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Dlongest

450 swap confusion/help

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Hello all. Long time lurker first time poster.
I have read a lot on this and I can’t seem to get a straight answer.

I bought a 2000 foreman 400 bone stock and it was burning oil. I was hoping it was only the valve seals but as I took the head off to look at the jug I found the culprit. There’s scoring in the jug so I’ve decided to upgrade my 400 to a 450.
I know these are a direct swap from the 400 top end to the 450 top end. So my question is besides the jug, piston, seals, and carb 450 rebuild kit. What else has to be done?
Some say the head needs ported. Others say no? I need some help before I go already and order what I need.

Thanks in advance.

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Looks like you found us.

 

@Fishfiles has the souped up 450's.

 

@shadetree and I are currently rebuilding 450 engines.  My rebuild is for a friend, and I'm using a 400 Foreman head I had on hand on his 450 bottom end and cylinder to give him a compression boost (hopefully a bit more power) as the 400 Foreman head combustion chamber is a little smaller than the 450 head.

 

You should be fine with what you have planned.  I'd use the 400 head, and simply grind the valves and replace the stem seals.  Porting isn't necessary on these little single cylinder Honda engines.

 

 

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Found you guys! Thanks again for the heads up. I moved over to this site. 
 

I will go ahead with my plan to swap out the top end to a 450 because my piston and jug walls are shot. 
 

Unless anyone has an OEM jug for sale. The. I’ll just get the 450 piston.   
 

Thank you 

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2 hours ago, Dlongest said:

Found you guys! Thanks again for the heads up. I moved over to this site. 
 

I will go ahead with my plan to swap out the top end to a 450 because my piston and jug walls are shot. 
 

Unless anyone has an OEM jug for sale. The. I’ll just get the 450 piston.   
 

Thank you 

why not just bore the 400 cylinder out, go to a larger piston. i keep my engines stock, if they have a 450 head, or cylinder ?, i use what came with it. you will not gain that much hp if any at all ?, going from a 400 to a 450, its not worth it.

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I guess that’s an option too. I’ve never had anything bored over before. I’ll have to find a shop that can do that for me. 
 

If I bore the stock head out am I right in assuming I will need to reject the carb or will stock jets work. 
 

I’m new to all of this. 

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The 400 parts (OEM anyway) are getting harder to get because they are discontinuing them. The last 400 I did I converted to a 450 (cylinder/piston) and it didn't need any rejetting or anything. You just have to tune it when done. You might need to jet it or you might not.

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6 hours ago, Dlongest said:

I guess that’s an option too. I’ve never had anything bored over before. I’ll have to find a shop that can do that for me. 
 

If I bore the stock head out am I right in assuming I will need to reject the carb or will stock jets work. 
 

I’m new to all of this. 

just bore the cylinder to next size piston up, re-use everything as is, no need to re-jet or anything, a new top end gasket kit, bolt it all on, ride it !.

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9 hours ago, Dlongest said:

I guess that’s an option too. I’ve never had anything bored over before. I’ll have to find a shop that can do that for me. 
 

If I bore the stock head out am I right in assuming I will need to reject the carb or will stock jets work. 
 

I’m new to all of this. 

Welcome to atvhonda forums

 

Seems you are  a bit confused --  The head has nothing to do with the  bore  . 

 

 The bore is the cylinder walls inside the jug , the piston with its rings move up and down the bore to create compression , so the condition of the bore has to be  good  , if the bore gets messed up , compression and oil can bypass the rings then power is lost and the engine will smoke from burning oil  , a machine shop can  do a process called boring , which cleans up the metal by cutting it to a oversize and a slightly larger piston and rings replaces the original piston and rings , the best place I have found to do a bore job on my atvs is G+H Discount , they will bore the cylinder and supply all the necessary parts for the upper rebuild , which would include , piston , rings , wrist pin , keepers , valve stem seals , exhaust ring , etc , all for about $215 with the freight and takes about 2 weeks total from your door to your door 

 

 

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Thanks for the welcoming. Thank you for the information. That’s I will look into G+H Discount. I would like to keep it as close to stock parts as I can. It just seems the top end kits are cheap and I don’t want want to any issues. I want to keep it reliable.
 

Plus it’s the wife’s bike so that’s another reason to keep it up and running. 

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