Hi. I have a horribly inefficient 2 stroke dirtbike engine I would like to improve. It is a single cylinder, 368cc engine, with oil pre-mixed in fuel at 50:1. It has a bore of 78mm and a stroke of 77mm, and develops roughly 50hp. The attached photo is not the current state of the head, but it gives an idea. Since then the bowl has been increased and the squish angle decreased to a more normal 4 degrees. Current compression is roughly 11:1
Suggestions on number of grooves, location, and size would be most appreciated. Have the grooves been tried on high output 2 stroke engines before? Any expected results or potential problems? The engine is terribly inefficient, even by normal 2 stroke dirtbike standards, lacks crisp throttle response at low rpm, and runs quite rough but still powerfully at low rpm.
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Re:2 stroke dirtbike engine grooving
Date: 2006/10/18 05:25
By: Pinhead
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I don't see a pic...
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Re:2 stroke dirtbike engine grooving
Date: 2006/10/19 07:44
By: Blowtus
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after a little further reading, the main points I cannot determine are the width of the groove, and where it should be in relation to the exhaust port.
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Re:2 stroke dirtbike engine grooving
Date: 2006/10/24 09:40
By: mpgmike
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Karma: 4
Groove width should be between 0.10" and 0.15". Without seeing the piston, it is difficult to determine any exact locations. On the left side of the pic there is servere inactivity. That would be a good place for the groove(s). On the right you have washdown. That would be another good place for a groove(s). Too many grooves might reduce compression, but spur cylinder acitivity which will improve BSFC. Piston pics will allow better responses.
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Re:2 stroke dirtbike engine grooving
Date: 2006/10/26 12:44
By: Blowtus
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Ok, I have pulled the head off and taken a bundle of photos. The red line on the head page points to the exhaust port. Compiled a whole bunch of images in an attempt to eliminate lighting differences... It's all looking pretty carbon'd. Not sure what's up with the carbon pattern on head.
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Re:2 stroke dirtbike engine grooving
Date: 2006/10/29 03:31
By: singh
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The simplest layout would be to visualize the famous 3 pointed star displayed by Mercedes Benz. One small triangular file is sufficient to achieve the results ! Place the first groove above the exhaust port starting narrow close to the rim and widening / deepening through the available squish area pointing at the spark plug. The other 2 channels need to be placed above the transfer ports at equidistance to each other like the Star ! The channels are restricted to the squish band only, keep them narrow and give them an emery finish. Check the power valve if there is one and make sure the exhaust system is clean end to end and not disfigured to send an early pressure wave ? Keep every thing else as specified in the book and tell us what happened ?
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Re:2 stroke dirtbike engine grooving
Date: 2006/10/30 15:00
By: Blowtus
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Thank you Somender - I am just a little unclear from your description as to whether the 3 grooves / channels should be the same, or the ones above the transfer ports should be narrower?
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Re:2 stroke dirtbike engine grooving
Date: 2006/10/30 18:10
By: singh
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Call them grooves or channels ! They need to look like the famous 3 pointed Star ! i can't give a better e.g., ! Nor can i make it simpler ! This is just apt for ...... starters ! Sky is the Limit ! The rest of it is left to your Imagination?! i have done ~ One, Two & Three ! The Max i have gone up to is 13 ?? The famous un-lucky Number ~ And i still succeded to make it better !
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Re:2 stroke dirtbike engine grooving
Date: 2007/01/27 11:57
By: Blowtus
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The head has been grooved. Have ridden it a few times. Likes slightly leaner jetting. Deceleration surging is reduced somewhat. Feels like it has a bit higher peak power and revs longer / easier up top, but I replaced the rings at the same time - possible I've just forgotten how strong the engine was, but I don't believe this to be the case, I've rebuilt it a few times in the past. Fuel economy is still untested. Full discussion, photos, and results from others who have tried it on very similar bikes, available here. http://ktmtalk.com/index.php?showtopic=193738
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Re:2 stroke dirtbike engine grooving
Date: 2007/06/07 09:17
By: Blowtus
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fuel economy appears largely unchaged so far. Very marginally better if anything.
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Re:2 stroke dirtbike engine grooving
Date: 2009/11/19 07:15
By: sandipjagtap
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Karma: 0
Hi !!
I have 100 cc ( yamaha rx 100) bike
I have tried grooves .. but unfortunately there might be some mistakes; I cant get results as MR. SINGH stated...
followiing is the picture I tried to show you ( pic may take little time to download)
here I have made two groves one at exhaust hole side and which is close to gascate area directed towards spark plug and another intake port side this is quite small and not close to gascate as well as spark plug
there might be some wrong thing whatever I done so you are kindly requested to guide me on same
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