By
Chile
2018 Massimo MSU 700 EFI. I realize that this engine is essential the same as in all of the HISUN based Yamaha clones out there. I am in the process of performing a top end diagnosis/rebuild. I have an AMAZON top end rebuild kit on order in anticipation of this activity.
Question 1: When exploring the myriad of top end rebuild kits on the market for these units there are some cylinder assemblies that have "686 cm3" badging next to the cam cain tensioner boss. Others compatible with the unit do not have this badging. The existing cylinder assy does not have the 686 badging. I am assuming that this simply verifies that the cylinder assy is for a 686 cm3 engine which of course the stock 700 series HISUN engines are. Am I missing something here or is this just a manufacturer artifact? With or without the badging the application listings all indicate compatibility with the MSU 700 series engines.
Question 2: I have reviewed at minimum a dozen videos associated with this rebuild. To date I have not found one that deals with piston/cylinder clearance and/or ring gap verification. The advertised specifications for these various "top end rebuild kits" all indicate: Cylnider bore = 102mm and piston diameter=101.5mm. The math yields a .5mm (as in 1/2 mm) difference. That seems to be a very large piston/cylinder clearance. I realize I am referencing advertised specs rather than emperically measured values but the numbers have gotten my attention. I have referenced the FSM and found it to be somewhat confusing in this regard. Hopefully the experts on this forum can enlighten me as to where my observations are faulty here.
Any and all assistance is greatly appreciated .
Thank you all in advance,
Chile
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