TC front crankshaft oil seal

[YellowS4DHC]

I've just reassembled my twin cam after doing the valves and rebuilding the water pump.  The head, pan, and front cover were all removed and reinstalled with the engine remaining in the car.  Everything is dry, no leaks, except one:  my (new) front crankshaft oil seal leaks badly. 

My crankshaft pulley OD has an excellent seal surface.  I suspect the seal isn't properly centered relative to the crankshaft due to the position of the front cover/backplate.  I was thinking that a more flexible seal might help here.  Does anyone know of any oil seals that might be an improvement over the standard?

Suggestions welcome.

regards
Rick

[jbcollier]

Often you can get seals with a double lip, ask at your local industrial supply.  You will need dimensions to the thousands of an inch or hundredths of a millimetre: diameter of the crank pulley seal run, diameter of the hole in the timing cover, width of the seal.

I thought the front cover was located by dowels so perhaps it is not out of line.  It is moderately easy to miss-install or damage a seal.  Make sure the seal goes in straight and is not distorted.  Make sure there are no sharp edges on the pulley.  Repair sleeves are available if you have any doubts about the pulley's seal run.  Lastly, make sure you grease the sealing "lips" on the seal !! This is the only lubrication a seal receives and the seal will quickly wear out otherwise.

[YellowS4DHC]

The seal (double lipped) was put in square, undamaged, and was lubed prior to insertion of the pulley.

It's my understanding that the front cover can be misaligned relative to the crankshaft if the backplate is slightly mis-positioned.  Also, there is a small bit of play in the alignment of the front cover plate with respect to the back plate.  I don't believe there are any dowels to fix the front cover's position but given there are 11 bolts, the tolerance stack up on hole position clearly limits any play. 

However, given the harmonics of the crankshaft, there wouldn't need to be much misalignment to casue leakage.  The harmonics of the crankshaft can make a good seal difficult even with perfect alignment as the motion of the pulley can, in some cases, be enough to cause leakage at the seal.  If one is unlucky enough to frequently hit resonance, the amplitude of the motion of the pulley will be sufficient to cause leakage.  This is a function of the mass of the crankshaft pulley being used and engine RPM.  My pulley is a special one that uses a toothed belt and is heavier than the stock item.   Given that I don't get much leakage at low RPM, I'm inclined to think harmonics is the bigger factor.

So, with a new seal in place, correctly installed, and a good seal surface on the pulley, the two likely reasons for leakage are misalignment and harmonics.  Looking for a more tolerant seal (more generous lips) would address either potential cause.   I could also play with a heavier or lighter pulley to see if I can luck out with the harmonics, or simply let it go and be content with a single drip spot.

Rick

[jbcollier]

Well, the first thing to check is if the crankshaft is concentric with the timing cover.  Remove the seal, and use a suitable sized tool to check (drill bits work well).  if it's tight in one spot and flopping in the breeze in another, then you know for sure.