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need help with engines

2556 Views 8 Replies 4 Participants Last post by  Honda Mechanic
hey i just bought a bottom end out of a 96 foreman(isnt that from the 400) do you think the 400 bottom end will fit in the 450 frame and will the 450 top end fit on there also how hard is it to rebuilt the bottom end compared to the top end cause now that ive done a fe times its not that hard.
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I have a 450 cylinder on my 400 and yes a 400 bottom end will bolt in where a 450 does. They are the same engines just the cylinder bore is different.
I am not for sure about the the 95 model foreman 400 motor, but the output shalfs on a 98 foreman 400 motor are shorter than the 450 foreman output shalfs. you might have problems with the drive shalfs. I have a 450 motor in a 400 frame and had to change over to 450 driveshalfs for it to hook up. everything else will hook up fine as ctown said.
They are the same crankcases ... The final shaft is different and some gears are different between the TRX400 & TRX450 ..
Dirty4man, you are right I totally forgot about the output shaft on the front and I shoulda remembered that since i'm about to install a 450 output shaft on my 400 since i have a spare 450 output shaft laying around. The 450 shaft sticks out about 2 inches more than the 400 shaft, meaning the 400 shaft is longer than the 450 shaft. I'll see if i can't get a picture of the shafts compared.

There have been debates on differences in the gears in a 400 and 450. Some say the 400 has lower gears (what I believe) and some say they are the same. We will find out this weekend when i tear down my 400 motor to replace the output shaft.

Also off topic but is there any difference in the 400 and 450 cam shaft?
The gears are:

1996 TRX400FW
1 gear 49/12
2 gear 43/18
3 gear 37/23
4 gear 33/28
5 gear 29/33

2003 TRX450FM
1 gear 49/12
2 gear 43/18
3 gear 37/23
4 gear 33/28
5 gear 28/33


The camshafts are different , the lift are the same for both cams but the duration degrees are altogether different ..
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HM thanks for the #'s
Well there is something in them there 400 motors that are lower, I swears by it.

Just wondering if it would be worth it to install a 450 cam shaft i have laying around in the 400 if it would make a difference.
Final reductions (ring gear & pinion) are different (400= 41/13 ) (450= 42/13 )
Tires are different:
400= front 24/8/11 -- rear 24/10/11
450= front 25/8/12 -- rear 25/10/12

I'm not sure which cam would be best because I don't know much about cam durations but this is the duration numbers:


intake opens 10 BTDC
intake closes 40 ABDC
exhaust opens 40 BBDC
exhaust closes 10 ATDC


intake opens 6 BTDC
intake closes 45 ABDC
exhaust opens 36 BBDC
exhaust closes 10 ATDC
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