Murray 5725 lawnmower 8hp Tecumseh no compression

Recently bought a used (non-running---i know, i know) Murray 5725 riding mower with an 8hp Tecumseh engine (TVM195 150269E). Owner assured me it ran fine last summer but had sat all winter and now would not start, just needed carb work. I have cleaned many carbs so I bought it for $100. First bad sign was when i took the carb apart and it looked fine, clean and not gummed up at all. Someone had been in the carb recently. Still, double checked everything and put it back together and back on the engine. Put some fresh gas in it and tried to fire it up. Plenty of spinning but no firing. Tried starting fluid in the intake with no results. Took sparkplug out and checked for fire, plenty of spark. Tried starting fluid sprayed in to the cylinder, no results. Checked compression, no compression. Uh-oh! Took sparkplug out and turned motor over while watching valve action through sparkplug hole. Looked fine, both moving up and down. Tried some oil in the cylinder for a "wet" compression test, still not even 10 pounds. Tried putting thumb over sparkplug hole just for feel of what is happening and could feel it sucking and blowing on my finger quite a bit, not enough for real compression though I guess.

I am about to take the head off and see what I can see there. Does anyone else have any other suggestion for what to look for? Any help would be appreciated.

 

Make sure the valves are sealing,,,,,,,,,,,,,,,,,,,,,,just did a 8 hp BS and the intake valve was not seating and blowing gas back out of carb. Ya might put some air pressure to the cylinder to see if it can tell ya where the compression is going,,,if not pull the head!

 

Does anyone know the secret? to taking the gas tank off on one of these Murray mowers. Got the obvious two top screws out and the tank is quite loose but seems to be held in place by the oil filler tube which is held in place by a bracket bolted behind the gas tank. Tried taking the shroud off but apparently it has a bolt behind the gas tank as well. Hoping to find someone who has the secret combination before I just take it off with a sledgehammer.

 

Allright...got the tank off. A really igmo method by Murray for holding the gas tank on. Had to pry the gas tank away from the engine while prying the oil filler tube towards the engine and pulling like mad. Idiots.

 

Well i got the head off and couldn't see any obvious clues for a blown head gasket. Turning the crank moves the piston up and down and in time with the valves. At TDC both valves are closed. No obvious scoring on the cylinder wall. Not really sure how to proceed from here. Anyone got any suggestions?

 

If you didn't even get 10 lbs with a wet compression test, the problem should be glaringly obvious I would think. Can you rotate the valves when they're closed?

 

Yeah, my thinking exactly. With so little compression I figured the problem would be obvious with the head off. But no. The valves are tight when closed. Guess I will throw another head gasket on it and see what happens.

 

Decided to remove the valves and check them before I put the engine back together. However, I cannot figure out how to remove the guard over the valve springs. Took the cover off and removed the filter but the inner guard won't budge. Is there a trick to removing this guard?

 

Allright...got the breather body out using a slide hammer like tool. Now there is a cover with a tab like looking thing on it. As far as I can tell this part does not show up on a partstree diagram of the engine. Hate to break it getting it off. Does anyone know what this cover is? And how to remove it?

 

After checking it out further, it appears to be some kind of one.way breather-reed valve. Still do not see how to remove it. when i bend it back i can see the exhaust valve shaft and spring.

 

Turned out to be the reed-valve breather plate covering the valves. Removed the whole plate and now have unfettered access to the valves.

 

Bought this mower in non-running status (bad idea). I cleaned the carburetor, replaced the head gasket (now has 80 pounds of compression), checked for fire at the sparkplug while i tried starting it, looked like plenty of fire. Carburetor appears to be getting plenty of gas to the float bowl. But it would never fire up. I tried starting fluid with no noticeable results. When it finally did do something it looked like the engine kicked back and then went on turning over, but still never fired. Any help would be appreciated.

 

Have you checked to see if the flywheel key is sheared?

 

No I didn't actually. Didn't think about it. I did check the valve action while I had the head off. Just to make sure that they were opening and closing correctly with the movement of the piston, mainly thinking of a compression issue at that time. Both valves were completely closed at TDC. I will now check the flywheel key. Thanks.

 

Just checked the flywheel key and indeed it was sheared smooth off. Replaced it with a woodruff key I was able to find at Ace hardware. Cranked right up the first time i tried it after fixing it. Later I checked the blade and it was obvious it had hit something hard...one tip bent down. I appreciate the advice "cheese".

 

No problem, but next time you hit something your flywheel may explode like a frag grenade. The woodruff key isn't made to shear when it hits something, so it could fracture the flywheel at 3000 rpm.

 

I couldn't find an OEM replacement flywheel key in PartsTree. Do you know where I can find one? Also, in taking the blade off for examination/replacement I found that it was held on by one nut with one cupped washer and a lock washer. It seems like there must be a blade adapter of some kind missing to keep the blade from freewheeling as the crank spins. Do you have any information on that? Thanks!

 

32589 is the tecumseh part number, shown as part #89 on partstree.

I'm not familiar off the top of my head with this mower. Is the blade mounted to the crankshaft on this, or to a belt driven shaft? In either case, there should be a flange above the blade for the blade to press against when the cupped washer is tightened against it with the nut.

 

Yes you are right. I said crank but it is a belt driven spindle. Thanks.