I rebuilt the top end on my moped yesterday ( I realize this is a dirt bike site, but you guys are the best for my dirt bike problems) and after i finished it wouldn't start up.I replaced the piston,rings,circlips, and wrist pin. I went back in and realized I had the piston facing the wrong direction (arrow not towards exhaust) is this why it won't start. I haven't been able to put it back together again, but would like some ideas as to why it wouldn't start.
Rebuilt Top End and now it won't START :(
Started by
04HondaCR125
, Jul 24 2012 09:06 AM
7 replies to this topic
Posted 24 July 2012 - 09:20 AM
If it's a four-stroke there could be some clearance issues with the valves to the piston. Intake valves are generally larger than exhaust valves, if the piston's in the wrong way the smaller notches for the exhaust valves may not allow the intakes to open.
Does it turn over at all? Got fuel, spark?
Make sure everything's reconnected afterwards.
Just did a complete rebuild of my moto engine. Put it back together, kick it over a few times to make sure it spun over, then hit the e-start and it fired right up. Heat-cycle a few times, then an easy break-in ride varying the throttle up to ~80%, let it cool off, another break-in ride over the whole range, then go make up for the riding you missed.
Does it turn over at all? Got fuel, spark?
Make sure everything's reconnected afterwards.
Just did a complete rebuild of my moto engine. Put it back together, kick it over a few times to make sure it spun over, then hit the e-start and it fired right up. Heat-cycle a few times, then an easy break-in ride varying the throttle up to ~80%, let it cool off, another break-in ride over the whole range, then go make up for the riding you missed.
Posted 24 July 2012 - 09:23 AM
SnowMule, on 24 July 2012 - 09:20 AM, said:
If it's a four-stroke there could be some clearance issues with the valves to the piston. Intake valves are generally larger than exhaust valves, if the piston's in the wrong way the smaller notches for the exhaust valves may not allow the intakes to open.
Does it turn over at all? Got fuel, spark?
Make sure everything's reconnected afterwards.
Just did a complete rebuild of my moto engine. Put it back together, kick it over a few times to make sure it spun over, then hit the e-start and it fired right up. Heat-cycle a few times, then an easy break-in ride varying the throttle up to ~80%, let it cool off, another break-in ride over the whole range, then go make up for the riding you missed.
Does it turn over at all? Got fuel, spark?
Make sure everything's reconnected afterwards.
Just did a complete rebuild of my moto engine. Put it back together, kick it over a few times to make sure it spun over, then hit the e-start and it fired right up. Heat-cycle a few times, then an easy break-in ride varying the throttle up to ~80%, let it cool off, another break-in ride over the whole range, then go make up for the riding you missed.
Posted 24 July 2012 - 10:28 AM
The 3 things an engine needs to start is spark, fuel, and compression. When you get the piston back in do a compression test to see where your at. If you have compression check your reeds and intake, and make sure your not running soft fuel. Then check to make sure your getting spark, ground the spark plug wire against the frame or engine with a flat head on see if your getting any spark. If it the reeds, spark and intake were good before your top end rebuild chances are they would still be good because they are not related but crazier things have happened. Oh and when you take that head back off make sure to replace the head gasket!
Posted 24 July 2012 - 10:32 AM
The piston needs to be in the correct direction. The piston skirt controls incoming air/fuel charge timing. Fix it.
Posted 24 July 2012 - 01:05 PM
If you put the piston in backwards, then cranked/kicked it over 100 times it might have damaged the cylinder wall and piston/rings. Check your compression.
Posted 24 July 2012 - 03:56 PM
It was probably not the best idea to post on TY that you own a moped...
Anyways, since it is a two stroke, the piston direction needs to be correct because of the method of air/fuel induction. It may appear symmetrical but it most likely is not.
Anyways, since it is a two stroke, the piston direction needs to be correct because of the method of air/fuel induction. It may appear symmetrical but it most likely is not.
Posted 25 July 2012 - 08:38 AM
my roommates friend owns a moped... we call it the Yard Runner and we have a track in the yard for it. We call the jump over the driveway "RedBud"... We strip every part off of it we can to reduce weight and we've become rather obsessed with it lol! it's sooo hard to ride it's hilarious - Fun Factor is rediculous... 25mph feels like certain death haha
