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It was running fine last night then acted like it ran out of gas and quit. It probably did so today I added gas and it will not start. I checked:

Fuel - I can see it at the fuel filter.
Spark - I have a handy tool that lets me see if the cylinders are getting spark. Both are. I cleaned the spark plugs anyway.
Air - I'm pretty sure I have plenty of air, but to be sure I removed the filter.
Compression - 120 psi on the right, and a not great 90 on the left. But, it is and old tractor and neither are at zero.

It cranks strong but never fires, not even a puff, even when using starter fluid.

Possibly timing? I have no idea how that is set or checked.

Any ideas?

Thanks, Mike

That series came with a Kohler or Briggs engine and we need the engine model and spec numbers. But current I thinking you have a valve related issue.

Thank you for your reply.

The engine model is a Kohler SV735S.

I found manuals for it. It says compression should be 160 psi, so I am a bit low or did not test under the same conditions. Still, low compression alone shouldn't keep the engine from starting.

Get a pair of new spark plugs
put a SHORT shot of starter fluid down both plug hole & crank the engine
It should fire at least once
If it backfires through the carb or exhaust that suggest a valve problem
If it does not fire at all that suggest an ignition timing problem
You might need to do it a couple of times to get a definative answer
Get back & let us know what happens

I just did those things. New plugs, correctly gapped, starter fluid in the cylinder, fresh battery, and the engine cranked strong but never even puffed. I pulled a plug and confirmed it was firing, and with a nice blue spark, too.

I'm not a mechanic but I know my way around engines (classic Opels), and this makes no sense. Even if mis-timed I would expect something, even a backfire.

Mike

Not if the intake valves are not opening to allow in fresh air. Fuel can't ignite without oxygen. Or if the ignition is off quite a bit. Pull the rocker covers and check the rockers movement as you may dropped a push rod or two.

Will do. Give me a half hour.

Welp, the right side cylinder looks okay, but the left?

I suspect more than a little mis-adjustment is the problem here.

Right:

Left:

Push rods are bent. The question now it, what was the root cause, and how bad is the damage?

I was given this mower a few years ago. I wonder if I've been running on one cylinder this whole time. Motor ran smooth, but...

The rocker arms on the right side move like they should when I crank the engine.

Usual cause is overheating
The valve guide shifts so the valve spring becomes coil bound before the pushrod has finished pushing
Other cause is the valve hitting the piston
Inlet & exhaust cam , pushrod & valves are the same lengths so should sit exactly in the same position when unloaded

I'll pull the head tomorrow and take a look. Then I guess I am shopping for a head gasket, as well as push rods.

More like you need a new head too.

Now you would need to look-up the with both its model number (drop the ending "S") and spec number. "S" just indicates it has an electric starter. Something like SV735 - ##### without the spaces on either side if the dash. Sometimes when using Kohler dealer site we just go by the spec number.

Why a new head? What issues should I be looking for?

I pulled the head and looked inside. I see no signs of contact between valves and piston, cylinder walls look okay, nothing except a little oil in the bottom of the cylinder. I cleaned up the piston using a little Brakleen and will get to the head once the day cools to anything under 100F.

Photos are attached.

I was given this mower a few years ago. I forget why the previous owner quit using it, but when I got it it needed tires, drive and mower belts, a couple of pulleys and a gas tank. And a battery. The engine was packed with dirt and grass and it took me a while to wash it all out. I can see a motor like this overheating with all the cooling fins clogged. After using the mower a bit the ring gear broke and I managed to find one on the Internet. Sears did not carry it.

With the damaged push rods the 90 psi compression I was getting sounds pretty good actually. Maybe once the valves can open and close I'll get better numbers.

One thing though, it seems I should have been able to get the motor run, if poorly, on one cylinder. Or at least give me a puff or two once I squirted starter fluid in it.

Mike

P.S. What is a good source for parts for this mower?

The head cleaned up okay and the valves seems fine. I didn't take them out but the move okay.

I ordered a gasket set and push rods. Crossing fingers that this fixes it.

Mike

did you check the valve guide positions?

StarTech said:

did you check the valve guide positions?

Click to expand...

And check the left agains the right
They all should sit at identical heights if the valves & seats have not been ground

Valve guide positions? What is that?

I'll check valve heights. I assume you're hinting that the valve seats wear out, like in classic Opel motors when you don't use leaded gas and the valves pound themselves into the head.

Apparently never did cylinder head reworks.


These are located under the springs. They sometime move out and limit the amount the springs can compress once the springs hit their limits then push rods will bend. In these heads they are usually the same height for all the valve guides present.

Never have. Thanks for the explanation. I'll find a spring compressor and will check it.

There is nothing to hold the valve guides in position other than the fact that the hole in the head is slightly smaller than the outside of the guide .
The heads are case aluminium which has been heat treated to make it harder than in the as cast condition.
When overheated the heat treatment reverts to the softer as cast microstructure which allows the metal to move around the valve guide hole which becomes larger so the guide is not held as tight as it should be
The valve guide is pushed in from the top so it moves up when the head gets soft an then when the rocker tries to push the valve down the top of the spring keeper hits the top of the valve guide before the rocker finishes it's travel so the weakest bit, the pushrod bends .
In this soft state, the valve seat ( the ring that the valve sits on when closed can also fall out because like the guide, it is just pushed into a hole that is a tiny bit smaller than the seat .
This also causes the push rod to bend when it gets really loose .

Depending upon how much the head has overheated, the thread that hold the rocker stud can also shear so the stud will continually go loose.
All of this is because the pervious owner did not pull the blower cover off at the end of each season & the fins cleaned
Always a good thing to do then leave it off over winter to discourage furry critters deciding to set up home under there .

Parts came in and I am installing them. Easy enough. But, with the rocker arm nuts all the way down I still have an 0.024" gap. Worn lifters? Cam? I checked the other cylinder and the gap is 0.015". Specs are for 0.004" to 0.006", which is way tighter than I ever see on my cars where 0.016" to 0.022" is more common (Opel engines, solid lifters). I can probably adjust the "other" cylinder's gap, but I may be stuck with the huge gap on the one I am repairing until I do a complete rebuild.

Farther down in the procedure it says to turn the crank by hand and check for bending of the push rods and minimum gap of 0.010", which is nearly double what the manual said in an earlier paragraph. Not sure who to believe now.

I turned the crank by hand a few times and everything moves right, but that big gap!

Mike

Either the pushrods are for a shorter engine ( always a possibility ) or you have omitted to replace the lash caps on the ends of the valves ( very common )

I don't see lash caps in the drawings. I think I will try hardened washers between parts N and O in the attached diagram.

Still, 0.004 - 0.006" gap seems awfully small.

The new push rods are shorter, as suggested above.

I checked the other cylinder and one was straight and the other bent. I did not see any sign of valves contacting pistons, so I'm wondering what caused this.

See a mudslide in 2 areas. What is behind the green crayon shroud I wonder? Overheat city possible.

Hydraulic lifter alert.

Adding lash caps that are not in the parts schematic is bold.

Are you ordering the proper push rods for this engine?

Cooling issues sound plausible. I cleaned it recently but I think it had been run choked with dirt for years.

The engine model is Kohler SV735S. I'm getting parts from here: https://www.partstree.com/models/sv...varna-26hp-19-4kw/04-cylinderhead-breather-3/

Mike

I showed the dirt at the valve cover area to make you wonder what's under that shroud. Those aluminum fins and block dump heat. You have a little oil cooing and mostly air cooling. When the fins are clogged, you get engine damage like yours. Just want to drill this into your nog'in LOL. Keep the fins surgically clean on all mowers and trimmers ect.....