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Old 06-07-2010, 12:16 PM   #1
Airhead Wrangler OP
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How effed am I? Or am I? (Airhead carbon cleaning)

I finally got back to Seattle on Thursday after 8 months on the road. After unpacking and getting settled in, I decided to replace my pushrod seals that have been pissing oil since mexico. I pulled the top end off and found some pretty impressive carbon buildup in the heads and on the piston tops. I hit it with WD and degreaser and let it sit in an attempt to loosen it up, but it was baked on like cement. A neighbor across the street who is a retired mechanic recommended using oven cleaner. Sure enough it worked really well, but discolored everything pretty seriously. Only AFTER I did all this did I go online and found all sorts of dire warnings against using oven cleaner to clean off carbon deposits as it attacks aluminum. Luckily I didn't let mine sit over night as the instructions tell you to do. They were only exposed for about an hour per piece while I was brushing out the carbon with a brass brush and were then rinsed well with water, dried and sprayed with WD. My question is: do (did) the pistons have some sort of antifriction coating on them that I have now removed and if so, how bad is the damage? I remembered seeing that the piston skirts appeared to be coated with something as it had visibly worn off on the tops and bottoms of the skirts.
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Old 06-07-2010, 02:14 PM   #2
Reposado1800
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You should be fine. Discoloration is normal. If you had let it sit all night, you would have been toast.
There have been cases of people hot tanking aluminum car heads, which is a caustic basic solution, and the next day hoist the chain and only find a chain left... no heads.
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Old 06-07-2010, 02:38 PM   #3
Bill Harris
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Shouldn't have hurt things after only an hour. Oven cleaner contains lye (sodium hydroxide) which can dissolve aluminum. In oven cleaner, it is in a low concentration and turns the baked-on grease into a water-soluble soap. If you look closely at the pistons, you can see tool marks left when they turned them on a lathe and they should still be there.
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Old 06-07-2010, 07:49 PM   #4
boxerboy81
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Soak in simple green will do the job.
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Old 06-07-2010, 10:03 PM   #5
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Old 06-07-2010, 11:04 PM   #6
Phreaky Phil
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Sounds like yours was like mine. Does it use oil ? Even after fitting new BMW valve guides which were right in the middle of spec it would suck oil down the guides and carbon things up to hell. After talking to Paul Rooney I fitted K liners with minimal clearance( 1 thou ) it now uses practically no oil and no carbon buildup.
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Old 06-08-2010, 03:05 PM   #7
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Quote:
Originally Posted by Phreaky Phil
Sounds like yours was like mine. Does it use oil ? Even after fitting new BMW valve guides which were right in the middle of spec it would suck oil down the guides and carbon things up to hell. After talking to Paul Rooney I fitted K liners with minimal clearance( 1 thou ) it now uses practically no oil and no carbon buildup.
It may also be due to 8 months of burning third world gas, much of it at VERY high altitude without any jetting changes. Also, my breather seems to be puking a lot of oil into my intakes. I checked the valve guides and the valves were nice and tight.
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Old 06-08-2010, 09:46 PM   #8
bgoodsoil
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my breather pukes a lot of oil into the airbox too. I think it's because of the 2 liter sump on the G/S. Some folks recommend a deeper sump, a deeper pickup, and the same amount of oil.
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Old 06-08-2010, 11:02 PM   #9
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Quote:
Originally Posted by bgoodsoil
my breather pukes a lot of oil into the airbox too. I think it's because of the 2 liter sump on the G/S. Some folks recommend a deeper sump, a deeper pickup, and the same amount of oil.
I have a deeper sump and pickup off of a '92 GSPD along with the dipstick with deeper level marks. Still pukin.
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R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 06-09-2010, 05:28 AM   #10
robsmoto
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Oak has long recommended the Hydro-Seal II shown above. Based on his recommendation I purchased a bucket (with soaking basket) of this stuff. I've decarboned the pistons and heads on several airheads using the Hydro-Seal.

It does work quite well without damaging the pistons and heads. Pistons are removed from the conrods and rings are removed from the pistons (note location and orientation of rings BEFORE removal!) I found that complete carbon removal requires several days of soaking. About once per day I remove the part from the soak basket and use an old toothbrush to remove the softened carbon. The part is then returned to the soak basket.

For the heads I remove the valves. Several days of soaking work best with intermitant cleaning with a toothbrush. I've also tried using a soda blaster to clean up the heads after soaking - the heads are washed with soap and water after soda blasting. The soda blasting can remove the baked-on spooge from the otherwise inaccessible areas between the fins. I use compressed air to blow out the water from the washing, then use a spray of my WD-40/Marvel Mystery Oil solution (90% WD / 10% MMO) to coat the parts if re-installation is going to be delayed for a bit. The parts are then placed in an appropriately sized zip-lock freezer bag.

On the airlist many folks claim to have had good success using Simple Green. I do use a mix of Simple Green and water (10% SG / 90% H2O) for cleaning the exterior of the bike - followed by a thorough wash and dry. I've not tried to use Simple Green for decarboning aluminum parts.
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