M-18 running rough/missing - Page 3

john hall · #21 01-22-2017, 10:24 PM

Quote:

Originally Posted by J-Mech

John, your better off taking it apart and cleaning the valves than you are trying to get it to free up with MMO. It's not a big ol' motor that takes hours to tear into.... just pull the heads and valves and clean it up.

As far as it being carb related... it's a single carb on an open manifold. Unless something is blocking the flow in the intake, it can't run good on one cylinder and not the other unless there is a valve issue. (You've eliminated ignition and it sounds like you have tested for intake air leaks.) Time to take it apart bud.

What are you thinking on the valves, carbon buildup? The clearances are pretty close to book. Maybe a stem is gummy? Thinking outside the box, what about too much stem clearance? Just wondering if somebody did something stupid given the other stuff I found. Compression on both sides was in the 120-130 range.
Think I can get by just cleaning them up or do I need to grind the seats valve heads---grind clearance as and if needed.

Oh yeah, one thing I had never seen before, a big wad of of hard carbon/crud around the left side exhaust spring, on top of it actually. Seemed to me an odd place for crap to build up. I dug out as much of it as I could.

john hall · #22 01-22-2017, 10:27 PM

Quote:

Originally Posted by J-Mech

See post #18.

TAKE THE HEADS OFF. Skip the carb and cylinder temps. We KNOW that one of the cylinders isn't working right.... like you proved it 3 or 4 times now.

OK OK, I'll get a gasket set on order.

J-Mech · #23 01-22-2017, 10:31 PM

Quote:

Originally Posted by john hall

What are you thinking on the valves, carbon buildup? The clearances are pretty close to book. Maybe a stem is gummy? Thinking outside the box, what about too much stem clearance? Just wondering if somebody did something stupid given the other stuff I found. Compression on both sides was in the 120-130 range.
Think I can get by just cleaning them up or do I need to grind the seats valve heads---grind clearance as and if needed.

Oh yeah, one thing I had never seen before, a big wad of of hard carbon/crud around the left side exhaust spring, on top of it actually. Seemed to me an odd place for crap to build up. I dug out as much of it as I could.

John, until you open it up, it's just speculation. You haven't posted a vid of it running... so I'd just be making a SWAG on it. I'd say your going to find a burnt valve/seat or at least one that is leaking, and a gummed up stem. You could do a cylinder leak down test..... but I think you'll just end up back to this same point... time to take the heads off and have a look.

john hall · #24 01-22-2017, 10:44 PM

Probably be a few days before I open it up. That will give time for gaskets to arrive. In the meantime the deck needs painting and reassembling. I'll post more as progress is made!

yeeter · #25 01-23-2017, 08:02 AM

Dont know if its useful for checking engine temp differences, but I have one of these:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

john hall · #26 01-29-2017, 07:50 PM

Just about done with the mower deck this M18 is going to pull so hopefully I can open it up later in the week. Did one last bit of checking today. Cranked it up, really missing bad, seems to be getting worse I swear. Used infared thermometer gizmo and could tell a very noticeable difference in the exhaust elbow--right side much colder. Swapped plug out, still the same thing. Checked spark strength one last time, both sides equal. Compression on left side 110, right side (the one missing) is 120--this is after engine had ran about 5 minutes. I got my gasket set last week, just haven't had time/wanted to begin a new project until something else is FINISHED (mower deck rebuild). Unfortunately the gasket set does not have head gaskets with "fire rings", I'll deal with that later. The side missing is the one somebody had the breather/valve cover off and put the mesh screen in with the valves. I'm kind of hoping they stopped playing mechanic at that point given some of the other stuff we have found with this machine. I know all this info is in a way pointless, but maybe when we find the real problem it will help someone diagnose their issues.

Can the heads be pulled with the engine in the machine---asking more about removing the sheet metal over the head I guess. Hood and grill already out and the engine was hosed off when I had it out to change the coil.

J-Mech · #27 01-29-2017, 08:31 PM

You can take the tin work off and remove the heads in the frame.... if you have the right tools. Takes some not standard stuff to make it easy to do. I do it.... but I have an assortment of different angled wrenches, flex head rachets, flex joints and such that make it easy. I'd still recommend pulling it though. If you find what I think you will, it sure makes it easier to work on at work bench height. That sitting on a little stool down low gets old... fast. (Seems to be getting worse as the years go by.

)

john hall · #28 01-29-2017, 09:12 PM

OK, thanks. We'll probably pull it. I think it is more than a gummed up valve stem. I hope to have it opened by mid-week.

Lets assume we have multiple bad valves, if I'm in to it that deep I'll probably get a set of rings--or should I just break down and buy pistons as well? Obviously I'll measure the bores to make sure nothing is way out of spec. If this were my main or only mower, then it would be an easy choice, send it to the machine shop and let them have at it. However with multiple mowers, I doubt this one will see an hour's work a week. Before dad retired, they pretty much wouldn't put rings in an air cooled engine, usually did piston and rod exchanges. If anything needed machining, it was done. Different situation though as they were charging for the labor and their reputation was on the line.

J-Mech · #29 01-29-2017, 09:14 PM

At 110lbs compression on the "good" cylinder, I wouldn't touch it. You don't have to remove the jugs or pistons to do a valve job. I'd fix it, plane the heads new gaskets and go.

Check and/or pin the governor pin though. That's a common problem with catastrophic results upon failure. I haven't pinned mine, but I keep an eye on it. It hasn't ever moved.

john hall · #30 01-29-2017, 09:30 PM

Quote:

Originally Posted by J-Mech

At 110lbs compression on the "good" cylinder, I wouldn't touch it. You don't have to remove the jugs or pistons to do a valve job. I'd fix it, plane the heads new gaskets and go.

Check and/or pin the governor pin though. That's a common problem with catastrophic results upon failure. I haven't pinned mine, but I keep an eye on it. It hasn't ever moved.

Now you've done it--gonna make me go look in the service manual (yes I bought one actually

) and look into the governor. How big a deal is this to do? You know my "pampered pooch" has an M20 right? Whatever is good for the goose is good for the gander.

Seriously though, you are grinding valves and seats right? I've talked to a couple guys locally that were just grinding valves. Seems wrong to me--way wrong. I wish we would have bought the valve grinding machine and the machine for doing seats when the dealer dad worked for closed. Of course a lot of stuff we worked on in recent years needed guides and springs. I remember one tractor head that got everything new--valves, guides, and springs.