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There's no replacement for displacement


littlemarv

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Would Briggs have really cast two different outsides of these blocks for these engines?  It would seem they would all be identical casts, and just bigger bores for the 15-16 vs 12-14 from the factory?  Maybe I'm wrong as wall thickness and cooling all comes into play, but it would seem that as they are all physically the same size, and share the same stroke, it would all be about bore and not different castings?  I ask because I am hoping to learn, not to contradict anyone who has the knowledge. 

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Has anyone confirmed a successful sleeving of an iron block Briggs as suggested earlier so that a standard piston can be used again?  This goes hand in hand with the large overbore question - a block needs to have enough meat to hog it out for the OD of the sleeve to be properly retained.

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Yes, I had a 12hp 30ci 1969 BS engine bored out to hold a std 16hp 32ci piston.  I had the valves ground, and new guides, and the head milled (probably a little more than needed to get it flat) and put in a pulling tractor.  Ran great, and still running.  Ran noticeably stronger.

 

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On 11/24/2019 at 8:11 PM, MikeES said:

I had the valves ground, and new guides, and the head milled (probably a little more than needed to get it flat)

Wink wink, nod nod........B|

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OK, finally got a chance to open the motor up. First off, wheres the mouse nest? Must be something REALLY wrong if they won't even shack up in it!

 

b5ma4HF.jpg?1

 

Here is the underside of the head. I'm assuming this means 32.5 cubic inches, which would mean its off of a 16HP engine. Guess I never thought about it before, heads interchanging?

 

JjfQlZi.jpg?1

 

Cylinder walls show some scuffing. I measured it two different directions, came up with 3.446" one way and 3.447" the other. So its worn 0.007" or so.

 

hya5KWJ.jpg?1

 

Did a little checking. 10, 20, and 30 over pistons are a no go for this engine.

Can a fellow just hone it and re ring it? A standard piston ring set is $70.

Someone suggested honing the cylinder and knurling the piston?

 

Or, stop overcomplicating things, like I always do, get a gasket for it, slap it back together, and run the damn thing?

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I would install a set of chrome rings, B&S P/N 299745. B&S states no honing or deglazing is required and cylinder bore can be a maximum of 0.005" oversize. I would purchase the set on eBay from Jones Farm Supply for $75. Make sure the bore is absolutely clean of any and all debris when installing.

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On 11/23/2019 at 8:01 PM, TimJr said:

Kohler has different blocks with different cylinder wall thicknesses for the same cubic inch displacement I believe, so why wouldn't Briggs?  

I believe this is incorrect,K and M series blocks are the same up to 16hp. Many a worn out 12 has been bored to 14. If you try to go 16,you will end up with a big window.

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Are you sure the bore is still standard? Hone marks are visible in the cylinder and they don't look factory. This may have already been bored 0.10 over. 

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10 hours ago, oldsarge said:

I believe this is incorrect,K and M series blocks are the same up to 16hp. Many a worn out 12 has been bored to 14. If you try to go 16,you will end up with a big window.

Incorrect.  See the following.

http://gardentractorpullingtips.com/engine.htm

 

The Major Differences Between the Kohler K-series and Magnum Engine Blocks -

  • Some Kohler blocks have wide base flanges (for the wide, deep oil pan) and some have a narrow base with no flanges (Cub Cadet, John Deere, Wheel Horse or Ford).
  • Most Magnum blocks are wide base, and very few are narrow base.
  • The very early K241 10hp blocks have no indentation for installing an upper mount gear starter (mounting bolts are below the starter motor). Also, some of these older blocks with flanges have no holes drilled for converting to a narrow base oil pan. (But holes can be drilled and tapped.)
  • Some blocks have either a drilled or threaded oil dipstick tube hole next to the cylinder, above the crankcase, while others have no hole present.
  • Some blocks have provisions for a starter-side oil dipstick tube, and some don't.
  • Some blocks came with counterbalance gears and some didn't. Some have expansion plugs where balance gear stub shafts can be installed, and although certain blocks have the bosses, some have no holes drilled for the stub shafts.
  • The later model Kohler blocks with Breakerless Ignition and all Kohler Magnum blocks have no provisions for ignition points.
  • Some blocks have two threaded holes for installing an exhaust pipe flange, and some don't.
  • Some blocks have provisions to install a mechanical fuel pump, and some don't.
  • Some blocks have different bolt patterns on the PTO end, and Gravely blocks have a raised circular flange. (See below.)
  • Some K241 blocks with K301 embossed on the PTO end have a thicker cylinder wall, and some K241 blocks without the K301 embossing have an ordinary thickness cylinder wall.
  • The 12 fin K341 blocks have an ordinary thickness cylinder wall, and the 13 fin K341 blocks have a thicker cylinder wall.
  • Other than all of the before mentioned È, everything else on the Kohler K-series engine blocks are pretty much the same.
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1 hour ago, TimJr said:

Other than all of the before mentioned È, everything else on the Kohler K-series engine blocks are pretty much the same.

Pretty muchsm00...That's funny.

Thanks for posting.  That is good information.

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  • 2 weeks later...
On 11/13/2019 at 7:02 PM, RAC said:

... The swept volume filling efficiency ... the mathematical compression ratio ... the small valve block ... the combustion chamber size... the real running compression ratio ... Re-degreeing the stock cam, a way longer connecting rod, stiffer valve springs, and a bunch more ...

Dang.  So.... How fast can you do the quarter mile in that baby?  

But seriously folks; I have a "collection" of Briggs 16hp's, some in tractors, some in crates.  I saw above that the heads can improve HP?  Without changing anything else?  Inquiring minds want to know...

Edited by JohnFornaro
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56 minutes ago, JohnFornaro said:

Inquiring minds want to know

By shaving the head, you increase the compression ratio.  That actually REDUCES (albeit only slightly) the displacement but increases the energy derived from the existing fuel.  By increasing the bore and or stroke, you increase the amount of fuel taken in.  These steps are usually accompanied by re-jetting the carb or using a larger volume carb to satisfy the thirst for more fuel. 

Generally speaking, increasing the bore of an engine will increase top end speed.  Increasing the stroke increases the torque.  Which explains why those old, long stroke John Deere's could "chug, chug" their way through anything.  With regards to comments above about increasing the bore from 30 to 32 cubic inches, they are only doing that because we can (usually) no longer rebuild the 30 CI block to slightly oversized specifications.

Edited by wwbragg
clarification
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1 hour ago, wwbragg said:

By shaving the head, you increase the compression ratio.  That actually REDUCES (albeit only slightly) the displacement but increases the energy derived from the existing fuel.  By increasing the bore and or stroke, you increase the amount of fuel taken in.  These steps are usually accompanied by re-jetting the carb or using a larger volume carb to satisfy the thirst for more fuel. 

Generally speaking, increasing the bore of an engine will increase top end speed.  Increasing the stroke increases the torque.  Which explains why those old, long stroke John Deere's could "chug, chug" their way through anything.  With regards to comments above about increasing the bore from 30 to 32 cubic inches, they are only doing that because we can (usually) no longer rebuild the 30 CI block to slightly oversized specifications.

Compression ratios in flatheads generally suck. Higher compression ratios (within limits) generally result in improved power. Heads with smaller volume will increase the compression ratios. You can get the head so tight around the valves that flow will be restricted and reduce power, but probably never with a stock carb at normal operating rpm's. So compression increases will probably always benefit the average flathead engine. We took a Tecumseh OH180 (ohv) to 13.5:1 and it ran great on race gas. You will NEVER get a flathead in that range. For what it's worth, displacement is a function of bore x stroke only. So reducing combustion chamber size by shaving the head has no impact on displacement. It does however reduce the "swept volume" of the cylinder (as a system) which impacts the compression ratio calculation.

The single most effective way to increase power in your engine? A competition quality 3 angle valve job. Ya have to be able to get air in the motor before you fret over being able to compress it.

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19 hours ago, RAC said:

For what it's worth, displacement is a function of bore x stroke only.

Right.  As I  understand the definition.  But in the real world, that volume above the cylinder contains a compressed air/fuel mixture, so *technically* that's a part of displacement, right?  Many years ago, I had a flat head V-8 '53 F-100 with, wait for it, Mecury heads.  Which apparently was quite the improvement over the factory heads, but I never understood why.  "Way better heads" was the best explanation my mechanic  could offer at the time.   I was much younger then, and had to sell the truck for financial reasons, but hey:  That was the most fun truck I ever had.  It's especially nice when you and your truck are the same age.

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I once built an air cooled VW motor from scratch; new case, new heads, new pistons, new, new, new.  I used oversized cylinders/pistons that took it from the stock 1584 (1600) to 1776 CC.  I had the flywheel, crank and pistons all balanced to within 1/2 gram.  But I used a small carburetor so, while it was better then stock,  it was basically starved for fuel - -but that is another story. 

In the build process, I had to "CC the heads".  In this step you measure ( in CCs) the amount of water each combustion chamber holds.  Smaller chambers are ground out so that all chambers are equal.  That way, each piston is delivering the same level of power.  @RAC is correct in that the combustion chamber is not part of displacement.  In fact, the volume of the cylinder divided by the volume of the combustion chamber is how we calculate the compression ratio. But the shape of the combustion chamber plays an important role.  In the VW motor, the fuel is ignited more toward one side of the cylinder.  So Dr. Porsche built the pistons to be off center on the rod so that the force of the explosion pushes equally on the entire piston (the thrust side) surface.  If you put a piston in wrong, it will run like crap - - if at all.

Chrysler stole the show when they introduced hemispherical heads which radically improved the combustion chamber and therefore, the amount of power from the existing fuel.

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1 hour ago, wwbragg said:

If you put a piston in wrong, it will run like crap - - if at all.

Oh, it'll run. But it may knock like the dickens. Aside from sometimes being used to improve the thrust angle of the rod and improve performance offset pins are also commonly used to reduce Piston slap at the top of the stroke. Really make a racket if you have em wrong way around. The OH series Tecumseh motors had off set pins. We turned it around once to try to get a better rod angle on the power stroke. It didn't like it.

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