500 top end on a 420

[Rolandtd 13]

Hey guys about to do a 500 top end kit on a 2016 420. My question is will I need a fuel programmer or will it be fine without one and not run too lean? I've seen things online going both ways, it'll be fine without a programmer and it needs one or it'll run too lean. Any advice?

[shadetree 5,884]

i always use the correct top end parts. is there a reason you are not using the correct top end parts for the correct engine ?. can't answer your lean question ?, as i don't gamble on something i know nothing about..lol.

[Rolandtd 13]

Fair enough. I figured I'd put the bigger kit on there to see some possible gains and didn't think about it possibly running lean until now. I did some looking into ot some say it's the same but woth a different tuning others say it's different and will go lean.

[ATC4ever 1,082]

Ive done it with a kit from a Kentucky dealer. No issues with the machine after doing it.  Fi model. Its really 475cc vs the 420.

[Rolandtd 13]

Alright I'm gonna give it a try and see what she runs like. Hopefully alls well. I will send my scope down to check the piston just to see at some point

Edited April 25 by Rolandtd

[jeepwm69 7,619]

Try without first.   If it acts like it's running lean get a programmer.

 

I did one on my wife's 09 DCT Rancher.  I put a Weisco programmer on with the top end, but I honestly think it would have run fine without it.

 

Didn't make much of a difference at all over the stock 420 cylinder.  Not worth doing unless your original 420 cylinder is gone too far to be bored oversize again.

 

I was curious as to the 520 top end, but you have to either turn down the outside of the bottom of the cylinder (Reduction Boss sells those ready to bolt on) or grind the cases a little to clear the bigger jug. 

 

I've gotten away from 420's and am sticking with the older machines, so never got around to the 520 swap.

 

 

[Melatv 792]

This is a chart of HP

Make/size Horsepower Lowest ratio (final:1)
The numbers after the HP is the gear ratio

Recon 250 15.5 HP 36.8
300 Fourtrax (after 1988) 16.5 HP 55.0
300 Fourtrax (1988) 18 HP 55.0
350 Rancher 21 HP 54.1
350 Foreman 24.5 HP 57.2
400 Foreman 21 HP 56.9
420 Rancher FM/TM 26.5 HP 46.5
420 Rancher AT (IRS) 27 HP 38.8
450 Foreman 24 HP 56.9
500 Rubicon 33.5 HP 58.6
500 Foreman 27 HP 51.0
500 Foreman (FI) 28 HP 53.4
650 Rincon 35.5 HP 17.7
680 Rincon 38.5 HP 17.7
 

420 Vs 450 HP

[shadetree 5,884]

5 hours ago, jeepwm69 said:

Try without first.   If it acts like it's running lean get a programmer.

 

I did one on my wife's 09 DCT Rancher.  I put a Weisco programmer on with the top end, but I honestly think it would have run fine without it.

 

Didn't make much of a difference at all over the stock 420 cylinder.  Not worth doing unless your original 420 cylinder is gone too far to be bored oversize again.

 

I was curious as to the 520 top end, but you have to either turn down the outside of the bottom of the cylinder (Reduction Boss sells those ready to bolt on) or grind the cases a little to clear the bigger jug. 

 

I've gotten away from 420's and am sticking with the older machines, so never got around to the 520 swap.

 

 

it truly boggles my one brain cell, trying to figure out why atv owners who ride an utility atv, want to '' get that one extra hp '' ?!..lol. you can only get so much from these machines, after that..its all over but the crying. soo..bottom line: don't bother trying to get 100 hp from an engine that is designed to give you 10 hp..lol.

[ATC4ever 1,082]

12 hours ago, shadetree said:

it truly boggles my one brain cell, trying to figure out why atv owners who ride an utility atv, want to '' get that one extra hp '' ?!..lol. you can only get so much from these machines, after that..its all over but the crying. soo..bottom line: don't bother trying to get 100 hp from an engine that is designed to give you 10 hp..lol.

I hear that, i did try to get him to buy a bigger machine, but the kit he found online was a lot cheaper than buying another wheeler. The difference in power was deff noticeable. I have video proof! Honest! 😹

[jeepwm69 7,619]

If I had a 420 cylinder that couldn't be bored, sure I'd go bigger.  Why not if you're having to buy a new jug and piston anyway.  500 jug costs the same as a new 420 jug.

 

But if your 420 jug hasn't been bored yet and can simply be bored, save your money and just bore it OS with a new piston.

 

After doing it, and looking at the $$$ I spent doing it, minuscule bang for my bucks.

[Rolandtd 13]

Yeah my jug was messed up pretty bad and took the crank with it. I figured same cost might as well go with the bigger kit.

[jeepwm69 7,619]

8 minutes ago, Rolandtd said:

Yeah my jug was messed up pretty bad and took the crank with it. I figured same cost might as well go with the bigger kit.

 

That's what I did with the wife's.   I actually had a 420 footshift with a cracked cylinder, so I had the wife's 420 cylinder bored and used it on that footshift, and bought a new 500 cylinder for the wife's.

 

I wonder what the 520 would do?   Looking at the chart @Melatv posted, the HP difference in the EFI 500 and 420 is negligible, but you're only actually going to a 475.  A 520 would be almost double the CC increase of the 500 cylinder.

[ATC4ever 1,082]

22 hours ago, jeepwm69 said:

 

That's what I did with the wife's.   I actually had a 420 footshift with a cracked cylinder, so I had the wife's 420 cylinder bored and used it on that footshift, and bought a new 500 cylinder for the wife's.

 

I wonder what the 520 would do?   Looking at the chart @Melatv posted, the HP difference in the EFI 500 and 420 is negligible, but you're only actually going to a 475.  A 520 would be almost double the CC increase of the 500 cylinder.

Yea its too bad the 520 wasnt out when we did the change, but he had his mind made up, i couldnt change it 😬

[Rolandtd 13]

I'm not expecting anything crazy with the 500 top end this ones my do dumb stuff bike my 21 is my baby. Should have it back together sometime today case wanting to not cooperate today. 

[Rolandtd 13]

So somehow I can't get the crank cases together.  I've done everything lined up and heated the one side.  I've never had an issue with the cases before

[jeepwm69 7,619]

3 hours ago, Rolandtd said:

So somehow I can't get the crank cases together.  I've done everything lined up and heated the one side.  I've never had an issue with the cases before

You had cases split?

[Rolandtd 13]

Yeah con rod broke. 

[jeepwm69 7,619]

! grind that bore hold out while you have it apart and do a 520 jug then!

[Rolandtd 13]

I'm not to confident I'd not mess it up.  ! I can't get the cases back together even though I've torn this motor apart multiple times. It wins this week. Might try again next weekend. 

[jeepwm69 7,619]

Do you have the crank seated in the rear case?

Make sure your dowel pins aren’t out-of-round.

 

[Rolandtd 13]

Everything is seated and pins are in good shape. Might pull everything apart again and check again

[Rolandtd 13]

just attempted to put back together for over 2 hours. still wont go down. i took all the bearings out of the case made sure they were in the right place and seated trans is seated crank and counter shaft are seated and pins are in place. still wont go down. last time i split the case i didnt have any issue putting it back together. i believe its something on trans side but as far as i see everything is seated properly

[shadetree 5,884]

57 minutes ago, Rolandtd said:

just attempted to put back together for over 2 hours. still wont go down. i took all the bearings out of the case made sure they were in the right place and seated trans is seated crank and counter shaft are seated and pins are in place. still wont go down. last time i split the case i didnt have any issue putting it back together. i believe its something on trans side but as far as i see everything is seated properly

what about the shift drum ?, or the shift fork rod ?.. is the shift arm hanging on the end of shift drum ?.

[Rolandtd 13]

19 minutes ago, shadetree said:

what about the shift drum ?, or the shift fork rod ?.. is the shift arm hanging on the end of shift drum ?.

took the arm off. i though it could be the fork rod but its fully down. i need to find my scope cam maybe ill be able to see whats catching

[shadetree 5,884]

1 hour ago, Rolandtd said:

took the arm off. i though it could be the fork rod but its fully down. i need to find my scope cam maybe ill be able to see whats catching

the fork rod has too seat in both case halves.