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Post by carasdad on Jun 9, 2013 15:38:48 GMT -5
Does this look normal to you?..sure don't to me! Just got a 2012 Peace Sports B09 from somebody. It was running horribly and lacked power for a BBK. Pulled head from engine to have a look see... This is what I found in the pics. Guy told me it was normal and the piston comes that way. To which I argued..."They come domed..and they come flat top...but they don't come concave and burned black" Then I was told that my plug was not tight enough...causing an air leak..which in turn caused this...so it was my fault. Say what?...this is how it came to me. I put maybe 5 miles on it and it just did not seem to have any power..ran hot...and compression was soooo high I could not even kick start it. It is a 50mm kit that has a #  jet. I find that super lean as the many many 44mm and 47mm kits I have installed needed a # or #87.5. Was hoping my explaining a 50mm kit with compression sooo high you could stand on the kicker and not crank it..and the too lean jetting caused this. Looks like I lost out on this argument and will be footing the parts bill and spending my time to rebuild this engine. Taken to the the cleaners...but you live you learn as they say.  I would like opinions on this so maybe I can prove to him that I am NOT wrong. Does the Piston look normal?? Do they typically come with a 4mm deep dished top? Would you put a # jet in a 50mm BBK?... Attachments:
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Post by carasdad on Jun 9, 2013 15:39:28 GMT -5
Pic # 2... Attachments:
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Post by millsc on Jun 9, 2013 15:46:37 GMT -5
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Post by millsc on Jun 9, 2013 16:03:18 GMT -5
All the old pistons i take out are also black
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Post by carasdad on Jun 9, 2013 16:04:30 GMT -5
Where did you find that kit for 49 bux....got a link? I am shocked..235psi is a bit much for ANY engine. Plus..just a # jet. Did not know any of this until I got home..tested compression and checked Main Jet size. But by then it was too late...the owner had been riding it...so the damage was done.. I am sure the crank has taken a beating as well.... Man I feel ripped off... |
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Post by millsc on Jun 9, 2013 16:08:02 GMT -5
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Post by millsc on Jun 9, 2013 16:14:54 GMT -5
i like my b09-r so much i'm gonna sell my tapout scoot and buy another one
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Post by millsc on Jun 9, 2013 16:19:07 GMT -5
# jet with a 50mm kit stock exhaust and airbox wouldn't do too much damage it should be fine, if i was going to run it like that, which i wouldn't use an airbox with the bigger kits id probably run an  i did try the airbox just to see on my b09-r barely made it up the street without bog |
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Post by triker on Jun 9, 2013 16:22:02 GMT -5
They do come concave on the top. I have a gotten several that are concave. This is a 39mm piston. I have a 47mm that is concave that is installed in the engine I have in my trike. I have a 50mm some where on my shelf, I just didn't want to dig it out.  Roy |
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Post by millsc on Jun 9, 2013 16:24:13 GMT -5
My stepsons 47mm piston from scrappys was dished also
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Post by carasdad on Jun 9, 2013 17:19:17 GMT -5
[replyingto=millsc]millsc[/replyingto]Thanks all. Triker this piston is way more dished than the one in your pic. You'd have to actually see it I suppose. It starts at the rim and goes about 4mm deep. Thanks for the pic...never saw a fresh new one slightly dished. Have seen many Diesel Engine pistons come that way. Now I am curious why they do that...what is the benefit...especially on a Diesel which is designed to run super high compression. Regarding compression though...does anyone agree the 235psi was too high for a 139QMB engine and is what caused the excessive dishing?
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Post by triker on Jun 9, 2013 17:29:16 GMT -5
I think if they start out concave the top of the piston is already weak. A high compression engine plus running hot and pre-detination will all contribute to this also. Larry001964's stroker engine did this to a piston also, and he had a better quality ncy domed piston.
Roy
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Post by domindart on Jun 9, 2013 18:58:16 GMT -5
Was the bike in this working condition when you bought it? WHy did you buy if it was not to satisfactory running condition? I'm confused lol
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Post by JR on Jun 9, 2013 19:13:33 GMT -5
I am wondering, if it is domed and the compression was so high you could not kick start it, a flat top would have just that much more compression. Might the timing have been very retarded to prevent ping? if so that can rob some power.
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Post by carasdad on Jun 9, 2013 21:08:04 GMT -5
I am wondering, if it is domed and the compression was so high you could not kick start it, a flat top would have just that much more compression. Might the timing have been very retarded to prevent ping? if so that can rob some power. Timing was not messed with. The 235psi probably caused it from detonation and heat from running lean. Compression when BBK was installed should have checked when it was so high starter barely cranked it. Then do as I do after a BBK....compression check and add gaskets to bring it to within normal limits. |
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jet. I find that super lean as the many many 44mm and 47mm kits I have installed needed a #
jet and its a beast in my opinion all kits over 47mm run best with an open air filter 
i did try the airbox just to see on my b09-r barely made it up the street without bog
