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baja 5b engine "kingmotor 30.5cc" random cut out and not starting or sounding ok


mattytheking1

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hi all i am having trouble with my engine

the other day it was running like a treat and then it just cut out randomly, i got it home and taken spark plug out and checked for spark, there was no spark, so i though it was just the coil witch has been knocked off track with the flywheel so i relined it all and then i started getting spark after messing around with it 

after that i started sticking it all back to try and start it, so yanking on it for ages and wondering what is going on...getting fuel to spark and thought i was just flooding it, so i remember seeing a little trick online "might be this forum site" to stick a little bit of 2 stoke oil down the spark hole to see if it is compression

so i stuck some oil in and tryed to fire it up, this was not on choke and it just popped like it would on choke when you pull and try and start so i gathered this is where the problem is 

i had a new piston head and the piston ring is not very old so i just stuck new piston in and used the same piston ring due to not being very old and worn 

now i have tones of compression but it dont sound right when i pulled on the starter making everything going round in the engine, its sounding like a tubo charger on a car when you up shift on gears,making that kind of whistle sound

i did manage to get it started with this strange sound yesterday and it did fire up but it was running at full revs and going nuts 

i am stuck on ideas and possible things witch could be doing this, this is my second engine in this and dont want to get more parts or anything like that right now, these parts are not even 3 months old crank case and head, crank shaft is from original engine and its a stuffed crank they call it, 

it was running fine before it just conked out on me the other day and never made this sound before sticking this new piston into it 


any help would be amazing for me, i have writing it how i can remember how everything went 


 

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Could it be a carb issue if when you got it running it was going all out?

Or at the very least, could that be adding to the engine problem that you're having?

Edited by MAZ
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Could it be a carb issue if when you got it running it was going all out?

Or at the very least, could that be adding to the engine problem that you're having?

i did think of that but i have not fired it up again just yet, but it was not making this weird sound before i stuck the new piston in it

was running fine 

ill maybe try and start it up and stick the back to stock settings 

thanks for getting back to me 

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i did think of that but i have not fired it up again just yet, but it was not making this weird sound before i stuck the new piston in it

was running fine 

ill maybe try and start it up and stick the back to stock settings 

thanks for getting back to me 

i have just tryed setting it back to stock and does not want to pop on choke

i might have a video to show, but i dont know how to upload one on here, would i need to upload to youtube and give a link? 

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How did you set your coil mate? Sounds like you might have the coil catching on the flywheel. Best way to set the gap is to put a business card between the coil and the magnetic part of the flywheel. Did you have the tx an rx switched on when it went nuts?

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How did you set your coil mate? Sounds like you might have the coil catching on the flywheel. Best way to set the gap is to put a business card between the coil and the magnetic part of the flywheel. Did you have the tx an rx switched on when it went nuts?

yeah i did all that, i have been using one from day one, i am getting spark and im sure its not rubbing on the fly wheel 

also tx and rx? dont know what that means sorry, im guessing you mean kill switch? i had all that sorted and was not on "kill" the engine. 

cheers for the message 

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i did manage to get it started with this strange sound yesterday and it did fire up but it was running at full revs and going nuts

I'd say you have an air leak. Pull it apart again, and check / replace the gaskets. Also check the carb isolator block isn't cracked / warped.

Edited by Jolly_roger_uk
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Tx rx controller and receiver mate just wondering if throttle was open when you starterd it;)

a, no the throutle was not wide open, i did try to do that as well to start it, if it needed a little more fuel 

I'd say you have an air leak. Pull it apart again, and check / replace the gaskets. Also check the carb isolator block isn't cracked / warped.

ok i will try and get my hands on some new gaskets this week and ill strip it down

cheers 

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ok so time for an update

i have not bought a gasket kit just yet, but when i did replace the head gasket when replacing the piston, so only just back in from messing around with it again and i seen the head bolts with lock washers, they were not full flat or flush screwed in fully, so i did them up a little and it start and the weird sound i was getting went away a little, but it did run for couple of seconds

now my plan with it i think is to still get a gasket kit and make sure bolts are done up right  :thumbsup: 

so my next questions is, what gasket kit i could get? 

i have seen ddms steel heavy duty one on ebay or what about copper ones, or should i just stick with the paper "standard" ones? 

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ok so i got my gaskets today, and i have stuck one of the coppers in and boom it was popping on choke and little mess about with the idle screw and it was running 

looks like jolly_roger_uk was right, it was a air leak, when i took head off, 3 corners were dry, expected for one 

thanks to all who commented, was a good help :D 

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Good stuff mate, glad to hear something so simple fixed it. But are copper better?

me to and i also have no idea, this is still my first 5th scale but second motor in it

id maybe ask someone else on here about that, but they seem fine, also wont be able to rip or tare if you take head off your engine. 

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copper ones can be a pain.

 

you can't use them straight off like you can paper ones as they don't give a whole lot and so don't seal fully and leak, there are 2 ways around it

 

 

use gasket sealant, which is more expense, and personally why would i use it on something that's meant to do the sealing in the first place.

 

or you can heat them up, which makes them pliable, takes abit long and you gotta be quick in bolting it up, it also limits the use a fair bit as you deform it slightly each time.

 

 

 

personally speaking i prefer using the paper ones, yes they often break each time to strip the engine and yes they don't last as long, but its less hassle to fit one.

 

maybe go copper if i was racing or stripped down my engines often, but for bashing, there really isn't any point imo

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copper ones can be a pain.

 

you can't use them straight off like you can paper ones as they don't give a whole lot and so don't seal fully and leak, there are 2 ways around it

 

 

use gasket sealant, which is more expense, and personally why would i use it on something that's meant to do the sealing in the first place.

 

or you can heat them up, which makes them pliable, takes abit long and you gotta be quick in bolting it up, it also limits the use a fair bit as you deform it slightly each time.

 

 

 

personally speaking i prefer using the paper ones, yes they often break each time to strip the engine and yes they don't last as long, but its less hassle to fit one.

 

maybe go copper if i was racing or stripped down my engines often, but for bashing, there really isn't any point imo

i see your point there,

witch is why i am glad i bought a paper one and a other copper one

thanks for the info thunderwolf 

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  • 4 weeks later...

copper ones can be a pain.

you can't use them straight off like you can paper ones as they don't give a whole lot and so don't seal fully and leak, there are 2 ways around it

use gasket sealant, which is more expense, and personally why would i use it on something that's meant to do the sealing in the first place.

or you can heat them up, which makes them pliable, takes abit long and you gotta be quick in bolting it up, it also limits the use a fair bit as you deform it slightly each time.

personally speaking i prefer using the paper ones, yes they often break each time to strip the engine and yes they don't last as long, but its less hassle to fit one.

maybe go copper if i was racing or stripped down my engines often, but for bashing, there really isn't any point imo

When I rebuilt the engine on my 5ive, I used the steel reinforced heavy duty ones ddm sells.....

Best of both worlds I think .... Haven't had a problem since

Sent from my iPhone using Tapatalk

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