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Hello, I recently purchased a 2003 foreman 450. I got it for $150.00 because the guy was tired of looking at it and didn’t want to mess with it. The top end was off because he said the piston and cylinder had damage. I took a look at it and they both have obvious scaring. My question is, How do I know if the bottom end is good. I messed it with a bit and I can rotate the piston in one direction and I switch the gears and it seems to hit every gear. Now I stripped it down to the frame. Next week I start ordering parts to get it back together. But I would hate to do all that work if I’m missing something with the bottom end. This is my very first build so I just want to make sure it goes back together the right way. Does anyone have any advice? TYIA.

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I would see if the connecting rod has any up and down slack or play in it and check the condition of the inside of the small end of the connecting rod and see if it’s smooth or all galled up

If it looks good, I would check fitment of new wrist pin and make sure it has no play in it at all

To  be honest I would split cases and clean it out if you are not 100% sure it has not been sunk

If the top end is really scored up bad, you might have an oil issue such as a plugged up filter screen or backwards oil filter etc

you also might have had an overheating issue so I would check fan operation as well as plugged up cooling fins on oil cooler. (Mud) when you get it running

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first thing you need to do is down load the service manual from the site here, FOR THAT MODEL AND YEAR !. second thing you need to do is rip that motor all the way down, go through it piece by piece, and inspect every part. chances are, the rod is bad, and this means the rod will need to be replaced ?, or the whole crank might need to be replaced ?. once you get this done, its a matter of seeing what all parts you may need to put it back together. count on a new D.I.D. cam chain, complete engine gasket kit, complete oil seal kit, tube of yamabond or hondabond ( this is just for any place there is not a gasket ?! ). you will more than likely need to have the top end bored over, and a larger piston kit. BE WARNED !!, this is a electric shift model going by the pics you have posted ?, personally, i would not own an electric shift..9 out of 10 times they are a money pit, more trouble than what they are worth. some folks love them, i myself , hate them !..lol.

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2 hours ago, shadetree said:

first thing you need to do is down load the service manual from the site here, FOR THAT MODEL AND YEAR !. second thing you need to do is rip that motor all the way down, go through it piece by piece, and inspect every part. chances are, the rod is bad, and this means the rod will need to be replaced ?, or the whole crank might need to be replaced ?. once you get this done, its a matter of seeing what all parts you may need to put it back together. count on a new D.I.D. cam chain, complete engine gasket kit, complete oil seal kit, tube of yamabond or hondabond ( this is just for any place there is not a gasket ?! ). you will more than likely need to have the top end bored over, and a larger piston kit. BE WARNED !!, this is a electric shift model going by the pics you have posted ?, personally, i would not own an electric shift..9 out of 10 times they are a money pit, more trouble than what they are worth. some folks love them, i myself , hate them !..lol.

Hey, I just took a look down inside the engine from the piston side and it looks new. Well oiled. The top end was off when I bought it but it was well covered when I first saw it. There is not any up and down play in the arm thing that hold the piston nor does the piston have any play where it is connected to that arm thing. The arm turns in one direction abut I didn’t like about putting it in neutral and try going both ways. I don’t know if it works that way but I’ll try it later if it does. That arm did turn very smoothly though. When it was all together I did try the gears and it was going into every gear. The piston and cylinder wall does have scoring. Not real bad but it does have surface rust. I figure from weather change and being off of the engine. I will be order a whole new top end kit that includes the cylinder so I won’t have to worry about boring it out and matching a new piston. So wish me luck!!!

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43 minutes ago, DLBeltran74 said:

Hey, I just took a look down inside the engine from the piston side and it looks new. Well oiled. The top end was off when I bought it but it was well covered when I first saw it. There is not any up and down play in the arm thing that hold the piston nor does the piston have any play where it is connected to that arm thing. The arm turns in one direction abut I didn’t like about putting it in neutral and try going both ways. I don’t know if it works that way but I’ll try it later if it does. That arm did turn very smoothly though. When it was all together I did try the gears and it was going into every gear. The piston and cylinder wall does have scoring. Not real bad but it does have surface rust. I figure from weather change and being off of the engine. I will be order a whole new top end kit that includes the cylinder so I won’t have to worry about boring it out and matching a new piston. So wish me luck!!!

take the wrist pin, install just the length of one end into the top of the connecting rod, the width of the top of rod, now lift up and push down with the outside end of wrist pin, there should not be any movement what so ever, if there is ?, the the rod is bad.

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Posted (edited)

The rod is broken on this engine? Thot i read somewhere that the rod broke. If that’s the case I think you will need to fit the new rod to perform a proper evaluation. LMK if I’m missing something here. 

Edited by Goober
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No, nothing broken on the inside. Not that I can tell. When it was all together I could switch all gears and then when I would turn the piston arm, I moved smoothly with no obstruction or noises. So what I’ve been told is the bottom end is in good working order and just to finish it off with a new top end. I also check the piston arm thing and it did not have any abnormal play. 

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10 minutes ago, DLBeltran74 said:

No, nothing broken on the inside. Not that I can tell. When it was all together I could switch all gears and then when I would turn the piston arm, I moved smoothly with no obstruction or noises. So what I’ve been told is the bottom end is in good working order and just to finish it off with a new top end. I also check the piston arm thing and it did not have any abnormal play. 

 

 

Pay very close attention to " the piston arm thing " as you call it , it  is called the connecting rod , I can't say enough how important it is to have a good fit , any play in the wrist pin bore or the crank end journal and the piston will wobble in the bore , it will egg shape the bore and shorten the life of your new top end rebuild dramatically , after 50-100 hours  it will be smoking ---  

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I sure will. Thank you for the information. Yeah, I’m not much of a mechanic. For the past 8-9 years I’ve picked up the hobby of wood working for the wife and all her Pinterest dreams. This is my first complete rebuild of a four wheeler. I rebuilt a go kart, but there wasn’t much to that. No engine work because that worked great. 

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47 minutes ago, DLBeltran74 said:

I sure will. Thank you for the information. Yeah, I’m not much of a mechanic. For the past 8-9 years I’ve picked up the hobby of wood working for the wife and all her Pinterest dreams. This is my first complete rebuild of a four wheeler. I rebuilt a go kart, but there wasn’t much to that. No engine work because that worked great. 

You got to decide if you plan on keeping this atv long term or just patch it up and see what you get out of it , if you arer going to keep it and  you do it right  ,  it can last 30 years and if you do it yourself , it is not going to cost you an arm and a leg , you got a lot of help here ----- 

 

 

 I kind of got back into wood working recently , built a TV cabinet  , we have a thread called Hobby and Crafts , if you got some time some us some of your work 

 

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1 hour ago, Fishfiles said:

You got to decide if you plan on keeping this atv long term or just patch it up and see what you get out of it , if you arer going to keep it and  you do it right  ,  it can last 30 years and if you do it yourself , it is not going to cost you an arm and a leg , you got a lot of help here ----- 

 

 

 I kind of got back into wood working recently , built a TV cabinet  , we have a thread called Hobby and Crafts , if you got some time some us some of your work 

 

Sounds good, I’ll check it out!

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Posted (edited)
On 8/3/2021 at 2:09 PM, Fishfiles said:

You got to decide if you plan on keeping this atv long term or just patch it up and see what you get out of it , if you arer going to keep it and  you do it right  ,  it can last 30 years and if you do it yourself , it is not going to cost you an arm and a leg , you got a lot of help here ----- 

 

 

 I kind of got back into wood working recently , built a TV cabinet  , we have a thread called Hobby and Crafts , if you got some time some us some of your work 

 

I just finished this today! Now back to my four wheeler project!!!

C9BEF4D8-AB74-483E-B427-9F504FF38888.jpeg

024DE28D-97F6-46F0-8695-2FA74E569C27.jpeg

E929D005-F86B-4A7F-B28C-FD4949B2A0AC.jpeg

B37C3E21-92A5-40D3-8843-C6F502B8B876.jpeg

Edited by DLBeltran74
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Nice , with the cost of lumber now days , that must have cost a pretty penny ...  

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2 hours ago, Fishfiles said:

Nice , with the cost of lumber now days , that must have cost a pretty penny ...  

yep! About $700

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very nice, is that a wooden tile floor ? i remodeled my down stairs washroom a few years back and and used textured walnut tile for the flooring,

image.jpg

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6 hours ago, _Wilson_™ said:

very nice, is that a wooden tile floor ? i remodeled my down stairs washroom a few years back and and used textured walnut tile for the flooring,

image.jpg

It’s just tile. The one that looks and feels like wood. Not real sure what it’s called. 

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wood-look tile flooring..... yes it has the textured wood feel, a bit more expensive then non textured wood tile flooring. 

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