Decarbonize - still needed with unleaded fuel?

[rogerf]

Hallo folks ,

I'm using an MTD ride-on mower I 'inherited' when we bought this place about ten years ago. The engine is a 12hp Briggs type 289707 01540 9308 124D.

Apart from oil, air filter, carburettor cleaning and sparking plug changes and fitting a recoil starter I don't believe any work has ever been done on the engine. It starts well even with the recoil starter.

I read somewhere that small engines should be decarbonized as a preventative measure, but I'm reluctant to mess with an engine that is working fine, but don't want a chunk of carbon to fall off and score the cylinder. I haven't even checked the valve clearances for the same reason. I also read that decarbonization is needed much less often when using unleaded fuel.

Should I leave well enough alone, or maybe try to borrow a bore sight camera and have a look in the combustion chamber? I'm hoping that someone with real experience can give me some real information. I don't really have an idea how many hours the engine has been used, but the previous owner had a reputation for looking after machinery. The tyres don't show much wear and I have had to replace the blade spindle bearings once (amazed how small those bearings are).

Looking forward to getting some good information

Cheers, Roger

[bgsengine]

It is a rare thing to just simply decarbonize as a specific maintenance item - Decarbonizing is usually done only as a part of a service job

- on a good running engine that does not burn oil, look at the spark plug if you replace it every year - if the plug appears relatively clean, it'll be indicative of how the combustion chamber looks too- If it is heavily fouled , then decarbonizing may be a viable maintenance point.. but it'll have to BECOME a regular maintenance - (read on..)

MOST carbon deposits come from contaminated fuel or oil, or poor maintenance (dirt bypassing air cleaner, air leaks after air filter, bad breather, overheating, etc.) - regular maintenance and using fresh fuel always, probably won't ever have to pull the head off specifically to decarbonize.

If it is bad enough to have heavy carbon buildup, then your engine is NOT running at top performance anyway - heavy Carbon is a symptom not a cause.

If you have heavy carbon, you're using old fuel, engine is burning oil, or has had poor maintenance, or a combination of all of the above.

By the time you need to decarbon a modern engine, you'll likely have other issues needing service as well in any case.

[TwoCycle]

Best practice would be keeping the crankcase and cooling fins clean of debris. Pay particular attention to resolving oil leaks as they will attract dust and cutting debris buildup. If you have the proper tools, it's pretty easy to pull the head to inspect for buildup. Clean as necessary, check head/block for flatness, and use a new head gasket.

I read somewhere that small engines should be decarbonized as a preventative measure,

Decarbonizing is essential for two cycle engines. Once the ring(s) stick in the piston land, combustion gases are able to blowby the ring.

An easy way to limit carbon buildup in modern two cycles is to use the correct oil.

[rogerf]

Hallo bgsengine and TwoCycle ,

Thank you for your speedy replies. Last time I replaced the sparking plug on the 12hp Briggs it was about 12 or so running hours ago and the old plug was reasonably clean, no carbon build up and certainly no hint of oil.

It does get an annual cleaning of all of the cooling area with the blower cover removed - sorry guess I should have mentioned that

I guess it's obvious that if the plug is reasonably clean then so is the rest of what's inside the combustion chamber - but I hadn't thought of it

There are no significant signs of oil leaks and the engine uses very little oil. After your advice I believe that I should leave well alone until there is a reason to do anything more than regular oil and air filter changes as well as the annual cleaning of the cooling fins and crankcase.

Regarding my two stroke engines, they are all given fresh fuel with a high quality air cooled two stroke oil (Castrol) mixed in the ratio called for by the manufacturer. The plugs on these engines are not so clean as on the four strokes, but then I wouldn't expect them to be. They are still far from being carboned up or heavily oiled. I try to run the two strokes flat out, although that's not always easy with a line trimmer.

Thanks again for your helpful and fast response to my question.

Cheers, Roger

[Mek-a-nik]

"If it ain't broke, don't fix it".
You must have more spare time than me. (I'm jealous.)
Too bad you don't live closer, I have a list...

[NevadaWalrus]

The big advantage of unleaded fuel is the carbon that does form from normal combustion is much softer then leaded fuel. Not nearly as damaging if any does flake off and much easier to clean when needed.

[Skywatcher]

if the plug appears relatively clean, it'll be indicative of how the combustion chamber looks too-

Hi Roger

This is why I ask my customers when ever possible to either leave the spark plug in the engine or bring the old one in when they bring in the machine. So often a machine will come in with a brand new spark plug so I have no indication of how the inside of the combustion chamber looks. That's when I show them the colour pictures of spark plug ends in a tech manual I have and ask the customer to pick which picture best matches the plug that came from their unit.

On a similar note; Have you ever wondered why when you have your annual medical, the doctor will use a lighted scope to peer into your eyes? He's visually checking the condition of your retina and in particular the optic nerve. The optic nerve is connected directly to the brain so gives the doctor a good indication of the overall health of your brain. Looking at the business end of a spark plug gives us mechanics a good indication of the overall health of the inside of the combustion chamber.

I had one customer who was a doctor in our town before he transferred out. He also brought his lawn mower in with a new incorrect plug. When I explained to him the similarity of the spark plug to the optic nerve in the retina, I saw the light bulb come on in his mind. He then told me that he learned more in those 3 minutes than he sometimes learned in a day at university when he was studying for his doctorate.

The other thing to remember about spark plugs is the life expectancy of a spark plug is 500 hours of running time. This means that one spark plug can last the lifetime of a properly maintained average* lawn mower engine. How often do people change the spark plugs in their car or truck as compared to their lawn mower? and how often do they change the oil in lawn mower as compared to their car or truck? All the best,

Sky

* Honda, Suzuki and Kawasaki are not your average lawn mower engine.

[wristpin]

All of the above and use a decent quality oil of a weight and spec suitable for an air cooled engine.

[rogerf]

Hallo again folks ,

Thanks again for all the replies to my question.

Yes I do have a "list", but some things just seem to be stuck at the bottom of the list! Bet I'm not alone on that one.

Thank you Sky for pointing out the life expectancy of a sparking plug - I won't be changing the plugs every year from now, but I do keep a maintenance record on a sheet of paper stuck inside the back cover of the user manual. I guess the cast iron liner Briggs are also better than the 'average' machine. Just to be on the safe side I've installed Maintenance Minders on the machines or engines I've bought new. They do help with their flashing warning that an oil change is needed

I guess I'm a bit of a pain when it comes to oil, always using what the manufacturer calls for - Briggs 30 weight for the Briggs engines (it's actually close to the cheapest here when bought in the 4 liter/1 gallon size) and automotive 10/30 for the Honda and clone.

Funny when I'm in the USA with our daughter it drives my son in law nuts when I tell him to go and buy some oil because his mowers and snow blower are all way low on oil. They also get left in the yard with stale fuel and he says they are hard to start. Must be a US thing

Thanks again for all your replies - now where's that list

Cheers, Roger

[bobodu]

There must be a LOT of "US thing(s)" for the kids to keep coming HERE!!
Take heart....it won't last much longer....