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Discussion Starter · #1 ·
Hello guys, sadly, my engine is blown, the right crankcase is cracked, (left side crankcase looks fine) see the photos attached. (The bike have the Big 5: big 3 + bored TB and Custom camshaft similar to HC3). I use pump 93octane gas and I ride Mr. Cuevo Racing Fuel and Ignition MAP.
I have a couple questions:
1) Its fixable since there are no missing pieces? or I need to buy a new crankcase?
2) What could have been the cause of the break? I take care of the bike, good mateinance and it have only 2800 miles. Also I never hit the rev limiter when ridding, I usually ride in the highest gear possible when im not racing. The engine cracked under normal acceleration, nothing crazy and not too high on the RPM, I think I was in 3rd of 4th gear.
3) How can I prevent this to happend again? wichs parts should I buy to achive this and make it more reliable?
4) Could the crankcase breather hose become clogged have caused this break?

Any help will be very much appreciated, thank you!
 

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You’re going to have to take it apart and see what happened. Definitely need new cases.
Did it make any noise and die? Or did you just notice the cracks?
 

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Discussion Starter · #5 ·
You’re going to have to take it apart and see what happened. Definitely need new cases.
Did it make any noise and die? Or did you just notice the cracks?
I was riding and I feel and hear the sound of a dull metallic thump and the engine die, the wheels blocks. Stop the bike and I notice the cracks and a few oil. The bike was riding great, never hear any strange sound, it dont smoke, It didn't overheated (I have Trial tech vogayer Gauge on my handlebars with light indicators for temps), coolant full allways. I cant uderstand what happened.
 

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Discussion Starter · #6 ·
It looks like the head bolts were too tight and eventually the stress and heat cycles caused the cracks.
Engine was never open, bolts are factory tight.
 

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I would bet that when you take it apart you’ll find that the wrist pin is all chewed up and piston is stuck in cylinder. Your counterbalancer tried to come out the front of your engine because the crank suddenly stopped.
Since you’re counting ride time in the thousands of miles, I would assume you’re riding on the road, which equates to long periods under throttle. These were never meant for the road and this is a common result.
It sounds like you’ve been doing everything right to prolong the life, the only other thing I would suggest is that when you rebuild it, do the “oil sprayer mod”.
 

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Discussion Starter · #9 ·
I would bet that when you take it apart you’ll find that the wrist pin is all chewed up and piston is stuck in cylinder. Your counterbalancer tried to come out the front of your engine because the crank suddenly stopped.
Since you’re counting ride time in the thousands of miles, I would assume you’re riding on the road, which equates to long periods under throttle. These were never meant for the road and this is a common result.
It sounds like you’ve been doing everything right to prolong the life, the only other thing I would suggest is that when you rebuild it, do the “oil sprayer mod”.
I dont ride on roads, Its a trail bike and I do some MX tracks. Today I sent the bike to my local mechanic to disassemble the engine and see that's broken. I will let you know what we find guys.
 
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I dont ride on roads, Its a trail bike and I do some MX tracks. Today I sent the bike to my local mechanic to disassemble the engine and see that's broken. I will let you know what we find guys.
Good call not riding roads, that seems to be a pretty common way to kill these.
I recently blew one up as well, but I know how I did it.
 

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What is the difference of riding on the road vs a trail or forest road? On a trail/dirt road, I am riding at 3000-4000 RPM with bursts of power when needed. When on a road, I am in the same RPM range but in a higher gear at a higher speed but very little throttle. I would think cruising on a road would be easier on a motor then trail running where you are on and off the throttle a lot harder then crusing. Not looking for a debate, just curious on the thinking.
 

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What is the difference of riding on the road vs a trail or forest road? On a trail/dirt road, I am riding at 3000-4000 RPM with bursts of power when needed. When on a road, I am in the same RPM range but in a higher gear at a higher speed but very little throttle. I would think cruising on a road would be easier on a motor then trail running where you are on and off the throttle a lot harder then crusing. Not looking for a debate, just curious on the thinking.
X2. Would be cool to know why.
 

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Discussion Starter · #15 ·
Well, this is the update: the connecting rod broke, and it broke also the crankcase, the piston and the cilinder.... The transmission, crankshaft, clutch and head are like brand new. So, since I need to rebuild it I was thinking to buy Forged Rod and Piston. Which one will be the strongest? I want reliable power. Keep in mind I have pump 98RON octane gas. What do you think about Saenz Rod and Carrillo 11:1 Piston and 734cc Cylinder? Where I can buy the parts and also the gaskets? Any help will be very much appreciated
Thank you!
 

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Looks like I was wrong, broke the big end of the rod.

I would do a carillo or crankworks rod and a cp piston. 105.5 bore is fine, but avoid the Chinese cylinders. Oem re-bored cylinder or CPI are the best. I would just stay stock bore if you aren’t porting the head.

These are all parts that Cuervo racing tends to keep in stock, as well as the gaskets. And he does ship internationally.
 

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The road riding reffered to that blows engines is from riding at or near the rev limiter for extended periods of time.
That's alot of heat and stress on one cylinder.
OK, that makes sense. Any motor run for long periods of time near the rev limiter is not going to last very long.

It was the general comment that running on the road was going to blow the motor had me scratching my head.

OP, sorry to see the damage. That hurts.
 

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Discussion Starter · #20 ·
Hello guys, just an update of the building procedure, and some questions. I finded parts, I will do: New cases, new oem cylinder, forged Rod and forged 11:1 CP piston and also I sent the Head to be ported (stock valve sizes). Im now waiting the parts to arrive. I need to replace the clutch disc also, Im looking to do the Full fiber mod: 8 full fiber discs and 7 steel discs, I saw the Mr. Cuervo Racing video about it and he recommended the YFZ 450 2004-2005 clutch fibers the part number is: 5TG-16321-00. I was told by my local engine builder I need to change the springs of the clutch to make the clutch to last longer, to make it happend I need to use 3 oem springs and 3 aftermarket, wichone should I use?

2) Another question is if I need to replace also the steel discs of the clutch, the spects should be from 1.5 to 1.6mm. My steel plates are 1.59mm, so almost no wear on them, but they look quite dark, I dont know if they are dark from factory (my bike is 2015) or if they should look like ¨silver¨ colour. If they should be ¨silver¨ but they are not wear out on thickness, can I still use them or not? and why?

3) My bike is Big 5 (please look at my description in my signature) and Im doing the 11:1 Piston on new oem Cylinder and Ported head with stock valves size, how much power it should deliver?

4) Where I can find a map to use with? I have the Autotune, so, a very close map should work for me. There is no dyno near me, the nearest are 2 days travel distance so I dont know when I will be able to travel so far to put it on a dyno and I need a map to start seat the new engine build.

5) Should I need to make the seat of the new engine by the Yamaha recommended way?

6) Where I can find a the Maintenance and Repair Manual in Spanish? since my engine builder cant read in english and I the one I have is in english and he need to know the correct Torque for the bolts in the assembling procedure.


I will be waiting for your help, and always grateful for it. Thank you guys!
 
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