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Post by new2scootin on Aug 9, 2018 5:37:02 GMT -5
Ive searched and cant find any if there is but on the gy6 50cc 1P39QMB engine is the valve lash different or did you guys change from the manufacturers suggested setting after installing an A9 cam? I also have a 47mm BBK on in it with a stock 39mm head. I did port match as well as widened the intake to 20mm at the spacer but let it taper to the factoey size about halfway into the intake port because Im not 100% sure that I wont mess it up plus I dont have the correct bits for my rotary tool to do it correctly. The reason I started out at 20mm is I havea 20mm spacer so I just port matched it because in the near future there will be a 20mm carb to mount on top of that spacer. On the exhaust side I widened it at the mouth all the way to the gasket and then gave it a taper that runs about halfway into the port as well. I didnt want to take out a bunch of material knowing I had a A9 cam coming and that would lower compression some.
Anyway what do you guys set your valves at with a BBK and A9 cam?
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Aug 9, 2018 6:19:03 GMT -5
Or first startup, I set the valves at ..006”. After about an hour and a half run time, I reset both to .004” and that’s what they are running at now. The first B.B. engine now has about 20 hours on it and seems to be good with the .004 setting. I’m still screwing with the second engine, but I plan to set it to .004 also. The outfit that sold me my stuff did not respond when I sent them emails for their suggestion.
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Post by eclark5483 on Aug 9, 2018 8:28:35 GMT -5
I have my brat's gapped at .004. Pops off in a split second when she pushes the start button, never have had any issues. She's also running a 47mm BBK, A9 cam and 20mm carb.
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Post by AtariGuy on Aug 15, 2018 2:10:33 GMT -5
50mm bbk (50mm head with stock diameter valves) and a9 cam - i did my break-in at 0.004"in and 0.005"ex, currently at 0.003"in and 0.004"ex now. Runs great
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Post by humanshield on Aug 15, 2018 5:20:49 GMT -5
For those new to engine mechanics.....
Exhaust valve is more critical because it runs hotter. It's cooled primarily by the aggregate time it spends in contact with the valve seat. The smaller the gap, the less time it spends in contact with the seat, the hotter it runs. Excess heat slowly burns the valve. Too large a gap compromises performance. Intake valve does not have that problem as it is always cooled by the incoming cold fuel mixture from the carb/intake so it can safely be set a bit tighter for optimum performance. Also, setting the lash gap to wide can cause premature wear of the valve stems aka mushrooming. some typical settings..... Intake 0.002″ – 0.004″ Exhaust 0.003″ -0.006″
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