B&S engine question

[Alfred_B]

I have an MTD tractor with a B&S engine that gave up ghost. It's 4 years old and the engine just slowly died one day, with symptoms like no fuel.

So I took the carburetor apart and everything is in order. Put everything back, tried to crank it and the engine would turn half a turn and stop. Removed the spark plug and the engine turned fine. Closed the spark plug hole with my finger and it stopped turning. There was compression.

All the time it didn't pull in any fuel.

What would the issue be -- this has gone beyond my skill level of diagnosing an ICE issues.

 

[Alfred_B]

I'll be buying a new tractor so this is just a question of curiosity.

 

[racer12306]

What kind of B&S? Is there a fuel pump on it?

 

[eljefino]

Flywheel pin and all that still lined up right?

 

[old1]

OHV engine? If so pull the valve cover and check the tappet clearances, and if maybe a push rod is out of place???

 

[55Test]

Any chance the engine and carb has sat for any length of time with fuel in it? Could be gummed up

 

[ATS-V]

Probably need to adjust the lash on the valves.

 

[Alfred_B]

Originally Posted By: racer12306
What kind of B&S? Is there a fuel pump on it?


No, it's a gravity fed line to the carburetor.

 

[Alfred_B]

Originally Posted By: 55Test
Any chance the engine and carb has sat for any length of time with fuel in it? Could be gummed up


The carb is sparkling clean and the float functions well.

 

[Alfred_B]

Originally Posted By: eljefino
Flywheel pin and all that still lined up right?


Good thing to check -- how would I know what to look for?

 

[Alfred_B]

Originally Posted By: old1
OHV engine? If so pull the valve cover and check the tappet clearances, and if maybe a push rod is out of place???


It is indeed OHV.

 

[EricG]

I had one of the aluminum pushrods collapse once. Either that or valve lash as mentioned above. When mine gets hard to start, I adjust the valve lash, then it's "all good" for a while.

 

[Alfred_B]

@EricG would this be how it's done?

Actual work starts at 4:00

https://youtu.be/1-XlET33VHM

 

[EdwardC]

I'm not EricG, but that looks to be procedure. It's a very similar to many other engines. Good luck!

I gotta say though, 4 years doesn't seem like very long at all. Is it under heavy/commercial use?

 

[mk378]

A weak battery will do about the same thing. The compression release from properly adjusted valves helps, but you still need a stronger battery to crank with the plug in than with it out. Suggest charging the battery and measuring battery voltage while cranking. It should stay above 9 volts.

 

[Yah-Tah-Hey]

You put fuel with

air in the right proportion, provide a spark at the right time and you can't keep em from running.

 

[Alfred_B]

Originally Posted By: HosteenJorje
You put fuel with

air in the right proportion, provide a spark at the right time and you can't keep em from running.


The piston doesn't seem to be able to overcome compression to then rotate enough to create vacuum to pull air in. It actually created vacuum in the cylinder when I removed the spark plug and cranked it.

 

[Alfred_B]

Originally Posted By: mk378
A weak battery will do about the same thing. The compression release from properly adjusted valves helps, but you still need a stronger battery to crank with the plug in than with it out. Suggest charging the battery and measuring battery voltage while cranking. It should stay above 9 volts.


It was hooked to my Audi jump start posts to provide further boost.

 

[tig1]

Originally Posted By: 97 GTP
Probably need to adjust the lash on the valves.


+1. These engines have a compression release system that operates off the exhaust lash clearance. The tolerance is within 3-4 thousands. Find the clearance for the intake and exhaust valves. Pull the valve cover and check them, especially the exhaust side.

 

[Lubener]

Originally Posted By: old1
OHV engine? If so pull the valve cover and check the tappet clearances, and if maybe a push rod is out of place???


Good call.