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CRracer

2003 cr 125 motor rebuild

13 posts in this topic

just thought i'd share my experiance of buying used toys i've been very lucky in the past when it's comes to buying snowmobile quads, dirt bikes you name it, but after buying my cr i got screwed turn out when the guy drilled the stud because it was stripped he drill into the exhaust port and now becuase of his shitty top end job i need to pour about 600 dollars worth of motor into my new bike. now had i gotten the bike up to tempurature when i was test riding it i would have noticed it leaking antifreeze aswell. so i guess i learned my lesson also i was wonderin should i try and buy a used jug? or pay 240 4 a new jug?

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Thats ironic the 2003 cr 125 I used to own was a piece and cost me probably 500 dollars in parts til the crank seized/case cracked. I ended up selling it as is. Sorry Im of no help but it brings back bad memories. Actually I would check out ebay for a new jug. Or you could always send yours to eric gorr for a 134 kit (highest cc for that year of cr). That cost about 500 I think but its a new top end and the big bore and everything.

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Actually everything in my research regarding my 2003 CR125 states that you can NOT big bore it. I had my piston blow up due to a drop of water getting past the head gasket just 2 weekends ago. The piston grenaded on the exhaust side and scratched the jug pretty bad. I ended up getting a brand new jug from service honda for $255 as well as new top end kit and head for a really good price.

Just so you know, when ordering parts from them it will not show the discounted price until you put the items in your shopping cart. I ordered on October 29th (late) and the parts are scheduled for delivery today.

Good Luck

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+1 on the Eric Gorr big bore kit. I had him do a supermini on my son's 80 and my experience with him was very positive. As soon as my 94 125 needs another top end, it is going to go to him for a 144 kit.

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Actually everything in my research regarding my 2003 CR125 states that you can NOT big bore it. I had my piston blow up due to a drop of water getting past the head gasket just 2 weekends ago. The piston grenaded on the exhaust side and scratched the jug pretty bad. I ended up getting a brand new jug from service honda for $255 as well as new top end kit and head for a really good price.

Just so you know, when ordering parts from them it will not show the discounted price until you put the items in your shopping cart. I ordered on October 29th (late) and the parts are scheduled for delivery today.

Good Luck

Thermal shock? Did the piston shatter?

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I don't think the stud backed out, I tried to take them out last week and they're not budging. I used a level and feeler gauge and there's a bit of a gap where the head and cylinder meet at the port where the coolant enters the cylinder from the head. There's also a black mark that I wasn't able to remove on both in the spot where I think the coolant got thru.

When I was cleaning the parts up I was trying to figure out what happened i.e. too lean, over reved it, ect. and came across that mark and then it came to me. The piston blew off a chunk, which hit the spark plug and degapped it. The piston ring split and thats what gouged up the cylinder wall. I will take pics this weekend and post them if you guys/gals want. This was a Weisco piston, and no I'm not saying anything bad about them, it would have happened to any piston given these circumstances.

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Should all of the studs sit at the same height? The two that flank the coolant flow are sitting higher than the others. I'm at work and no where near the cylinder, but looking at a pic I took with my phone they're maybe 2mm above the plain of the top of the cylinder...if that makes sense.

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Ok, got the bike rebuilt this weekend, here are some pics and some answers/comments.

The power valve sucks to get put back in.

The studs are all the same height, but the two on the exhaust side don't sit as low in the cylinder than the others.

All in all, it was a fairly easy job to do and putting it back together took me maybe an hour and 15 minutes.

It is easier to put the cylinder back on the piston with the piston about 1/2 way thru it's stroke, and compressing the ring while putting the cylinder on would have been easier with a second person to help.

If you have any questions let me know and I'll try to answer them as quickly and accurately as possible.

In these pics you can see the black spot on the cylinder and head where the coolant was able to get past the gasket. I didn't measure the head but there is a .002 or was it .02 gap where the black spot is on the cylinder.

DSCN2337.jpg

DSCN2339.jpg

DSCN2344.jpg

DSCN2347.jpg

DSCN2349.jpg

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