Upgrade Stihl BR340 piston/cylinder to BR420 Magnum

rixtag

LawnSite Senior Member
Location
Lehi Ut
Anybody have experience with going to a bigger piston/cylinder? The 420 Magnum I use has way more power than the 340 my guy uses and it'd be awesome to upgrade it. I know I would need a carb to match so no big deal there.
 

BigFish

LawnSite Fanatic
Location
chesapeake, va
I would think ya gotta check into the stroke fer each unit.
Ya might could GOOGLE it.
Or mayhaps the resident Stihl guru, Dr. Jeff will chime in...

I'm thinkin' it ain't gonna work.
There might be 'big bore' kits out there, but IDK.
 
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Jeff in AL

LawnSite Senior Member
Location
Alabama
Anybody have experience with going to a bigger piston/cylinder? The 420 Magnum I use has way more power than the 340 my guy uses and it'd be awesome to upgrade it. I know I would need a carb to match so no big deal there.
Looking at the IPL between the 340 (non-L version) and 420, the crankcases, crankshaft/rod, coil, muffler and carbs are the same.
The 2 biggest differences I can see are obviously the piston/cylinder which is 41mm on the 340 verses 46mm on the 420. The other is the flex tube to the tube tips are different for more flow. The tubes are 67mm on the 340 verses 80mm on the 420.

Never heard of anyone doing it, but looks like it would work. Just not sure it would be economical to do if using all new parts.

I'll post the IPL's for them if you want to compare further for yourself if you want?
 
OP
rixtag

rixtag

LawnSite Senior Member
Location
Lehi Ut
Why not? My 340 is getting long in the tooth and I like what the Magnum can do. I can do the work and it's less expensive than a new one. I don't blow anything but clippings so I don't need a huge cfm.
 
OP
rixtag

rixtag

LawnSite Senior Member
Location
Lehi Ut
Looking at the IPL between the 340 (non-L version) and 420, the crankcases, crankshaft/rod, coil, muffler and carbs are the same.
The 2 biggest differences I can see are obviously the piston/cylinder which is 41mm on the 340 verses 46mm on the 420. The other is the flex tube to the tube tips are different for more flow. The tubes are 67mm on the 340 verses 80mm on the 420.

Never heard of anyone doing it, but looks like it would work. Just not sure it would be economical to do if using all new parts.

I'll post the IPL's for them if you want to compare further for yourself if you want?
The IPL would be very helpful and the 340 needs a new flex tube anyway. Do you sell the stuff?
 

knox gsl

LawnSite Fanatic
Location
knoxville, tn
Why not? My 340 is getting long in the tooth and I like what the Magnum can do. I can do the work and it's less expensive than a new one. I don't blow anything but clippings so I don't need a huge cfm.
Go for it then. I know for me doing all that work would cost more than just going and buying a new one.
 

Jeff in AL

LawnSite Senior Member
Location
Alabama
The IPL would be very helpful and the 340 needs a new flex tube anyway. Do you sell the stuff?
I am a Stihl Dealer but I don't ship anything. If you conclude that you want to order parts just get them from a dealer near you.

On the bottom left of the IPL pages it shows the Versions. You mentioned the BR340 (which is 1) and a BR420 (which is 4). So at the end of each Part Description pay attention to the (numbers) which is the Version. If there is no version it is a common part for all.

Still not sure it would be economical to do but...
 

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rixtag

rixtag

LawnSite Senior Member
Location
Lehi Ut
That's freaking awesome! Thank you. Soon enough I'll be watching it snow and that will be a good project to get me through it. Thank you!!
 
OP
rixtag

rixtag

LawnSite Senior Member
Location
Lehi Ut
Go for it then. I know for me doing all that work would cost more than just going and buying a new one.
I work pretty fast and it might take an hour. Even at full rate I'm still way less than a new one.
 

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