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03 cr 125 top end roasted?

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So i was riding at the track today, and was getting a mid bog a lot which it has always had but it was worse today, thought nothing of it just kept sending it, and coming into a corner bike just completely bogs down, and steam starts coming from the head and coolant hose was melting at the end, and motor was extremely hot (was only out there for a time span of 5 mins). Bike has no compression now and havent taken it apart, but im wondering what caused this. To start i bought the bike from a guy for a very good price, he /SAID\ he replaced the top end and hasnt put any hours on it which, me not wanting to turn a wrench i never opened up to see if it was new or not so it mightve been a old top end in it but my gut tells me i jetted the thing too lean. First thing i did was put vforce reeds in and a jd jetting kit, has 420main, 32.5pilot, and has the red needle with clip in 3rd groove, before i even took it on the track. I knew instantly that it mightve been too lean as the engine got way hotter and faster than it was with old jetting, but it ran good besides a occasional mid bog. The carb also has a very small leak from the float bowl part of the carb im thinking the seal is bad on it but i ran it like it was and maybe this was also a factor, im not too sure. And heres a pic of the plug https://gyazo.com/9e1d5102617a2902773f09b241cea148 i will take it all apart tomorrow but i would like some opinions on if i jetted it too lean and if the carb leaking had a factor. Forgot too add, i was using VPR and 32:1. And just called the old owner of the bike, he told me he was having issues with it blowing up every couple of hours too so im guessing im in some shit right now and gonna have to get someone to split the case and look if there isnt any debris inside

Edited by fleckzter

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your plug does look lean. white and orange it may be the jetting but you may have an air leak some where. if the engine is blowing up every couple of hours sounds like an air leak in the crank cases or some where on the induction side of the engine. before you split the cases take the top end off and fill the crank void with fuel and let sit for a bit see if there is any leaks. might leak at the case joint. might leak at the crank seals. worth a look to see if you can find the leak before you pull the engine down. that way it can be fixed knowing what the problem is and saving you from another blown engine! good luck and let us know how you went......cheers

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Just now, vicxr400 said:

your plug does look lean. white and orange it may be the jetting but you may have an air leak some where. if the engine is blowing up every couple of hours sounds like an air leak in the crank cases or some where on the induction side of the engine. before you split the cases take the top end off and fill the crank void with fuel and let sit for a bit see if there is any leaks. might leak at the case joint. might leak at the crank seals. worth a look to see if you can find the leak before you pull the engine down. that way it can be fixed knowing what the problem is and saving you from another blown engine! good luck and let us know how you went......cheers

Ah reading into leak down tests that definitely seems like this is the issue i have way which would make sense for such a old bike.

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not exactly a leak down test. leak down is combustion pressure getting past the piston.....what I suggested is more of a crank case seal test.  as the fuel air mix is pressured in the crank case to force it up the transfer ports to the combustion chamber. but your problem does sound like an air leak.

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Just now, vicxr400 said:

not exactly a leak down test. leak down is combustion pressure getting past the piston.....what I suggested is more of a crank case seal test.  as the fuel air mix is pressured in the crank case to force it up the transfer ports to the combustion chamber. but your problem does sound like an air leak.

Wouldn't a leak down test test the crank case seal too? That might have been a dumb question but ive never done this stuff before so trying to take in as much as possible, thanks

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I would also check out the whole cooling system to make sure its not blocked any where. some build up with slime and cut down the surface area for cooling.

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I doubt it because the pressure can escape through the exhaust port. rather than pressurise the crank case.

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Yehh you can but you may still have small leaks past the power valve any leak like that will upset the test and give you false results. plus you cant see air. putting fuel in you can see where the leak is because the leak gets wet. fuel will leak through tiny holes that even water wont get through.

I mean by all means try the leak down test if you want there is no harm in doing it. I was just thinking that by the sounds of it your top end is toast and your going to have to take it off any way. and the leak you are looking for has to be in the bottom end to be leaning out the fuel mix. how is your carby boot and reed block?? can leak there to.

basically you are looking for a leak between the carby and the cylinder.

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55 minutes ago, vicxr400 said:

Yehh you can but you may still have small leaks past the power valve any leak like that will upset the test and give you false results. plus you cant see air. putting fuel in you can see where the leak is because the leak gets wet. fuel will leak through tiny holes that even water wont get through.

I mean by all means try the leak down test if you want there is no harm in doing it. I was just thinking that by the sounds of it your top end is toast and your going to have to take it off any way. and the leak you are looking for has to be in the bottom end to be leaning out the fuel mix. how is your carby boot and reed block?? can leak there to.

basically you are looking for a leak between the carby and the cylinder.

That's all fine, took that apart and installed the vforce couple rides ago, what about the leak I'm having from the float bowl part of the carb? It has a very slow drop of gas and I'm guessing I need to replace the gasket in it, could this also be sucking in extra air and making it too lean? 

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mmmm I wouldn't think so the carby bowel has an atmospheric vent to allow air to be displaced when fuel goes in. ie. if no air gets out no fuel can go in. the gasket/oring needs to be replaced as leaking fuel is not good also id check the float level. is there a build up of crud under the engine? sounds to me like the  leak is in the crank case or cylinder base gasket or crank seals. although crank seals would not lean out the mix that bad unless theyr real worn out. I think if they wer that bad youd have fuel in the engine oil.

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13 minutes ago, vicxr400 said:

mmmm I wouldn't think so the carby bowel has an atmospheric vent to allow air to be displaced when fuel goes in. ie. if no air gets out no fuel can go in. the gasket/oring needs to be replaced as leaking fuel is not good also id check the float level. is there a build up of crud under the engine? sounds to me like the  leak is in the crank case or cylinder base gasket or crank seals. although crank seals would not lean out the mix that bad unless theyr real worn out. I think if they wer that bad youd have fuel in the engine oil.

Nope no build up of oil under, when I bought the bike the countershaft was leaking but all idid was powerwash the bike and it went away 

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did you check the engine oil for fuel?  to be honest theres not much more I can suggest with out some pictures and or you try some of the checks to narrow it down.

I hope the info helps and that you find the problem. let us know how you go and what you find.....cheers

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Finally took it all apart, all the gaskets are like melted on, has to exacto them off, the piston doesnt look too bad but im unsure of what mm i am supposed to order, the only thing it has ontop of it is 69, here are pics of everything, im still unsure of what caused this lmk what you think, should i be worried about the bottom end being toast too?

 

 

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Edited by fleckzter

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hmmmm  doesn't look to good.  your going to have to ether bore and replate or get a new cylinder because that ones toast. new piston to suit. looks like its blown the head gasket and may have been consuming coolent.  may be the sauce of the lean condition and the damage to the piston and cylinder. the head looks reusable with a good clean as long as its not warped. its hard to tell from the pix but did the burnt section of the head gasket line up with the exhaust side of the cylinder???

as for the bottom end grab the con rod with crank at tdc and carefully move the rod up and down and side to side as well as twist if the big end is toast you will feel the movement. the workshop manual should give clearance specs that can be checked with a feeler gauge. also take side engine covers off and try to move the crank up down side to side to feel any movement in the crank bearings. if any movement they need to be replaced along with seals. if your lucky it will only be the top end. good luck and let us know how you went.....cheers

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The gouge inline with the exhaust bridge looks pretty deep, 

that cylinder needs to be re-plated before dropping in a new piston.

 

No matter if the crank & rod show no excessive play, the crank seals should be preventatively replaced.

Having your newly rebuilt top end melt down sooner than expected due to an air leak would suck.

Edited by mlatour

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Just now, vicxr400 said:

hmmmm  doesn't look to good.  your going to have to ether bore and replate or get a new cylinder because that ones toast. new piston to suit. looks like its blown the head gasket and may have been consuming coolent.  may be the sauce of the lean condition and the damage to the piston and cylinder. the head looks reusable with a good clean as long as its not warped. its hard to tell from the pix but did the burnt section of the head gasket line up with the exhaust side of the cylinder???

as for the bottom end grab the con rod with crank at tdc and carefully move the rod up and down and side to side as well as twist if the big end is toast you will feel the movement. the workshop manual should give clearance specs that can be checked with a feeler gauge. also take side engine covers off and try to move the crank up down side to side to feel any movement in the crank bearings. if any movement they need to be replaced along with seals. if your lucky it will only be the top end. good luck and let us know how you went.....cheers

 

Just now, vicxr400 said:

hmmmm  doesn't look to good.  your going to have to ether bore and replate or get a new cylinder because that ones toast. new piston to suit. looks like its blown the head gasket and may have been consuming coolent.  may be the sauce of the lean condition and the damage to the piston and cylinder. the head looks reusable with a good clean as long as its not warped. its hard to tell from the pix but did the burnt section of the head gasket line up with the exhaust side of the cylinder???

as for the bottom end grab the con rod with crank at tdc and carefully move the rod up and down and side to side as well as twist if the big end is toast you will feel the movement. the workshop manual should give clearance specs that can be checked with a feeler gauge. also take side engine covers off and try to move the crank up down side to side to feel any movement in the crank bearings. if any movement they need to be replaced along with seals. if your lucky it will only be the top end. good luck and let us know how you went.....cheers

yup head gasket's burnt section was exhaust side, and yes it sucked up literally just about every drop of coolant, im very puzzled on how that happened. Well looks like im in for a ride to fix this ol hunk good thing i have multiple bikes to ride in the meantime. The head does seem warped when its seated on the cylinder. As for the cylinder can i just get it replated or will i have to get it bored out? i dont want to go the route to bore it out as i would like to keep it stock but if i can just replate it thatd be great or i will have to just get a new cylinder

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ordered a top end rebuild kit from namura 53.94mm

 

is this what i should be ordering to replace the crank seals? http://www.ebay.com/itm/Main-Crank-Shaft-Bearings-Seals-Kit-Honda-CR125R-1999-2000-2001-2002-2003-2004-/362001570464?epid=937256410&hash=item5448f99aa0:m:m5yhxljh-bSXbbRcjIedLmA&vxp=mtr

as for replating the cylinder im looking on http://www.maxrpms.com/free-cylinder-exchange/cylinder-plating/#scr 

they charge $225 shouldn't i just buy a brand new OEM cylinder of ebay for $270?

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If a new cylinder is available and isn't much more expensive than

having the old one re-plated, indeed I also would rather go that route.

 

Don't be too quick to order parts, make a list.

More familiar with Yamaha stuff but likely a CR125 also has A-B-C-D piston & cylinder sizing,

I'd make sure to measure whichever cylinder you'll be using before ordering a new piston.

 

I've always had a preference for genuine OEM engine parts,

unlike aftermarket stuff you rarely read comments on sketchy quality control, bad fitment etc. 

 About the only complaint some have is the higher price. 

Edited by mlatour

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you can check the head for warp with a strait edge or fine wet and dry on a sheet of glass(if using sand paper and glass keep even pressure and rub as little as possible to see high and low points)  namura have good pistons but be wary of theyr gaskets. I not long ago got a namura top end kit for my xr all went good but the base gasket was a dud and leaked oil from new I double checked the torque and all was where it should have been. have since replaced the gaskets with oem Honda and no more leak!

those bearings and seals look good should do the job. and if the cost diferance is that little between replate or new definitely  get new

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