Tecumseh HH120

[Miker-1 1]

Just got a 1974? C-120 with a apparent Tecumseh replacement engine 12 hp. Wiring harness was changed, but works. I' am pretty sure it was a Kohler. My problem is it turns over through 3 compression strokes and stops starter. continuously. Bought new starter same problem. IT did start and run great, good idle and rpm range. Shut off and will not start same turn over problem. I placed my hand over carb and turns over as it should with no stopping .Lots of fuel on hand as expected. Any ideas! Do I need to include more information?  Model 10495 9  ser.# 46429  Thanks

Edited December 12, 2016 by Miker-1
More Infomation, no replies

[pfrederi 17,788]

What happens if you pull the spark plug does it crank freely??? Do you feel compression in the plug hole.

[Lee in RI 8]

Sounds like an ignition issue to me. Make sure it is firing on every compression stroke and not intermittently firing. Almost sounds like it is trying to fire just as the piston starts to come up from BDC. Is this point or electronic ignition? 

[Miker-1 1]

59 minutes ago, Lee in RI said:

Sounds like an ignition issue to me. Make sure it is firing on every compression stroke and not intermittently firing. Almost sounds like it is trying to fire just as the piston starts to come up from BDC. Is this point or electronic ignition? 

Not sure about ignition, would this help HH88120-12018od Ser.# 4042

[gwest_ca-(File Mod) 11,080]

You likely have the original engine to that tractor

Garry

[Miker-1 1]

On ‎12‎/‎12‎/‎2016 at 2:43 PM, pfrederi said:

What happens if you pull the spark plug does it crank freely??? Do you feel compression in the plug hole.

yes it does and I grounded plug to check premature firing. same problem occurs. Ordered replacement starter. It acts like starter does not have enough torque. Do not want to burn up new starter. When it started it sounded great. Lost?

[Lee in RI 8]

On December 12, 2016 at 7:16 PM, Miker-1 said:

Not sure about ignition, would this help HH88120-12018od Ser.# 4042

 If it is a 12HP Tecumseh with solid state ignition, those coils/modules can do some very strange things. It could be advancing the timing to the point where it is causing the ailment you describe. I have had it happen on an old Sears suburban. 

[Lee in RI 8]

1 hour ago, Miker-1 said:

yes it does and I grounded plug to check premature firing. same problem occurs. Ordered replacement starter. It acts like starter does not have enough torque. Do not want to burn up new starter. When it started it sounded great. Lost?

Oops, I did not see that last post about you cranking it with the plug in and wire grounded. Try this before you condemn the starter: remove the valve cover and stick a .010 feeler gauge between the exhaust valve and tappet, crank the engine like this. If it spins over fine check to make sure your compression release is working properly. 

[Miker-1 1]

12 hours ago, Lee in RI said:

Oops, I did not see that last post about you cranking it with the plug in and wire grounded. Try this before you condemn the starter: remove the valve cover and stick a .010 feeler gauge between the exhaust valve and tappet, crank the engine like this. If it spins over fine check to make sure your compression release is working properly. 

How do I check compression relief, I have been thinking about ?

[Miker-1 1]

14 hours ago, Lee in RI said:

 If it is a 12HP Tecumseh with solid state ignition, those coils/modules can do some very strange things. It could be advancing the timing to the point where it is causing the ailment you describe. I have had it happen on an old Sears suburban. 

What was your solution

[Miker-1 1]

On ‎12‎/‎12‎/‎2016 at 2:43 PM, pfrederi said:

What happens if you pull the spark plug does it crank freely??? Do you feel compression in the plug hole.

yes

[Molon_Labe 731]

Sure sounds like it is compression locking. Have you pulled the head and checked for carbon buildup? Excess carbon can increase compression due to the reduction in the amount of combustion chamber area. More carbon = less "squish" area for the fuel/air mix.

[Miker-1 1]

37 minutes ago, Molon_Labe said:

Sure sounds like it is compression locking. Have you pulled the head and checked for carbon buildup? Excess carbon can increase compression due to the reduction in the amount of combustion chamber area. More carbon = less "squish" area for the fuel/air mix.

I will check this out, I have a new head gasket

[pfrederi 17,788]

11 hours ago, Miker-1 said:

I will check this out, I have a new head gasket

That will also allow you to check your ACR (automatic compression realease0  The exhaust valve should open slightly during the compression stoke as you turn the engine over.

[Miker-1 1]

 The 010 feeler trick worked, what does this mean. What's next. Thanks

[Lee in RI 8]

On December 16, 2016 at 2:24 PM, Miker-1 said:

 The 010 feeler trick worked, what does this mean. What's next. Thanks

Sorry I have been away so long. It sounds like your tappet is a little worn on the valve end causing insufficient valve clearance. Pull the exhaust valve out and file a little bit off at a time until you have the correct valve clearance. You should be all set once it is corrected. 

[Miker-1 1]

15 hours ago, Lee in RI said:

Sorry I have been away so long. It sounds like your tappet is a little worn on the valve end causing insufficient valve clearance. Pull the exhaust valve out and file a little bit off at a time until you have the correct valve clearance. You should be all set once it is corrected. 

If I'am filing valve wouldn't that give me less clearance. putting in feeler gauge increase's lift right. It makes  the ACR open more to reduce compression? Pulled head not much carbon.

[Lee in RI 8]

1 hour ago, Miker-1 said:

If I'am filing valve wouldn't that give me less clearance. putting in feeler gauge increase's lift right. It makes  the ACR open more to reduce compression? Pulled head not much carbon. Omg, I have not had much sleep in the past 3 days! Lol! I'm sorry, yes you need tighter clearance! You will have to replace the exhaust valve or the tappet. I would try a new valve first as that way you don't have to disassemble the engine. New valves are slightly longer to allow filing. 

[pfrederi 17,788]

Is your acr working??  with the head off crank the engine over.  the exhaust valve should popup for a moment on eh compression stroke.

[Miker-1 1]

4 hours ago, pfrederi said:

Is your acr working??  with the head off crank the engine over.  the exhaust valve should popup for a moment on eh compression stroke.

ACR lifts enough to get fingernails under, but spins great with 010 under tappet. Manual mentions  ACR pin but do not know where to look. Valve is .20 clearance TDC per spec. FYI picked up C-120 today Kohler 12 hp with a small electrical problem,  hoping it is a safety switch. But will not give up on Tecumseh HH120.I read Horses are like chocolate you want more! 

[pfrederi 17,788]

[tbarnhart 240]

.020 clearance is a bit high for the exhaust valve and is likely part of the problem. The other possible issue is the pin on the camshaft mechanism that actually contacts the valve tappet and releases the compression. These will get worn over the years and will require either replacement or possibly a welding repair. The only problem is that you have to break the engine down to get to the cam. Try getting the valve specs back closer to correct and see if that doesn't work. Several different ways to accomplish this, although none are free. If the valve sealing surface is still thick enough, a machine shop can lightly grind the valve and seat which will close the stem clearance. A new valve may be necessary. A less recommended patch would be to have a good welder build up the valve stem with a hard filler and then grind it back to the proper clearance. Good luck. Those old Tecumseh engines are worth saving. When they are right, they have a lot of bite for their size and run very efficient.

[Miker-1 1]

If .020 is a bit high what would you recommend. I thought .020 was spec. How much lift should you have for ACR ?

[tbarnhart 240]

You're right, .020 is correct specs for the exhaust. The compression release will not open the valve very far. Probably only a few thousandths. Most likely the operating pin on the cam is worn. If the lift is less than the valve clearance, it won't open and the compression stalls the starter. That's why putting a feeler gauge in the gap makes it work again. You could try lowering the clearance to .015 and see how that works, but its not simply an adjustment. You're looking at one of the methods I described above. I have a 16hp ohv Tecumseh that has some of the same issues at times. Mine calls for .010 ex valve clearance, but I keep it a tiny bit closer to help the compression release work properly.

[Miker-1 1]

Thanks, Mike