Reconditioning for tired Briggs twin

[cjolson140]

My dad has a yard machine riding mower with hydrostatic drive that he really likes. Nothing wrong with the machine except that the Briggs flathead opposed twin (I think 18hp?) is fairly well worn out. It burns 4-6oz of 40wt oil to a tank of gas, and if you shut it off it will not restart until it cools down, sounding like low compression. It still runs strong however, if a little hot.

I read somewhere online of an air cooled Briggs in a similar tired state, where the owner did an extremely low effort "rebuild" that consisted of ball-honing the cylinder without removing the piston, with the idea of re-bedding the old rings for better compression and oil control. My plan is to give this a shot, as well as lapping the valves while the heads are off. Maybe I'll even do compression and leak down tests before and after the job to see how much (if any) improvement is gained.

Thoughts? I should be able to do both cylinders in a few hours tops so I don't mind wasting the time on an experiment.

 

[kd5byb]

My few cents...figure out why its got low compression before you do anything. If it is the rings...the ball hone may do more harm than good as you're removing a tiny bit of metal from the cylinder walls and making it even harder for the rings to seat.

thanks,
ben

 

[oldhp]

Try 1/2 can of Restore first.

 

[Donald]

Get a new engine from HF.

 

[bullwinkle]

Originally Posted By: Donald
Get a new engine from HF.
Best idea-I replaced my half-dead Briggs 2 cylinder on the log splitter with a 13 HP Predator Chonda & never looked back.

 

[Chris142]

I think your plan is going to wear your worn out rings even more.

 

[ShotGun429]

Originally Posted By: Chris142
I think your plan is going to wear your worn out rings even more.
+1

 

[Lubener]

I have seen egg shaped cylinders. If it is not sleeved, I wouldn't waste any time with it.

 

[andyd]

If you lap the valves you will have to grind the stems to properly set the lash. I would be looking at a Chonda replacement. I just completed season 4 with my Chonda powered Ariens snow blower. Totally satisfied.

 

[cjolson140]

Little bit of an update... She fired up for the first run a week ago, ran for 10 min and I changed oil to rotella 15w-40. Few days later, starter could not spin over fast enough to catch, even with a strong booster battery connected directly to the starter. Burned up the starter after about ~20 seconds of cranking.

Replaced starter with new B&S unit (80$!!), now she spins over faster than I've ever seen and even restarts hot! I did notice that with the choke pulled about 1/10th out while mowing, it runs much smoother instead of surging on the governor like I'm accustomed to. Running slightly richer/cooler may be why hot restarts are now possible.

Burned maybe 2oz of oil mowing the entire yard (about 2.5 hours.) May have been a little pessimistic in my belief it was worn out... Either way I'm confident this engine will easily last another season or two. Next chance I get I'll check for any vacuum leaks & go through the carb, maybe open up the main jet a teeny bit.

 

[dwendt44]

Need for some choke indicates a carb problem plugged jet.
Hard to say if oil use will remain constant. a couple of oil changes
with 10W-30 HM oils may free up rings. A dose of SeaFoam may help with
that as well.

 

[JTK]

If an eBay carb is cheap enough, I'd slap a new one on there, make sure the breather tube and assembly is all free and clear and run 15w40 oil in it. Call it a day. If you're rebuilding it for fun/nostalgia, that's one thing, but I'd put very little time, effort and resources into a horizontally opposed Briggs twin.

 

[ironman_gq]

Clean the carb first, that could fix a lot of the problems. Once you've got the carb sorted out try doing a piston soak with sea foam. A lot of these engine burning oil due to sticking oil control rings, getting them freed up and cleaned up often helps. Running a good HDEO will also help clean them if you do some short change intervals as will adding some cleaner like sea foam to the oil.

 

[jeepman3071]

Those opposed twins do tend to run a bit hot. I'd definitely run a HDEO like Rotella 10w30 or 15w40 in it. A carb rebuild and fuel pump gasket kit will do wonders for it as well. I do love the sound of an opposed twin, they have a unique exhaust note.

 

[meep]

do note if you open this one up, these B&S opposed twins have an issue with the exhaust valve seat coming loose and chewing up the head-- I wouldn't do a thing to this motor before checking the head condition. IDK if there's a solution to harden it against failure - re-peening the head? Though I do not think you have a problem with this now, it's the first thing I'd look into if you get into it.

-m

 

[wag123]

If an exhaust valve seat has come loose, one cylinder won't fire and it will be WAY down on power or the engine won't run at all. This is not a problem that will fix itself and it will need a valve job. On a flat/L head engine this won't damage a head.
Your engine is running lean so you have a carb problem. Before you try to clean/rebuild the carb, check the throttle shaft. On this engine they are subject to wear and when they are worn, the hole in the carb body is also worn. Trying to get an engine running well with a worn-out throttle shaft is an act of futility. Before you mess around with trying to clean/rebuild the carb, grab the throttle where it goes into the carb and jiggle it to see just how worn/loose it is, if it is worn-out you will need to replace the carb. I can fix this problem in the shop for less than the cost of a new carb, but this is something that a homeowner can't do.
Burning a couple of oz oil in 2.5 hrs is not a problem on an older B&S engine.

 

[DeafBrad]

If you want to reduce oil consumption even more you could run sae 30 (if the manual says it is ok). The manual for mine states I can use xW30 but sae30 is recommended. The manual states you may have increased oil consumption when using xW30 oil.

 

[JTK]

^^ Good call on the possibility of a sloppy throttle shaft. I've seen that myself on old, high hour OPE engines.