Author Topic: 390/420 rod  (Read 10837 times)

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Offline Mayhem#8

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390/420 rod
« on: July 03, 2012, 12:43:25 am »
Is the arc 390 rod same size as th hf 420 rod? will it work in a 420 Preditor?

Offline Ron Atchison/A.C.E. Race Engines

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Re: 390/420 rod
« Reply #1 on: July 03, 2012, 10:05:58 am »
yes. though, they need a "crutch" to make them live if you turning it up!
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Offline Tim Toleson

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Re: 390/420 rod
« Reply #2 on: July 03, 2012, 10:54:29 am »
Do these rods have bearings or do you gotta replace the rod every so often, if so how often?
Thank you to Whitney\'s Garage (315) 675-8592, and Mountain Man\'s Famous Fudge  (315) 623-9598 for your support in the 2012 ARMA racing season!

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Offline George Herrin

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Re: 390/420 rod
« Reply #3 on: July 03, 2012, 12:42:40 pm »
arc rod has bearings
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Offline Tim Toleson

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Re: 390/420 rod
« Reply #4 on: July 03, 2012, 12:45:57 pm »
ok cool! i thought i read some where that it didn't. Thanks George. I know i can get a 420 predator at harbor freight up here for $279 right now. I just gotta decide if im gonna go to single mod or something else next year
Thank you to Whitney\'s Garage (315) 675-8592, and Mountain Man\'s Famous Fudge  (315) 623-9598 for your support in the 2012 ARMA racing season!

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Offline Mayhem#8

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Re: 390/420 rod
« Reply #5 on: July 03, 2012, 01:45:49 pm »
So if i turn it 6000 rpm will i need a crutch? and can i get rid of the balance shaft?

Offline Ron Atchison/A.C.E. Race Engines

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Re: 390/420 rod
« Reply #6 on: July 03, 2012, 09:12:47 pm »
So if i turn it 6000 rpm will i need a crutch? and can i get rid of the balance shaft?
6k and you'll be fine, 6500 with a mild build and you will probably be fine. If you wanna make some nice power  with a big valve, high flow head and unrestricted carb, you'll need to address the rod!. Unfortunately, when i do a 390/420 build with an ARC rod, i recommend it gets replaces every 10-15 nights or, you stand a huge chance of destroying your engine! I have the proof many times over in a box. Delete the balance shaft unless you're pulling.
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Offline Mayhem#8

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Re: 390/420 rod
« Reply #7 on: July 05, 2012, 01:36:21 am »
I ran it 5800 k and spun the rod bearing (stock rod)an galded the crank up, does anyone make a am crank for the 420?

Offline cubcadet70

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Re: 390/420 rod
« Reply #8 on: July 05, 2012, 12:12:51 pm »
There's no aftermarket crank for any big blocks out there!!! But the only best thing to run is a good Honda Crank. The Honda crank wont fit in the 420 motor. I know EC Carbs sells 420 replacement crank.

Offline Ron Atchison/A.C.E. Race Engines

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Re: 390/420 rod
« Reply #9 on: July 09, 2012, 04:17:18 pm »
There's no aftermarket crank for any big blocks out there!!! But the only best thing to run is a good Honda Crank. The Honda crank wont fit in the 420 motor. I know EC Carbs sells 420 replacement crank.

Honda doesn't make the 420 so, you will have to go with the 420 clone like Blue max or Predator. There is a 2mm stroke difference from the 390 to the 420.
I ran it 5800 k and spun the rod bearing (stock rod)an galded the crank up, does anyone make a am crank for the 420?

generally the rod breaks before it eats itself up. what oil were you running? these splash engines really need a thin oil that goes places or places wont get enough volume to keep cool. 28oz. of FHS62R is what i recommend but, i'm sure other race splash specific oil will work fine.
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Re: 390/420 rod
« Reply #10 on: July 09, 2012, 06:05:28 pm »
Bert stole my cookies!!
 I think he used them to bribe Ed into something naughty?

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Offline Mayhem#8

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Re: 390/420 rod
« Reply #12 on: July 11, 2012, 11:38:14 pm »
Mobile 1 5-30 synthetic was running 28oz
So i ordered arc rod and Crank from ec, removed the balance shaft, shaved the head 25 thousands, polished the ports and combustion chamber, was wondering if the chinese bearings are decent or should i go with ceramics or stainless steel like a abec 7 bearing? or does it really matter. also i have the engine mounted flat maybe is should have a 5 degree motor plate or more, or is it not necessary, any imput regarding anything else i can do to make it live or make some power out of it would be be appreciated

Offline George Herrin

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Re: 390/420 rod
« Reply #13 on: July 12, 2012, 06:48:48 am »
Jakes is a clone and runs stock bearings and flat its been running two seasons turning 6500 to 7000 with no problems at all. BUT I run the balancer shaft. I drove one w/o it and man it shook so hard at certain rpoms it took my breATH AWAY literally. And we are as fast and dont have parts falling off either.
George Herrin #6
Indian Power.. You gotta Go big to beat em or Go HOME
8 time ARMA National Champion
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Retired from BP
www.herrinmowersports.yolasite.com
www.allamericanmowerchampionships.yolasite.com
My other racer is a 1/5th scale Dirt Late Model!!!!