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Post by 2strokd on Mar 7, 2009 19:28:53 GMT -5
The weather has been great here, the last couple days it been in the 70s. Today i decided to take out the head gasket and sand down the head a bit. As soon as i pulled the head off i noticed a nasty carbon buildup in the combustion chamber. I wish i would have taken pics, this thing was chunky bad...So, i cleaned the head up real nice, then i took 1000 grit sandpaper and some soapy water, and a piece of glass from the entertainment center  . I taped the sandpaper to the glass door, wet the paper and sanded away. I went in a 8 pattern with the head, turning it 90 degrease every ten revolutions, trying to keep the head surface as true as possible. After about ten minutes of this, combined with taking out the gasket i shaved off about 1 millimeter. Doesnt sound like much, but im still sportn 49 factory cc,s. Im not that good at math, but if you put that in V8 terms, thats probably close to 1/8 inch on a small block Ford  . So, i cleaned the head again, then installed it with copper coat only(very light coat). Now my scoot runs noticeably better from a dig to top speed, about 48mph with the variator washer in, it takes off better with it in. My uncle also has a scoot that runs(ran) about even with mine. I like this because i can really tell when im getting more power to the ground. We went out for a ride, and i ended up pulling away from him all around from stop to 48mph, after that his Kymco Cobra would cruise on by. We rode for about 15 miles stop and go, mostly WOT with no problems ;D. Thanks for the info! |
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Post by 90GTVert on Mar 7, 2009 21:00:30 GMT -5
Nice work. Did you check your squish band clearance by any chance? All you really need is some fat solder (2-3mm) and a set of calipers or some way to measure it. Take out the spark plug and get teh solder positioned in there so it will go all the way to the edge of the cylinder, pulled up against the head. Crank the bike over. Measure the solder. That's your squish band clearance. I usually do it twice just to be sure I'm getting an accurate measurement. It sounds like it worked out great for you and clearance is fine, but to avoid possible issues in the future it's not a bad idea.
+1 Bone
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Post by 2strokd on Mar 7, 2009 21:25:54 GMT -5
Thanks! I forgot to check the squish band, but thanks to you, rally, momo, and all the others ive read about it. I got alittle ahead of myself lol, i just spun the motor over slowly w/my hand a few revs, then fired it up. Im gonna check the plug again tomm, so i will check the squish band then, and let you know, im curious now. I forgot to mention that it still runs better with the enricher unpluged.?. Im sure it works, if i plug it in and it warms up it runs slugish, and has a dead spot. If i leave it unpluged it pulls hard w/no dead spots. It runs rich as hell at idle, but its worth it. Im thinking jets, but i wasnt sure, because its pretty much stock.
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Post by rallyrrr on Mar 8, 2009 2:18:56 GMT -5
Wow! That's fast material removal for 1000 grit paper. I assume you are using premium gas now.
As far as squish bands are concerned. I think that most stock scooter heads are not squish band types. My Piaggio engined Derbi Atlantis came with what is known as a quiescent combustion chamber, which if were turned on it's side looks kind of like this: (|. A squish band combustion chamber has a much smaller hemispherical combustion chamber surrounded by a clearance band which duplicates the contour of the top of the piston up to the point where that smaller combustion chamber resides. This encircling band of very close piston-to-head clearance area encompassing the reduced combustion chamber is known as the squish band.
It's purpose is mostly three fold:
1. Creating turbulence as piston approaches TDC, thereby ensuring a homogeneous air/fuel mixture.
2. Reducing the possibility of detonation principally by confining the flame front to less volume.
3. Reduces piston and head heating (less heat losses mean more power) and less heating of the mixture on the other side of the piston in the crankcase (more dense mixture equals more power).
There are other benefits to low squish clearance and squish-type combustion chambers, but these are the main ones.
Anyway checking the squish clearance on a non-squish type combustion chamber is meaningless.
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Post by kliff on Mar 8, 2009 8:09:18 GMT -5
LOL....no offense meant, and I know I've either unintentionally, or hopefully exaggerated a time or two in the past myself.... but 1mm is about .040", on a 12x40 lathe, that job would have taken multiple cutting passes, at slow speed for a near mirror finish, time about 45 minutes. On my mill, about the same time, followed by 15-20 minutes on my cast iron lapping block, for final finish.
With 1000 grit paper, in your time frame, I would estimate you removed a couple of thousandths of an inch.
The good news is, at that little amount truing the head, the squish band would have been hardly disturbeb, and the increase erformance do to the decarbonizing, and truing of the head.
"Tiddlers" as we called anything under 100cc back in the day respond to even minute changes, and maintenance more noticeably than larger engines!
Well done, and no offense meant, just trying to relate some perspective as to metal removal...btw, I measured a .010" cutt, via lapping block years ago, on a B&S 5hp head... 4 hours, 45 minutes of stead work, and 1/3 can og clover lapping compound, COARSE.
+1 to ya too, have a bone!
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Post by 90GTVert on Mar 8, 2009 8:30:24 GMT -5
As far as squish bands are concerned. I think that most stock scooter heads are not squish band types. Oh yeah, probably not. Sorry about that. |
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Post by 2strokd on Mar 8, 2009 9:26:50 GMT -5
I probably did get alittle carried away with my millimeter. LOL! Maybe it was a half millo... Runs better, and is alot cleaner than before. I run 92 or higher octane, its so cheap to run so i always use premium. No pinging, or noticable heat changes, but it wasnt to hot out either, and it wasnt much of a change. It did help in my case though. Just cleaning out all the carbon out off the combustion chamber might have been the cause of improvement. Thanks for the input.
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Post by kliff on Mar 8, 2009 11:49:32 GMT -5
I probably did get alittle carried away with my millimeter. LOL! Maybe it was a half millo... Runs better, and is alot cleaner than before. I run 92 or higher octane, its so cheap to run so i always use premium. No pinging, or noticable heat changes, but it wasnt to hot out either, and it wasnt much of a change. It did help in my case though. Just cleaning out all the carbon out off the combustion chamber might have been the cause of improvement. Thanks for the input. Running better and cooler is all whas important anyway! ;D The rest is jus details....LOL! |
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. I taped the sandpaper to the glass door, wet the paper and sanded away. I went in a 8 pattern with the head, turning it 90 degrease every ten revolutions, trying to keep the head surface as true as possible. After about ten minutes of this, combined with taking out the gasket i shaved off about 1 millimeter. Doesnt sound like much, but im still sportn 49 factory cc,s. Im not that good at math, but if you put that in V8 terms, thats probably close to 1/8 inch on a small block Ford 
. So, i cleaned the head again, then installed it with copper coat only(very light coat). Now my scoot runs noticeably better from a dig to top speed, about 48mph with the variator washer in, it takes off better with it in. My uncle also has a scoot that runs(ran) about even with mine. I like this because i can really tell when im getting more power to the ground. We went out for a ride, and i ended up pulling away from him all around from stop to 48mph, after that his Kymco Cobra would cruise on by. We rode for about 15 miles stop and go, mostly WOT with no problems ;D. Thanks for the info! 
