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exhaust bridge cracked AGAIN!

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Well when I picked up this 03cr250 it had fairly low hours, but I decided to do a top end to be safe. Pulled my cylinder off and found that it was cracked. So I sent it out and had US Chrome send me a new one. Rode it for a year( and not very often due to injury) decided to do another to end. Found the cylinder had cracked again. So I sent it back to US Chrome and had this cylinder repaired. In the meantime did the research on this issue.... so I used an oem piston and even drilled relief holes in the piston at the bridge. Also made sure US Chrome relieved the exhaust bridge... ran that for about forty hours and wallah another cracked exhause bride..

Not sure whats going on here. Am I missing something. I ride it hard! But not nearly as hard as a pro! I would think the bike would be a little more durable and be able to last longer than that.

Any input would be appreciAted

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Well I'm sure someone else can back me up here, but you're not supposed to drill an OEM piston. They're cast pistons and they're not supposed to be drilled, only forged pistons like Wiseco.

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Ive heard that too but all three times It cracked I was running an oem piston. I figured the holes wouldnt hurt any. I talked to a few old timers who say they used to do it to their cr500s aswell.

Is 40 hours too many on a stock piston? Or maybe the bran new cylinder is the waY to go?

I switch to the two stroke open the save money on maintenance! You're right now it's just as expensive as running my four stroke lol if not more

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I know I'm in Honda territory here, but the OEM piston's for the YZ's come pre-drilled. 40 hour's running hard is quite excessive imo. I'm sure your'e running the right ratio ?

Edited by Alan48

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44:1 ratio is what I run... and am also suspecting a slight crank seal leak now not sure how that would affect it.

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Don't drill a cast piston, it weakens them too much and you could get piston failure.  You would only drill a forged piston like a wiseco or wossner piston.  I think the reason your exhaust bridge keeps cracking is because it cracked in the first place.  There have been guys here who have said that once the bridge is cracked you can't fix it.  I would try a new OEM cylinder. 

 

IMO I would run more oil in your gasoline as well, like 32:1.  If you suspect an air leak, do a pressure test to see if your crankcase will hold pressure.  If you have a leak that can definitely cause lots of extra heat (Lean condition) you don't want in your engine.

Edited by frdbtr
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ive had the same problem....but on my last cylinder it only had 20 hrs on it...I sent mine to millennium and they told me that they have good luck with repair.   told him it was the second time they've replated it and he suggested a new cylinder.  pretty honorable if you ask me, they are great people to work with and he also said to run more oil (32:1)  I was 40:1 so im going to try that and if it happens again,  ill buy a new one....I just couldn't bare to part with my 02 cr.....not a mx racer by any means ( I race dirt track) but its always a feather under the cap when you go out and wax 450s on a mx track....

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Yeah same here! Mike at US Chrome was really cool and even gave me a discount the second time. Notbing bad to say about them... i think I will try a new cylinder this time. Are the two strokes just that "delicate" that u can over heat them or let it get lean, not even for a few minutes? I came from a four stokr and this is my first two stroke. With the exception on expensive top ends I ran the crap outta that bike with no issues.

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The motor was designed to run at 32:1. 40 hours is a bit much. I don't recall how far up the skirt rides in the cylinder and if it slams the bridge. They are not delicate but the service intervals are tighter to maintain peak performance. I have an 05 cylinder that is really worn but the bridge is intact.

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Okay, thanks for all your input. Im feeling better about trying this again and definitely run the 32:1 on this new cylinder!! Would u recommend staying with the oem piston? Or are the aftermarket ones the way to go in terms of durability and life?

Also was thinking this time around maybe do a full motor rebuild. I found a kit online made by weisco, they any good?

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44:1 ratio is what I run... and am also suspecting a slight crank seal leak now not sure how that would affect it.

 

i would drop that down to 25-30:1 range. I measure residual oil in the crankcase to determine the correct ratio. It took 25:1 in my rm250 to-get 1/8 residual in the bottom end. (what engine builders have told me to run)

 

You dont have a crank seal problem, you would be melting topends.  Try a wossner piston for your next rebuild, drill the oil holes and run more oil. I ruined 2 cast pistons in my 02 before going forged. No more problems after that.

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Well there is some good information in here and some for what I would say interesting information. 

 

Your fuel mix will have alot to do with it. Adding more or less oil to the mix will effect the general overall jetting and heat in the cylinder. Adding more oil to the mix Ie 20- 25:1 will lean the mix. As the fuel atmosiation going through the jets is less. Now you are on 40;1 which is better than 25:1. Stick with the recommended which I believe is 32:1.

Your seals may also effect the mix. A leaking mag or left side seal will lean out the mix. Now it may not be much but enough.

There are a few things to consider here. You said this was the second cylinder as the first was cracked - so this one was not cracked when installed as I am assuming it was an exchange cylinder but second hand none the less?  

Your jetting needs to be considered......check it and see if it is stock or has been oversized. 

Leaking seals need to be considered. 

Exhaust bridge relief needs to be considered.......I like to allow 3 thou.

The type of piston....forged or cast and piston clearances. A forged piston will expand faster than a cast piston and rule of thumb for clearances is 1 thou for each inch of bore size. I like to allow a little more if it is a forged piston. Say an extra .5 thou and drill a hole for extra oil lubing on the bridge but a forged piston is most likley to be supplied with the hole. Cast pistons expand slower and drlling holes in these will weaken them, as previously mentioned. 

Cracking bridge will be from heat and heat comes from oil mix, jetting, piston type cylinder clearances, radiator cooliing, waterpump, leaking seals, air/fuel mix, sparkplug heatrange and altitude above sealevel to name a few IMHO. 

If it was me I would be considering taking the bike back to factory standard specfications. I.e. OEM or OE barrel,piston,sparkplug,jetting,fuel mix,and fuel ratio settings.

I am no expert just my opinion of what I would do if it was my bike. 

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I think I will do that. I still have the stock jetting. Which is the way the bike was when I got it. It never ran lean tho. Actually seemed to be a little fat and "blubbery" like it didnt wanna clear out in low to mid. I have a 400 main jet and 32.5 pilot. Needle is on the very top clip.... leanest position. I did however overheat it last weekend at an enduro! But wasn't for a lot of time and didn't drain all the fluid out. But the bike did start running really laen when it got hot! I've been thinking that is when I cracked it. like I said I would think the bike should be able to take a little more abuse then that

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Don't drill a cast piston, it weakens them too much and you could get piston failure.  You would only drill a forged piston like a wiseco or wossner piston.  I think the reason your exhaust bridge keeps cracking is because it cracked in the first place.  There have been guys here who have said that once the bridge is cracked you can't fix it.  I would try a new OEM cylinder. 

 

IMO I would run more oil in your gasoline as well, like 32:1.  If you suspect an air leak, do a pressure test to see if your crankcase will hold pressure.  If you have a leak that can definitely cause lots of extra heat (Lean condition) you don't want in your engine.

32:1 is too rich and IMHO a waste of oil.

I have run as lean as 70:1 with race gas, a good quality oil on a built engine when I was racing nationals back in the day.

50:1 is fine, it's middle of the road and provides plenty of lubercation to the lower end, I have run this ratio for 20 years on stock engines without any issues or excessive wear...and still run it today in my 01.

As far as a crack in the aluminum at the bridge behind the sleve, I have see this, well more that a few times and most didn't worry too much about it.

I think because at the time cylinder replacement was big bucks, I remember guys ran them for many seasons like that.

Edited by moto9
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32:1 is too rich and IMHO a waste of oil.

I have run as lean as 70:1 with race gas, a good quality oil on a built engine when I was racing nationals back in the day.

50:1 is fine, it's middle of the road and provides plenty of lubercation to the lower end, I have run this ratio for 20 years on stock engines without any issues or excessive wear...and still run it today in my 01.

As far as a crack in the aluminum at the bridge behind the sleve, I have see this, well more that a few times and most didn't worry too much about it.

I think because at the time cylinder replacement was big bucks, I remember guys ran them for many seasons like that.

 

if you run 50-1 without issue, that is your choice.  I run 32-1 because that is what the manufacturer recommends.  If your cars owners manual recommended running 5 quarts of motor oil, would you run 3 because it gets plenty of lubrication with 3 and 5 is a "waste of money"?  Me neither. 

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if you run 50-1 without issue, that is your choice.  I run 32-1 because that is what the manufacturer recommends.  If your cars owners manual recommended running 5 quarts of motor oil, would you run 3 because it gets plenty of lubrication with 3 and 5 is a "waste of money"?  Me neither. 

They recommend it because the factory didn't want any warrenty issues.

Do you replace your piston and rings per the recommended service spec time located in the manual...I think not!

Do you think the any of the race teams ran 32:1 'NEVER" most were 50:1 to 90:1 and here's a bit of info you probably didn't know, the more oil you run the leaner the mixture, which is harder on the top end...cylinder, piston, rings!...more fuel= cooler tempertures...fact!

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They recommend it because the factory didn't want any warrenty issues.

Do you replace your piston and rings per the recommended service spec time located in the manual...I think not!

Do you think the any of the race teams ran 32:1 'NEVER" most were 50:1 to 90:1 and here's a bit of info you probably didn't know, the more oil you run the leaner the mixture, which is harder on the top end...cylinder, piston, rings!...more fuel= cooler tempertures...fact!

 

Oh, I am aware of more oil less fuel rich vs lean.  I am also aware that fouling plugs is a jetting issue and not an oil fuel mix issue.  I don't care what factory teams with their millions of dollars ran as oil\fuel mix, but if you can name even one that ran 90:1 I would be surprised.  I chose an oil/fuel ratio based on my riding style, what the manufacturer recommends and also what I read by 2 stroke experts in various articles in magazines and on the internet.  Next time you pull your main jet, take a look at how small the hole is that your fuel and oil has to pass through in order to get into your motor, then divide that by 50% or 90% and then think for a second about that amount needing to lubricate your piston, and crankcase bearings.  If you think about that logically, you might reconsider the amount of oil you run in your bikes.  Like I said, I wouldn't run 3 quarts of oil in a car requiring 5 quarts just because it would save me a couple of bucks on oil changes.

Edited by frdbtr

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Oh, I am aware of more oil less fuel rich vs lean.  I am also aware that fouling plugs is a jetting issue and not an oil fuel mix issue.  I don't care what factory teams with their millions of dollars ran as oil\fuel mix, but if you can name even one that ran 90:1 I would be surprised.  I chose an oil/fuel ratio based on my riding style, what the manufacturer recommends and also what I read by 2 stroke experts in various articles in magazines and on the internet.  Next time you pull your main jet, take a look at how small the hole is that your fuel and oil has to pass through in order to get into your motor, then divide that by 50% or 90% and then think for a second about that amount needing to lubricate your piston, and crankcase bearings.  If you think about that logically, you might reconsider the amount of oil you run in your bikes.  Like I said, I wouldn't run 3 quarts of oil in a car requiring 5 quarts just because it would save me a couple of bucks on oil changes.

Ha, this is like discussing religion or politics,  let's just agree to dissagree...and leave it at that!

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