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Registered
Join Date: Aug 2001
Location: New York, NY, USA
Posts: 128
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Decarbonizing intake valves with carbs off?
After pulling the carbs on my '68 S for overhaul, I saw that the intake valves had big ugly carbon/junk buildups on their back (intake) faces. Does anybody have any idea about getting this stuff off while the carbs are off and I can reach in easily?
I saw another post (from Early S man) about using a direct application of lots of B-12 chemtool to dissolve chunks of carbon lodged in a stuck valve or piston, but am not sure if it is a good idea to wash this crap down into my combustion chamber and then risk having smaller bits jam in rings, etc. Any thoughts? David 1974 914 2.0 Track Tool 1982 911SC - 175k and going strong, never had heads off! 1968 911 S being reborn as vintage racer PS:The little bit of the combustion chamber that I could see showed few signs of carbon buildup, but I welcome any other ideas about general piston/valve/combustion chamber carbon removal. |
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12-11-2001, 01:05 PM
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Registered
Join Date: Dec 1999
Location: TX USA
Posts: 9,804
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David,
This will be a messy, smelly process, but ... and, charcoal-filter respirator mask recommended! You may want to try putting each cylinder at TDC firing point, one at a time ... and fill the intake port with B-12 or Techron, and let it sit overnight. Then with 10 cc syringe or siphon, draw remaining solvent out next day (into glass container) and use popsicle sticks to scrape out loose carbon residue, and paper towels to wipe out the port ... aided by dipping in the used solvent after the majority of softened carbon has been removed. After no additional carbon comes off when rubbed with B-12 soaked rag or paper towel, you can proceed to the next cylinder ...
__________________
Warren Hall, Jr. 1973 911S Targa ... 'Annie' 1968 340S Barracuda ... 'Rolling Thunder' Last edited by Early_S_Man; 12-11-2001 at 02:05 PM.. |
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12-11-2001, 01:57 PM
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Registered
Join Date: Aug 2000
Location: Deep in the bowels of UCLA hospital
Posts: 2,316
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tell me if I am wrong...but at TDC of one cyl...is another at TDC too????
I am just guessing here because although I have not done valve jobs (yet) the rotation is 120 degrees no??? or are they staggered so that at no time is more then one at TDC???? just thinking this may be a way to do two at a time... |
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12-11-2001, 02:06 PM
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Registered
Join Date: Dec 1999
Location: TX USA
Posts: 9,804
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There may be another intake valve or two closed, but it won't be at TDC ... because #4 is at TDC 'overlap' ... the cam timing 'lift' point when #1 is at firing point, and the #6-#3, and #2-#5 pairs are all mid-stroke, somewhere else ... but you could pop the intake valve covers and wiggle the rockers to see how many are loose.
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Warren Hall, Jr. 1973 911S Targa ... 'Annie' 1968 340S Barracuda ... 'Rolling Thunder' |
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12-11-2001, 02:15 PM
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Registered
Join Date: Jul 2000
Location: So. Calif.
Posts: 19,910
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"just thinking this may be a way to do two at a time..."
It takes two revolutions of the crank to fire all the cylinders. Thus each cylinder on the 911 fires 120 deg. apart. You could do it by the book by placing No. 1 cylinder at TDC, ready to fire (both valves closed), then adjust both intake and exhaust, then rotate the engine 120 deg. and adjust the in/ex. valves for the cylinder next on the firing order, etc., etc. You can also adjust the valve clearance on any valve as long as it is closed; i.e. the rocker arm is on the heel of the cam lobe; not on the opening or closing ramp. Since the camshaft rotates at 1/2 the speed of the crank, there are several places a valve remains closed. Sherwood Lee http://members.rennlist.org/911pcars |
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12-11-2001, 03:29 PM
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