Cam seal type for MFI drive
 

I’m about to replace the cam seal for the MFI drive for the third time in three years:mad:

Last time around I went all in with a speedy sleeve and dual seals. To no avail.

The seals seems to be pushed out. I have noticed that most common seal types are rated to max. 0.5 bar (7.35 psi). I have no idea about the oil pressure behind the seal, but 0.5 bar does not seem that much. Seals type ASP are rated to 5 bar and should then be a safer option.

Anyone with experience on this matter?

I would contact Mark Jung . .he knows everything about MFI pumps and is always very helpful with questions.

How are you installing the seal?

And where is it leaking - seal to cam tower interface, or seal to camshaft interface?

Well, I have previously installed the seal as carefully as possible following the common guidelines. As for where it leaks, that’s not possible to determine once you gained access to the seal. The front seal was pushed slightly out of the cam housing, the inner most seal was in place and my guess is it was leaking via the lip against the cam.

Couple things ...
I asked how you installed because some lube the outside of the seal. If you did that, it might explain why it's pushing out. Most recommend installing seals dry.
If it's leaking on the cam interface, check your camshaft for pitting or unevenness on the surface where the seal rides. That could cause leaks. One other possibility is that the seal as it starts to push out, now no longer has a smooth surface on the camshaft to properly ride on, causing a leak. You should be able to see a polished area(s) on the camshaft surface where the seal was riding.

Seals where installed dry on the outside and lubed towards the cam. I have actually installed a speedy-sleeve last time around to ensure a perfect smooth surface for the seal to run on.

Apparently this very seal seems to leak more than others on MFI engines, that’s why I was wondering about using a seal rated for a higher pressure.

The commonly available seals are OA types (single lip) rated for 0.5 bar, I will source an ASP type which is a double reinforced lip rated for 5 bar. I assume there is no downside doing this, so worth a try.

If I recall correctly, some seals are single lipped while some are double lipped. And can be rated for direction of shaft rotation as well. Things to consider if you're buying generic seals.

MotoMiata . . did you ever find a solution for this leak? I am experiencing the same problem with my 1972 911 MFI.

I've always just used the OEM seal and have never had any problems. I did have to install a speedi-sleeve on one of my son's motors (2.4T) because the end of the camshaft was pitted, but that's the only unusual step I have ever taken.

As far as I can tell, there is no "oil pressure" behind these seals. I believe they are lubed by whatever small amount of oil manages to creep forward past the forward most camshaft bearing.

Sometimes stacking two seals will stop the leak. The good news with this approach is that you don't have to dig the old one out, just press the new one in right over the top of it. Plenty of room for both.

If you’ve already used a speedy sleeve and dual seals with no luck, you might want to inspect the seal area for any irregularities or think about a more custom solution

I'm not surprised that people are having difficulties with the seal for the camshaft nose that provides the MFI drive.

The cavity behind the seal fills with oil from the forward most camshaft bearing journal and does not have a drain path to return this oil to the cam box. The only way for oil to return to the cam box is thru forward most camshaft bearing journal clearance. With the engine running some oil pressure is likely to develop in the cavity.

In the first 911 engines with carburetors this cavity was sealed with a large metal freeze plug; MFI came later.
A modification to vent the cavity behind the seal to the cam box would be helpful.

E.g. look closely at the Number 8 bearing; the cavity behind the seal and in front of the bearing journal is vented back into the crankcase by two 6mm drillings at about 4 and 8 O'clock.
Incidentally the Number 8 bearing also has an external slot to vent the O ring groove back to the crankcase, without this slot the O ring is less effective.

Are you suggesting to drill a hole in the seal cavity just forward of the bearing. Rob

The crankshaft bearings are pressure fed and bleedoff is required for the ones on the extremity. The camshaft bearings are lubricated by splash. So not apples and apples. Not saying that a bleedoff for that seal ins't a good idea, couldn't hurt I think. Will examine a housing to see how one might do that. Bob

Since when are the camshaft journals lubricated by splash?

They are not. They are pressure fed. I finally got curious enough to take a look at a spare set of cam towers to confirm. It's not real obvious, but the oil introduced into the spray bars also gets routed from them into the casting to feed the cam bearings via holes drilled through the bearing locations. There are threaded plugs visible under the intake valve cover where these holes go through.

Examine twice speak once, I stand corrected. The oil ports in the cam bores are plain to see. I suppose no solid bearing connection could survive without pressure. What else don't I know? Bob