View Full Version : OT - Small engine repair

05-25-2012, 09:29 AM
Had a Briggs & Stratton 5.5 HP engine dropped off to fix as it "wasn't running right". There is a rubber hose that runs from the valve cover to the air filter housing, assuming it does some sort of crankcase ventilation. The air filter is soaked with oil. What is causing the oil to come into the air filter housing? Worn oil rings on the piston? Worn valve guides? Some other part that is clogged? The spark plug has a fair amount of carbon from running rich but is not oil contaminated. The top of the piston has carbon deposits but nothing excessive.


05-25-2012, 09:50 AM
Excessive crankcase pressure is usually caused by high blowby (piston rings) or crankcase ventilation device (if fitted) restricted. Pull the hose off, start the engine and watch what comes out of the valve cover with the engine under load. If it's smoking heavily and has much pressure behind it, rebuild time.:(

If not, check the hose and the valve cover to make sure they're not restricted. I think they have a baffle with a filter screen or the like in the valve cover. Could be clogged causing pressure build up.

Good luck!:)

05-25-2012, 10:12 AM
From what a neighbor who teaches small engines at the trade school has suggested in other cases, valve guides can be a problem, not suggesting that rings might not be either.

05-25-2012, 12:42 PM
One time my neighbor's riding lawn mower started blowing white smoke like a fogging machine. It turned out that the air filter was clogged with debris and manifold vacuum was being applied to the crankcase ventilation hose because it entered the manifold down stream of the filter element. So it was sucking oil out of the crankcase and into the manifold. A new filter fixed it.


05-25-2012, 12:51 PM
The hose you mention is a crankcase vent hose. as others have mentioned, high crankcase pressure can cause oil to be blown out of this hose. Another source of the problem can be oil level too high or using the equipment on a hill (angle) that allows the oil to cover the internal vent hole that the normal blow by gasses take to escape. If angle or level isn't your problem it's probably rings, a crack or small hole in the piston (with associated reduced compression). There is what amounts to the Briggs & Stratton version of a PCV valve called a Crankcase Breather, which the hose is connected to on the block, usually held in place by two screws. If the internals of that part are missing or inoperative that could also cause the problem. Follow this link: http://www.briggsandstratton.com/support/frequently-asked-questions/Additional%20Maintenance/ and look about halfway down the page for Crankcase Breather maintenance information.

05-25-2012, 05:41 PM
How old is the motor? Is it overfull of oil?
I've run into this problem a couple of times. The steel seat in the alum. block comes loose and jams under the exhaust valve.

05-25-2012, 06:22 PM
Small gas engine equals consumable. Why fart around spending your valuable time and cash when you can replace it for a HF Honda knockoff for less than $100 and be done with it. I have one that always starts within a pull or two. If your in the repair business then buy a bunch when on sale and resell them as replacements. You'll make more money/hour but will have to endure the rathe of people who think you should we working for $5.00 an hour to fix this crap.

05-25-2012, 06:39 PM
small briggs, oil spewing out breather, like some suggest I would look at rings/piston or bore damage. And if its a non IC variant, it wont have a cylinder liner, they just ran the piston right in the crankcase material after boring it and called it "cool wall technology". You can't even compression test them to see if they're good without dismantling because the "easystart" cam grind keeps the ex valve open till a set rpm to give the crappy underpowered starter motor a chance to spin it up without cylinder pressure to load it up.

I'd just open the lid, see the oil, note it was a briggs then go off to buy a honda engine to replace it.

05-25-2012, 07:26 PM
re: Wilhem's post-"Why fart around, go buy a new one"----

There ARE people who enjoy diagnosing a problem and fixing it.:(

05-25-2012, 07:35 PM
I see a couple of Briggs bashing posts here and find it a little it a little unfair. Maybe Honda makes a better small engine, maybe not.

I've had Briggs & Stratton engines on my equipment since my Dad's lawn equipment in the late 50's and had great luck with them. We ran them on home made mini bikes using bicycle frames, wheelbarrow wheels, Speed Queen washing machine clutches, belt drive and dryer pulleys on the back wheels through mud, sand and over dirt roads when I was 14, under loads and conditions that were never envisioned by the manufacturer and they held up fine. These were plain bearing, aluminum cylinder without cast iron sleeve engines to boot. Many of those engines were put together from parts of many worn out engines found in the trash or at the dump. In all that time I've had one failure in a 12 HP vertical shaft Industrial engine which threw a rod within a week of purchase on a commercial lawnmower. That engine was replaced, no questions asked, under warranty with a 12.5 HP version. That was at least 15 years ago and that mower still runs great today, with the same engine.

B&S makes engines to meet different markets and sometimes they are blamed for something the manufacturer of a product did. Using a plain bearing engine in an application where the all the load is borne by the crankshaft bearing is a recipe for sure failure. I saw that with a Craftsman mulching machine. Sometimes manufacturers cut corners to remain competitive or make more money and choose a less than ideal engine series for their product. Honda and Briggs both make different levels of engines and when chosen properly either will perform well for many years.

Maintenance, or lack of, is another issue. Those little engines put out all they have with little complaint. So little, in fact, it's easy to overlook oil changes, cleaning air filters, spark plug replacement or other maintenance. Gas is left in them until it's rancid between uses as well, but still they run until they break or won't run in may cases then the engine gets blamed not the lack of maintenance.

Then there is the government and it's regulations. Emission and safety regulations have made these engines more vulnerable to breakdowns yet when they quit the engine gets blamed, not over regulation.

Competition from copycat foreign manufacturers, mostly Chinese, will take their toll of Honda engines eventually, if they haven't already. Honda will be forced to use cheaper materials and engineer weaker designs to compete with the Chinese knock offs and eventually will be put in the same category as some here have put the B&S engines.

05-25-2012, 08:45 PM
One of the very best engines i ever had was a 9Hp B&S "Vanguard".

Got it on a Lincoln 125 amp welder generator.

Used it to weld but also used it to run my AC power while i was living off grid in the bush.
Had it for 13 years and put over 7000 hours on it ,,when i sold the place it went with it.
When i got it, it burnt 1 liter of fuel per hour @ 1/2 load, when i sold the place it still was using 1 liter per hour.
All i ever did, was plug changes , steady oil and air filter changes,,,AND it usually started first pull! At -20-30F it would require 2-3 pulls.

Oh, and i put one recoil spring in it and 3 starter ropes.

One hell of a GOOD engine!!

A.K. Boomer
05-25-2012, 11:21 PM
Everybody's pretty much covered most of the stuff I would look for - high oil level - running on a slant - excessive blowbye,

Sometimes you think oil level is fine cuz you changed or checked it recently but rich mixtures or leaky needle and seats with higher fuel tanks can up the ante on the oil level because its diluted with fuel...

also make sure the air cleaner is not restrictive and that the internal crankcase baffling is in tact...

05-26-2012, 09:28 AM
I just rebuilt our briggs (15hp I believe) in our 0 turn. Same thing, running bad, using oil. I thought for sure the rings were shot because someone hadn't checked the oil before mowing the whole block.

Well after pulling the motor off the chassis (pain in the arse) and tearing it down I soon realived it was justa blown head gasket between the cylinder and valve chamber (push rods next to the cylinder). So in the end I could have left the motor on the mower and just pulled the head off and threw a new gasket in...

otherwise looks like everything has been covered. Not much to these motors, quite fun to work on honestly because everything is small and easy to work with. Working on heavy diesel engines all the time make you appreciate small light things.

05-26-2012, 10:33 AM
The cause of the oil in the carb is there is a flapper valve in the valve cover. If the flapper valve does not close the back pressure from the crankcase will blow into the carb and will migrate into the air filter.

Replace the valve cover, DO NOT rebuild the engine.

05-26-2012, 02:50 PM
I see a couple of Briggs bashing posts here and find it a little it a little unfair. Maybe Honda makes a better small engine, maybe not.

I don't think its unfair at all. I spent 6 years fixing lawncare equipment as a profession and my opinion is based entirely on what I experienced in that job.
And I saw a LOT of dead brigg's motors, most of which I would lay firmly at the door of that piston and oil flinger design.
Are the other manufacturing entities mentioned subject to the same regulation changes? Perhaps they just had a better design and didn't cut corners to be the cheapest engine on the shelf in the pursuit of the almighty $ regardless of quality.

I think the chinese copies of the honda will eat brigg's lunch, not honda's. Because all the people who buy on price point will buy them instead, and then we will all see engines failing from poor quality control and materials instead of design shortcuts.

Saasquatch, the vanguard and the IC series motors are a different beast to the small engined briggs you see in lawnmower's and sit&ride mowers etc. They are actually designed well with a oil pump and a cylinder liner amongst other innovations.

I post too much, off the shed instead.

05-26-2012, 07:02 PM
Mr.Fluffy, there was no oil pump in my model of vanguard, just the usual oil slinger. Flywheel end of the engine just had a bronze bearing, the rear of the crank had a bearing.

05-26-2012, 07:21 PM
I was never very fond of the "oil slinger"

05-26-2012, 08:11 PM
Well, Andy the oil slinger or "Dipper" certainly worked ok in that engine going over 7000 hours for one of those engines , best engine i ever had.

A.K. Boomer
05-27-2012, 09:33 AM
It's just varying degree's of quality --- to me "real" engines have an oil pump and at least pressurized rods and mains and while were on the topic of "real" engines they also have connecting rod bearing inserts instead of just running the aluminum rod on the crank itself, Again, you want a bic lighter or you want a Zippo... (ok - bad example but u get the idea)

05-27-2012, 11:12 AM
Yeah I like oil pumps too. Oil slingers just seem to "good enough". I know the crank case looks like a tornado of air and oil when running but still it is the absolute bare minimum way of getting oil around.

05-27-2012, 05:11 PM
Steve, I sent you a PM a day ago. Please read it.

05-27-2012, 06:37 PM
I just worked on two Briggs & Strattom 3.5HP vertical shaft mowers today. The first was discarded by a guy at work, it was near impossible to start and running very poorly. Local dealer said it was most likely the carb diaphragm so I bought a new one for 2.99. Didn't help much, it ran a little better but still poorly.

I was working away during the week so my stepson tried to run it but it kept dying out. He turned it on it's side and had a look at it, got it running again but now it was pouring out smoke and dripping oil from the exhaust. My wife told me on the phone that the engine had died.

I had occasion to visit a scrapyard on Friday with a skip of steel and a guy had just bought in a mower with an identical engine. The scrappy let me take it home. That one wouldn't start at all.

The problem with the first one leaking oil and smoking, was that having tipped it on it's side oil had got past the one-way valve and into the chamber behind, and was being drawn into the engine. I cleaned that out with some aerosol degreaser, got it running but still it was poorly.

The poor-running problem for both mowers I found out was zero valve clearances, so you might want to check yours Steve whilst you have it apart. Remove the small cover behind the exhaust muffler, turn the engine to TDC when the valves are not over-lapping and see that there is clearance between the tappet and valve stem. If there is none, you have to use a file to make a gap. I took a thin flat file and ground a short taper wedge on the end, forced that in between the tappet and valve stem against the valve spring pressure and filed away with the very end of the file until I had about 10 thou gap on both. After doing that, both engines start first pull and run very healthily.

Only other issue I had was one of the recoil pull-starters sticking where it was worn - I just swapped out the six ball bearings for larger ones and now it too works perfectly with no sticking.

Going by today's experiences, I'd say the owner has tipped the engine on it's side whilst 'looking at it' and pooled oil in the breather, but the real running issue is with the valves.

05-27-2012, 08:17 PM
Steve, I sent you a PM a day ago. Please read it.

Got it, thanks.

Pulled the valve cover, not much oil residue and the flapper seems to be operating properly. Hosed it down with WD-40 and did get a fair amount of dark residue out of the small drain hole at the bottom. Maybe that was plugged.

Discovered the air breather cover is damaged so I'm replacing that and doing a general tune-up. Should have the part on Tuesday. Also, drained all the gas and putting in fresh gas as the owner couldn't tell me how long the current gas was in there. :eek:

Peter - didn't see your email until after replacing the valve cover. I'll pull it again if the tune-up doesn't get it going.

Thanks all for the suggestions.


05-27-2012, 08:50 PM
Make an air hose fitting that will fit in the plug hole, make sure the pistom is at TDC & the engine is locked so it wount rotate. Turn the air on slowly & listen where it escapes, oil fill= rings,muffler=exhaust valve,carb=intake valve,between head & block=head gasket.
As far as quality remember the plastic carbs, I think that was profit mandated not goverment. When H-F closed out the 6.5HP for $49 I bought 12. I've let a 6.5 honda clone like these on a gererator sit over a year & it always starts on the 1st pull,runs quit,has low oil shutdown, what more do you want for the price. these Honda clones are 10x what the old noisy,shaking B&S used to be. I agree they're much better now because the had to keep up or go belly up but for a while they were junk.

John Stevenson
05-28-2012, 03:58 AM
I'm having problems with mine at the moment and it's a honda powered model, bad starting but to be honest when it finally dies I'm doing a Tiffie on it...........binit

It's 6 or 7 years old, cost about 100, the deck is going rotten, spares will cost more than it's current worth.

End of the day it's a consumable and my time is worth more than pissing about with one of these things.

Every time a post comes up saying what would you charge for making this part and the general consensus is that the average home shop guy with limited skills and equipment should charge $80 per hour.
Then the next post is about pissing about with a B&S or Honda engine that has a net worth of what ? $40 total.

Where's the logic ??

05-28-2012, 08:21 AM
There isnt any!!

05-28-2012, 09:55 AM
I think the logic is that it is time related and not money!
If its your business you are concerned about then the time is more important not he money w=however when one is retired the emphasis changes, I have all the time in the world (baring death) so I save the money.

When I was working I cauldnt spare or waste the time just get another or pay someone else to repair it!

My 2p worth!


05-28-2012, 10:03 AM
I'm still working and I like saving money!

Instead of fixing up all those old machines a guy should just buy all new bridgys and encos.

A.K. Boomer
05-28-2012, 11:24 AM
If you have the time - there's a challenge to saving something from going to the bone yard - and in many cases it's environmentally friendly and most of all its a great way of "sticking it to the man" with not having to always replace things,
Im very comfortable in making the statement that im one of those "statistics" they really can't count on :D and I take great pride in that fact.

05-28-2012, 11:33 AM
I guess if you have endless expendable income you can just toss things out rather than repair them. The rest of us with more limited resources take the time to repair rather than replace. Besides, as already mentioned, there a challenge factor, the opportunity to learn, the possibility of reviving an old trusted "friend" and many times the "new and improved" versions aren't as good or reliable as the older, less complicated machines that can be repaired with what us found in the well equipped home shop.

05-28-2012, 12:37 PM
If you have the time - there's a challenge to saving something from going to the bone yard - and in many cases it's environmentally friendly and most of all its a great way of "sticking it to the man" with not having to always replace things,

Absolutely, here's my garden mowing device. When I bought it, it had snails living inside the crankcase and was sold for spares. Its now got a 12v simca car starter, 12v ignition system and a homebrew cat1 hydraulic 3 point (too old to have one as standard...)
Just off outside to top 1/2 a acre of waist height marsh grass and thistles etc with it, after doing the season prep, ie disconnect the battery saver, check the fluid levels and change the oil. It'll work all year doing mowing every other weekend, then the odd bit of plouging for the wife's veggie plot and whatever else little jobs we need it for without complaint. A tractor collecting friend is aghast I still use it for its intended purpose and update it here and there, but I see it as helping a old friend along.
Some things are worth investing some time saving, because they're made of nice materials and the design is good. And once they're fixed, they go on giving good service for years.

Analogy, would you put time into restoring a first gen chinese mini lathe, or a southbend?