Kickback issue...I'm stumped, need help

[arch252]

I posted earlier about a Tecumseh 4 hp vertical shaft engine with an auxiliary horizontal shaft. The engine code is TVS115 56022B. This was a tech. shop engine, meaning students took it apart and put it back together but it had never been run. I have picked up a few of these engines, both the horizontal shaft and the vertical shaft, mostly B&S but this is the fist Tecumseh dual shaft like this one I have gotten. It was in parts when I got it.

It went through it and got everything together on it and it was hard to start but I did eventually get it started. It ran for a couple of minutes and then I shut it off. I tried to restart it but it would not start and it was kicking back on the compression stroke, jerking the cord clean out of my hand. I checked and sure enough, the flywheel key was sheared. I replaced that, it was the "L" shaped key. It was still kicking back and would not start. I have checked the valve clearance, both set right around .006. I have checked the linkages on the carb, it all appears to be set right and working properly. I checked the ignition gap and it was correct. I took the plug (J19LM) out to make sure no oil was causing it to lock up. I had already removed the valve cover, checked the piston and valves and put in a new gasket. As a last resort I split the case and checked to ensure the timing was set correctly on the camshaft, and it was. I went ahead and put in a second new flywheel key, just in case.

In spite of all of this the problem remains, still kicking back and will not start. It is getting spark, it is getting fuel. The muffler is new, OEM for that engine.

Any thoughts or suggestions?

 

[Lawnranger]

As you already know, ignition timing can cause the kickback you describe. You found a sheared key and replaced that. Are you absolutely sure you have the correct key for the engine? I'm just making sure here.

Since this engine came from a tech school and was in pieces when you got it, the students may have had several engines apart at the same time and switched flywheels. I know this is a long shot but it appears you have covered all the possibilities with the exception of the flywheel. You probably know that the magnet passing by the coil induces the spark but if you have the wrong flywheel for the engine and the magnet is in a different location then that could also cause timing to be off. Again, I know it's a long shot but that is what came to mind as I read your post.

I'm not familiar with that particular engine but is it possible to mount the coil upside down?

 

[arch252]

I appreciate the reply, sometimes it takes someone talking you through it to figure out the problem. I am almost positive the flywheel is correct. As far as I know Tecumseh only made one type of the "L" shaped flywheel key. The thinner edge of the key fits the shaft correctly and the wider edge fits the flywheel groove perfectly. Also, the inside of the shaft opening of the flywheel is conical in shape, and the flywheel key only fits one way, the flywheel will not mount without the correct key and it is obvious in looking at it that the flywheel is shaped specifically for that shaft. I'm very confident that is the correct flywheel.

As far as the engine being in parts when I got it, well...not entirely. The carb, air filter housing, muffler and fuel tank had all been removed. The block itself with flywheel were intact.

The coil is a possibility and I'm pretty sure it could be mounted upside down, I'll have to pull the cover off and take a look for sure. The fact that it did run momentarily at one point makes me want to exclude that possibility. I have not removed the coil so I have not inadvertently switched it.

If I have moved any of the linkages incorrectly, could that have anything to do with the kickback? I wouldn't think so but then again if I knew for sure I wouldn't be here asking for help!

 

[Lawnranger]

If I have moved any of the linkages incorrectly, could that have anything to do with the kickback?

On the probability scale, low.

Again, I'm not familiar with that particular engine but if they are like other small engines then the theory of operation will be the same. Of the possible linkages on the engine, there should be throttle, choke and governor. Moving or incorrect installation of these linkages should not produce the kickback you are experiencing. Almost always it's ignition timing and that's why I'm looking at all the ignition components. The only way to know for sure is to verify all the components in the ignition system by either comparing them to known good parts, testing, parts look-up or a combination of these. For some reason the spark is arriving at the incorrect time (early) so looking at the involved components should lead you to the answer. If you are certain the flywheel and key are correct for the engine what about an incorrect coil?

Does the engine have points & condenser? If so, take a careful look at the setup. Replace if in doubt. And do tell us when you sort it out.

 

[arch252]

So I went back over it all again, rechecked the flywheel and key. I went back over the governor linkages. I checked the coil and made sure it was mounted correctly.

I took pictures of the coil and top of the flywheel. I also attached a picture of my forearm after I blistered it for the third time with the handle from the pull rope jerking back on me, I though you all might enjoy that.

Is there anything internally that could be causing the problem. When I split the case I made sure the marks lined up on the crankshaft and camshaft. Is there ANYTHING else internally that could be out of whack?

I'm at a complete loss here. Good spark, good compression, flywheel and key are snug and fit correctly, throttle and governor linkages are correct, valve clearances have been checked, so on and so on.

Here's something I have noticed. I took the air filter out when I first attempted to start it. The first two or three pulls it did not jerk back and acted like it was cycling through with normal compression but did not fire. About the third pull I noticed the fuel mist was pretty heavy coming back out of the air filter housing when I turned the engine over, when that fuel mist started to get heavy is when it began to jerk back violently, every time.

 

[Lawnranger]

I feel your pain. Everything in the pictures look to be correct, as far as I am aware, with one exception - the arm. Just pickin'. Is it possible that the flywheel key is in upside down? In other words, if you removed the key is it possible to install the "L" the other way? I ask only because Tecumseh engines just don't exist on machines where I live. I know it sounds strange but Tecumseh engines aren't popular in lil' ol' podunk, Texas and I have never had one apart for inspection.

Here is engine theory I'm basing my thoughts upon: An engine needs three factors present and in the correct proportion to start and run properly 1) the correct air/fuel ratio (fresh, quality fuel is a must), 2) sufficient compression (see manufacturer specification) and 3) sufficient spark at the correct time.

Correct timing is critical and every time I had an engine pull the starter rope out of my hand it is because the timing is incorrect and the reason the timing is incorrect is because the operator hit something and sheared the flywheel key. When the key shears it causes the timing to advance and when timing is advanced the spark comes early and when the spark comes early the air/fuel charge is ignited as the piston is moving up on the compression stroke sooner than specified and the expanding gas reverses direction of the crankshaft which rips the starter handle out of your hand. You may already know all this but if you do then what else could possibly cause ignition timing to be incorrect? Let's look at the possibilities. Wrong flywheel, ignition coil, crankshaft (key slot cut in different location), key installed incorrectly? What else could cause timing to be advanced?

I'll be the first to say I am far from knowing all there is to know about small engines but when you go back to theory of operation, something is missing. I admit that I could be barking up the wrong tree chasing ignition timing and maybe I'm stuck on theory too much but theory has always helped me in the past.

If it were my engine I would physically verify the key slot vs. magnet location on the existing flywheel to a known-good flywheel and the same for the rest of the components I mentioned above. I can only think back to the days when I was in auto shop in high school doing the same small engine work thinking "what if we swap a whole bunch of parts from this engine with the engine the other guys are working on" - just to get a laugh when the next students have to work on this engine with mismatched parts. Kids do crazy things and at this point you can't rule anything out until you verify 100%. But hey, it was a free engine, right?

I'm going to keep thinking about this one and follow this thread hoping you get this sorted out. By the way, you never answered my question about the points & condenser.

Let me know.

 

[arch252]

As far as I know that is the only "L" shaped key that Tecumseh makes, and it fits both the flywheel and shaft perfectly. I have tried the key in every position possible, the way it is shaped, as with the shaft and flywheel, make it so that the flywheel can only be installed if the key is in that one position.

Here's a clue that I just thought about. The one time I did get the engine to start was with the initial sheared key. So for it to run the flywheel was likely "out of position".

All goes back to a timing issue. I'll verify the correct flywheel. I'm wondering if there is something internally, perhaps the piston connecting rod installed backward, if that's possible. Some of those rods have a longer mounting bracket on one side, not sure about this one. I'll manually check that the crankshaft and camshaft position marks actually put the piston at TDC.

 

[Rivets]

If I remember correctly, your must have this engine connected to a load to get it to run properly. Running without a load will give you the kickback problem.

 

[arch252]

Can anyone confirm that, because that would make sense. The flywheel is extremely light.

 

[Micah Haarhoff]

he is right about the load at least on my Tecumseh.

I have a Tecumseh engine and it did the same thing with the kick back, and it was the timing
I know you checked ,it but you might just want to double check it and make sure that it is set right





by the way where do you get your engines from? when you get your engines from a tech school do you just go ask for their extra engines or what?
I want to get some to mess with.:smile: