Carrera valve guide advice

[Nathan M]

After a rolling road session at the back end of last year my Carrera started smoking (immediately!!). At the time panic set in but a few people thought things might improve after an oil change to thicker oil (was running v.thin Mobil 1). Well, things haven't and if anything have got worse. I've had a compression test done and all the cylinders gave good results with less than 3% between the best and worse cylinders. As the car smokes after over-run (when the throttle is re-opened) I guess it's from the guides.

I therefore have a few questions:
1. Could one of the valve stem oil seals have dislodged (may be wishful thinking but it did happen very soon - prior to this the exhaust was always clean and never used any oil)

2. If this is the case will it be visible with the valve covers off (I've not had them off yet but I would guess so?)

3. Can the valve stem seals be replaced with the engine in the car?

4. Is it easy to determine the amount of guide wear with the covers off and the engine in the car?

And finally, what actually constitutes a "top end rebuild" other than changing the guides and possibly replacing the valves/recutting the seats?

Thanks for any advice,

Nathan

[cowtown]

I've had a compression test done and all the cylinders gave good results with less than 3% between the best and worse cylinders. As the car smokes after over-run (when the throttle is re-opened) I guess it's from the guides.

I don't think a compression test will show guide condition, because the valves are closed when pressure is built up.

3. Can the valve stem seals be replaced with the engine in the car?

I haven't done it, but I have just rebuilt an engine out of the car and I'd say you probably could. You would have to
-pull the rocker arm
-keep compressed air going into the cylinder through the sparkplug hole to keep tension on the valve surface
-compress the valve spring, remove the keeper
-remove the retainer (or whatever it's called - the spring base rides on it)
-remove the spring
-remove the seal
-don't let any shims fall off
-reverse

Maybe someone has actually done this. I do know firsthand of replacing the valve springs in the car, and I think this would just be a bit more work.

Having said this, it's a longshot that it's just the seal. The guides are usually the culprits.

4. Is it easy to determine the amount of guide wear with the covers off and the engine in the car?

Yes, you can pull the covers and measure side-to-side play of the valve stem within the guide (see Chris' post below for details). An experienced eye can tell by using a screwdriver on the stem.


And finally, what actually constitutes a "top end rebuild" other than changing the guides and possibly replacing the valves/recutting the seats?


Depends. Could be just guides, or...
+head studs (you have 12 of the dilivars)
+cams
+rocker condition/seals
+valves/seats
+rings
+pistons/cylinders

It all depends on the shape the engine is in. Many don't recommend getting the top-end super repaired because it will overstress a tired bottom end. FWIW, I had the guides and nothing more done on my '88 when I bought it at 93K six years ago. Back then I did not know what I was doing, and just trusted the mechanic (Ken Mack). I must say, he was right...I've got 160K now, and it's just starting to show signs of needing work.

Hope this is of some help. You get a bump out of it, at least!

[Gunter]

Nathan: What is the milage? Replacing the valve stem seals only with the engine in would be such a horrible job with you ending up hating your car and it may not solve your problem. The problem is access in the confined engine compartment. Are you running 20W50 in the warmer months? What is your average consumption? (Of oil, not beer)

[ChrisBennet]

Originally posted by Nathan M

4. Is it easy to determine the amount of guide wear with the covers off and the engine in the car?
Nathan

The valve must be lifted off the seat by 10mm (I think) and then the valve stem is pressed sideways with a screwdriver. I forget what the spec is.
Pull your plugs and see if just one is wet with oil if you think it is just one valve seal.
-Chris

[Nathan M]

Thanks guys. I've had all the spark plugs out and they're all clean. The car's done 112000kms (70000 miles) but I've not got much service history to verify this. I'm now running 15-40 oil and planned on doing year round. I probably only do around 2000 miles per year. In terms of oil useage I've not done enough miles since the smoke started to get a good idea. Prior to that it probably used around 1 litre every 1500 miles or so. I'm lucky enough to work for the company which manufactures valves & guides, so hopefully this will lessen the financial blow if I have to have a rebuild done.

[cowtown]

Originally posted by ChrisBennet
The valve must be lifted off the seat by 10mm (I think) and then the valve stem is pressed sideways with a screwdriver. I forget what the spec is.
Pull your plugs and see if just one is wet with oil if you think it is just one valve seal.
-Chris

Oops, thanks for that Chris. I'll edit my post.
Colin

[john walker's workshop]

the guide generally wears most at the end toward the valve head, (taper), as do the valve stems, so moving the spring end of the valve to check guide wear is not going to give you the whole picture. carreras also wear the intake stems very badly.

[Steve W]

Are you sure the smoke is not a result of the car running rich instead of oil burning? I've seen it happen before exactly on overrun as you describe. Black smoke usually equals rich, blue smoke means burning oil.

[stlrj]

Steve,

I don't think it is possible for a Carrera to belch fuel rich smoke on overrun since the DME shuts off the fuel on overrun.

Another thing to consider is the possibility that oil may be getting past the rings with the high manifold vacuum on overrun. This might be a possibility if the rings were never seated properly in the first place or if the engine had been run too rich too long.


Regs,

Joe

[Nathan M]

The smoke's definately blue and oily. The fuel mixture is correct (if anything a little on the lean side going from what the dyno guy said). If oil was getting past the rings wouldn't it smoke when the engine was under load/accelerating hard? I would also have guessed the compression test to have shown something if the rings were not sealing well (?)

Thanks
Nathan

[Oldporsche]

I might try a leak-down test in conjunction with your compression test. It might help with your diagnosis.

Good luck,
David Duffield

[stlrj]

Nathan,

Here's some info that was posted some time ago that might explain the ring seating issue better than I could: http://www.mototuneusa.com/break_in_secrets.htm

Cheers,

Joe

[930fan]

What was the dyno test result?

[Nathan M]

The car's fine on power (well, could always be better!). Dyno showed 185 rwhp. It's still performing well in spite of the smoke. It's now really beginning to annoy me as every time I have the heater on and the car's stood still I get a horrible oil burning smell in the cabin.


Nathan

[Thomas Owen]

Remember, if the exhaust guides are worn, oil can enter the exhaust system without ever entering the combustion chamber. Result, dry plugs and smoke at startup. Have rebuilt several 3.2's with just these symptoms.
Good luck,

[Nathan M]

Thanks Thomas. The strange thing is is doesn't particularly smoke much on start up. When the engine's hot it sometimes does it whilst idling but the biggest plumes of smoke come when the throttle is re-opened after coasting down a hill (there's lots of them where I live)

Good thread. I like the info in it.

It got me thinking. If the car didn't smoke/was all perfect before the rolling road run would the problems have come anyway the next time the car was driven hard on the street? OR is a rolling road test harder on the car than driving on the street?

[dickster]

sounds like valves/guides. i would definitely start with a leakdown - that should give a good indication.

maybe as it was sudden you have damaged seals rather than worn guides etc. or perhaps the session just pushed hard enough to cause the smoke to start.

i wouldn't think rolling roads were harder on the car than on "real" roads - other than air flow. you need a large cooling fan. it does make a hell of a howl when they power it up though.....

[ChrisBennet]

Originally posted by dickster
sounds like valves/guides. i would definitely start with a leakdown - that should give a good indication.

I agree with dickster, it sounds like valve guides. I leakdown will tell you if the rings are the culprit (but it won't tell you anything about the valve guides).
-Chris

[kepperly]

Have you checked the oil level, I think if you had slightly overfilled it and went for a spirited drive after topping off the oil tank. The level
might have gotten to the point were it was pulled into the air
cleaner. Check the inside of the intake port and if your air cleaner element for it being oil soaked. Its a cheap fix anyway and a good
reminder to never fill over 1/2 way up on the dip stick when warm.
Also the new concense is to use kendal 20w50 dino oil in 89 and older 911's as per ba and the rest of the PCA Tech committe.


Keith