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So i have a 125 fr max that has been running perfect and yesterday at the track for a practice day it died on me and wouldnt start back up for the life of me. battery is charged its getting spark and fuel even put in a new plug. Im not sure how to explain the sound but the typical sound of the motor turning when it starting isnt sounding the same since it died. im getting compression and the starter turnes the clutch and the drum spins but nothing like its trying to fire up. It almost sounds like its not getting compression inside but when i pull the plug it blows out and i can feel compression if i plug it with my finger. Please help me with any other suggestions or advice.
Jason, Pull the plug and stick it back into the plug cap and lay the plug against a metal ground. Then spin the motor slowly by hand with a 14 mm socket over the gear nut. It should spin quite smoothly and quietly with very little resistance. Your feeling and listening for any clunking or grinding that would indicate that either the lower rod bearing went out, the balance gears went out or the clutch isn’t disengaging. Next I would take the carb off the reed cage boot and examine with a flash light the condition of the reeds. You could also look at the condition of the exhaust side piston face and compression ring by taking off the exhaust. Feel free to post back with what you find.
I pulled the carb off last night and looked at what i could see of the reed cage and its looked good..nothing broken or abnormal looking. Ill pull the exhaust off today and turn motor by hand again like you stated. Ill try to get a video and maybe that will help with what im experiencing. THANKS for the advice so far 🙂
I haven’t seen one that has blown a reed cage, but pulling the exhaust and checking the back side of the piston would be good. Hopefully it is something simple like a fuel pump, or a plugged carb. Sometimes when they seem like they are getting fuel they actually aren’t. Post back with your findings and let us know. There are also a few Rotax Service Centers here in town that can help you out, including us here at Unser. Feel free to bring it by the shop if you can’t get it figured out.
didnt get time last night to dig more into it but i did check the compression…its not getting enough comoression to start…wouldnt even reach the 30 mark. It was hitting around 20. What would all of a sudden keep it from getting compression? Crank bolt is fine and tight…clutch 17mm is properly.on and torqued to specs per manual. Carb and power valve are both throughly clean. I guess tonight ill inspect the reed cage more and remove the exhaust to check side of piston at least as well. Any other ideas?
It could be a blown main seal, or a soft stick on the top end. I would say the top end failure is more likely as I don’t see them really ever blow seals. Pop the pipe off and look at the back of the piston, and that will tell you if it needs a rebuild.
Alright guys sorry for the delay but today i messed with it some more and went ahead and took the motor off the frame and out it on my bench to further dig into it. Reed cage looked ok to me no obstructions or damage, piston from exhaust side looked ok…so i went ahead and opened up the side case cover to inspect gears and such…….this is what i found!
How in the **** does this happen! I was surprised to see all the gears are just plastic! But anyways…bottom and top end appear and spins freely so here lies my issue UGH! I tried to compile my parts list for all new gears in there but some diagrams dont show the piece thats in front of the crank water pump pulley? Could someone help me with a list of exact numbers or something that i need to order to get them back together.
Thanks guys…any suggestions or ideas what would cause this??????
Haha, dumb design on Rotaxs part. Plastic gears? Really?! I had that exact thing happen on an engine of mine, I believe that Rotax has a retrofit kit for it that updates to steel gears.
Reeds look ok to me.
@Jon Romenesko wrote:
Haha, dumb design on Rotaxs part. Plastic gears? Really?! I had that exact thing happen on an engine of mine, I believe that Rotax has a retrofit kit for it that updates to steel gears.
Reeds look ok to me.
Yeah i was dumbfounded…like whats the logical reasoning behind using some plastics gears in a “race type motor”
Do you have any info on this retrofit kit by chance?You got lucky the engine internals are all good! You have a couple options here. First you can replace the plastic balance gears with more plastic gears, I have a new set I need to get rid of that I can let go for $20.
If you plan on racing you need to upgrade the clutch.
The new style clutch kit which comes with new steel gears is $524.48Or if you don’t plan on racing you can just swap over to the steel gears which are $48.64ea
I would assume there could be some damage to the other gears in the case. They only run the larger two gears as steel and the other 3 remain plastic. I have never had a failure in the balance gear case with the new gears. Check the other 3 gears for damage and see which ones you will need.
Greg-
All the plastic gears are broken cmpletely or have busted teeth so I need ALL the plastic gears and the other single or double piece that is at the end of the crank essentially if you look in the pics. Im not racing…I just go to all the tracks for fun basically at this point. So replacing them with plastics for now i think is my option then I can either upgrade the clutch and everything later if i decide to stay with this motor but i have other plans for motor setup i think. Anyways…could you get all the gears I need and if so what am i looking at cost and availability?Here is a pretty good expanded view for parts needed. http://www.accelerationkarting.com/crankshaftpistonbalanceshaftbalancedrivewaterpumpdrivegearbox.aspx
@Rodney Ebersole wrote:
Here is a pretty good expanded view for parts needed. http://www.accelerationkarting.com/crankshaftpistonbalanceshaftbalancedrivewaterpumpdrivegearbox.aspx
thank you…does the #5 part come with both of those gears? Both are messed up
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