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Hello all.

So, I am in the process of doing some fixing up on my new (to me) John Deere LT155 and I am trying to solve an oil leak that the engine is experiencing. When I pulled the engine out of the mower, I went ahead and replaced the oil drain valve and dipstick seal, and then checked and torqued down all of the oil pump and oil pan bolts. I did find an oil pan bolt that was just finger tight so I figured that to be my issue with having oil sitting on the frame around the base of the engine. From what I can tell, this mower has probably been leaking oil for quite a while as I spent a TON of time cleaning up the area around the engine and on the bottom side of the frame where oil, dirt and grass clippings had been stuck to the metal. In doing this cleaning I figured that once I got it back together I would see if there was still a leak.

Well, after about an hour of mowing, I opened the hood to find some oil on the frame near the back side of the engine. I cannot tell where the oil is coming from since the engine is quite clean and the oil is new. From what I can tell, oil is not coming from the crank seal or the valve cover.

I have ordered a tube of Loctite SI 5900 instant gasket which Kohler calls for when re-sealing the oil pan, as well as a new crank seal and oil pump cover o-ring since I will already have the bottom end off. Is there anything else that would or could cause this problem?

Thanks in advance.

Mike

Once the RTV sealant breaks its bond on the parts is doesn't reseal.

ILENGINE said:

Once the RTV sealant breaks its bond on the parts is doesn't reseal.

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So is safe to say that the RTV that was applied at the factory has subsequently failed and that cleaning and replacing of the sealant should resolve my issue?

Normally I prefer to use an UV dye to find the oil leaks. Oil has a habit of not appearing where the actual leak is.

You will need clean off all of the old RTV, clean the mating surfaces of all the oil residue, (optional apply a surface prep/accelerator, just makes sure the RTV adheres well) , assembly parts while torquing to finger tight, do not add oil at this time as the RTV need time to cure properly (I usually wait overnite) then torque to final spec, then don't to refill the oil. I usually put a tag on the engine as a reminder to add the oil.

EDIT: Don't forget to add oil before starting the engine.

StarTech said:

Normally I perfer to use an UV dye to find the oil leaks. Oil has a habit of not appearing where the actual leak is.

You will need clean off all of the old RTV, clean the mating surfaces of all the oil residue, (optional apply a surface prep/accelerator, just makes sure the RTV adheres well) , assembly parts while torquing to finger tight, do not add oil at this time as the RTV need time to cure properly (I usually wait overnite) then torque to final spec, then don't to refill the oil. I usually put a tag on the engine as a reminder to add the oil.

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Thank you for the tips. I was going to do this when I had the engine out earlier this week, but I was hopefully optimistic that the one loose bolt was my problem and that torquing it, and the rest down would fix it. I guess that's what I get for not doing the work when I had the engine out. Now I have to tear the machine half down again. It's really not so bad as I found these rider type mowers pretty easy to disassemble.

I will report back once I get the job done. The sealant wont arrive until sometime this coming week so I will have it done by next weekend if I am lucky.

I just wanted to give an update on the oil leak. with the help of my thirteen-year-old daughter I pulled the motor out of the LT155 and started disassembling the bottom end. there was actually quite a bit of oil that was sitting underneath the engine even though it only ran for about an hour and a half. when I inspected the outside of the engine it appeared as if most of the oil was coming from the section of the gasket that is behind the starter on the back left side of the engine. when I took the oil pan off of the block it was surprising how little sealant there was between the two pieces. I have included a picture of the inside of the engine which I believe looks pretty good for being 22 years old. I am just waiting on the parts that I ordered including the loctite 5900 silicone gasket. Meanwhile I have reached out to Kohler for a printout of the service bulletin that the engine service manual references when replacing the gasket. I have not been able to find the service bulletin 252 on the internet anywhere so I'm hoping that Kohler can give it to me or possibly someone on the forum here has access to them and would not mind sending it my way. I will give an update once I am finished.

Now of course you refill after everything is cured.

StarTech said:

View attachment 53384
Now of course you refill after everything is cured.

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Thank you so much. I just wanted to make sure that I do this job correctly. The last bottom end I reassembled (Briggs 24 ELS) used a paper gasket. The service manual for this engine makes reference to a point A and point B which it might get a double bead of sealant. The only issue is that the image in their manual isn't very clear. I have attached what their manual shows and from what I gather, the entire thing gets a single 1/16" bead and the area that is marked gets he double bead?

I think this A - B area is where my leak was happening; where the pan curves to accommodate the starter.

See if this is any better image.

StarTech said:

See if this is any better image.
View attachment 53386

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Oh my gosh, that is so much better. Now I can clearly see where this stuff is supposed to go!!

Would Lacquer Thinner for old sealant removal and Acetone for final cleaning be okay to use prior to applying the sealant? Is use of a brass brush absolutely necessary? The two pieces look quite smooth and are pretty clean.

The idea is to make sure the surfaces are clean of all oil type residues. So the acetone should work to make sure they are clean and not contaminated. It doesn't take much oil to turn this into a repeat job. One of those green scrub pads would also work

ILENGINE said:

The idea is to make sure the surfaces are clean of all oil type residues. So the acetone should work to make sure they are clean and not contaminated. It doesn't take much oil to turn this into a repeat job. One of those green scrub pads would also work

Click to expand...

One last question, when replacing the crank seal, would you recommend doing installing while the oil pan is off or waiting until the engine is reassembled. I want to say that the last time I did it the latter, but it would be so much easier with the shaft not in the way and then I can see the clearance on both sides of the pan for the oil port.

I always install the crank seal after installing the oil pan. Easier to control and protect the surfaces from getting cut.

You are obviously a hero and should be awarded a medal for soldiering your way through this kind of issue! Especially if you wind up solving the problem.

But Custer and Davie Crocket were heroes even though they both got massacred....

Well, I finally got the engine put back together. A couple of things to note: I read and followed all of the information in the Kohler Service Manual and on the service bulletin but for whatever reason I still ended up having a lot of RTV squeeze out of the side of the oil pan. I assume that a bunch squeezed into the engine as well. The RTV that I used was the Kohler part so it should have been a 1/16" bead but it appeared to be closer to 1/8th. Either way, the engine is running fine and I did not see any leaks after an hour of use. I figured I would just do another oil and filter change now in case any of the RTV has broken down and into the oil (and yes, I waited for the RTV to cure before putting oil back in). I think worst case the RTV gets caught in the oil pickup screen which I did clean thoroughly before putting it all back together so it should be able to take some slight clogging without causing any damage. Also, when replacing the main seal, I found that an old deck spindle with the bearings and shaft pulled out worked perfectly for setting the seal into the bottom of the oil pan. I think at this point I might educate myself on adjusting the valve lash and do that sometime soon since I have a little bit of RTV left.

cruzenmike said:

Well, I finally got the engine put back together. A couple of things to note: I read and followed all of the information in the Kohler Service Manual and on the service bulletin but for whatever reason I still ended up having a lot of RTV squeeze out of the side of the oil pan. I assume that a bunch squeezed into the engine as well. The RTV that I used was the Kohler part so it should have been a 1/16" bead but it appeared to be closer to 1/8th. Either way, the engine is running fine and I did not see any leaks after an hour of use. I figured I would just do another oil and filter change now in case any of the RTV has broken down and into the oil (and yes, I waited for the RTV to cure before putting oil back in). I think worst case the RTV gets caught in the oil pickup screen which I did clean thoroughly before putting it all back together so it should be able to take some slight clogging without causing any damage. Also, when replacing the main seal, I found that an old deck spindle with the bearings and shaft pulled out worked perfectly for setting the seal into the bottom of the oil pan. I think at this point I might educate myself on adjusting the valve lash and do that sometime soon since I have a little bit of RTV left.

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Do yourself a favour with the valve lash.
Get a drill bit about 3 sizes up from the rocker cover bolts and put a slight countersink on all of the holes
Then get a new rocker cover gasket and put axle grease on both sides so it will strip off clean
Then do up the cover bolts till the cover just snugs up and follow this with a tension wrench .
99 % of the people do them up way too tight so they chop up the gasket & it leaks everywhere.
Then they slather on silicon like it is shaving cream ( remember that ? ) so every time they do the lash they risk bending the cover and spend 1/2 hour cleaning the old silicon off.
The cover bolts are done up just barely more than finger tight

bertsmobile1 said:

Do yourself a favour with the valve lash.
Get a drill bit about 3 sizes up from the rocker cover bolts and put a slight countersink on all of the holes
Then get a new rocker cover gasket and put axle grease on both sides so it will strip off clean
Then do up the cover bolts till the cover just snugs up and follow this with a tension wrench .
99 % of the people do them up way too tight so they chop up the gasket & it leaks everywhere.
Then they slather on silicon like it is shaving cream ( remember that ? ) so every time they do the lash they risk bending the cover and spend 1/2 hour cleaning the old silicon off.
The cover bolts are done up just barely more than finger tight

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Bert,

My specific engine does not use a gasket and instead uses that same Loctite SI 5900 RTV that is used on the oil pan to seal the valve cover to the cylinder head. With that being said, so long as I follow he same cleanup and prep procedure for removing and applying the new RTV, would I still benefit from countersinking the holes for the valve cover bolts?

Sorry, got the models mixed up
The answer is yes always as the threads tend to pull and make a small mound that prevents the cover sitting flat.
As for a gasket, the factory uses silicon to cut costs making the engine.
They are not concerned about how long it takes to check the valve lash and cleaning off silicon takes longer than adjusting the valves .
So I always cut & fit a gasket if there is not one there .

The cover with RTV is fairly simple to remove. Remove retaining screws. Now get a block of wood like a short section of 2x4 and heavy hammer. Place the wooden block on one side the cover and strike side ways shearing the RTV. Just don't whole hog when hitting the wooden block as just want to shear the RTV and not damage the internals of the head. Work much faster and without bending up the rocker cover. Note: Don't use this on plastic covers.