV!!!!
Once seen an automatic trans with so much of this poop in the valvebody (Motec grad mechanic built it