Reading Plugs in Kohler V Twin

[t5montecarlo]

My Kohler 25-hp V twin started acting up this year (the engine is 13 years old and has only been used for my property, never for commercial use). The first time I started it up, it gave out a large blue smoke cloud that I thought dissipated until I set it to full throttle and began cutting the lawn. I looked back after the first pass and saw I had left quite a cloud. For the next few weeks, it has produced less blue smoke, but is consuming about 1/2 quart of oil after about 1.5 hours of work.

If I run the engine for just about 1 minute, and then remove the dipstick, there is a lot of smokey vapor in the crankcase.

Today, I removed the plugs and 1 looks great and the other does not.

I have to take quite a lot of parts off of the engine in order to remove the valve cover, so I can't easily put compressed air into each cylinder and see if I can hear any difference in how much air is leaking past the rings through the dipstick tube. I did a compression check and both were the same at about 170 psi.

Before I open up the engine or buy any parts, what are your immediate thoughts on what has failed?

 

[Doober]

Re: Reading Plugs

I would think probably rings as well, unless it was overfilled like my aunt did once on her little push mower :lol: She filled it until oil came out the dipstick opening, and then she couldn't start it. I went over and when I finally got it started I fogged her yard and 2 of her neighbors!

 

[t5montecarlo]

The more I read about the Kohler CV730S engines, the more I suspect a head gasket issue as it seems common. They leak into the return valley where the pushrods are.

The failure is sudden. The symptoms did not occur last year, just at the first start up this year.

I am a little stumped at the consistent compression readings. I need to do a leak down test (but don't have the tool) and compare cylinders or just open it up and see.

I know there are some on here with small engine backgrounds. I hope they chime in.

 

[t5montecarlo]

Yesterday when I tested the compression, the engine may have been slightly warm. The readings today are quite different.

Today, I checked the compression and the good cylinder was 170 psi and the bad one was 110 psi. I added some oil to the bad cylinder, engaged the starter for a few seconds to spread the oil, and then tested the bad cylinder at 140 psi.

The first pulse on the good cylinder is 120 psi. The first pulse on the bad cylinder is more like 20 psi.

I tested for leak down with with just shop air and and slowly cranked up the compressor regulator.

With the good cylinder at TDC, there is no leakage via the intake or exhaust, and a normal amount of noise from the dipstick tube.
With the bad cylinder, there is leakage at the exhaust at both TDCs. I can't tell which is the compression stroke. The exhaust valve must be closed on the other cylinder at both TDCs since pressure will build in the exhaust system if I cover the end with my hand.

The engine runs and sounds OK, but consumes a lot of oil.

The compression testing results usually indicate a ring issue, but I don't understand the leak test results.

The worst case is I need a bore (x2 to keep the engine balanced), 2 pistons, 2 sets of rings, 2 valve jobs, gaskets, 2 connecting rods (the new piston design is different from the old piston design, and require different connecting rods).

Does anyone have any thoughts? I need to understand if it is worth opening the engine or looking for another one.

 

[Doober]

It'd be interesting to see regardless... maybe that cylinder got hot? The 350 in the Malibu originally had bad oil rings on #1 (why I put it in knowing that is beyond me... I was younger & dumber then). It burned a quart of oil every 100 miles, I guess part of me hoped it might've been a valve seal (wasn't as experienced then). Took it apart and now it still has the original 215k mile rotating assembly (balanced, and new rings/bearings/gaskets/etc.), uses 0 oil, 0 leaks, and spins happily to about 5500rpm on occasion.

 

[t5montecarlo]

Since it still runs, I can't afford the downtime just to have a look inside. I don't have a backup machine and have 2 acres to mow.

 

[t5montecarlo]

Today, I took it apart. What a pain. It took a few hours just to get to the point where I could remove the valve cover. The carburetor linkage is very complex and I did not want to remove any of it.

I looked underneath and could see what looked like oil weeping from the head gasket. I looked at the good side to be sure, and it was clean.

My first WTF was that the exhaust could not be removed without lifting the engine. Then I struggled to get the housing cover off.

The first 3 head nuts were very hard to break free. The last one was not nearly as tight.

After removing the head, it is clear that the gasket is breached at the lower side and to the crankcase. From what I have read on tractor forums, my head gasket failure is typical. I saw a different kind of head gasket; I have to look into it more. The factory gasket looks like an exhaust gasket.

The cylinder looks good.

Since I have it apart, I will do the other side at the same time. I don't want to go through this again when the other side fails. Now I have to order lots of gaskets. I will replace the intake valve stem seals while I am at it.

 

[StreetBu]

Wish I had seen your post sooner. They are very common to fail. Yes do both sides while its apart. Also take your model & spec # and check for an updated valve cover. Seems as though they updated the design of one cover to prevent oil burning issues also. The pcv system was sucking oil vapor IIRC. Did you have a mouse nest in the engine? Very common for them to climb in and fill the fins up with crap. Overheats the engine and pops the gaskets or in bad cases, gets the head hot enough to cause the valve guides to move which keeps the corresponding valve stuck open. Only fix is a new head.

 

[t5montecarlo]

I was hoping you would chime in, StreetBu.

I had no nest or other blockage.

I haven't studied the head yet. I will first see if the valve will hold any fluid, like brakecleaner. If not, I will take it apart and see if the valve is burnt. If not burnt, I suppose I will need to invest in a new head? Do the heads come fully assembled or bare? I already ordered all of the gaskets to do both sides, including new intake valve seals. I ordered a different design head gasket that has a fire ring, like a car engine does, rather than the original style.

While I have the valves out, I was going to lap them for good measure. Would you advise for or against lapping the valves?

I have the 2nd design valve cover, which is the first with an o-ring (black). The 3rd design (latest design) uses a yellow o-ring, but I don't know why there was a change. The engine has never consumed oil before now.

There is an oil separator that sits on 1 valve cover that acts as a PCV and connects to the intake. There is a breather behind the carburetor that I have to be sure is not blocked.

I would like to strangle the designer who thought it was a good idea to put cooling baffle bolts behind the carburetor.

 

[StreetBu]

The heads come completely bare. Thanks for nothing Kohler. If you had no mouse nest and can't spin the valve with your thumb when its in your hand, then the head is fine. Lap the valves if you want. No real need to but it won't hurt anything. Basically slap the gaskets on and stuff it back together! B&S seem to be worse for cylinder heads. We even stock one for single cylinders. But they come complete from Briggs.