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Boring out cylinders: Questions, comments, concerns

Old 08-12-2011, 10:57 AM
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Boring out cylinders: Questions, comments, concerns

OK, so the new rings came in so I went to hone the cylinders out. Turn out they are marred up. I'm surprised I did not see that before. Well I tried to hone best I could, but still the scar remains in the rear cylinder. Which would explain the little-bit low compression. Here's what I need to know:

1. Boring out the cylinder. Who's done it, any advice would be greatly appreciated.
2. What size do you suggest I go up? The cylinder is just slightly scarred, so that's not an issue. I'm kinda thinking to go ***** out, but don't know for sure.
3. What jet size do I need to go up to?
4. Holy ****, this bike is getting really expensive. Looks like 200 bucks wasn't the bargain I thought it was. Damn!
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Old 08-12-2011, 11:45 AM
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might be easier to source another rear cylinder head???

Personally, I think a 1200 Superhawk would be really cool!
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Old 08-12-2011, 11:47 AM
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Originally Posted by Old Yeller View Post
might be easier to source another rear cylinder head???

Personally, I think a 1200 Superhawk would be really cool!
The cylinders don't split.
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Old 08-12-2011, 11:51 AM
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Superchickenmoster, did you ever get the PM I sent? Was interested in those fairings if they were available?
Thanks
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Old 08-12-2011, 12:20 PM
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And just to make you aware you have to order 4 pistons from je if you want oversize
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Old 08-12-2011, 12:57 PM
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Can you re-sleeve the cylinders?
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Old 08-13-2011, 07:02 AM
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Originally Posted by Hawk98MD View Post
Superchickenmoster, did you ever get the PM I sent? Was interested in those fairings if they were available?
Thanks
Hey, bud. Yes, I got the PM. The distribution of my free parts is dependent on weather or not I can get this bike running. I'll let you know.
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Old 08-13-2011, 07:06 AM
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OK, here's an update. I checked the depth of the mar in the cylinder. It's extremely shallow. So, about 30 minutes of honing took the scar out. Or rather, I removed enough material from the cylinder. I put the new rings on and got the engine back together. Without starting the bike, I checked the compression. 145 in the front and 150 in the rear. I know the book says 164, but this is with new rings that are not set in to the cylinders, on a cold engine. I think I may have fixed the issue. I should have the bike up and running before the end of the day, I'll let you all know.
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Old 08-15-2011, 05:11 PM
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I've bored my engine. Take it to a good race-car engine builder and they should fix you up. Be prepared to take the bore dimension and tolerance with you - they won't "figure it out" for you.

Good luck!
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Old 08-15-2011, 06:24 PM
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Pistons are going to be very loose in the bores. Piston to cyl. wall clearances are going to be off, and I am willing to bet that the bore is probably tapered now.
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Old 08-15-2011, 06:35 PM
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As long as the bores measure within service limits it should be ok. Maybe not ideal, but workable at least.
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Old 08-16-2011, 06:23 PM
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When I had SuperChicken II rebuilt and tweaked, a very well-respected race engine builder told me that it is usually a bad idea to go anywhere too far beyond 20% outside of OEM specs when it comes to modifying engine bore, compression, and horsepower. Motorcycle engine design is quite complex these days, and there are physics involved relative to engine-casing size, effective heat dissipation, and engine-life. For example, a twenty-five percent increase in horsepower might shorten the life-expectancy of the engine to the point that you find yourself going through another engine rebuild, in far too short an interval. It's kind of like the devil's bargain: get too greedy for power, and the engine might have a very short life-span.

It's freakin' expensive to tweak an engine with forged pistons, tricked-out cams, light-weight valves, and the whole sha-bang, and it's my understanding that this is one of the reasons why the 20% rule makes good sense (in the long-run).

The day it was stolen, SuperChicken II made several dyno-runs at 120 h.p. (with gobs-and-gobs of torque). A SuperHawk with aggressive street cams, light-weight valves, and 120 h.p. is a nasty beast indeed--so much fun to ride.



cheers,
--Professor Chaos

Last edited by ProfChaos; 08-16-2011 at 06:40 PM.
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