Chile

Update to my original post: 2018 Massimo MSU 700 burning oil. I disassembled the top end of this HISUN based 686cc motor over the weekend. The cylinder head was unremarkable other than the combustion chamber was completely involved with a heavy black soot deposit. That was to be expected as the unit was burning oil. The piston top was dark brown but again to be expected. I actually expected to find a stuck ring as I removed the cylinder. This was not the case but I have to consideer that a ring could be siezed while in position in the piston ring groove but may immediately "free-up" upon extraction from the cylinder. The cylinder walls while shiny were not scored. There was no detectable (fingernail test) ridge at the top of the cylinder. Of course there was no trace of any original honing crosshatch as the engine has about 350hrs on it. At that point I had not discovered an obvious causal factor for the excessive oil burning. An interesting observation is that neither the top compression ring or the second ring had any identifying marks on them to: 1. Identify which was which and 2. Denote the top of the rings. I am the original owner and know that this engine is as "factory delivered" -- no intermediate ring replacement has occurred -- factory install. The piston skirts did not indicate unreasonable wear ( I have not measured the piston yet). Today I received the top end rebuild kit. As I began the process of measuring the new components I decided to evaluate the existing ring gaps from the smoking unit. Here is what I found: Top (compression) Ring Gap: .051 inch. Second Ring Gap: .125 inch (That is not a typo: .125 inch). At that point I did not evaluate the Third (oil control ring rails) for gap. I am at a loss as to how to explain these numbers. If this were attributed to ring wear I would have thought the cylinder walls would have at least indcated more wear and there would have been at least some discernible ridge. I will measure the piston itself tomorrow. My thought is that if this is indeed ring wear that the piston measurements will reflect significant wear as well. Of course the other possibility is that this is manufacturing/assembly failure and the unit was delivered in this condition. What is strange about that theory is that the unit began smoking excessively only recently and the condition onset was rapid. I have maintained the air filtration system responsibly and prior to disassembly I inspected the filter/the intake ducting to throttle body/the throttle body itself/the intake manifold runners and the intake chambers in the head. No sign of contamination. At this point all I will reassemble with new cylinder/piston and rings. I will check/set end gaps to FSM specs. Additionally I will install new valve stem seals even though the originals appear to be fine. I would appreciate any and all opinons/observations/conspiracy theories etc that may help explain these strange findings. Thank you, 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

Thamk you Joe for your response. We were out of touch for several days. Back home now. I will do a compression test this PM. This machine has about 350 hrs. on it. Oil burning issue occured literally overnight. Really strange. Post compression test I will do a leak down test. I've run many compression tests on 4 and 2 strokes. Never a leak down test as basic comp test always indicated issue/no issue. Does the HISUN engine compression relief mechanism interfere with performing a basic compression test? I have avoided the extra 1 1/2 qts of oil experiment after observing my neighbor's results with this experiment on his Polaris. His wasn't so much an oil consumption issue as a beer consumption issue. However, he does have a very refreshed motor and his motor was tired with way more than my 350 hrs. I'm running 15W40 here in the deserts of New Mexico. We do use the unit in Colorado during the summers however. I can't imagine that 15W40 may be too heavy for 70 degree days in Colorado but I am no expert in that regard either. Your mentioning crankase ventilation is interesting as the machine only smokes off idle usually under load. Zero visual smoke at idle or below approx 2200RPM or so. I will chase that aspect down as well. Thank you again for your assistance with this. Chile

2018 Massimo 700 MSU. The machine started burning oil all of a sudden. One day fine-- next morning burning oil. Looking for advice. Do I pull the engine to inspect the top end or can it be done with the engine in place? Pro? Cons? Any and all assistance is greatly appreciated in advance. Chile

I have a 2018 Massimo 700 MSU with the Delphi MT05 ECU. I have seen an alternative ECU reset procedure that involves running the engine at WOT for 5 seconds in neutral and then shutting down while throttle still at WOT. The articles include comments that the rev limiter will prevent engine overspeed ad attendant damage. 1. Is this actually a recommended procedure for restting the ECU on a 700 MSU? 2. What is the rev limited maximum RPM for the 700 MSU? I initiated this procedure but when the RPM exceeded 6000 I immediately terminated the process. It simply seemed excessive to me to continue. Any and all responses are greatly appreciated. Chile