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Project Addicted
Join Date: Jul 2012
Location: Eastern Shore. MD
Posts: 919
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Excess Carbon Buildup
I just received some heads for our 3.4 build and I'm surprised at some of the excessive carbon build on the combustion chambers. I have included pics below.
Here are the specs: 3.4 JE Pistons 10.5:1 compression Twin Spark Andial Splitter 20/21 cams Wong Chip These are 15K heads and the carbon is thick!      I'm loosening the carbon with a simple green soak and it really works!! Softens the carbon so it can be scraped from the chamber. The heads were fully rebuilt 15K ago by Ollie's but I guess there could be a bad valve stem seal. I have NOT run these parts but just bought them and beginning to clean them up.
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Jon 1966 912 1976 911 3.4 Backdate Project 1986 944 |
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01-26-2014, 05:07 PM
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Registered
Join Date: Oct 2013
Location: Prescott, AZ
Posts: 1,062
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It also could have been caused by worn rings or rings that we're never properly seated, so you may find that the valve guides are okay once you've got the heads cleaned up and apart.
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01-26-2014, 05:27 PM
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Straight shooter
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...or someone who thought they were treating the engine right by not driving it hard. Did a nun own it prior?
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“Of the value traps, the most widespread and pernicious is value rigidity. This is an inability to revalue what one sees because of commitment to previous values. In motorcycle maintenance, you MUST rediscover what you do as you go. Rigid values makes this impossible.” ― Robert M. Pirsig, Zen and the Art of Motorcycle Maintenance: An Inquiry Into Values |
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01-26-2014, 05:43 PM
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Registered
Join Date: Jul 2001
Location: Portland Oregon
Posts: 7,007
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If they were here, I'd take them apart for proper cleaning and measure the guide clearances as well as valve stem taper. Naturally, new Viton seals should be installed.
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Steve Weiner Rennsport Systems Portland Oregon (503) 244-0990 porsche@rennsportsystems.com www.rennsportsystems.com |
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01-26-2014, 10:45 PM
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Project Addicted
Join Date: Jul 2012
Location: Eastern Shore. MD
Posts: 919
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No, no Nuns were involved..to my knowledge. It does look like it was never heated up though. I don't know for sure. I will send the pictures to Steve Wong for his input as well, if he has any.
I will pull the vales out of #3 as it was the worst of the 6. I can measure the stems and looseness in the guide. With liquid in the chamber, there was zero leakage past the seats. I will post pics and more info later.
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Jon 1966 912 1976 911 3.4 Backdate Project 1986 944 Last edited by Jcslocum; 01-29-2014 at 03:15 PM.. |
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01-27-2014, 07:31 AM
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Project Addicted
Join Date: Jul 2012
Location: Eastern Shore. MD
Posts: 919
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We did un-spring the 2 heads with the worst buildup and found the guides to have zero detectable play in the movement range and very little as the valve was extended. The stems measured at .352 with no taper at all. We re-assembled and filled the chambers with lacquer thinner with zero leakage.
Here are some pics of my daughter doing the work as I watched/guided. I have 5 daughters and she is the one that got the motor head gene! A great garage buddy too.     I've had that spring compressor for 40 years and it's still coming in handy after sitting in it's drawer for the last 30 or so. A little mod to make it it in there nicely and she popped the retainers out. I think this will eliminate the heads as the root of the problems.
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Jon 1966 912 1976 911 3.4 Backdate Project 1986 944 |
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01-29-2014, 03:18 PM
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P911
