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Author Topic: Engine Blew Up - Kinda  (Read 1343 times)

Jim Moore

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Engine Blew Up - Kinda
« on: January 05, 2015, 01:48:43 PM »
HI Guys,

I lost a cam bearing, which caused the cam chain to jump off the sprocket and bury itself in the tunnel. I'm in the process of taking everything apart right now. Valves and piston look good. My plan is to pull everything apart and clean out the scrap metal, then put it back together with a new cam and cross my fingers. Wish me luck.
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zombie

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Re: Engine Blew Up - Kinda
« Reply #1 on: January 05, 2015, 07:04:53 PM »
It's a straight forward job. You can get a new gasket set on Ebay that includes a new oil pump for around 30 bucks but the timing chain has to come from Kymco.
I have snapped a GY 6 (qmb 139) chain in the past so I would stay away from those.
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BettinANDlosing

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Re: Engine Blew Up - Kinda
« Reply #2 on: January 05, 2015, 07:19:14 PM »
+1 on the oil pump, could be the cause of the bearing failure. Anyway, lack of lubrication for sure, did it have plenty of oil? To do the chain you have to crack the engine case, quite a job for the first time. Make sure your work area is clean. Depending on the mileage you might as well re-ring and hone the cylinder while you have it open.
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2002 Kymco B&W 300; MRP 78MM "300CC", Naraku cam, Yoshimura rS3 exhaust, 17g Sliders, Yellow torque spring drilled airbox, stock carb #115 main #40 pj.

2001 "Yamaha" Zuma AKA MBK Booster; MHR OverRange, Dellorto 19mm BHBG, Polini "big" intake, RS-3 Rear shock, Stock cylinder.

zombie

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Re: Engine Blew Up - Kinda
« Reply #3 on: January 06, 2015, 05:08:25 AM »
50mm cylinder kit!!! Now's the time bro!

Actually it's an easy job to split the cases. The hardest part is getting the bike stable to remove the engine to begin with.

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Jim Moore

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Re: Engine Blew Up - Kinda
« Reply #4 on: January 06, 2015, 02:18:35 PM »
I have the engine out and halfway pulled apart. I have found all the balls, but I feel like I need to split the case to clean everything out. I'm waiting for a tool to remove the castle nut in front of the starter clutch. My original plan was to just replace the cam and the gaskets  / seals, but maybe I'll replace the oil pump too.

What is this 50 mm kit of which you speak?
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zombie

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Re: Engine Blew Up - Kinda
« Reply #5 on: January 06, 2015, 11:23:24 PM »
http://www.ebay.com/itm/100cc-Big-Bore-Performance-Kit-GY6-50cc-139QMB-Chinese-Scooter-Parts-50mm-Bore-/161018154007?pt=Other_Vehicle_Parts&hash=item257d6e0c17&vxp=mtr

Everything you need to rebuild the engine Minus the cam/timing chain.

My kit has run approx 20 miles every day for 4 years. Better torque, and higher top end (with the right CVT mods)
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