2HP Briggs & Stratton cart engine project

[asand1]

I received a pile of equipment from a friend a couple of weeks ago and pulled a 2HP B&S off of an edger. I have replaced the cast iron flywheel, mag, points and condenser with a flywheel and magnetron from a later model vertical shaft mower engine.
I have a two stroke dual needle carburetor I intend to use with a homemade manifold.









Well, I had a mower with a ~3.5HP engine (10A902 2286 B1 01092554) that had about another 1/2" of stroke. Being the tinkerer that I am I striped both engines down and started comparing parts.
The 3.5HP crank has the same main bearing journal diameters as the 2HP. The 3.5HP rod is sorter than the 2HP rod by just the right amount to net nearly 0 deck height (sunken maybe just 1/16". I will need to fabricate a dipper for the rod, as it has the angled spit on the big end.
The plastic 3.5 cam is a perfect fit with slightly more lift and no easy spin start lobe. I removed the centrifugal compression release before this idea came to fruition, wish I had left it on now.
The 3.5HP cam followers are slightly longer than the 2HP followers, so I may grind the backsides of the lobes for a smaller base circle, and grind the longer followers to fit, netting more lift.
The exhaust port is not machined for bolts or a gasket, just a pipe thread. For the exhaust I was thinking a shower head pipe with a 45* bed and as much length as I can find for a header.


"Stroker" crank with the stock 2HP crank in the foreground.


Higher lift plastic 3.5HP cam with stock 2HP in the fore ground.


3.5HP rod and 2HP piston assembled.

There is no obvious mark indicating the flywheel side of the piston, only these two marks on the pin bosses. If no one here knows, I suppose it probably wont matter too much.

 

[Michael_P]

Seeing your project which is totally cool, makes me want to get back in the game. Long live small engines!

 

[Michael_P]

Will you have to mill the head?

 

[asand1]

Originally Posted By: Michael_P
Will you have to mill the head?

Only if i choose to mill a fire slot. The compression is already bumped up from the added stroke.

 

[asand1]

Today I modified the 2HP dipper for the MOD 9.6 3.5HP rod.

https://www.youtube.com/watch?v=Xvt-BZDw9ps
https://www.youtube.com/watch?v=c6sQPDxQ-Qw

 

[Shannow]

Great thread, thanks for posting.

 

[asand1]

Since this is BITOG after all, I will post the oil I chose while spending my Fred Meyer gift card.

 

[asand1]

Today used the Dremel with a sanding drum to remove material from the backside of the cam lobes. I now have .005" clearance on the valves. I also did a conservative port and polish.

Before;

After

 

[asand1]

Next project will be grafting the B&S Quantum recoil onto the 2HP shroud.Then clean and assemble the engine. Next I will tackle making a custom intake manifold.

 

[asand1]

Copied from diygokarts

Quote:
Originally Posted by Russ2251
Very straight forward.

Three things are needed:

1.) A large workable surface such as safety glass and must be absolutely flat. The surface I use (accurate to a few millionths inch) is from a discarded wafer prober and is not readily available unless you have connections in the analog/digital IC manufacturing industry.

2.) LOCTITE 320 grit grease grinding compound

3.) Permatex Super "300"

Apply compound to flat surface and begin lapping by applying pressure on head and move in random figure 8 and circular patterns-clockwise and counter clockwise.
Check every few minutes for a grayish color to begin to appear. After a while you will begin to understand why gaskets are used in the first place. I have yet to find any cylinder head that was not warped to some degree.

Head lapping is complete when entire surface is a uniform gray color.

Block is done the same way but is somewhat more difficult because of it's bulk/mass.

Clean up with mineral spirits, paint thinner, or kerosene.
I highly recommend that block be completely stripped of moving parts before lapping.
Thorough cleaning after lapping cannot be over stated.
If any compound is left behind, engine damage is a real possibility.
Assembly is done using Permatex Super "300".
Apply thinly to one or both surfaces and torque to maximum factory spec and done in the correct order. You'll know if you've done it correctly when a very small amount of sealant oozes out between head and block. Remember that what ever excess oozes out is also oozing into combustion chamber. Keep it to a minimum.
Clearances must be checked before final re-assembly.
Typical Briggs head gasket thickness is about .060" which is equivalent to milling off a pretty big chunk of metal.
My 1969 5hp Briggs and all four of my Lawn-Boy DuraForces had no clearance issues, but remember that no two engines are identical. Check and re-check clearances.

Addendum 4/30/10:
Would be a good idea to re-torque head bolts after a couple of cycles...that is...warm engine up to operating temperature and then let cool (couple hours) to ambient temperature, one or two times, then re-torque to max factory spec.



I may do this rather than try to make a thin gasket myself.
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[bubbatime]

I see two problems:

1) The crankshaft on the old engine was most likely 5/8 while the mower crankshaft is 25mm or 7/8. Will be almost impossible to find a centrifugal clutch that fits unless the crank is machined down to 5/8

2)) The flywheel off the vertical mower is most likely a lightweight aluminum flywheel. ALL engines, minus mower engines, need a heavy cast iron flywheel. The blade acts as a heavy flywheel. The only exception that I'm aware of is lawn mowers that use a blade brake clutch tend to use a heavy flywheel.

 

[asand1]

I once had a 5hp b&s running an aluminum 3.5hp flywheel and centrifugal clutch. It ran fine and acceleration was instant.

 

[asand1]

Small Update, the engine is assembled but I still need to mate the Quantum recoil to the shroud, and put together an intake/carb combo.

 

[jeepman3071]

Sweet build! Looking forward to hearing it run!

 

[old1]

Yes, it will run with an aluminum flywheel, although slow idle may not be smooth. IF you can get it started with your increased compression, without it jerking the rope out of your hand and nearly breaking you fingers. As stated above there is a reason for cast iron flywheels.

 

[asand1]

Small update, I got the recoil mounted today. I wrapped the recoil spool "nose" in cardboard and duct tape to center it, and drilled and pop riveted it.

 

[RF Overlord]

Originally Posted By: asand1
"Stroker" crank with the stock 2HP crank in the foreground.
Don't usually hear the words "stroker crank" and "Briggs & Stratton" in the same sentence...I love it.

 

[JTK]

Interesting to see the plastic cam gear and cams on that old (looking) 2hp. I would have thought the 2hp was older than the 1980s.

 

[asand1]

Originally Posted By: JTK
Interesting to see the plastic cam gear and cams on that old (looking) 2hp. I would have thought the 2hp was older than the 1980s.

Aside from the piston, all of the internals are from a newer 3.5 vertical shaft mower.

 

[asand1]

Assuming it runs, what do you all think I should do with it?
Go cart, barstool racer, motorized Cooler, I have always thought a 6 wheel skid steer wheel barrel would be cool. Unfortunately I am on a shoestring budget, so I have to Macgyver everything I can out of garbage.