# Tecumseh 6 HP compression order



## mljd7

I've got a sears lawnmower (Eager 1) with a tecumseh 6 hp that I had to take all apart, but when I put it all back together, match the timing marks, check the valve activation order... When I try to start it, the rope only pulls out maybe 2/3 of the way, the compresion seems messed up, and the compression pattern seems to just lock up the motor. If I pull the rope out slow, it will come all the way out, but the compression pattern just doesn't feel right.I have done this twice to double check everything and still get the same results!
Can anybody tell me what I might be doing wrong?


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## bugman

compression release is either not working or messed up


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## mljd7

Are you talking about the valve itself not moving? Because I have taken the head off and turn the motor by hand, and follow it all through the cycle, intake, compression, and exhaust. Everything looks like it is all moving at the proper time.


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## bugman

the compression release is not kicking in and making the exhaust valve pop open a little while turning it over fast enough to start it.


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## mljd7

I don't know where or how to locate or correct the compression release you are talking about, I do notice however, during the compression stroke (when the piston is on the way up), the intake valve opens just the slightest bit. Is this what you are refering to?


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## bbnissan

Yes, that was the compression release. The compression release is a mechanism on the cam that works off of engine speed...at slow speeds it actuates and pops the valve open slightly, but at high speeds it doesn't engage at all.

BTW, did you use plenty of assembly lube when you tore this motor apart and put it back together? It almost sounds like the crank is hanging up on the journal bearings or the rod because of a lack of lubrication. Also, are you sure you installed the piston and the rod correctly (there should be a mark on both of them indicating which side goes towards the flywheel)?

If you used plenty of assembly lube I would say you probably have the valves adjusted incorrectly.


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## mljd7

I did not use assembly lube but I did use motor oil when I re-assembled it. I never removed the piston, only the 2 small bolts that hold it on the main crankshaft so I could pull the crank out and inspect it. I'm sure the piston is in the correct position, I just had to tweak it slightly to line it back up with the crank when I put it back together. Also, I never adjusted the valves, only removed the valve pushrods for inspection and put them right back in. Where is the journal bearing located? The sears manual is very lacking in detailed parts listing.


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## bbnissan

The journal bearing is the portion of the block and crankcase cover that supports the crankshaft. If I were you, I would go ahead and readjust the valves to see if that solves your problem. To adjust the valves you need to rotate the engine until the piston is at top dead center on the compression stroke. After this, rotate the engine a little more until the piston drops down approximately 1/4" (you can determine how far it drops down by inserting a screw driver into the spark plug hole until it touches the top of the piston). Once you have it 1/4" below TDC, loosen up the rocker arms and use a feeler gage to adjust the valve clearance. I'm not sure exactly what the clearance should be on a Tecumseh, but someone around here should know.

For future reference, you need to use assembly lube rather than motor oil when you are putting an engine back together. You need a lube that will stay put until the engine has time to pump oil back through all the oil passages in the engine.


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## mljd7

The reason I took the whole thing apart is because I hit a stump, and oil started leaking all over the deck. I thought their may be a crack in the block assembly and proceeded to "dicect" it. I found not one crack but learned that the oil fill tube must have come loose and the oil ran out. I am very receptive to all the advise I have gotten from everybody, but I never re-adjusted or re aranged anything. I know you all are much more educated about small engines than I am (I am a jack of all trades but master of only a few!) but the engine was running perfect when I shut it down and took it apart (looking for the oil leak). Do you really feel it is a valve adjustment issue? I will try anything, and taking it all apart again is no problem for me. If I could start at square one with your education behind me, what might you recomend I look for or do differently?


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## bbnissan

I would definately start with the valves and then go from there.


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## scrench

i would have to say it sounds like a timing problem flywheel key <----((((( ? ? ? would be my first try ,,,,,


"""The reason I took the whole thing apart is because I hit a stump, """


flywheel key any bets ?


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## bugman

yeah, forgot about that, i second that bet.


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## bbnissan

Oooooh...I missed that part. If he hit a stump, it could also be a bent crank shaft that is binding up in the journal bearing on the sump.


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## bugman

yeah that also


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## scrench

yea i would look @ the crank and see if it is bent , take the plug out to be safe about it and have someone pull the rope and watch the crankshaft and see if it wobbles if it does she's done , you might straighten the crank but im not going to tell you how , dont want to get anyone hurt ,, its not a good idea to do it but it does sometimes work but i dont recommend it and i dont do it ... but it might not be bent so look @ it and see


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## bugman

yeah its extremely dangerous when its not totally bent back right. it would cause increased wear, bad cuttin of course! but would most likely end up with the connecting rod flying out.


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## mljd7

When I inspected the the crank, I removed it, set it up on my bench and spun it around (I have a pretty sophisticated basement shop) with a concentricity tool and found it to be only about .0015 to .002 off. So I ruled that out. The flywheel key (from the top end of the tapered shaft) seems to be made of some very soft metal. It is ever slightly deformed but still fits good in its place (sorry whoever bet on that one, but I did put it in!) I found a new motor on the internet for $120, but I hate to have to do that, this has got to be something so simple, it's driving me nuts! I can get the valve tolerances, but I don't know where or how to adjust them.


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## scrench

still taking bets


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## bugman

yeah i don't care if its slightly deformed, they can be just a slight indention and it will not fire over but fire wrongly at the most. yeah its a soft metal, alluminum, wish they made a stronger key but since you had it off, go ahead and place a new one in, they can be up to 3 bucks for a nice sized pack of em and most of the time the problem, try that before you go and buy another one.


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## mljd7

I could try the key, but it seems to be special, the key itself is not square, it is "L" shaped if you look down at it, AND tapered, to match the form of the tapered shank it sits on. From all the info you all have provided, I think we can narrow it down. The sole reason there is a compression release, from what I understand, is for ease of starting. Once the motor fires and starts to run at a speed faster than it can be spun with the pull rope, the amount of compression lost is so minimal, or non-existent, it doesn't effect the performance. I have no problem taking it all apart and doing it again. 10 minutes, and it is in a million pieces. I know what an engine is supposed to feel like (compression-wise) when you pull the rope, fast or slow pull, and this does NOT feel right. The timing mark on the crankshaft gear is stamped on a PROTRUDING tooth, the timing mark on the camshaft gear is stamped BETWEEN 2 teeth. I line them up, and the whole sequence works great when I spin it by hand, but does NOT FEEL right when I pull the rope, like no compression release. Does assembly lube have that much effect on the cams signal to relieve the compression? If so, I will apply some in there. There are no rocker arms so aren't the valves preset? And the flywheel, if it is set right or not, should have no effect on the odd feeling of the compression. Am I wrong on that one? This thing has got me stumped. I hope a piece of advise from anybody will will get this thing going, I will send you beer or coffee!, whichever you prefer!


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## bugman

as for tecumseh's. all i can tell ya is go to a small engine shop for your keys, most regular hardware stores etc sell em for briggs, not sure if one would work since i havn't worked on a tec for a long......... time. havn't needed to, all briggs. as for the compression release it kicks in when your pulling on it to start it but goes away once its started. if the valves are opening right and close all the way. some engines i've seen the sheared key didn't affect the compression much or at all but if its firing wrong it will. tecs are picky anyway


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## mljd7

When I hit the stump, the motor stopped dead, and I immidiatley thought, oh great, the shaft is bent and the motor is shot. I re-started it right away, being extremely alert to any vibration or odd noises. It fired right up and ran perfect, for 5 seconds when I noticed the oil and shut it down. So although I am going to replace the key anyway (special order from Sears) I don't consider it a "prime suspect" because the machine ran fine, after I hit the stump. The valves, are they adjustable? I want to do one thing at a time, because if I replace the key, re-set the valves and use assembly lube, it will probably run, and none of us will have learned anything. Could also be a combination of more than one thing. I feel its Bugmans original diagnosis, compression release problem.


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## scrench

mljd7 said:


> When I hit the stump, the motor stopped dead, and I immidiatley thought, oh great, the shaft is bent and the motor is shot. I re-started it right away, being extremely alert to any vibration or odd noises. It fired right up and ran perfect, for 5 seconds when I noticed the oil and shut it down. So although I am going to replace the key anyway (special order from Sears) I don't consider it a "prime suspect" because the machine ran fine, after I hit the stump. The valves, are they adjustable? I want to do one thing at a time, because if I replace the key, re-set the valves and use assembly lube, it will probably run, and none of us will have learned anything. Could also be a combination of more than one thing. I feel its Bugmans original diagnosis, compression release problem.


to set the valves you have to grind off metal off the valve stem and check it witha feeler guage , you lap the valve down in the seat to tighten up the clearence and grind off to give more simple but kinda tricky . be sure when you put the flywheel on the crankshaft that it is clean and dry dont put anything on the crank shaft or the inside of the flywheel be sure it is spotless dry clean !!! also look @ the flywheel verry close and make sure it is not cracked have seen them crack have also seen people for whatever reason who knows put oil on the crankshaft b-4 they stick the flywheel on


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