I do not think I would grind down the exhaust valve stem to remove that slight lifting of the vavle. It will cause the exhaust valve not to open as much as it should when needed, It would be better to take out the cam and have that spot removed off the exhaust cam lobe. But I would not do it to one of my engines. Not fun when the pull starter rope/handle is ripe out of your hand when starting the engine.
So you losing .020" of lift from the camshaft then?? It would seem to me that the component resposible for opening the valve (I.E. the cam/lifter) would be responsible. Now you have + .020" of valve lash. If it's ground into the cam, I've never heard of it. Definitely not how I would rectify the problem.
ut:
ut:
seems if it was at the midpoint of the compression stroke it would greatly reduce compression because it lets half the air out. If it was at the end of the intake stroke as the piston is at the bottom perhaps its to prevent a backfire or somthing. but it wouldnt effect compression so that would make the most sence
Absolutely! That's why I noticed the floating valve in the first place. I was trying to fix my friends' 8HP Tecumseh on his snowblower. I couldn't get the carb adjusted right, engine wouldn't hold a smooth rpm, wouldn't idle right. I checked and the compression was around 60psi. I did a wet compression test and it was the same. Finally in frustration I popped the head off and as I turned the crank, I noticed the exhaust valve lift during the compression stroke. Since then I've seen the same problem on 6-8 other motors. it seems to be just Tecumseh because I haven't seen any B&S motors do it.
I'll bet if some of you guys take your high hour HM50-HM80 motors and remove the head, you'll see the same thing. Don't tell me they're only in Canada!!
I'll bet if some of you guys take your high hour HM50-HM80 motors and remove the head, you'll see the same thing. Don't tell me they're only in Canada!!
You need to think about this, just a tad bit more, ut: before you break out the power tools & start cutting away all halfast.
To build compression, both valves must be closed. If the valves are closed, what is the position of the camshaft & lobes? More importantly... Where are the tappets? Most likely sliding along the backside of the cam, or more commonly referred to as the base circle.
I believe that is where I would be looking for a strange little bump, instead of :grind: on the peak of the lobe or :hack: your valve shorter.
Anyone recall that old saying about, A little bit of knowledge...?
ut: before you break out the power tools & start cutting away all halfast. To build compression, both valves must be closed. If the valves are closed, what is the position of the camshaft & lobes? More importantly... Where are the tappets? Most likely sliding along the backside of the cam, or more commonly referred to as the base circle.
I believe that is where I would be looking for a strange little bump, instead of :grind: on the peak of the lobe or :hack: your valve shorter.
Anyone recall that old saying about, A little bit of knowledge...?
Well said JM. It could be weak springs as well, but doubtful. If you are grinding .020" off the stem of the valve that would increase the lash. If this was such a problem, I would think someone else in the small engine world would have discovered it as well?
I'm not disagreeing with you that it's happening, just trying to figure out why. Jm said it better than I could but i think he's on the right track.
I'm not disagreeing with you that it's happening, just trying to figure out why. Jm said it better than I could but i think he's on the right track.
E-Z start
The bump in the intake lobe you are talking about is a method of lowering the comp. so that some wimpy guys can start the engines, once the motor spins at a reasonable rpm you never notice the lack of compression. Briggs called it EZ start and still use it in their engines, if you take a brand new flathead and clearance the valves(set valve lash) on the intake to 16 thou. you will see the same thing as in a great increase in comp. and effort to turn engine over and in power. I'm not a tec. fan but i'm sure they use the same method.:thumbsup:
The bump in the intake lobe you are talking about is a method of lowering the comp. so that some wimpy guys can start the engines, once the motor spins at a reasonable rpm you never notice the lack of compression. Briggs called it EZ start and still use it in their engines, if you take a brand new flathead and clearance the valves(set valve lash) on the intake to 16 thou. you will see the same thing as in a great increase in comp. and effort to turn engine over and in power. I'm not a tec. fan but i'm sure they use the same method.:thumbsup: