Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Technical BBS > 1- Porsche Technical Forums > 911 Engine Rebuilding Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Herb_911_76's Avatar
 
Join Date: Apr 2010
Location: Ohio
Posts: 10
Valve guide replacement

Hi, I dropped my heat exchangers to find a source for warm up smoke. It appears I might have a bade exhaust valve guide on cylinder 2. Oil/soot is building up in the exhaust port and appears to accumulate in the heat exchanger. This is what probably causes severe warm up smoke. After a while it seems to stop instantaneously and no then there is no visible smoke during accel or decal. I have not removed the spring to see if the stem is loose in the guide, as it is too cold to work on it. But I am trying to prepare myself for work in the spring. A couple of questions: Can the valve guide be replace without dropping the engine? Can anybody talk me through the steps? I guess if I position the piston all the way out, I shouldn't have be concerned with the valve falling in (falling up?). Any help would be appreciated. Note that all other exhaust ports look normal.
Old 12-30-2017, 03:09 PM
  Pelican Parts Technical Article Directory    Reply With Quote #1 (permalink)
Under the radar
 
Trackrash's Avatar
 
Join Date: May 2007
Location: Sebastopol, The Republic of California. Land of wine and redwoods.
Posts: 4,494
Garage
No way to change an exhaust guide with out removing the head.

Have you considered it could be rings? A leak down test could give you an idea of any trouble or how worn the motor is.

What you might want to try is to remove the valve spring and get a good idea of how bad the guide is. If you are lucky, very lucky, and the guide is within the wear limit, you could replace the valve stem seal and be good to go.

The reality is if one of your valve guides is very worn, you should consider a top end rebuild or at least a vavle job. Otherwise you may have a ticking time bomb.

What year car and what history on the motor?
__________________
Gordon
_____________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
<< See my Garage

Last edited by Trackrash; 12-30-2017 at 06:17 PM..
Old 12-30-2017, 06:14 PM
  Pelican Parts Technical Article Directory    Reply With Quote #2 (permalink)
Registered User
 
Herb_911_76's Avatar
 
Join Date: Apr 2010
Location: Ohio
Posts: 10
Thanks Gordon, it's a 76 Targa with a 2.7, German import. Was rebuilt including rings by previous owner mid 90's with all right bits as far as I can tell. I don't think there is more than 30k on the rebuild. I think that after shutting the engine off, oil drips into heat exchanger that burns off during next warm up. I will remove the spring and check for wobble, then go on to leak down. Any other idea why this port could be so filthy (soot and oil)?
Old 12-31-2017, 04:57 AM
  Pelican Parts Technical Article Directory    Reply With Quote #3 (permalink)
Under the radar
 
Trackrash's Avatar
 
Join Date: May 2007
Location: Sebastopol, The Republic of California. Land of wine and redwoods.
Posts: 4,494
Garage
Well at this point we are just guessing.

Is the motor using any oil?

Also, the mag motors are known to pull head studs. You should confirm that during the rebuild that case savers, or inserts were used.

But the first thing I would do is a leakdown test.

You can also get a good idea of valve guide wear by listening to the valves when running. If that valve is clacking louder than the rest, that could be a clue.

You can also pull the valve cover and use a screwdriver to gently try to move the top of the valve spring and retainer up and down. If the guide is very worn it will move easily. Compare that valve to one of the intake valves.

If you are getting smoke on start up out the exhaust, I would suspect rings.

If you are getting a drip on the top of the exhaust, that could be a leak from a number of sources.
__________________
Gordon
_____________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
<< See my Garage
Old 12-31-2017, 10:58 AM
  Pelican Parts Technical Article Directory    Reply With Quote #4 (permalink)
Registered User
 
Herb_911_76's Avatar
 
Join Date: Apr 2010
Location: Ohio
Posts: 10
I can't really tell if its using an undue amount of oil. I am also dealing with a cracked air box, so I didn't really get to drive enough lately. I am coming to grips that I have to drop the engine, so I will reassemble CIS at that time.
I never heard any undue valve noise or other suspicious noises, but I don't have a lot to compare to. Thanks for the tip on moving spring and retainer. Will try that on the other side of this arctic blast. I pulled the documentation for the rebuild that was done in 1992: only one heli-coil was installed; piston/cyl set Nr. 911-103-949-01 was used, but head studs are conspicuously absent from the invoice, unless they are part of the kit (nuts and washers are listed on the invoice, which tells me the studs are probably not part of the set and werte not replaced!) So I guess a pulled stud is a real possibility. Ugh, this might be turning into a bigger job than I need to be.

Thanks again!
Old 12-31-2017, 01:18 PM
  Pelican Parts Technical Article Directory    Reply With Quote #5 (permalink)
Under the radar
 
Trackrash's Avatar
 
Join Date: May 2007
Location: Sebastopol, The Republic of California. Land of wine and redwoods.
Posts: 4,494
Garage
Interesting that the #911-103-949-01 is for a single piston and cylinder set?
__________________
Gordon
_____________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
<< See my Garage
Old 12-31-2017, 03:20 PM
  Pelican Parts Technical Article Directory    Reply With Quote #6 (permalink)
 
Now Available for Ordering:   101 Projects For Your BMW 3 Series 1982-2000  [more info]
Registered User
 
Walt Fricke's Avatar
 
Join Date: May 2004
Location: Boulder, Colorado
Posts: 4,947
Leakdown and compression are the valuable tools for general engine condition. Torquing the head nuts (which you can do any time the valve covers are off) will quickly tell you if there is a stud pulling problem, though often this is announced more dramatically because you find a loose barrel nut rattling around, sometimes with a stub of stud still threaded in. In general, some advice I once received from a shop for my 2.7 was if the heads held torque, don't worry. With regular maintenance you should catch a broken or loose stud soon enough before something really disastrous happens. You can drive for quite a while with a broken stud with no significant extra damage. It isn't a good thing, but it is not like the engine will blow up one mile later.

Smoke on start up, however, is fairly common, and the longer the car sat the more it can happen on an otherwise good engine. There are a variety of theories as to where this oil came from, but as you probably know, after you shut the engine off oil starts migrating from the tank to the sump - think of how much comes out of the sump when changing the oil.

There are tools (one intake, one exhaust) which allow you to change valve springs - or seals - with the engine in the car. Not super easy, but can be done.

The 3.2s had a bad reputation for oil consumption, which I think I recall was thought to be due to over rapid wear of the valve guides. Porsche's spec was something like one quart per 600 miles, which most thought was way too much oil consumption. The usual diagnostic for valve guide wear is oil consumption, which is not the same as smoking on cold startup or dripping, though both can contribute. I suggest you adjust your valves - or just check the lash - and put a torque wrench on each barrel nut to see if you have a head stud issue. If not, watch oil consumption.

If you decide to remove the valve spring to check the guide, or just the retainer, I suggest you use the string method to keep the valve from moving: with the piston below TDC, feed string into the cylinder through the spark plug hole. Then rotate the piston to TDC firing, compressing the string against the valve head. You can also use air pressure with a fitting to go in the plug hole, but the string method seems simpler and more positive, especially when it comes to the task of putting the retainer back on and getting the keepers properly settled.
Old 12-31-2017, 06:13 PM
  Pelican Parts Technical Article Directory    Reply With Quote #7 (permalink)
Registered User
 
Herb_911_76's Avatar
 
Join Date: Apr 2010
Location: Ohio
Posts: 10
Gordon: Sorry if I wasn't clear, #911-103-949-01 contains six sets, but only one head stud was heli-coiled during the complete rebuild in 1992 (bearings and all).

Walt: Thanks for your input. I have heard anecdotally about oil seeping back down into the engine, although I can't say that I fully understand what actually happens. The oil tank sits higher than the engine with only the oil pump preventing oil from flooding the sump. If the oil pump lets oil pass down through and into the sump it would fill first, then the oil return tubes would get flooded and eventually the cam housings. This doesn't sound right to me, but maybe that's exactly what is happening with my engine. If the valve stem seal/valve guide allows for oil to pass through, it will end up inside the exhaust. In that case the oil tank should be near empty after the car sits for while. I should have checked that before I drained the oil...

The trouble with that theory is that smoke comes billowing out immediately after a cold start up and not just after the exhaust gets hot enough for the oil laying in the heat exchanger to start smoking. Maybe the cam housing is full of oil and the valve stem acts as a dipping rod and "pumps" oil into the exhaust port until the oil pump returns all the oil to the tank. That shouldn't take 10 minutes, though. Sorry for rambling on, anyways I don't understand the whole oil seeping back phenomenon.

Appreciate the tipp on the "string theory" - I had not heard of that before.

On oil consumption: I don't drive enough to be concerned about "consumption". As long as there is no visible smoke or smell, I will be happy. But the warm up smoke after it sits for a few weeks is extrem, a real smoke machine and beyond embarrassing that goes on for about 10 minutes after which is suddenly subsides.

Thanks again!
Old 01-01-2018, 06:56 AM
  Pelican Parts Technical Article Directory    Reply With Quote #8 (permalink)
Registered User
 
Josh D's Avatar
 
Join Date: Apr 2011
Location: Gilbert, AZ
Posts: 1,536
Garage
What Walt was saying about oil consumption is that it is another tool used to diagnose the condition of the engine. So you should be concerned with high oil consumption even if it doesn’t bother you.
__________________
'80 RoW 911 SC non-sunroof coupe in Guards Red
It's not a Carrera.... It's a Super Carrera!
Old 01-01-2018, 12:19 PM
  Pelican Parts Technical Article Directory    Reply With Quote #9 (permalink)
Under the radar
 
Trackrash's Avatar
 
Join Date: May 2007
Location: Sebastopol, The Republic of California. Land of wine and redwoods.
Posts: 4,494
Garage
My old motor would OCCASIONALLY blow a cloud of smoke on start-up. More often when I had parked on a hill. My oil consumption was less than a quart per 1000 miles.

My theory is that the oil rings can migrate so the gap is at the bottom of the cylinder. Under certain conditions oil will then seep into the combustion chamber.

I once disassembled a T1 VW motor, I had built, that was smoking on startup. I thought I had a broken ring. Turned out that one cylinder had the oil ring gab at the bottom. (I am certain that I didn't assemble it that way). YMMV
__________________
Gordon
_____________________________________
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
<< See my Garage
Old 01-01-2018, 04:18 PM
  Pelican Parts Technical Article Directory    Reply With Quote #10 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 02:01 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2017 Pelican Parts LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.