how do I modify my 14hp opposed twin briggs?

So my murray trail tractor is pretty close to being able to run. I could slap the twin on and it would run, but not very well. The motor is an 85 model and other than oil and plugs I seriously doubt it had any work done to it. I did rebuild the fuel pump to get it back running though, so that's new.

I just got a compression tester and have never used one before. I tried to get a reading off both cylinders but must have been doing something wrong. I used jumper cables on the starter and could only crank it over a few turns due to the low battery charge. But I thought it would be enough to get a reading on the compression gauge, nope. One cylinder didn't budge and the other read about 30 psi. Obviously that's wrong since the engine runs right? Anyway, before it got too cold I pulled one cylinder head and it was gunked all up. Everything was black and chunky with carbon and oil, the cylinder wall looked like it had wear marks on it but felt smooth to the touch. Also the piston has a notch taken out of it, which looks to be machined from the factory?

Anyway, when I get the chance I'll be taking lots of pics of all the things I'll be doing to this motor. I at least wnt to freshen it up, clean the carb, replace any worn out gaskets, lap the valves if needed. Beyond that I may shave the eyebrows and port the intake and exhaust a little bit.

I lucked out and found the repair manual online in pdf format. Most of it I already knew but the torque specs are nice to have.

Sounds like it needs a good cleaning. i wanna see pics cuz iv never seen a engine gunked up brfore


MY engines not that old but still couldnt find any repair manuals for it. what i really want is the specs it but i cant find nothin

model # 407777-0121 -E3 briggs

I have twin cylenders ranging from 86 to the 90's - ive been lucky with them, lil cleaning and tweeking they run pretty good- cept for my 88 - that was missing its intake/carb- sometime ill make a new intake and mount that scooter carb to it.

My 86 GTII's 18HP was in pretty bad shape, had been sitting outside for a long time uncovered- the whole upper intake was filled with rusty water right down to the combustion chamber. i had to pull the heads and drain the water, cleaned up all the rust that i could, sprayed everything in there with a healthy dose of PB blaster and turned the motor over by hand to clean and unstick the rings- i knew the rings were good because the water didnt go into the oil. i put it all back together, sprayed some more PB blaster in the spark plug holes for good mesure , added some gas and thing fired on the second crank. I used the old plugs at first, till it cleaned out a bit, then put fresh ones in.

Id clean all the 'gunk' out, then use PB blaster or even wd40 to see if the rings will loosen or to tell if theyre worn- more then likely itll need new rings- since its been leaking oil into the cylenders.

Twin cylenders will actually run on one cylender if a rod on one breaks and breaks clean- itll still run. Id clean up the motor, then try doing another compression test- they should read at least 100psi.

The other cylinder's plug was much cleaner so maybe like you say, it was running mostly on one cylinder. No broken rod but the rings may not be sealing which means that cylinder isn't adding much power to the engine total. I already cleaned a lot of the gunk off but just envision 1/8" of black sludge all over everything up to the head gasket. Does anyone have a favorite place online to buy parts that's cheap, or would the local repair shop be best for the parts? I'll definitely need a gasket kit. Like I said, the engine ran before, but I like to do things the right way. Plus I've never messed with the internals of any engine before and experience can be a valuable thing. I'll take some pics this evening and pull the other head off, though it won't be as bad looking.

Did nothing today other than snap some pics and pull the other head off as I was parking the car in the garage. You can see where I cleaned up the first head/cylinder and the other side. The other side is only partially gunked, so just imagine that completely covering everything and that's what the first cylinder looked like. Why is the exhaust valve white on this side?

definitly looks like the one is leaking oil , the white valve could be just that it was burning hotter possibly ( burning the oil n gas ).

I just go to the local tractor parts places nearby , at the local cub cadet dealer i bot a pan gasket and lower crank seal for my one 12HP briggs- was less then $5 - carb kit was $20 for my 17HP twin briggs. One of my buddies up north bot a new rod, piston and rings for a single cylender for like $45 for a 12HP single cyl.

I was able to use my head gaskets on my 18HP twin again.

Well I am at least moving forward, slowly. I cleaned up both cylinders heads and the surface of the pistons and valves. I bolted them back on and tried a compression test again, this time with a fresh battery and making absolutely sure of a good seal. I got 60 pounds on both cylinders. I know it should be higher but the manual said that balance was important also. My next thought is making a leak-down tester, maybe track down where the compression is being lost. Though we all suspect rings.

Then I moved on to the carb. Took it loose from the intake manifold and found the manifold has a crack. The front bolt hole for the carb, broke off. Good thing is that it isn't part of the air/fuel path, just the mount for the carb. Hopefully I can take it off and weld it back good enough to hold the carb on and make a good seal. All I have is a mig with fluxcore wire. Times like this, I miss my old stick buzzbox.

I took the carb all apart out of curiosity and it looks pretty good, no holes in the float, nothing clogged. Then again it worked before, but I expected some dirt and stuff from old gas. Getting a rebuild kit for it tomorrow.

Got a carb kit and took it apart and it was surprisingly clean. I expected much worse. I build a leak-down tester and checked #2 cylinder and got air escaping past the exhaust valve. Hopefully I can lap them and it will seal. So I'm just going to wait til I lap all 4 valves before further testing, only replace/fix what's needed. The old head gaskets seem to hold up well enough and I didn't notice any air escaping from the vent tube for the air filter. Maybe it was easier to escape through that exhaust valve though. So plug one hole and check for the next is the plan.

While I have the valves out I'll port the intake and exhaust and shave the eyebrows. So for those who have done it and know more than me, I have a couple questions. First, I've heard mixed reviews on smoothing the intake port. Some say leave it, the rough helps mix the air/fuel. Others say a smooth flow is better. Is there a definitive answer to this? Second, I saw a youtube video where the guy had only shaved the intake side of the eyebrow, and was told to do so by his "engine guy". I was planning to shave all the way across, both intake and exhaust areas. Also what depth to you go to? Up to but not touching the valve seats?

Ive herd briggs motors like a lil turbulance in the intake - if theyre smoothed totally out they run choppy.

I really wouldnt bother with any major cleaning unless you plan on high performance parts- from some stuff ive read on racing tractor sites, opposed motors dont take to modding well and have more issues , the v twins do tho- with roller rockers, and stuff.

Thats what ive tryed to prove- using a stock governed opposed twin and seeing how fast itll go- from what ive ran with it on my murray- itll do 40 - 50 mph easily ( i had it over 30mph ) - theyre a strong motor stock.

Ok, I think I'll just deburr the intake and exhaust ports a little, maybe more on the exhaust. And leave the rest, maybe round off the corners where the eyebrows are but no shaving. The main thing is to get these valves to seal really good. Also I tried soda blasting yesterday on the carb. I had a cheap spot sand blaster and tried pouring baking soda into it. It works great on aluminum if only my compressor could keep up. I might clean off the whole motor with this process.

Did some more work this evening. Pulled one head, took out the valves, and did some lapping. I am being cheap and not wanting to buy a spring compressor. Getting the valves out wasn't hard, and getting the intake back in wasn't even bad. However getting the exhaust retainers back in is proving difficult. I tried the trick someone mentioned about compressing the spring and wiring it before install. My wire seemed too weak and broke on me after a little bit of movement. If nothing else I may try the wire again. Does anyone have any other tricks? As for the lapping, I think it did a good job of sealing and I cleaned up both ports. At the very least it should remove the chance that the valves are leaking, and the gaskets are sealing good. So after this if I still have bad compression, new rings it is.

Got the springs back on for the first cylinder and checked it again, definitely rings. At least I know the valves are seating good though. Then I moved on to the other cylinder and found RTV on the valve cover. Pulled the head and cleaned it up and find that the exhaust valve seat has been peened. So much for thinking this engine had never been worked on. It was my uncle's mower originally, so I will ask him who he had to work on it. He isn't mechanically inclined and has a bad habit of hiring locals to do jobs they aren't always competent at. Man is this engine freshening starting to look like a money hole. I figured a gasket set and some elbow grease.

Worked on the second cylinder, #1 I think, and found all kinds of disturbing things. Here are some pics of the exhaust valve, exhaust port, and head. The valve has wear that you should be able to see in the pic. You can see the seat was peened and there is a sleeve in the valve guide. In the last one, I'm thinking that is a mark from exhaust valve contact on the head. I priced some of the parts and all this stuff is adding up fast. It ran pretty good before so I think I'll just slap it together and see how long it lasts. I'm not looking to put much money into it.

Can I get some help from someone who owns an opposed twin? I apparently lost the metal rod that runs from the throttle to the plastic L-shaped lever part of the governor setup. Could someone give me a measurement for this thing, it should be simple to make a replacement if I knew how long to make it. It's the rod circled in red in this pic.

I dunno if id slap it back together the way it was- if it breaks itll either be toast or more expensive- save up and buy the new parts, youll appreciate doing it now.

I have a few motors i got with thrown rods- sometime id like to rebuild em - i picked up a free shelf setup from work that i plan on storing tractor stuff on- ill see if my motors fit on it - have like 10 spare motors for an emergency.


I have like 5 twins- when i get a chance to check ill see what length that piece is.

I don't know, I'd expect it to burn oil but not break. Thanks for the measurement.