M18 valve questions

[mhopkins]

My 1811 was loosing power and compression was down to 60. I pulled the heads off to check it out. The cylinders look good but the valves need to be replaced. I am wondering if just replacing the valves is an option, or if the valve seats and guides are normally part of the fix. I've never opened one of these motors up before, so any advise on what I may be missing would be appreciated

 

[lcarter]

Mike, if you google "Kohler Engines" you will find the Kohler website. Under Manuals & maintenance select "Owners and Service Manuals". Enter "M18" for model #. Click on "Find Manuals". On left side click on "Magnum". On right side click on "Service", select "English". This should tell you all you need to know.

Larry

 

[jchamberlin]

Mike Hopkins: I'm not sure why you think the valves need to be replaced, but as far as guides and seats, I'm sure that normal machine-shop procedures are appropriate. Upon dis-assembly, the entire cylinder, complete with valves, guides, and springs comes out.

Personally, I would replace the springs, adjust the valves (grind the ends), and re-surface the seats/valves as necessary, i.e., lap them in. If the machine shop tells you the seats need work, I would take their advice, especially if they are loose; otherwise, I would do what I could to tighten everything up, put it back together, and go.

If you're looking at valve or seat damage, that is, chips and chunks missing, then I would take the assembly to a shop for an evaluation.

 

[mhopkins]

Larry, Jeremiah,

Thanks for your response. Sorry my question was so general. I have been maintaining this tractor for almost 20 years, and it was my Dad's before that. He was a Cadet dealer and I remember when they first came out. My Lawn Boy push mower didn't get replaced until '64.

I've replaced parts on the 1811, but never even looked inside the sheetmetal shroud except to pull the starter. I'm reasonalbly familaiar with the mechanics, but inexperienced with this motor. I've benefited from checking this site in the past, but never registered.

Mike, I've been reading the manual for a couple of days. It's not the worst I've seen.


Jeremiah, The valves are down to a razor edge. I haven't pulled them out in order to check the seats and guides yet, but I don't intend to open this one up again. Sorry, my question was premature.

Thanks

 

[jdiederichs]

Many people simply install the new valves as a fix. The Magnum valves are a softer metal, sort of a sacrificial material to save the surrounding parts. I always hand lap the new valves some to get a good 360 degree seal .

You only need to pull the cylinder heads (after removing the "wonderful" shrouding (I'm sure you will have another name for it soon) and open up the valve covers/breather covers.
Then using a standard small engine spring compressor you can remove the keepers and the valves. No stem grinding needed on these, lash is tappet adjusted.

It may be wise to replace springs, especially the exhaust as these weaken over time. When you reassemble I prefer the valve lash be set towards the loose end, as the valves will soon take a seat and reduce the lash a few thousanths. In the Magnum you really extend life by running a good grade of fuel, as the ethanol stuff is hard on these older designs.They were a leaded fuel design as you know, so this new gas does take it's toll on valves much sooner.

In my area Kwik Trip premium grade is an ethanol-free gas, one of the few. I use it religiously in my older engines. Much easier on carb components as well!

 

[jchamberlin]

Jim: "The lash is tappet adjusted" --are you sure?

Last time I was in my service manual I thought it told me to grind the stems, maybe I missed something.

I did file them a bit, but it turned out to be too much, so if I could take out my own "adjustment" I would be glad to hear of it.

 

[jdiederichs]

I stand corrected, brain freeze told me they had adjusters, but they do not. Sorry for the wrong info in the post earlier, Magnum valve clearance is set by grinding the valve stems, there are no adjusters...... although there should have been, this isn't a Briggs ya know!

 

[mhopkins]

Just to follow up on this project. The engine got new ehaust valves,seats, and guides, along with all new valve springs and rings. The cylinders were still to spec., so they were honed. I found a great machine shop to do the work and that took some stress out of it.
The engine is running strong again, but not for very long. In the first 20 minutes it is a beast with the snow blower, then it acts like it's running out of gas and has to sit for 15 minutes or so, then it's good for about another 20 minutes. There is some response to a little choke, as it's dying, but it won't take any load with out cooling off. Is there an electrical component with a history of this, or is the carb needing more than adjustment?

 

[mgonitzke]

Is the valve lash within spec?

 

[mhopkins]

Well, I didn't actually check that, I had the guy at the machine shop do the valves, with the specs from Kohler. He said everything was to spec. Mistake?

 

[jchamberlin]

Mike, Matt: I wonder if an exhaust valve is sticking.

 

[kmcconaughey]

Mike, a failing condenser can cause symptoms like that. With one of my 125s it would run just fine for 15 to 20 minutes then it would act like it was running out of gas. Choking it would help for a very short while then it would die. After cooling down for 15 minutes or so it would start and run fine for about 5 minutes. I replaced the condenser and all was well. One other thing, if the vent in the gas cap is plugged it can cause similar symptoms. As a quick test loosen the gas cap slightly and run it to see if it changes anything.

 

[aaytay]

Kraig-
A Mag-18 doesn't have a condensor.

Stick to the ugly-tractors.

Mike-
Kraig does touch on something important though. When the tractor dies again, pull a plug wire and check for a strong BLUE spark. If it doesn't have a strong spark, you may need to replace the magneto (Not a fun job, been there done that!)

Also, if it seems to have decent spark, pull the fuel line off the carb and stick it in a small container, then carefull turn over the engine with the key to see if it's pumping fuel. A warm fuel-pump will also show itself if it's near the end of it's life. (Again, been there done that.)

 

[mhopkins]

The gas cap vent was one of the first things I rulled out (had that issue with a motorcycle years ago and it drove me nuts). I was concerned about the spark when I checked that, but I didn't check it when it was "hot". I wouldn't call it strong spark, and wonder if that contributes to the hard starting when its below freezing out. (I solved the hard starting by keeping it in my neighbors heated barn) I'll check the fuel pump and spark the next time it stops on me, but that will have to wait until I get the blower put back together. Now that it's got lots of power, I am chasing week links. The parts for the old QA-42A aren't easy to find and I will be using a couple that are marginal. Is there a way to check the magneto with a meter?

Thanks for all the info guys, Mike

 

[kmcconaughey]

ARG! I checked a 782 (KT series) to see if it had a condenser, it did and I thought the M18 was the same.

Yep, guess I'll stick to the 1x4/5 series...

 

[aaytay]

Sorry Kraig. I wasn't trying to FLAME you, just having a bit of fun at your expense.

Mike-
I would focus on the possible lack of spark when this tractor gets warm as the issue. One quick thing for you to check... What are the conditions of the spark-plug boots at the end of the wires? Since the wires are a molded-in part of the magneto which can't be replaced seperately, if the boots look old and cracked/dry, you can bet that your magneto is probably at fault. These things have a FINITE lifespan, so if those wires look old it's probably time for replacement anyway. The UGLY part of the story is that the engine needs to be pulled from the tractor to remove/replace the magneto.

 

[kmcconaughey]

Art, I know.

 

[proessler]

Mike , you may want to check fuel lines from tank to carb & go thru carb. As I had similar issues years ago that I had multiple times trying to get to the bottom of the problem/s. I replaced fuel lines & added fuel filter & multiple times breaking carb apart, then finally it survived to blow snow again!

 

[mhopkins]

Thanks Guys, I ordered a fuel pump and will replace the fuel lines and check out the carb. Sure hope that's the problem, since it's getting worse, and we're getting lots of snow.
In the mean time, I'm tearing down and refurbishing another QA42A Snow blower that I found this weekend.