Tecumseh flathead burning oil

[Pyrotechnic]

I've got a tecumseh 2.5hp on a motorized bike. I've been running Delo 400 15w-40 just because its what I keep around for my truck and it seemed like a good choice. The problem is, the motor doesn't have any oil smoke on startup or when its cold, but half way on my commute home in the evening when its hot, I start seeing oil smoke out the exhaust, and sometimes quite a bit. The engine is obviously pretty old and I have no idea on its history. It was headed for the trash after the owner didn't know how to clean and set the points. All I know is that it runs strong still.

Is my choice of oil a problem here? I had thought about maybe switching to a straight grade for better high temperature stability or maybe something thicker for this tired motor. I had thought about sae 50 but I'm not sure if it may be too thick? What do you all think?

 

[abycat]

I dont know how old it is but most small engines are desinged for a 30wt. You might make matters worse with too thick causing improper lubrication. Id take the head off and check for gouging in the cylinder and if it has a big lip at the top meaning crazy cylinder wear. Essentially causing bad ring seal. I cant see the valve guides being worn cause they dont see too much oil. typed on my phone so exuse mistakes.

 

[HerrStig]

20-50 Castrol was the magic stuff for my Tecumseh powered Sears lawnmower. The deck failed after 22 odd years. The Honda I have now requires 10-30 and that's what it gets. Perhaps that engine has just had it.

 

[fdcg27]

An old Tecuseh burning oil?
Really?
In my old Tecuseh mower engine, I've been using GTX 20W-50, mainly because it swills oil and I have some quarts of the stuff laying around.
One thing that I have found is that if the oil level is maintained at the lower end of the safe range, consumption and visible smoke are greatly reduced.
Now, my mower will smoke more if worked really hard, like shoving it through tall, thick grass at a very slow pace.
It is likely that the engine on your bike is working hard most of the time.

 

[TFB1]

In a small air cooled engine no doubt well past it's prime, there is a 99.999% chance no oil will be of much help... The cast iron rings are soft and wear easily, I'd say you'll need to re-ring it or live with the problem...

For those who've never seen small engine rings, here is a pict of the oil ring(on left) from my 30 year old B&S that was check gas and fill the oil... Note there is severe wear, originally it would have looked like the new one on right... No oil or miracles in a can will fix this problem...

 

[Pyrotechnic]

Thanks guys. The motor does get worked really hard. I built the bike with a hand lever controlled belt/tensioner clutch so the motor gets loaded a lot more than it would with a centrifugal clutch that has a lot of slip to it. There's been times when I start from a stop and let the clutch out I see a big cloud of smoke pass me by that the wind carried.

The project was done with stuff that was free or cheap, so I don't mind living with the smoke but I'd like to find the best oil that might minimize the smoking until I rebuild the motor. Should I keep running the 15w-40 I have been using? Would rotella 5w-40 synthetic be a better choice? I don't mind spending a little for a better oil since it takes so little. At this point I've just been lazy and running what I have on hand for my truck.

Also, I have 6 quarts of Brad Penn 20w-50 laying around I had forgotten about until you guys mentioned that weight. Was just going to sell them since I don't have an engine that needs it anymore, but would it be a good choice for this motor? I certainly have enough to last awhile.

 

[Quest]

Originally Posted By: TFB1
No oil or miracles in a can will fix this problem...



What?! not even MMO could save this poor engine?! Afterall: MMO cured the cats and dawg's ticks, saved my friend's marriage, etc. why can't it cure this thingy?

Q.

 

[tommygunn]

It doesn't have a transmission, so you can't put LubeGard Red in it.

According to this forum at least: no, there isn't anything magical that people claim makes everything magically better to add to a lawnmower.

 

[Pyrotechnic]

Update: I bought some Mobil 1 15w-50 and dumped it in. The motor seemed to have a little less visible smoke but it will still shoot out a pretty good puff after an extended idle. The exhaust smell is pretty stinky now, I guess Mobil 1 just stinks when it burns.

Once I go pick up my stash of 20w-50 Brad Penn, I'll start running that since its already paid for and it is a racing oil.

You guys are right, this motor is tired and in need of a rebuild and no oil will fix that. A multigrade 50 weight seems to be the best way to at least tame the smoke in the mean time though. Thanks guys.

 

[tomcat27]

valve guides are likely worn also. find a small engine repair class... valve guide inserts are easy to install, as are new rings

 

[Scdevon]

Rings are cheap. Just re-ring it as long as there are no bearing knocks. You can get a lot more life out of that engine with just a light bore hone and ring replacement even if the bore isn't perfect.

 

[afoulk]

I took a small gas engines class my sophmore year of high school, next to the welding class I had the following year, it was the best elective I ever took. I learned how to winterize my dads 2-stroke lawn boy, learned how to adjust the carb on most small gas engines, learned how to take my go-karts 5hp B&S apart and put it back together, and my favorite part, we took a couple John Deere Model A tractors apart that had the pistons rusted fast to the blocks (cast iron pistons) and got them running again and then two of the guys in my class bought them. They were all great experiences and I learned so much. Small engines are pretty easy to work on. Even if you just by a book and attempt the repairs yourself, I think you shouldn't have a problem, just take your time.

 

[afoulk]

I took a small gas engines class my sophmore year of high school, next to the welding class I had the following year, it was the best elective I ever took. I learned how to winterize my dads 2-stroke lawn boy, learned how to adjust the carb on most small gas engines, learned how to take my go-karts 5hp B&S apart and put it back together, and my favorite part, we took a couple John Deere Model A tractors apart that had the pistons rusted fast to the blocks (cast iron pistons) and got them running again and then two of the guys in my class bought them. They were all great experiences and I learned so much. Small engines are pretty easy to work on. Even if you just by a book and attempt the repairs yourself, I think you shouldn't have a problem, just take your time.

 

[Pyrotechnic]

I had never seriously considered rebuilding this motor before but it might be a good winter project. If I can get away with just honing the cylinder with a drill and installing new rings then it may become a reality. Would also give me a chance the work the intake and exhaust ports over, they are pretty poor and could use a good cleanup.

What they say about Mobil 1 and leaks is very true. The motor seeped oil out of the pto seal, side cover, and governor shaft before but nothing too crazy. Now I've got drips and spots on the ground.

 

[WMSmotorhead]

No No No... you are all wrong. You need to buy some boutique racing oil, add MMO, Lubro Moly, and do a piston soak with Seafoam.

Or you could just fix the rings. I would suggest after it's fixed to use HD30... it's what flathead mowers are made to use.

 

[Pyrotechnic]

A closer look after work reveals that oil shot out of the valve cover breather and made the motor appear to leak from the gaskets/seals. This happens when I go over bumps at a high speed or high rpm. Disregard what I said about Mobil 1 and leaking. I need to make a new valve cover with an extended tube for the breather.

 

[TFB1]

If it's blowing oil out the crancase breather, no doubt has a high degree of blow by, caused by worm piston rings and/or scored cylinder...

 

[Fordiesel69]

The one piece oil ring is terrible. Tecumseh genuine parts still ship it that way too......

Get a stens or rotary piston kit in a std bore with the 3 piece ring. It will work much better and the best part is it will work in a slightly worn / scratched bore with no problem.

No air filter is the #1 issue for oil buring. Carbs were so terrible that some people got the engine to run excellent without the filter and when installing it, the engine would run terrible, so they left it out.

I would say that 95% of any tec engine I have ever worked on was missing the air filter completely. A quick way to ruin the rings.

 

[Pyrotechnic]

The oil only seems to spray out on a high speed high rpm run which I blamed on going over bumps at that speed and I had never considered blow by to be a problem. It makes sense that blow by would be pretty bad at high rpm and load though.

Thanks for the tip on the rings, I will definitely remember that when I order parts.

When I intercepted this motor before it landed in the dumpster, it was still on the edger and there was no air filter housing at all. I rebuilt the primitive factory carb and it was terrible. It would idle and run at governed speed, but when presented with the varying load and speed of vehicle use the motor ran terrible. I replaced it with a mikuni motorcycle carb and the engine runs excellent now at all times.