Cool work project

Just completed this cut away of a Briggs 7.5HP 2-cycle engine used in toro snow CCR snow throwers.

This is my first cut away that i did and it turned out ok i think. Basically its gonna be used in an animation to demonstrate 2-cycle theory as a visual aid in a theory of operation program i'm building.

This is the H.O. model with the boost ports in the piston and cathedral ports in the cylinder which is basically secondary intake ports.

http://i264.photobucket.com/albums/i...r/IMG_0347.jpg

http://i264.photobucket.com/albums/i...r/IMG_0348.jpg

http://i264.photobucket.com/albums/i...r/IMG_0350.jpg

http://i264.photobucket.com/albums/i...r/IMG_0351.jpg

I take it that the bolt that is showing on the lower half was a mistake?

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Originally Posted by Breecher_7

I take it that the bolt that is showing on the lower half was a mistake?

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No the 2 bolts are are not perfectly even on the sump.

It was cut through the center of the hole or cut further back and half the sump blocking the crank case view. Its like 1/8th inch diff.

I've cut Twin Disk valve bodies and Harley cylinders in half to look at and check certain features but never anything as elaborate as that. nice work, bravo !

I cut a whole Sanden a/c compressor apart last week, that was interesting to see the inside of. Little 6 piston pump.

Looks great!, how long did it take you...???

:3gears: :3gears: :3gears:

Is the tall narrow port that unshrouds first supposed to promote swirl or something? I am assuming it's small and narrow like that to promote high velocity.... then the main port unshrouds? And why do they intake it through the piston instead of conventionally? This is cool stuff.

Edit: I figured out the port in the piston. It's part of the porting..... I.e. no reed valve or schnuerle porting...

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Originally Posted by BAD LS1

No the 2 bolts are are not perfectly even on the sump.

It was cut through the center of the hole or cut further back and half the sump blocking the crank case view. Its like 1/8th inch diff.

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Gotcha!!! in that case it looks great!

Took about 4 hours including planning, cutting on a band saw, filing, and painting. Oil based enamel takes forever to dry! But looks alot nicer and is stronger in the end.

The othe cool part is that i have the flywheel and ignition coil on it, if i spin it fast enough it actually makes a spark jump the gap.

The idea is to have it video'd from over top while its spun with a drill slowly to make it appear it like its running and then they will superinpose fuel vapor leaving the carb and heading into the crankcase and into the combustion chamber, a flame front as it burns and then, smoke entering the muffler.

So much for a tuned exhaust system on this pickle heh?

Now cut one of mine in half :D

Turned out great. :thumbsup


Now spend time on turboing the sdime.

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Originally Posted by Kurt

Is the tall narrow port that unshrouds first supposed to promote swirl or something? I am assuming it's small and narrow like that to promote high velocity.... then the main port unshrouds? And why do they intake it through the piston instead of conventionally? This is cool stuff.

Edit: I figured out the port in the piston. It's part of the porting..... I.e. no reed valve or schnuerle porting...

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Thats on the right path.

Basically those "boost ports" which are the smaller tall skinny ports in the cylinder, work with the windows in the piston skirt to help move more air/fuel into the cylinder along with the larger ports. As you know the more air and fuel we can pack into a cylinder, the more power it will make.. Thats the main goal with it.

Having that port open slightly sooner actually helps to broaden the power band too, since this engine sits at about 3800 top no load, and can bog all the way down to 2500 under full load.

You are also correct on the velocity being higher through these smaller ports, as the piston come back down it applies a slight pressure to the crank case and forces the fuel into the combustion chamber. This is normal for all 2-cycles. Anytime we can force air through a smaller opening it will increase in speed, and decrease pressure in its wake. (this is how carburetor venturi's operate) When that pressure decreases, atmospheric pressure present in the crank case from that last intake stroke does what it can to fill that void and essentially helps push MORE mixture through the small ports.

All these means is, thats its good for 1.0 HP more than the standard engine. Thats pretty good for a little 8 C.I. 2-cycle. Being our 4 cycle 9 C.I. engines cant make anywhere near 7.5 hp....

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Originally Posted by Karps TA

Now cut one of mine in half :D

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Thats on deck! Im just waiting for some junk injection pumps to arrive to start with!

We've got a cutaway for shows.

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Originally Posted by Karps TA

We've got a cutaway for shows.

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Yeah but i need something that moves, they lock all those up on purpose so assholes like me dont come up and try and turn them:rolf

I love engine cutaways. My high school metals teacher had a two stroke Briggs and Stratton on his desk that the students would always play with. It wasn't that nice looking though, lol.

That is a pretty fvcked up induction system though, confused the hell out of me.

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Originally Posted by slickwilly

That is a pretty fvcked up induction system though, confused the hell out of me.

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I agree. This the first step to trying to take the mystery out of 2-cycle engines in the training piece im building. They were always an enigma to me for the longest time...

This engine here is deff on the low end of technology, get into some mercury outboards and shit gets hairy, even i cant understand how someone figured out how the special things those have done make even more power and clean up emissions.

Ive got a pretty lenghty section on tuned (expansion chamber) exhaust systems that use the divergant and convergants and + and - sound waves to acheive scavenging, essentially supercharging the engine through the exhaust.

friggin sweet! cut aways are always intresting to me, i like to see exactly how it works!