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Reseal for sure, Top end machine work? K27Turbo rebuild?

I hope everyone is enjoying their holidays.

I was going to wait until next winter for this project, but the car is leaking and consuming quite a bit of oil now (1qt per 3-400 miles). The oil leaks was my initial concern as they were plentiful, and of course the consumption was getting bad too.

At the end of the season, I noticed that the car was smoking but only at higher rpm's (above 4K) at WOT under full boost. It doesn't smoke otherwise, except for awhile at startup. I should also note that anything over .7 bar gives me a little detonation (my AFR's are descent).

My thoughts for this winter as a project were to

1) reseal the engine so I can rid it of all the oil leaks (for the first couple of months next season at least..).

2) But since I'm tearing it down to the short block, should I consider sending the heads out to get inspected/reconditioned (keeping in mind it was consuming oil)?

2) The turbo rebuild is another issue I think I need to address. When I removed it, it was full of oil at the top/inlet side of the oil line, and nothing on the exit side of the oil line. Could it be that there is some debris in the bearing journal, or oil passage?

I'm trying VERY hard to not do any further upgrades 'while I'm in there', SC cams are certainly bang for the buck.. but I just spent 2K on transmission parts, so I'm trying to keep the upgrades off the list. I also thought to inspect the rings/cylinders, however, have no intention of replacing as all is running great. I don't have any leak down numbers, but the compression numbers were all between 130-140PSI (on a warm engine).

I'm looking for some input and thoughts on the head machining and turbo/smoke issue under boost.
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1987 930
1956 Chevy 3100
2009 Subaru Forester
2003 KX250 X2(I like my toys!!)

Last edited by mark '87 930; 12-29-2009 at 06:16 AM..
Old 12-29-2009, 06:14 AM
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beancounter
 
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How many miles are on the engine? If the heads have never been touched, chances are they will need attention. I think at a minimum, a proper top-end job will include new valve guides and probably new piston rings. Once its apart, you may find other things that require attention.

From what I have read, when the Turbo blows its seals, you know it because the car puts out a ton of smoke. Yours may be fine. Check for any play in the turbine shaft...you can measure with a dial indicator. There are specs in the factory service manual. If it checks out ok, run it. You can always decide later to have it rebuilt.
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Old 12-29-2009, 06:36 AM
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Sorry, the car currently has 113K miles on it. It is 100% street, and if it was tracked in the past, it would have been a long time ago. I put about 4-7K miles on her every year and do not not of any rebuilds but I only have the service history from 77K miles onwards. To be honest, the heads look to be in good shape and the cam lobs are very nice. There is no visible wear on anything including the cam chain sprockets. I have not inspected the cylinders and pistons to a large degree yet, but I do know that the cross hatch was not immediately visible. The turbo itself I'd have to check the play with a dial gauge, but it was tight (no movement) when I checked it by hand.

I'll be taking the heads off the cam tower today as well as removing and inspecting pistons.

Again, the car ran very smooth, with the exception of the smoking and consuming of oil.

Money is a bit of an issue right now which is why I don't want to tear into the bottom end, but also replace anything out of spec on the top side.
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1987 930
1956 Chevy 3100
2009 Subaru Forester
2003 KX250 X2(I like my toys!!)
Old 12-29-2009, 08:17 AM
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Exhaust valve guides and valve stems wear out faster in a 930 engine than any other production engine I've seen or experienced.
They are usually somewhat worn beyond spec in 30,000 miles from new and just keep getting worse.

It's because of extreme intense localized heat in the cylinder head of a turbocharged air cooled engine and because the exhaust valve and guide is downstream from the intake valve in the cooling air and upside down at an angle and has a tight fitting valve seal so very little oil ever migrates up the valve stem against gravity and the tight fitting valve stem seal while the engine is running and lubricates it and the valve guide.

Hate to say it but that part of the 911 engine design really sucks in my opinion.

Some 935 exhaust valve guides had little cooling fins at the top to increase surface area to help cool them as oil splashed onto them.... maybe they all should.

If you have oil in the turbo compressor housing, charge pipe, and intercooler the turbo seals are probably worn and leaking to some degree. Make sure the air filter is clean. If there's also oil in the turbine housing or hot side than it definately needs to be rebuilt.

If oil is in the air cleaner housing and all over the CIS air flow sensor plate the piston rings are probably worn and letting some exhaust gasses blowby into the case pressurizing it a small amount.
Then the blowby gasses and oil mist goes to the oil tank through the breather hose where it eventually gets routed back to the air cleaner housing.

You need to do a leakdown test with leakdown gauges, and then your ears and a hose in the right places while filling the cylinders with around 100psi air pressure to diagnose the condition of the rings and valves at TDC.
Old 12-29-2009, 10:12 AM
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unfortunately a leak down test is no longer an option as it's in short block status right now. I only checked #4 compression ring end gap (first one only) and I'm not even close to the service limit. I'll check the others, but I presume (read hope) they'll all be within spec.

I was thinking of sending out the heads regardless as my oil consumption was always a little higher than I would have liked.

As for the turbo/oil issue. compression housing I haven't inspected much yet, but looked to be fairly dry. Ironically, the turbo itself was one of the leaks I had. I checked the upper oil inlet pipe and it was dry, the oil leak seemed to be coming from the compressor housing. I know there is a large o ring there, but like you said, I would see oil inside the housing for that. Turbo only seemed to leak a drop or so when I drove the car hard. It's not an old turbo either, it has only 10-15K miles on it.

Thanks for all the input thus far. I'm a virgin when it comes to Porsche engines, but I'm not new to engines at all.
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1987 930
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Old 12-29-2009, 11:23 AM
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If the motor has never been apart in 133,000 miles the exhaust guides are definately worn out and probably the exhaust valve stems too so they will likely needd to be repalced.
The intake valves run much cooler and may be OK, but the intake guides will be somewhat worn at that milage so they should be replaced along with the exhaust guides.
Stock valve springs are usually replaced while your at it, with that much milage but if it's driven on the street only without redlining it daily they may be ok to reuse if money restricts that.

Even if the ring gap is within spec the ring lands in the pistons wear getting bigger and oil and combustion pressure gets by.
The cylinders wear from round into a very slight oval shape at the scuff areas 90 degrees to the wristpin and taper from top to bottom gradually as they are used.

A good machine shop experienced with 911 motors can check all that stuff out.
Old 12-29-2009, 11:47 AM
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Quote:
Some 935 exhaust valve guides had little cooling fins at the top to increase surface area to help cool them as oil splashed onto them.... maybe they all should.
Here is a photo of the 935 exhaust valve oiling modification machining to the cylinder head to get more oil to the guide.

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Old 12-29-2009, 11:54 AM
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cool, that can't be too expensive to ask for...
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1987 930
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Old 12-29-2009, 12:11 PM
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Quote:
Originally Posted by Flieger View Post
Here is a photo of the 935 exhaust valve oiling modification machining to the cylinder head to get more oil to the guide.
Where did you get this fantastic photo!? I have been looking all over for a pic of this. Do you have any of the guide itself? This forum continues to amaze me.
Old 12-29-2009, 01:22 PM
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Sorry, no photo of the guide itself. I stole it off this forum some time ago, possibly from the engine forum. I think it may have been from DonE or one of those guys. It is also in Bruce Anderson's Porsche 911 Performance Handbook.
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http://www.flickr.com/photos/max_911_fahrer/
Old 12-29-2009, 03:01 PM
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finned valve guide

Old 12-29-2009, 03:15 PM
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Cool
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1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 12-29-2009, 03:27 PM
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Is there no gasket between the heads and the cylinders? It seems like the two fit into each other via the metal lip/indentation? My no.1 cylinder was leaking pretty bad at the head.. no gasket on any of them though.

I'm going to measure the cylinders for ovality tomorrow. Also measure the pistons. the ring wear limit is .8, I'm at .6.
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Old 12-29-2009, 03:47 PM
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No gasket, just the "CE" ring in the cylinder deck groove.

Edit: you later model engine has no "CE" ring. 3.2 Carrera engines began using a conical shape to the sealing flange on the cylinder head to take the place of the ring. This allowed a narrower cylinder sealing area as the bores increased and the "CE" ring groove would crack under the pressure of combustion. This sealing area should be in good shape to prevent leaks, if you had any broken head studs allowing the heads to slap, you may need some machine work.
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Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/

Last edited by Flieger; 12-29-2009 at 04:00 PM..
Old 12-29-2009, 03:50 PM
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Quote:
Originally Posted by Flieger View Post
Here is a photo of the 935 exhaust valve oiling modification machining to the cylinder head to get more oil to the guide.

I have seen this before.

So what exactly is happening here. Is oil being pulled off the cam tower and dripped over the exhaust valve stem area to pull heat off it?

If so, there much be a hole of a specific size drilled in the cam tower to maybe a cam bearing journal or supply. Any one know?
Old 12-29-2009, 04:05 PM
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Mark,

While there is an excellent chance that your valve guides will have to be replaced, there is also an excellent chance that your pistons and cylinders will be within specification, which could save a lot of cash. Be careful not to nick anything during disassembly. Check the cylinders for scratches, diameter and taper. If they are OK, I would certainly consider re-using them.

For sure you will need new rod bolts, and then there is the head studs. Do you have the original Dilivar ones?
Old 12-29-2009, 05:44 PM
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Quote:
While there is an excellent chance that your valve guides will have to be replaced, there is also an excellent chance that your pistons and cylinders will be within specification, which could save a lot of cash. Be careful not to nick anything during disassembly. Check the cylinders for scratches, diameter and taper. If they are OK, I would certainly consider re-using them.

For sure you will need new rod bolts, and then there is the head studs. Do you have the original Dilivar ones?
I was going to reuse all of the old stuff. How can I tell what they are? They're black, and none are broken. I was considering replacing the rings since they are so inexpensive.

You can tell on this one that no.1 was leaking pretty bad from the head.

(don't mind the lack of a yoke and engine stand.. those are on order)
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1987 930
1956 Chevy 3100
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Old 12-29-2009, 06:38 PM
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Quote:
Originally Posted by mark '87 930 View Post
I was going to reuse all of the old stuff. How can I tell what they are? They're black, and none are broken. I was considering replacing the rings since they are so inexpensive.
IIRC, Dilvars will be non magnetic while steel studs will attract a magnet.

I've got the cylinders that were take offs from my engine, if yours don't check out, perhaps mine will and I can help you out.
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Old 12-29-2009, 06:49 PM
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If they are black studs, they may be the 993 improved Dilavar studs. These are the only Dilavars that should be used, otherwise use the (much cheaper) steel.

911st, I believe the 935 oiling mod just makes use of an area of the head that receives splash lubrication from the cam tower spray bar. I think it is specially positioned to be in a chamber where oil is present.
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1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 12-29-2009, 06:57 PM
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Ignore the notes on this photo. You can see the oil groove is within the oiled area of the cam tower/valve cover.
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1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 12-29-2009, 07:00 PM
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