Ch25s head gasket

[Fordoldfart]

Does this look like a blown head gasket. It started using a lot of oil. Did a compression check what I would call #2 cyl had 160 psi #1 only had 90 psi squirted some oil in #1 and got the to 160 psi figured it was rings might still be but I took the number #1 head off and the bolts weren’t very tight and this is what I found

 

[Rivets]

Looks like the right hand side might not been sealing. Wouldn’t know for sure until I saw the other side of the gasket.

 

[slomo]

From what I can see, the bore was sealing.

Rivets, what are you seeing? I see oil buildup on the right and lower center areas.

As Rivets said, we are only seeing half of the gasket.

 

[slomo]

160psi sounds rather high. That comes out to 10.88:1 compression ratio. Valves must be rather loose.

 

[ILENGINE]

160psi sounds rather high. That comes out to 10.88:1 compression ratio. Valves must be rather loose.

160 is considered the minimum on Command engines since they don't use compression release.

 

[Rivets]

Slomo, where do you think that carbon and oil came from? The OP stated the bolts weren’t very tight and with the visual evidence I’m saying I don’t think the head gasket was sealing the cylinder.

 

[Fordoldfart]

I went ahead and tore it down. Will replace the rings but did not see anything wrong with the originals. I have already ground the valves and cut the seats. Parts will be here Tuesday or Wednesday.

 

[hlw49]

Was the exhaust valve black? Lapping Valves NOTE: Exhaust valves that are black in color cannot be ground and do not require lapping. Right out of the Kohler service manual. If it was black and you ground it you will have to replace the valve. From the looks of the top of the block the head gasket is blown to the outside. Could you hear a whistling sound when starting or shutting the engine down. If so it is a sure sign you have a blown head gasket to the outside of the cylinder. Always around the exhaust port. Don't work on many CH Kohlers but lots of CV Kohlers. It is a really good engine. Once they fixed the head gasket problem. After over 20 years they finally put a fire ring around the cylinder. I have seen these engines with thousands of hours on them and they still do not use oil. Have a friend with one with 8,000 hours on it and still runs good and uses no oil. I would check the head to see if it is flat. .003 According to Kohler is the limit. I use a granite block and emery cloth sheets in a figure 8 pattern so you will not lap it wedge shaped. I have seen these engines with 220 psi compression. They do not have a compression release.

 

[Fordoldfart]

Ok an update it isn’t a ch25 it is a ch22 use type A rings 1.5mm top ring no longer available from Kohler. Some after market available. Like red barn. I ordered a set through Amazon so far they haven’t sent the right size twice. Keep send me 77.5 mm which is basically .020 over. I found Hasting piston ring company has rings for it 2M4765 they are now on the way, I hope.

​

 

[slomo]

Over sized rings can be filed down to proper size. Check ring gap spec in engine manual and grind away.