Briggs and Stratton 11 Horsepower vs 12 Horsepower / Briggs Stroker (Mainly Plans)

Here i’m explaining the difference between the briggs 11 horse (model 252707 and the briggs 12 ( 281707 ) or 12.5 horse, this case a 12.5 (model 286707). the only difference is the length of the stroke, the model 28 has a longer throw. both engines use the same piston, rod, rings ( depends on bore type ), and camshaft. The valves are different, the model 25 has short valve stems. The block has to be ground here and there, and the cam shaft may have to be ground so the rod won’t hit it. My 11 horse ( i have 2 but they are both the same ) are not the I/C series and do not have cast iron sleeves, so they do tend to wear out faster, but are good engines, and can be bored and sleeved. And a popular trick is to take the head off the model 25 and put it on a 28 block to boost compression and get a little more power out of it. My main point in the video was to talk about how you can take a 25 block and 28 crankshaft and make a stoker out of it, a 28 cubic inch engine in a 25 block. but there is a lot of maching to do in order to get it all to fit right. And a custom connecting rod would have to be made, which i do plan to make and sale in the future. and you also have to switch out the dog bone rod on the synchro balancing counter weights to the one that comes on the 25 crank because the holes are different sized that go in the block. Which on any racing engine it is best to eliminate the synchro balancer and either use the brass counter weights or upgrade to a 28 crankshaft with built in counterweights, already balanced and everything. a project for a rainy day!!! or a rainy week!



40 thoughts on “Briggs and Stratton 11 Horsepower vs 12 Horsepower / Briggs Stroker (Mainly Plans)

  1. The 12 horsepower threw a rod because it was knocking or detonating. I got to about 4 minutes and 20 seconds on your video and that's when I saw it… your cylinder head has all kinds of dots all over it. those are the explosions from the fuel pre igniting or detonating. It was either running too hot or too lean or on bad fuel something was going on but that's what caused it… it wasn't an oil failure it was a pressure failure from detonation the rod can't change directions it tends to shoot out the other direction when the gasoline ignites before it's supposed to buy the spark plug.

  2. My 8hp Briggs and stratton engine I had on John Deere s82 threw a rod two years ago and it took out the cam and destroyed the block and oil pan

  3. I want to convert a few of these to horizontal. Do you know if they use a dipper or anything special to get the oil up to the valves and rings?

    I know there are a few videos out there to convert the smaller ones but not too much info out there with the bigger syncro balanced engines. Thanks for the great videos.

  4. Hi I am trying to id an engine I have and was wondering if you know the height to the cylinder head of them both as I don't have the cowling.

  5. I did a horizontal conversation to a model 28. And I'm having difficulty with a carberation set up for it. What caberator and intake do you suppose would work for it? An 8 or 9 hp up draft carb?

  6. i think i would make a spacer plate to go between the head and block  and try to keep the rod length the same, the longer rod keeps the piston parked @ tdc longer, and mill the head as flat as possible to make up for compression loss, though it might screw up the way the engine scavenges, ill let you know when i finish the project, im busy right now with a mod 28 putting a big exuast  valve and seat in it same size as intake hope it dynos good!

  7. I Have a 10 HP that just threw a rod. and pushed the balancer  right out the back of the motor.  I have a back up motor but they were all used and put a way wet. so the next motor will be taken a part and rebuilt. with new gaskets ect. so I will be watching your videos. 

  8. 1 more question if i was to advance timing on my engine with the cam what way would i turn it and how many teeth could i move it to make more power?
    could you possibly make a vid on how to advance timing to ??

  9. Nothing!!! They are both the same engine, 12.5 13 and 13.5 model 28 are the same engine, just a marketing idea, now the 12 and 12.5 are still 28's but may have the newer 2 piece carburetor that gives the extra 1/2 HP, but that is the only possible difference. Briggs is infamous for this!!! Thanks for watching!

  10. That is true. I'd have to agree, I prefer a longer stroke as well, just seems like your "using more of the piston" if that makes sense haha Getting more leverage from it. The only advantage with a short stroke is it will rev up to higher RPM's. but you loose power. Thanks for Watching!

  11. Longer stroke tends to raise the chances of breaking a rod, but it also delivers more torque at lower RPMs, and more potential power. I prefer longer stroker engine myself.

  12. Glad to hear! ehh hard to say without having it hand so i could compare to other blocks, yeah there is no number on the blocks, if you had the flywheel cover off of it, that would be great, wish i could help more! thanks for watching!

  13. Your vids have been super helpful! I have a bare block with no head. (converting to horizontal… wish you had a vid for that), not sure about it's specs as I can't find numbers anywhere. Got any ideas on how to I.D this baby? thanks!

  14. I use a wire brush on a drill, the cup type, put the head in a vice so you can dig down more. you can also soak it first in carb cleaner or even WD40 to dissolve the carbon some first. thanks for watching!!!

  15. Yepp, there is no difference at all! i have a 19.5, its the same thing as the 16.5. Briggs was bad about that, and still is from what i heard, same thing with the single cylinders they are putting out now, a 17.5 is the same as a 15.5. now on the older 12 and 12.5's, the extra .5 came from either the new 2 piece carb or switching to electronic ignition. now oddly enough my 19.5 opp twin is a model 46, go figure haha thanks for watching!

  16. Got my rings on the piston. thanks for your help. I need the torque pressure for the head bolts for that same 12 hp model 281707 engine if you would be kind enough to help. Once again, thanks so much.

  17. no problem! on most top comp rings there is a angle ground into them on the back side that faces the piston, this angle goes up. the surface that is on the outside is flat on the top ring. PM me your email address and i'll email a picture of how each ring goes, if that would be better

  18. Thanks for getting back so soon. I'm still a little unsure what you mean by " the rings slant". my new ring is flat on top, has a silver edge part way down and is then grooved on the bottom, if that is the way it should be installed. should the grooved out section face the oil ring below and the flat part face the top compression ring?

  19. It faces down, towards the bottom of the piston, the ring's slant goes up towards the top. I should make a video talking about this, it is often overlooked. Thanks for Watching!!!

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