valve guides/torn seals question

[simsalabim]

Hello All!

Well, I finally joined the air cooled society with an 81 sc a few months back, and though I'm not unfamiliar with a garage, I am definitely a Porsche rookie! This forum has been a tremendous resource for knowledge and community, so a sincere THANK YOU to everyone involved.

I am sorting out my car now and currently have the motor removed (as I intended to change out a blown air-box and chase down a few oil leaks). I was not naive enough (though admittedly hopeful!) to believe that there would be no mechanical rabbit holes exposed in the process and well.... here we go!

A substantial oil leak at the Head/Cam Tower interface led to a removal of the heads for a closer look. Studs are fine (replaced along with a top end rebuild about 35K miles ago, though car has 194K miles on it), but there was substantial burnt oil residue visible in many of the exhaust ports. Valve guides (replaced with rebuild) looked a little wet and numerous torn valve seals were found. The seals were not brittle, and they look like mechanical tears. It also looks like there are a few valve guides extended from their sleeves a bit further than others (will measure to be sure).

My mechanic is thinking that unless there was some past of over-revving incident, the next likely torn seals cause is some improperly seated (or installed) valve guides interfering with the seals at some point. Sounds reasonable to me but like I said, I'm a rookie.

Contemplating my next move as I try to do things right, but also keep costs down.

Any advice would be greatly appreciated and Thanks very much!

[Walt Fricke]

I think the manual wants you to install the seals by inserting the valve, putting a plastic cover with a bullet nose over the tip of the valve, and installing the seal over that. Maybe I am confusing that with installing some other seal. I've never done this, and haven't torn any seals, though I am using the white plastic-like ones, which some give a bad rap. I've not seen a torn seal. I assume the tearing was on the sealing part, not down lower where using a socket or something to press it on might have gouged an external part, which wouldn't matter?

Then again, I don't use seals on the exhaust at all. Little to no vacuum there, and the oil has to climb up anyway on the exhaust.

I'd think the springs would hit coil bind before the retainer could hit the top of the seal, but not on my list of things to examine.

Seems to me the questions are a) was oil consumption excessive, and b) are the guides worn (doesn't matter when replaced - are they worn), assuming they were all seated properly. Those would be the things which would most directly affect performance.

I suppose if a guide wasn't pressed in to the proper depth, the seal would sit up higher and thus maybe the retainer could hit it?

Maybe someone else has a more useful take for you.

[simsalabim]

Thanks Walt -

While I have only driven the car a couple of months on occasion, I believe I clocked the oil consumption (no smoke on cold start or on deceleration after high revving) at around a quart/500 miles. I know, that's more than the book says, but the oil puddling under car is what led me to drop engine in first place. I thought the extra oil usage was due to various seals/gaskets leaking (cylinder leakdowns were all under 2%).

Worn guides? How would you go about accurately determining this?

Also, no seals needed on exhaust valves? so.... all the burned oil crap in the ports was not caused by bad seals? wow.... I have a lot to learn!

Thanks again Walt

[Walt Fricke]

Well, be careful with what you read here. Porsche put seals on its exhausts. A mechanic long ago said why bother. Made sense to me, and I've had no ill effects I could see. But you need to consider the source - random mechanic and regular guy who likes to analyze and tinker vs Porsche engineers.

Still, I can't see issues with exhaust seals as leading to oil in exhaust ports. Unless, perhaps, the guides were really really worn (which they could be).

Search for something like "valve guide wear" on Pelican, and you may find suggestions on checking which don't require disassembly and tiny bore gauges. Like open valve a little and press the tip sideways several directions and see how much it moves. I may have seen this quantified some, but don't recall the numbers.

The quart/500 miles sounds like guides which are getting worn though, despite Porsche saying that is within spec (if barely. Of course, could be rings too. Porsche's spec for 78-81 SCs (I happen to have it on my desk at the moment) says oil consumption is 1.5 liters per 1000 klicks for the SC, and 1-2L for the Turbo of that era.

The two books which are or should be in your library (Anderson, Dempsey) both have something to say about this. One of the few issues the 3.2s had was premature guide wear leading to what some would consider excessive oil consumption. Me, if I had to add a quart every 500 miles on a trip, I'd think that excessive. Manageable if you knew to keep on top of it, but excessive.

[simsalabim]

Thanks so much Walt.... but by my more recent posting (Crankcase replacement), you can see I have a bigger fish to fry right now. I am still trying to digest whats happening and decide on the best course(s) of action. I hate to put the thing back together again with a broken stud even with a new valve job. Whew....

I appreciate your interest though Walt, that's for sure!

Best,
Bill

[simsalabim]

For anyone interested, this thread is being picked up in my other thread involving replacing my 930 series crank case. I am into a full rebuild now of my 81sc, and the heads are being looked into in more detail now and hopefully, the mystery of the torn seals will be revealed.

cheers to one and all,
Bill

[afterburn 549]

Originally Posted by Walt Fricke

Well, be careful with what you read here. Porsche put seals on its exhausts. A mechanic long ago said why bother. Made sense to me, and I've had no ill effects I could see. But you need to consider the source - random mechanic and regular guy who likes to analyze and tinker vs Porsche engineers.

Still, I can't see issues with exhaust seals as leading to oil in exhaust ports. Unless, perhaps, the guides were really really worn (which they could be).

Search for something like "valve guide wear" on Pelican, and you may find suggestions on checking which don't require disassembly and tiny bore gauges. Like open valve a little and press the tip sideways several directions and see how much it moves. I may have seen this quantified some, but don't recall the numbers.

The quart/500 miles sounds like guides which are getting worn though, despite Porsche saying that is within spec (if barely. Of course, could be rings too. Porsche's spec for 78-81 SCs (I happen to have it on my desk at the moment) says oil consumption is 1.5 liters per 1000 klicks for the SC, and 1-2L for the Turbo of that era.

The two books which are or should be in your library (Anderson, Dempsey) both have something to say about this. One of the few issues the 3.2s had was premature guide wear leading to what some would consider excessive oil consumption. Me, if I had to add a quart every 500 miles on a trip, I'd think that excessive. Manageable if you knew to keep on top of it, but excessive.

If you have "Experianced" Calibrated finges, can tell you if they are worn ...On a USED engine, obviously they will be.....But HOW worn ?...as a elbow guess...take a scrw driver and with some pressure try to move valem stem back and fouth in all direction...any precived movement mean (left or right, up or dwn) will indicate too far gone