Author Topic: New guy with 40cu oppy wants to upgrade  (Read 585 times)

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Offline 86turbodsl

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New guy with 40cu oppy wants to upgrade
« on: May 17, 2019, 05:42:42 PM »
New guy here, i have a 12.5hp horizontal opposed twin, i tore it down to fix something else and wanted to get more power and torque out of it while i have it out.  I'm not a racer really, but the mower it's normally in has always seemed underpowered. 

I'm trying to find out what to do to it while i have it apart.  It's a full pressure lubed engine, so i think parts are a little more hard to come by.   I do have access to a full machine shop and want recommendations on what i can do to this thing while its apart. 

Any ideas?  I'm not opposed to mods, but really would prefer not to spend a fortune on it.



Offline Mower Maniac

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Re: New guy with 40cu oppy wants to upgrade
« Reply #1 on: May 17, 2019, 09:37:32 PM »
you could try advancing the timing, and put a k and filter and velocity stack on it. Also, better exhaust... Less dramatic bends. If that doesn't seem like enough, you could try mild porting on the block.
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Offline 86turbodsl

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Re: New guy with 40cu oppy wants to upgrade
« Reply #2 on: May 18, 2019, 04:52:08 AM »
i was thinking more along the lines of stroker crank/rods, but i don't know what to get.  Are pressure lube cranks rare?  My rods are sketchy, so i need to get new rods anyway.


Offline PJG56

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Re: New guy with 40cu oppy wants to upgrade
« Reply #3 on: May 18, 2019, 10:43:19 AM »
Put a 42 crank and rods in it,or better yet 46 crank and rods..!!
Paul Guptill  (oppy) #238modX
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Offline 86turbodsl

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Re: New guy with 40cu oppy wants to upgrade
« Reply #4 on: May 18, 2019, 12:41:02 PM »
How do i find out what part number to look for?  I have full pressure lube and would want to keep that.

Offline 86turbodsl

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Re: New guy with 40cu oppy wants to upgrade
« Reply #5 on: May 19, 2019, 04:36:05 PM »
Saw a post about using vanguard rods, would that work?  I think they are all pressure lube.

Offline PJG56

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Re: New guy with 40cu oppy wants to upgrade
« Reply #6 on: May 21, 2019, 09:50:33 AM »
Look up rods for a 42477.
You cant use vanguard rods their shorter by a lot and crank journal and wrist pin is a lot smaller
Paul Guptill  (oppy) #238modX
2012 slmra mowstock champion(builder/owner)

2013 slmra mowdified champion(builder/owner)
2013 ARMA national champion Mod-X(builder/owner)
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2014 All American 2nd place SP(builder/owner)
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2016 OutlawTriple Crown FXT Champion (engine builder)


Offline 86turbodsl

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Re: New guy with 40cu oppy wants to upgrade
« Reply #7 on: May 21, 2019, 06:13:12 PM »
Look up rods for a 42477.
You cant use vanguard rods their shorter by a lot and crank journal and wrist pin is a lot smaller

Oh, i read a thread where vanguard single rods were really close just too wide journals, needed machined narrower.  and they were all pressure lube.

Offline 86turbodsl

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Re: New guy with 40cu oppy wants to upgrade
« Reply #8 on: May 22, 2019, 05:42:44 AM »
Ok, i found and ordered a set of rods for a 42cu motor with oil drillings.

Now i'm looking for a crankshaft that will fit my block.  I THINK 690784 is a pressure lube crank,
the parts lookup said it was for a 42A777 engine.  Would that crank fit a horizontal oppy 40cu block?

I know there were several variations of crank snouts, keyways, etc.

Offline PJG56

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Re: New guy with 40cu oppy wants to upgrade
« Reply #9 on: May 22, 2019, 08:30:19 AM »
40ci and 42ci block is the same,i think you may need a pressure lube 42 horizontal crank..
Paul Guptill  (oppy) #238modX
2012 slmra mowstock champion(builder/owner)

2013 slmra mowdified champion(builder/owner)
2013 ARMA national champion Mod-X(builder/owner)
2014 ARMA national champion Mod-X(builder/owner)
2014 All American Champion Mod-X/CP(builder/owner)
2014All American Champion FXT (engine builder)
2014 All American 2nd place SP(builder/owner)
2015 All American 2nd place BP (builder/owner)
2016 OutlawTriple Crown FXT Champion (engine builder)

Offline 86turbodsl

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Re: New guy with 40cu oppy wants to upgrade
« Reply #10 on: May 22, 2019, 11:05:32 AM »
Yes, i'm looking for one now.  In event i can't find one reasonable, i'll drill the oil passages on a non-lubed crank.


Offline 86turbodsl

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Re: New guy with 40cu oppy wants to upgrade
« Reply #11 on: June 10, 2019, 06:01:57 PM »
Anybody got a part number for a pressure lube 42cu crank?  I tried 690636, but it wasn't right.