oil leak where the intake manifold meets the head

[RobertE]

Well, in the last 48 hours someone on this forum told me how to pass the ADS-B performance test for the rebate (it worked) and where to find an addendum to the GNS430W manual explaining how traffic is displayed on that device (that worked too).  This is such a helpful site, let's see if I can go 3 for 3.

I've got a J model and have a very small leak (about 1 drop per 30 minutes) that seems located where the #1 intake manifold meets the head.  I have a very, very, very small leak (no visible oil drops but evidence of oil when the area is cleaned, then run for 10 minutes, then covered in talcum powder) at the same location by the #2 intake manifold.  The problem seems more pronounced when running at less than full power, but that may be my imagination.

Does anyone know what in the world this could be?  I simply can't imagine how oil could present itself there.  If, say, the intake guide is leaking oil then leaked oil would go into the cylinder and be burned, I should think.  Again, how could oil get on the outside of that manifold?  Is there a hidden leak elsewhere that affects two cylinders on opposite sides?  I've fully examined the pushrod tubes and am certain they aren't the cause.  In fact, they used to leak slightly which was what I once thought was the cause for this minor leak I've had for over a year.  Now that that leak is fixed I'm looking elsewhere and am at a loss to explain it.

Thanks.

 

[Piloto]

I had the same problem there are two likely leak sources.

1. Valve cover gasket. I switched to silicon gaskets (orange) and solved the problem.

2. Push rods shroud tubes O-rings. I cleaned very well the area with MEK and coated it with PRC-1422-A using a small brush. Not a drop in 100hrs. You can change the O-rings but they will leak again. The oil drips down thru the fins.

José

[RobertE]

21 hours ago, Piloto said:

I had the same problem there are two likely leak sources.

1. Valve cover gasket. I switched to silicon gaskets (orange) and solved the problem.

2. Push rods shroud tubes O-rings. I cleaned very well the area with MEK and coated it with PRC-1422-A using a small brush. Not a drop in 100hrs. You can change the O-rings but they will leak again. The oil drips down thru the fins.

José

Thanks, Piloto.  I'm sure those two areas are the likely culprits in most cases but I'm afraid they don't appear to be the root cause of my problem.  I switched to silicon gaskets a year ago (yes, those cork ones were starting to leak) and replaced the shroud tube seals about 4 months ago.  There is no evidence of leak there.  So it's a real mystery.

 

 

[Piloto]

I .also recoated with sealant the oil return elbow next to the intake port. Leaks at the elbow/head are hard to notice because oil runs along the cylinder surface to the intake port. Some annoying leaks don't show at the source but the trail down and you have to catch it before the oil gets cold. I just recoat anything suspicious.

José

[geoffb]

I've got similar leakage.  I'm convinced it's some valve guide leakage on the intake valve getting into the intake port.  I foul the same plug if the plane sits for a week a so.  Living with it.

[N201MKTurbo]

I've had that leakage at some point with four different engines. I just accept it as being a Lycoming.

So, oil leaking from the intake valve guides will drip into the intake riser. With low power there is a big pressure differential between the rocker box and the intake port, so it makes sense that it would be worse.

My experience is that if you spend a lot of money fixing it you will spend a lot of money, If you do nothing the outcome will be the same except you wont spend a lot of money.

You can try replacing the intake gasket. It won't stop the leak, but it will keep the leaking oil inside where it belongs.

Edited December 2, 2016 by N201MKTurbo

[Raptor05121]

I have the same leak on #2. My mechanic said it's the pushrod tube O-ring.

[N201MKTurbo]

Just now, Raptor05121 said:

I have the same leak on #2. My mechanic said it's the pushrod tube O-ring.

It might be. The Lycoming pushrod seals are marginal at best. I wish they would have spent an extra few dollars on them and put a real spring.

WOW, maybe that is my retirement business! Making better Lycoming pushrod tubes. I could fly to all the shows and write off all my Mooney expenses for the rest of my life!