Teardown and Inspection of Briggs and Stratton 12.5 HP I/C Flathead Engine

BRIEF INSPECTION of a Briggs 12.5. This engine overheated. Needs alot of work, gonna be put off for a while, needs bored out and resleeved and new valve guide bushings pressed in. Thanks for watching.



48 thoughts on “Teardown and Inspection of Briggs and Stratton 12.5 HP I/C Flathead Engine

  1. Hi. Great videos BTW. I have this engine in a Hayter 13/30 ride on mower. I recently tipped it on it's side to change a belt, went to start it, made a funny noise and stopped. Do you think I may have damaged the rings? many thanks.

  2. Thanks! I've tipped several motors over and never had no problems except the occasional oil burning if you tip it over the wrong way, it should not have damaged it at all, have you tried starting it back up since? Its possible that it may have flooded the engine and made it choke out. thanks for watching!

  3. Thanks for the reply. Theres no compression, I may have damaged the rings from an ingest of oil. Maybe not worth the expense of getting it repaired.

  4. It may have blown a head gasket, did it smoke any before it died? If it the headgasket your only looking at about 10 bucks (plus shipping of course) so its not a huge repair, but make sure thats what is first, just like checking a gas pipe or a tire for leaks use soap and water around it and see if it bubbles when you crank it over.

  5. If its really cold out you will have to choke for the first 4-5 minutes, in summer weather they usually only have to be choke for less than half a minute. thanks for watching!

  6. yes they are identical engines just a different sticker! now the only possible difference is the cylinder bore, on some power builts the bore is aluminum but on all I/C's they are cast iron sleeved, just check that first, because the rings will be different in a aluminum (kool bore) engine. on briggs motors look at the first 1-2 digits of the model number, on 12 and 12.5's (same again) they are model 28 which means 28 cubic inch. thanks for watching!

  7. Appreciate it! I have another video (4 part) on tearing a 12.5 horse down and completely rebuilding it, i go into alot of detail on it compared to this one! thanks for watching!!!

  8. I got an engine exactly like this one on my MTD riding lawn mower, that my brother got in 1995. Has given me years of service and the mower is still in great shape. However the engine needs a rebuild. And the tragic thing is that some critical parts like the exhaust valve and cylinder head are no longer available.
    It is sad that our society has become so "throw-away" and people just buy new and no longer fix things as our grandparents did. Sad that these parts become scarce after a few years.

  9. You can still buy valves for these motors, look on tulsa engine warehouse, it won't be briggs brand but a good aftermarket brand. You can usually get buy with re-using the same head, some will have them milled down and a new gasket. I do agree with you, it used to be R&R remove and replace parts now its TO&BN throw out and buy new equipment haha I hate that. Its really not fair either. Thanks for Watching!!!

  10. I'm in the process of rebuilding a 10hp Briggs model 254707 I need to bet a set of valve spring pliers so I can take the valves out. I have one all tore down, that I'm rebuilding, it needs to rings and the cylinder needs redone. piston and cranks all in good shape.  and with this rebuild I want to get ride of that balancer that's what broke on my last motor.  now to get it all cleaned up and all the old paint off. to repaint but not paint the piston part with the fins to make a nice new motor. ordered all the rebuild parts. cant wait to get the thing up and running again. 

  11. Great video and very helpful.  I'm new to small engine work and need help diagnosing an issue. I have about the same B&S engine and it's not getting gas to the carb.  Gas it getting to the fuel pump, but not going beyond that to the carb.  It has another hose that comes from the block that I assume provides vacuum to the pump?  That hose was pretty old and stiff, so replaced that but no change.  Got any ideas on what I should be looking for?  I first replaced the fuel pump but no change with that either.

  12. hi there. great video . I have a briggs diamond ic 12.5 engine. no problem starting. problem is engine is over revving.
    checked carb gaskets all ok. checked carb manifold going into casing all ok. governor spring is good – stiff at full throttle – weak at low throttle. engine seems to over rev even at low throttle. any ideas – thanks

  13. Hi I have stripped and rebuilt a 2003 I/C 12.5hp engine that would not start never found anything wrong with it the problem it blows petrol out of carb we can not find the fault every thing appears as it should be would appreciate some advice thanks Garry

  14. Im fixing to start working on a engine just like that I was wondering where do you get all the parts to rebuild that engine because I can't find a good place to get all the parts I need and where could I find a book to help me know how to tighten everything to what briggs and stratton want.think you very much if you can help me.


  16. I see I commented before here I just got a 12.5 HP Briggs just like the one you are rebuilding I will be using your videos to rebuild it. I only gave 7 bucks for it at and auction it runs. but it leaks oil like crazy from the oil pan gasket, and smokes like crazy, carb needs rebuilt because it burns to lean. when I got it it wouldn't start so I pull he head off and found a lot of carbon build up a round the exhaust and the fuel inlet valve look like it got to hot but looked really crusty.  so I just clean them up some and put the head back on and it fired up and it ran good other than the smoking, witch caused it to stop working again because of the oil.   I plan on doing a rebuild on it and use it to replace the 10 hp briggs on the mower I have it on there now and used it to get my yard under control LOL. it dose not nock so thats good. now to get to work on it and yes I will be using your videos to rebuild it LOL

  17. Hi. I have a 11.5hp version of this motor, can the valves be adjusted without removing too much of the engine??? Don't really want to take it apart (lazy) is there any other reason for engine not turning over??? starter works, battery ok, engine turns when lower pulley turned.Great videos keep up the good work.

  18. Have a similar motor that just blew on me caused by an oil leak. Trying to find a cheap replacement because I don't think the motor can be rebuilt.

  19. I just rebuilt this exact model since the shaft shattered. (NO other damage, cracks etc!)However, its  impossible to start, backfires heavily. Grinded the intake valve slightly inorder to reduce backfire into carb. Shaft gear key, timing marks aligned, no sheard fly key,new magneto, strong spark, checked piston, valves & fly -positions, all o.k in the cycle.I´am totally bewildered, Engine fires in totally wrong positions, different all the time.

  20. When I try to start my mower it will make a thud noise flywheel moves a half turn then locks. what could be the problem Briggs & Stratton 12.5, I have checked all of these, battery fuse, spark plug, fuel and oil

  21. Could you possibly do a video on rebuilding this? I've got one of those off a 1993 Murray and I just want the engine sounding new, and hopefully you have a video linking how to adjust the carburetor as well, only has two screws and between the two screws is a yellowish one, what is that for

  22. hi fnaguitarplayer9,
    i have an older 10hp horizontal shaft briggs, presumably 1970's vintage from what i can tell. probably a 233401 series. there's no ID number on the cowling. the piston is 3 1/16 diameter.

    the question i have and this is something no one has been able to answer:
    what are the basic jet settings for the carb? one turn, two, three? there are two screws, one at the bottom of the float bowl and another at the top of the carb at the throttle flap.
    i had the thing running last year and then one of my loving neighbors dumped a quart of water into the gas tank and it hasn't run since. i have drained the fuel, drained and cleaned the carb, but it still won't run. it has compression but it's hard to tell if it has spark since it's a pain to pull the rip cord and check to see if there is a spark. it has fuel to the carb but i am thinking a passage is clogged somewhere and/or the jet settings are whack….

  23. I have this same engine. It runs very well, but the crankshaft seal is leaking badly and oil is causing the belt to slip. Can the seal be replaced without opening the crankcase?

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