# Tecumseh OH140 Engine Won't Fire Since Replaced Head & Valves



## matt2491

I'm having a difficult time getting the 14hp Tecumseh OH140 single-cylinder engine on my 1977 Sears Craftsman garden tractor to fire since yesterday when I replaced the head and valves with a newer set I had from another same-model engine.

This type of engine has the OHV design with the rockers located in a box or housing right above the head, as seen in the pictures below. Pushrods run up the side of the motor through a couple tubes that work the rockers which work the valves, obviously.




























Here is the full story:

Previously, the engine ran alright and made good power but smoked quite a bit from the head and valves' housing (presumably from a crack(s) somewhere). I had another same engine sitting in my shed that had a cleaner head and valves, so I figured I would pull the old top end off the engine and replace it with the better parts. I carefully disassembled the parts from the running engine (valves and head), and scraped off all the carbon and crud that had accumulated on the piston. Then I generally cleaned up the newer head, valves, and valve housing, and installed it on the engine, with a new head gasket. I tightened it all up evenly, and reassembled everything I had taken off to do the job. I made sure there was some good gas in the tank, and sprayed some starter fluid in the carb. When I turned the key, the engine cranked over just fine, but it wouldn't fire. I sprayed some more starter fluid in there and it still wouldn't fire. I kept messing with the throttle and choke but with no luck.

Here's the facts:

- Replaced the old head, valves, and valve housing with a cleaner set that weren't cracked from another engine.
- Scraped off all the carbon and crud build up on the top of the piston. 
- New head gasket installed and bolted down tight with the newer head. I tightened the six bolts in a criss-cross pattern to draw the head evenly against the block.
- Has good spark
- Cylinder has approx. 22 psi pressure. However, it had less than that when it ran before with the old head and valves. Yes, I know it's ridiculously low, but I can tell you for certain that when it was running before it was even lower!
- Cylinder and piston looked to be in really good shape. No pits, grooves, or any other visible faults.
- Has the same carburetor with the same old adjustments.
- The only thing that was done to the engine was the installation of a new head with a clean set of valves, cleaning the top of the piston, replacing the cracked valves' housing with one that was good.

Here are a few pics:

Replacement head









Piston cleaned up with new head gasket









Any ideas? Valve adjustment tips? Advice? Any help would be greatly appreciated...

Thanks --Matt


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## mark777

Everything you've listed indicates the engine should run....except the valve adjustment.

I'm not positive but I believe you need to be 1/4 turn passed TDC and adjust the valves (cold) at no less than .004-, no more than .006. Even slightly (.001) either way and the valve face to seat will not fully close (or open) making it impossible to compress and ignite the fuel.

Check your pushrods too as they often bend on the OHV single cylinder engines from poor timing issues or to high RPM. If they are bent I would use the originals from the first engine.

I have found the above to be a common problem on the 5 and 10 HP Honda engines coupled to stationary equipment (power washers and trash pumps). 

I hope others more familiar with you Tecumseh OHV engine can offer more or better tips. Good luck,

Mark


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## matt2491

Thanks for your help, mark777.

The pushrods were not bent, but I just realized that I forgot to adjust the valves when I put the engine all back together! I set them at zero clearance; I don't know what I was thinking, but that must be my problem! 

I'll go adjust the gap and see if I can get the engine started.


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## matt2491

I just adjusted the valves, and gave it another try. It didn't start, but this time it did pop out of the carb a couple times. It wasn't backfiring, it was more just popping/spewing gas out the front.

I wonder what could be the problem now... Could it have something to do with the head from the other engine? Maybe the valves aren't fully sealing/closing around the valve seats? That's what I am suspecting now, but I wouldn't mind any of your advice.

The combustion chamber has to be totally sealed off (valves completely closed with no gaps) at the point of ignition to run, correct?

Thanks --Matt


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## matt2491

Alright guys, I bought some of the valve grinding compound at the local Advance Auto, and tomorrow I plan to tear the engine down again to lap the valves. But while I have it apart for the second time, is there anything else I should check/do while I'm in there?

Thanks --Matt


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## matt2491

Okay, I lapped the valves, and the engine started up and ran really smoothly.

Thanks for all the help!


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## Live Oak

bump


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## chadler2091

*Ignition Coil Tecumseh oh140*

i'm looking for the ignition coil for this engine. Does anyone know where I can get a new or used one?

Greatly appreciated!!!


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## wheelhorsemike

Hi my name is mike and i have the same engine on my wheel horse raider, just wondering what the model # of this engine is. I need a new head gasket and can't find any numbers on the engine, any help would be much appreciated, thanks! my Email is [email protected]


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## Country Boy

The numbers were generally on the engine shroud, either stamped directly in, or on a metal plate that was riveted on. What horsepower is the engine on your Wheel Horse? Tecumseh was nice enough to make engine numbers pretty easy to figure out. In the original post, the engine was an OH140. The OH means Overhead Valve, the 140 means 14.0 Horsepower. If yours is say 15 horsepower, then it would be an OH150.


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