Blown up CRF450 (pics) and questions...

[DIRTBIKES987]

I bought a 2004 CRF450 a couple weeks ago that was siezed up, and I figured that it needed a new crank, cylinder, piston, valves etc. Turns out the crank is still fine, but as you can see from the pics, the cylinder, piston, and head are FUBARed.

A few questions. I was looking under ebay for used cylinders, and it seems as though so many of them have a very faint scoring on the cylinder wall... I found a few of them like the one pictured below. Is this a common problem? Avoid bidding on them or hone it and run it? How many more hours could I expect to get out of a cylinder with the slight score?

The scoring is visable there. How bad is that? It seems common...

Heres my 450. The reason this happened (I am pretty sure) is because there was a crack in the ignition cover, oil slowly leaked out and ran low on oil. Kid I bought it from must not have checked it or cared about it or something.

Luckily, absolutley nothing fell into the bottom end of the motor. I flipped it uspide down and turned it over, blew it out with an air compressor, and no pieces of anything fell out. Everything fell into the water jackets on the cylinder.

[dlkraniak]

I am no expert, but just by looking at the damage to your piston I find it very hard to believe that nothing fell into the bottom end of your engine. Just flipping it upside down and blowing it out is probably not going to get every metal shaving out. Is thier any metal in your oil filter? How long did you ride it after it started making noise or running funny? I would suggest splitting the cases and replacing every bearing that you have.

As far as the cylinder is concerned I can only say that I did not see any scoring in mine when I changed my valves. Hope that this helps!

[huffster]

Considering what that crank just went through....it's far from O.K. ! Looks to my like the piston was worn and tried to flip, low on oil would show vertical scoring in the cylinder, prior to it sticking...

[flatracker]

Cranks arent that much,serious racers replace all that stuff every year if not twice a year. 4 strokes are not cheap and reliable anymore,racing ones anyways. A friends engine and suspension shop has more crf450's and crf 250's torn down then any other japanese race bike. They dont last long under a hard charging racer or a clumsy mechanic.Hence the two stroke in my garage. Good luck,they are a sweet bike when dialed in.

[2ski4fun]

A friends engine and suspension shop has more crf450's and crf 250's torn down then any other japanese race bike. They dont last long under a hard charging racer or a clumsy mechanic.

I would venture to guess that there are more Honda CRFs on the dirt than any other make of bike. Just go to any California OHV area on the weekend, it looks like it's sponsored by Honda.

[kjlectric]

I am no expert either but I do have an 04 that recently spun the main rod bearing which also took out the cylinder and piston. I have around 300 hours on it so I am replacing the crank, crank bearings, tranny bearings, piston and cylinder. About $900.00 in parts.

Do you know how many hours are on the bike?

I wouldn't recommend buying used parts if you plan on keeping the bike. I would recommend replacing the crank, main bearings and tranny bearings especially if the hours are high. It looks like you will need a new head and valves too. What, around $1400.00 in parts and head work?

How much did you pay for the bike?

If your plan is to get it running on the cheap , ride it and sell it. By all means, buy the used parts. I would avoid the cylinders with piston wear like the ones in your post.

Good luck. ?

[CamP]

I would venture to guess that there are more Honda CRFs on the dirt than any other make of bike. Just go to any California OHV area on the weekend, it looks like it's sponsored by Honda.

Yep, I'm pretty sure Honda sells more 450's than the other three manufacturers combined so it makes sense to see a lot of them in the shop compared to the other makes.

[DIRTBIKES987]

I am no expert, but just by looking at the damage to your piston I find it very hard to believe that nothing fell into the bottom end of your engine. Just flipping it upside down and blowing it out is probably not going to get every metal shaving out. Is thier any metal in your oil filter? How long did you ride it after it started making noise or running funny? I would suggest splitting the cases and replacing every bearing that you have.

As far as the cylinder is concerned I can only say that I did not see any scoring in mine when I changed my valves. Hope that this helps!

I bought it from a kid blown up. He said it started knocking, he turned it off, then started it up a few minutes later and it seized up a few seconds after he started it.

All of the pieces were inside the water jacket on the cylinder. I "puzzeled" all of the pieces back together... nothing went down in the crank. I find that hard to believe too, gravity normally wins, but for some reason they did not get down into the crank.

Thanks for the help!

[DIRTBIKES987]

Considering what that crank just went through....it's far from O.K. ! Looks to my like the piston was worn and tried to flip, low on oil would show vertical scoring in the cylinder, prior to it sticking...

Could you explain "tried to flip?" Do you mean that the cylinder had too much clearance and was rocking back and forth too much?

There was scoring on the cylinder, mainly the other side. I believe it ran low on oil since there was a crack in the case.

[Shawn_Mc]

Could you explain "tried to flip?" Do you mean that the cylinder had too much clearance and was rocking back and forth too much?

There was scoring on the cylinder, mainly the other side. I believe it ran low on oil since there was a crack in the case.

The piston has very little skirt, and when they get old and worked, they collapse a little from normal use and what they try to do is turn sideways in the bore, and they sometimes do. They usually take out the bore entirely, sometimes the crank. Just like yours did.

Id put a new crank in that thing. The amount of damage to the piston is enough to warrant the crank even if it was relatively new. Its a very remote possiblity that the crank is serviceable. It ran long enough to wear out the piston, that means the crank aint a spirng chicken if you get my drift.

It probably did run low on oil, and that accelerates calamity and bore scoring, skirt wear etc.

While youre in there, you may as well replace every bearing too. No sense in only doing half the job unless youre looking get out cheap and to sell it off.

[busted bones]

with all the damage you did to that piston i would find it very unlikely that the crank is still in good shape, i think youd be more likely to travel at lightspeed on that bike, you cant tell how many internal fractures it has with out an acid dip and x ray or a high powere microscope and at 13,000 rpm those little cracks become huge ones ending in bottom ends being destroyed

[Joe Haggard]

If the crank and bearings somehow survived the rod definetly should not be overlooked. I just had a valve spring break which caused the valve to hit the piston so I replaced the piston&rings, put on another head that I had, the crank and rod looked fine. About 20 minutes into the very next ride the rod broke right below the piston end and rotated the rod around and shoved it through the counter balance shaft which spread the cases and then broke through. It would have been cheaper to replace the crank,rod and all the bearings.

[k5kell]

Keep in mind that just because you can see how the pieces "Puzzle" together that doesn't mean that there aren't allot of smaller pieces that worked their way into the bottom end. In these motors even pieces the size of a few microns will lead to big problems. I would also have to agree with the previous posts about the crank replacement. Good Luck.

-Kell-

[crf176]

Put everything new in it so there is no wink link when you put it back together. Then your not doing this all over again down the rode in 2 months! I almost guarantee you that you bent the rod with the damage in the pics!

[mywifefarts]

I am no expert either but I do have an 04 that recently spun the main rod bearing which also took out the cylinder and piston. I have around 300 hours on it so I am replacing the crank, crank bearings, tranny bearings, piston and cylinder. About $900.00 in parts.

Do you know how many hours are on the bike?

I wouldn't recommend buying used parts if you plan on keeping the bike. I would recommend replacing the crank, main bearings and tranny bearings especially if the hours are high. It looks like you will need a new head and valves too. What, around $1400.00 in parts and head work?

How much did you pay for the bike?

If your plan is to get it running on the cheap , ride it and sell it. By all means, buy the used parts. I would avoid the cylinders with piston wear like the ones in your post.

Good luck. ?

Just wondering what kind of time do you get out of your valvetrain? Also do you race?

I just want to know what kind of beating these things can take.

[chilwil86]

Buddy you should thank your lucky stars that your rod didnt get loose fromthe piston and take out da cases..

[marktm200]

looking at your bike makes me feel good about mine. jk but that sucks i feel your pain

[sonobob]

Guys, he's already said twice that he bought it in this condition from a kid that obviously didn't know or care enough about maintenance to prevent the seizure.

[EddieTNT]

Would you be interested in possibly selling the roller? I have a CR500 engine that needs a good home.

[chillydog]

I'd look for a cr500 motor and a seat belt. ?