Heymow - Lawnmower Racing Forum

Engine Help => Briggs Flathead => Topic started by: 86turbodsl on May 17, 2019, 07:42:42 pm

Title: New guy with 40cu oppy wants to upgrade
Post by: 86turbodsl on May 17, 2019, 07:42:42 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.
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: Mower Maniac on May 17, 2019, 11:37:32 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.
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: 86turbodsl on May 18, 2019, 06:52:08 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.
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: PJG56 on May 18, 2019, 12:43:19 pm: Put a 42 crank and rods in it,or better yet 46 crank and rods..!!
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: 86turbodsl on May 18, 2019, 02:41:02 pm: How do i find out what part number to look for? I have full pressure lube and would want to keep that.
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: 86turbodsl on May 19, 2019, 06:36:05 pm: Saw a post about using vanguard rods, would that work? I think they are all pressure lube.
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: PJG56 on May 21, 2019, 11:50:33 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
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: 86turbodsl on May 21, 2019, 08:13:12 pm: Quote from: PJG56 on May 21, 2019, 11:50:33 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

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.
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: 86turbodsl on May 22, 2019, 07:42:44 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.
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: PJG56 on May 22, 2019, 10:30:19 am: 40ci and 42ci block is the same,i think you may need a pressure lube 42 horizontal crank..
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: 86turbodsl on May 22, 2019, 01:05:32 pm: 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.
Title: Re: New guy with 40cu oppy wants to upgrade
Post by: 86turbodsl on June 10, 2019, 08:01:57 pm: Anybody got a part number for a pressure lube 42cu crank? I tried 690636, but it wasn't right.