Kohler KT17 Crank Case Ventilation - Won't Run

[Gas Man 19]

I am trying to get my c175 barn find to start.  She's bee sitting for about 10 years.  Spark was the initial issue.  I only have 8.4 volts to the positive side of the coil.  I fixed that temporarily by running a wire to the battery.  I suspect and issue with the switch, but I'll deal with that later. 

It has 90 lb of compression on 1 cylinder and 95 on the other.  Those may not be great numbers, but I think it should run!  I need to look up what the compression should be. 

While cranking, I am getting a  bunch of air out of the crank case vent tube (PCV?) next to the carburetor.  So much that while spraying starting fluid in the carb, it blows it out of the way!!   On occasion, i will get a huge back fire through the exhaust (usually scares the crap out of me).  I have gone through the timing procedures in the manual and reset the points by a smidge, (something like .003)

 

BTW: I posted this in the tractor section first and don't know how to move it, so I reposted it here.

Edited November 20, 2019 by Gas Man
highlight

[Ed Kennell 41,954]

90 PSI is certainly enough compression for it to run.      I would look at the  exhaust valves not closing properly.

[Gas Man 19]

53 minutes ago, Ed Kennell said:

90 PSI is certainly enough compression for it to run.      I would look at the  exhaust valves not closing properly.

 

I have considered the exhaust valve possibility, but it seems if that were the case, compression would not exist?!?

[The Gman 476]

90 - 95 is respectable. I'd head to the valve cover nearest the battery and pull that off. There's the top cover plate then a second plate below that that contains the reed plate. Below that there should be a small sponge. Your reed plate could bent or loose. You can check your valve clearance with all that stuff removed at the same time

Intake is .003 - .006 (cold)

Exhaust is .011 - .014 (cold)

[Gas Man 19]

Found a wiring issue that was easily corrected.  It fired up and runs great.  I still don't understand the crank case ventilation on this thing....it has positive pressure while cranking???  I guess as long as it runs good, I don't have to understand it.

Thanks for your help!!!

[lynnmor 7,815]

We use the word "displacement" to describe engine size.  That is the total volume of both cylinders.  That same amount of air is displaced below the pistons on each revolution causing air to breath in and out of the vent.  In actual use the total amount doesn't go in and out at speed, only a portion of it as the crankcase pressures rise and fall as the engine rotates.

[Ed Kennell 41,954]

8 hours ago, lynnmor said:

 the crankcase pressures rise and fall as the engine rotates.

If I may Lynn...….and this rise and fall of crankcase pressure is the energy that operates the "pulse" fuel pump.

[wiesel 0]

On 11/24/2019 at 6:11 PM, Ed Kennell said:

If I may Lynn...….and this rise and fall of crankcase pressure is the energy that operates the "pulse" fuel pump.

shouldnt the pump work off a vacuum? cause my 782 is blowing the oil strait out the blow by tube.

 

Edited December 5, 2020 by wiesel

[wiesel 0]

but idk

[Handy Don 14,061]

1 hour ago, wiesel said:

shouldnt the pump work off a vacuum? cause my 782 is blowing the oil strait out the blow by tube.

 

The "pulse" pump has an internal diaphragm that creates two chambers, one on each side.  One chamber is connected to the crankcase by a hose so the diaphragm moves in and out in as the pressure in the crankcase changes. The other side faces a chamber with two one-way valves. The "in" valve is fed by the fuel line from the tank. The "out" valve goes to the filter and the carburetor. As the diaphragm moves toward the engine (low crankcase pressure) it draws fuel into the fuel chamber. As the diaphragm moves away from the engine (higher crankcase pressure), it pushes fuel out of the fuel chamber toward the filter and carb. It relies on the changes in pressure to work.  If it was only a vacuum connection, there would not be any variation in pressure to "pump" the fuel.

 

As @lynnmor noted, engines have crankcase vents because the motion of the pistons changes the volume of air in the crankcase. But not all the change in volume (the engines "displacement") moves in and out of the vent--some air stays inside and the air pressure just increases and decreases. 

 

When oil is being "blown out' of the filler tube or the crankcase vent it is because more air is entering the crankcase than the engine is designed to handle. And usually, this is from piston blow by--air leaking around the piston into the crankcase--both on the compression stroke and on the combustion stroke. (On these strokes, the pressure on the combustion chamber side of the piston is higher than on the crankcase side).

If the engine has a pulse fuel pump and is not seeing sufficient changes in crankcase air pressure because of blow by, it might not get enough fuel to run well.

All in all, these engines are a simply amazing balance of forces harnessed to get work done. 

Whew. Apologies for going so far into teaching mode. 

Edited December 5, 2020 by Handy Don
typos

[lynnmor 7,815]

 

Don explained it very well.  I hope you don't have serious problems with your engine, but so far it doesn't sound good.  Come back and let us know more about your engine and some history on how the problem developed.