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Old 06-11-2008, 12:45 PM   #1
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Default 1 quick question!

if one engine needs more bottom power,can i lower the height of the sleeve in the area that contact with the case.i know that all the port's timing will be changed.can it make any difference??is 0.1-0.2 enough?i am thinking to use shims under the sleeve in case that something will going wrong or i would like more high revving..
any suggestions?
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Old 06-11-2008, 01:54 PM   #2
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Yes you can do that ...BUT... Lowering the sleeve will increase low end and increase fuel mileage. However it is a give and take, what you gain in lower end you will lose in top end and once you drop the sleeve the piston is forced further up the sleeve and shimming must be changed. Once you do this you can't go back up cause you will lose compression.
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Old 06-11-2008, 03:06 PM   #3
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to be more specific.
i am speaking for the crf orion engine that has not too much pinch.
will lose compression this too?is saing that it does not makes compression from pinch..
Cfowler have you do this in an engine?anyone else guys?
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Old 06-11-2008, 03:59 PM   #4
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I assume you are talking about the CRF .12? If so, that is not a bottom end motor. It's all top end. Fortunately it turns so many RPM you can get more bottom end with a lower gear and let it twist. Drop a tooth on the clutch or go up a few teeth on the spur and let it twist. Just make sure you have a good rod in it.
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Old 06-11-2008, 04:07 PM   #5
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yes.i just replace rod and bearings.
so it's not good idea to do it?
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Old 06-11-2008, 04:11 PM   #6
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I don't think so. The motor is a top end screamer so take advantage of it's strength and gear it low. Lowering the entire sleeve will lower the exhaust port, which is good for bottom end but will also lower the intakes which is not good for a broad power band.

Low end with a broad power band= Low exhaust, high intakes.

Max power= low intakes with a high exhaust.
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Old 06-11-2008, 04:39 PM   #7
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Thanks wingracer!
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