Advice on Smoking
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6th Gear
Joined: May 2012
Posts: 11
Likes: 0
From: Joshua, Texas
Advice on Smoking
I have never used this forum before, but I could certainly use some advice and I’m hoping this will generate some. My issue: My best friend passed and left me a 93 Fatboy that had been down and left outside for a long time. It has a lot of corrosion issues (cosmetic) but also mechanical and I had no idea what was wrong with it. I’m a decent shade tree mechanic, but never worked on motorcycles. First thing I did was buy the repair manual and checked the compression. Front cylinder good (90 psi) and back cylinder bad (0 psi); I decided to do a top-end on it. When I took the rear head off it was apparent that the head gasket was blown. I checked the flatness using the method in the repair manual (it was flat). Tore both front and rear cylinders down, replace rings, put a kit in the carburetor and reassembled (compression good both cylinders). Visually the valves looked good so I didn’t do a valve job. The bike would start a run good when first started, but after a few minutes the front cylinder started to blow smoke and oil out the exhaust. I assumed it was the valve guides, tore it back down and had a complete head job done both cylinders. Put it back together and same deal. Runs good with no smoke for 3-5 minutes when first running, but then smoke and small drops of oil blowing out the front cylinder exhaust. When I first got it it had oil all over the area where the front exhaust blows so I think the problem was there from the start. I believe I clocked the rings properly. I didn’t measure the I.D. of the cylinders, but I have good compression. Any thoughts as to what my issue might be?
Thread Starter
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6th Gear
Joined: May 2012
Posts: 11
Likes: 0
From: Joshua, Texas
No, didn't replace the pistons or bore. Yes, I did inspect and clean the ring grooves. I assumed the good compression was an indication that the cylinders and pistons were good. but I'm starting to think you are right (there is not much left it could be). The pistons in it now are .030 over already. Do you know how much over you can go. Thank you for taking the time to respond!
Dirt don't hurt
Joined: Jan 2011
Posts: 21,065
Likes: 4,561
From: Haslet Texas
I'm thinking it is the ring grooves in the piston. Your problem seems to start when everything starts heating up and expanding.
As for the pistons I don't know how much more you can bore it out but I do know you have to have it under torque plates to really check it or bore it.
As for the pistons I don't know how much more you can bore it out but I do know you have to have it under torque plates to really check it or bore it.
Road Captain
Joined: Jun 2012
Posts: 533
Likes: 2
From: Virginia
Did you hone the pistons? Did you set the end gap on the rings? REAL dumb question, but, worth verifying: Did you get the placement of the two control-rings and spacer on the oil ring assembly right?
Road Captain
Joined: Jun 2012
Posts: 533
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From: Virginia
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Seasoned HDF Member
Joined: Aug 2007
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From: NW AR
Quitting cold turkey is the best way to stop.
Oh, and what about an umbrella valve problem, if that bike has those? I don't recall when they started. Or would that cause other symptoms?
Oh, and what about an umbrella valve problem, if that bike has those? I don't recall when they started. Or would that cause other symptoms?
Last edited by Dr.Hess; Oct 12, 2012 at 01:16 PM.
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Elite HDF Member
Joined: Sep 2007
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From: Bluffton, South Carolina
The cylinders need to be deglazed (lightly hoened with a "Match stick or dingle ball hone) when new rings are put in. Are the rings in right side up??? Yes they can be put in upside down!!! Were the ring gaps staggered??? I am asuming the valve job was done correctly and the seals weren't damaged when the valves were installed. Hope this helps.
John
John