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Discussion Starter #1
Hey y'all, bringing another mystery to the forum, this time a coleman mini.
Our children's friend has been riding bikes with us and we've been helping him care for his 79cc. We got the exhaust header/ muffler add on and opened up the air box a bit as well as drilled the jet up 1 jewlers drill bit larger, and did the governor override link, where it was running well for a good couple weekends at an OHV park and farm trails.

After, it was acting hesitant to start, so we cleaned the carb, and while we were at it, did the oil change, gov delete, cleaned the piston head, and re-lapped and adjusted valve lash (.003ish). Doing what we shouldn't have we messed with three or more changes to the bike instead of one job at a time, then try to start.. no go!
We've quadruple checked the valves aren't jammed or stuck, rods aren't bent, gaskets look good, gas new, air filter clean, spark looks strong; even tried starter fluid and to no avail. When I check compression I get -0-. I hear there's a decompression feature built into the cam of Coleman/Hisun mini bike engines, and was wondering if that's the reason for the reading, or is it possible to burn up a set of rings in one year??

I'm trying a new NGK plug this afternoon, and I'll re-check the coil gap, don't know what else to look at... Only other thing I was thinking was maybe getting a pred212cc and clutch/chain for the win as opposed to getting rings for a wussy 79cc. Would this be as bolt on/ease, does anyone suggest against such or better advise?

Thanks y'all!
 

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Zero compression means you must have a valve that's stuck open or the camshaft is not timed right

On some of those engines there's a wood riff key on the crankshaft gear that runs the cam if that inadvertently fell out then it will kind of seem like it's working but it will always have the timing off.

when I put those engines together I always line up the dots and then spin it around twice and make sure that the indexing dots line back up.

If that's overhead valve and you accidentally got the intake and exhaust push rods mixed up that can cause some major problems as well to where the valve sticks open but it's not detectable by the human eye.
 

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Discussion Starter #3
Thanks Mr.K - I could have swapped the push rods by mistake, they do look exactly the same to the eye. We'll pull the side cover and double check the cam timing etc, if it looks okay then maybe we'll pop the head and swap push rods.
If the rain keeps up we'll have some time to focus on a couple of the bike projects..
 
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