DGS 6500 Motor Will Not Start

[bertsmobile1]

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 .

 

[m610]

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

 

[bertsmobile1]

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 )

 

[m610]

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.

 

[m610]

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.

 

[slomo]

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

 

[slomo]

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?

 

[m610]

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

 

[slomo]

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.....