Re: Small Engine Death!

Would you believe it is a shopping bag? No sand, no oil, and not mine. Some people are just that stupid!!
I 'm guessing two years old at best,

Guido.

More oil in the mix is not the answer, as you already found out, 40 instead of 50 to 1! Doing so will have the same effects as too little oil. Now you are doing if again? If you had used the proper mix, your engine would STIHL be purring, pardon the pun! By adding more oil to the mix,you are lowering the required octane ratings that the engine requires. The engine may or may not smoke. But the issue is that you are LOWERING the octane ratings. That results in poor and cold combustion, which leads to early failure because of it. The owners manual should be your bible. Proper maintenace, quality gas and oil plus proper intented use of the product are the key to long equipment life.90% or more of the people that I ask, do not have the unit's manual say no..... chucked it! It never seems to amaze me!!!

Guido.

"More oil in the mix is not the answer, as you already found out, 40 instead of 50 to 1!" Would you clarify that please? I was using 50 syn and the manual said to use 40:1 didn't specify dino nor syn. It also said 89 octane gas.

Since Stihl sells syn plus storage additives in their private label engine oil, then there must be a reason. I don't see the problem with running 2.7x1.5 = 4 oz of oil to 127 oz of fuel vs 2.7 oz. That's a change of 4/2.7= 50% but an octane change of 87-89 would be 89/87= 2% if I went with the recommended 89 octane fuel. But I didn't see that as a need either....see comments below. I use 87 in everything around here including my 90 hp 2 stroke OB which doesn't care if I use 87 or the recommended 89 and it's stated (serv. man.) min compression is 120 psi.

Octane increase prevents preignition, detonation of the fuel air mix prior to the spark origination causing piston top damage, probably skirt slapping damage, cylinder wall scoring below the ring groove (2 stroker) which shouldn't matter.....remembering the 10.5 compression engines back in the 60's power race between auto OEMs requiring 95 [I think it was then...R rated or M rated, not (R+M)/2 as it is today]. I read that preignition burns holes in the top of pistons. Had no such deformation nor visual indication of any piston pitting in the crown.

The chain saw spec in the manual on compression min is 90 psi so I suppose the string trimmer would be about the same. Considering 14.7 psi atmosphere that's only a 6:1 compression ratio. The 10.5:1 of old days would be up in the 150+ psi reading.

So I don't follow you on more oil lowering the octane to the point where you would have preignition. What's that got to do with ring/cylinder wall wear. Would think just the opposite....take it to the limit....what would happen if no oil were used? I know. I helped to overhaul a neighbor's 1949 Mercury 110 hp flat head V8 when I was a kid and we put it together dry..... .obvious results.

Going to stop here and wait for you to come back. I'm interested in what you have to say and supporting evidence. I don't have a heavy background in small engines, or any for that matter. A few exceptions, like getting 4 kids through "rent-a-wrecks" and a few tractor restorations, but mostly just keeping all my stuff running, which usually didn't take much effort, over the years which was quite a bit but not like doing it commercially.

I missed the 89 octane, but more oil by volume will have a lower octane mix. I did not state any knocking as a result though. Colder combustion results in carbon collection and exhaust clogging. Engine wear soon follows. Maintaining your equipment as you do, it is a plus. Guido.

I don't think anything was gleaned out of this attempted opportunity, for me anyway. Oh well, the old stuff is out and the easy cranking new stuff is in. Hoorah!

Not sure about the octane theory, but extra oil does lean the mix. The oil is basically inert, so the main jet doesn't know the difference, it still lets the same amount of liquid through, but the ratio of usable gasoline is reduced, therefore leaning the mixture. Not a real concern with adjustable jetted carbs, as long as it is readjusted, but for fixed jet carbs, it can make enough difference to lean one out to the point of detonation, especially on a marine engine that can pull heavy loads for extended time.

Another problem with extra oil is the carbon build up, especially on the exhaust side of the piston/cylinder wall. This can be enough to decrease piston to bore clearance, and pack into the ring lands.

I've seen this to be more prevalent on marine engines, often occurs when the onboard tank is continually topped up with fuel, extra oil is added, guessing at the amount, go ahead and dump the rest in instead of wasting it... Then add in the evaporation factor.

It is amazing how stingy with oil the oil injected engines are! They start out at 200:1 at idle, only get 50:1 at full throttle.

Sea Foam is an anticarbon treatment that was always part of my marine engine fuel mix. Use it around the farm on other engines from time to time or as a fuel storage aid if not using something else.

On an inboard marine engine like the ones you see sitting for years at a time in marinas around the world, no telling what's going on in those engines considering todays fuel and the time they spend just sitting and sitting and sitting and when they do get used, it's half an hour of no wake to get to open water then put her on cruise speed for a couple of hours then back to the half hour to the dock then secure her to sit for more months at a time.

Also on 2 strokes, the oil in the mix helps to reduce any piston scuffing and being in the fuel gets on the crank, rods, bearings and piston skirt on the intake half stroke and on the crown on both strokes. On ratio, my 2002 Merc 90 VRO system was 80:1 at idle to 50:1 at WOT, obviously due to the lower stresses and temps.