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Question Posted By: CrazieHorse on 4-19-2010
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| Make of Bike: |
Harley |
| Model of Bike |
custom |
| Year of Bike |
76 |
| Engine Size |
86ci |
| Other info on Bike |
motor has s&s 86 stroker kit
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| What's your question? |
I blew the front piston and replaced both new. With the top ring in jug without the piston in, what should the gap be? I have .018. I honed both jugs
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| Details: |
I'm rebuilding the motor from bottom up. It's a custom 76 FXE 1200cc stroked to 86ci with s&s stroker kit, 4&5/8 stroke. Jugs are 3&7/16 + .030. Will the .018 gap work or do I need to shave the jugs ? |
Answers:
- You must have really put the hone to 'em. The ring gap for your engine starts out at .010 with a maximum of .020. I'd also assume that since you've honed your cylinders for the fresh pistons you no longer have a .001 to .002 piston skirt-to-cylinder wall clearance. I suggest you try and get an exchange for your .030-over pistons to .040-over pistons, bore & plateau hone your cylinders to the new .040-over pistons so that you have a .001 to .002 piston-to-cylinder wall clearance...then gap your rings to .010.
You might also call S&S and ask them if the weight of the .040-over pistons and rings will throw their stroked wheels out of balance. By: 47Knuckle-Dragger on: 4-19-2010
- Thanks 47Knuckle for the input, but I made a mistake in my question, the piston to cyclinder is within range. I was looking for expansion clearance on the rings. My Stupidity... By: CrazieHorse on: 4-20-2010
- Specifications for piston-to-wall clearances and ring gap clearances have a two-fold purpose. I'll skip the piston-to-wall clearances for post length, but on the ring gap clearance here's a quick synopsis.
Minimum clearances are there for temperature purposes. Let's say a guy lives in Texas and he's building his engine in a garage that's 100+ during the daytime. He gets his barrels bored and plateau honed by a guy that knows exactly what he's doing. Let's say the guy sets the ring gap to exactly .010. The break-in results in a final cold-engine ring gap of .012. Then the guy moves to North Dakota. Yeah, I know, why would a Texan ever fucking move to North Dakota. This is hypothetical. Let's say it's now wintertime, it's 20 degrees outside the bar at midnight. That ring gap that used to be .012 at noontime, in Texas, when the engine was cold, is now .005. Had he set the ring gap at a cold engine gap of .005 in Texas, the rings would now be bound together and the engine would be impossible to turn over. The same applies to the upper end of the ring gap specifications. You set your ring gap at .018 in a cold April...the rings wear in and settle at let's say .020, when late July comes around and you're grabbin' a hand full...it'll smoke like a '71 Pinto. By: 47Knuckle-Dragger on: 4-20-2010
- How much did you hone out of your cylinders and with what type hone? Have you checked your cylinders for taper and out of round? By: espuela on: 4-20-2010
- Thanks 47Knuckle, I'm glad someone here speaks my langue, got your point...
And I honed with 240 grit/6thrust @ ~2500-2800rpm one way and same thing the reverse. Mic'd was same all the way through... By: CrazieHorse on: 4-20-2010
- "Language" damnit By: CrazieHorse on: 4-20-2010
Reads: 1226
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