Balance Shaft Rear Plug - Feels Loose?

OK-944 · 08-26-2010, 10:09 AM

Got everything torqued down correctly on the upper balance shaft housing...but the rear circular disk ("plug"), held between the upper and lower housings, with its attached O ring, can still move a little bit. This does not seem right.

I seem to remember others comments regarding this on both this forum and on the Porsche Online forum (where I also post). Is this looseness OK? I'm tempted to take this apart and apply a bit of RTV to this area - to help ensure a good seal.

Anybody care to comment?

968 GUY · 968 GUY's Garage

search

HondaDustR · 08-26-2010, 12:33 PM

Mine were tight when I assembled the covers (did you get the right o-ring?), but it's definitely something I would glob a little bit of silastic type sealant on to make sure.

bazar01 · bazar01's Garage

Quote:

Originally Posted by OK-944

Got everything torqued down correctly on the upper balance shaft housing...but the rear circular disk ("plug"), held between the upper and lower housings, with its attached O ring, can still move a little bit. This does not seem right.

I seem to remember others comments regarding this on both this forum and on the Porsche Online forum (where I also post). Is this looseness OK? I'm tempted to take this apart and apply a bit of RTV to this area - to help ensure a good seal.

Anybody care to comment?

If you replaced the fat o-ring with a new one, the looseness in the circular disk is not OK. It should be tight. It gets loose over time as the o-ring shrinks and gets hard.

Wavey D · Wavey D's Garage

I have a loose upper balance shaft end cap also. Does one have to remove the balance shaft housing to install a new o-ring? Or is there a way to pop the cap off?

OK-944 · 08-27-2010, 02:49 PM

If you google RTV reseal of rear balance shaft seal - you can bring up a Rennlist discussion about several folks who've successfully resealed (with gray RTV) loose balance shaft rear seals from the outside, without any disassembly. There is also some discussion from folks doing rebuilds, regarding using gray RTV as a matter of course to help seal up this "rear plug" of the balance shafts.

I went ahead and used some grey RTV on the rear 0 ring of the lower balance shaft when I reassembled it, and I'm now contemplating whether or not to take apart my upper balance shaft assembly (which is locktited and the shaft resistance feels just right) so I can RTV this also - or just do it from the outside, and save myself the headaches of cleaning everything up once more, including the new locktite seal. I should probably take it apart and do it right.

But my question is this: it seems like a no-brainer to have a seal for this rear plug that's shaped with a channel, to accomodate the outer circumference of the opening in which to rear plug sits. Considering the PITA factor of getting this apart for a fix on an installed engine, I wonder why this wasn't addressed at the factory?

HondaDustR · 08-27-2010, 04:34 PM

Quote:

Originally Posted by OK-944

Considering the PITA factor of getting this apart for a fix on an installed engine, I wonder why this wasn't addressed at the factory?

Since when do things ever work that way?

fennacf · 06:22 PM

Define loose. This is an o-ring sealed joint so expect there to be some play. See the following links for a little more background on o-rings.

Dichtomatik Americas - Literature - O-Ring Handbook
O-ring - Wikipedia, the free encyclopedia

Porsche used an o-ring here for a reason so I would not recommend the RTV as YOU may create a leak path. The o-ring joint allows the seal to respond to changes in the thermal and vibratory environment. Please contact Jim and take a look at his plugs for reference as his low end was resealed last year.

OK-944 · 08-28-2010, 03:06 AM

OK - I'm going to run an experiment....I'll leave the upper balance shaft with just the O-ring alone, and the lower with its RTV-augmented seal - and I'll let you folks know what happens.

....do I hear any bets? : )

Wavey D · Wavey D's Garage

Mine's so loose you can spin it around and make a nice clicking sound by pushing in and out. It's gotta be a leaker. I guess I need to address it somehow with out complete disassembly of the shaft housing. Looks like I need to do some research. I wonder if I could stretch an o-ring over then under the cap somehow.

HondaDustR · 08-28-2010, 06:17 AM

Quote:

Originally Posted by OK-944

OK - I'm going to run an experiment....I'll leave the upper balance shaft with just the O-ring alone, and the lower with its RTV-augmented seal - and I'll let you folks know what happens.

....do I hear any bets? : )

That's not a fair comparison due to exhaust header heat near the lower one. That would also be the best way to test its durability, though. The o-rings alone can shink so badly over time that it creates a vacuum leak into the crankcase, which throws off the injection system via the crankcase breather and taking oil mist with it. I ran with the breather hose temporarily disconnected and the vacuum line plugged and it ran better, but then there was no vacuum to keep the majority of the oil inside the engine and they leaked oil very badly.