LA125 Overhaul

[BravoXray]

No, not really.
The 'tip' is to recognise when it is blowing.

In your 6th photo of the cylinder cross-hatching you can see the blown area right there at 3-o'clock between the cylinder and the pushrod cavity.
Understand that this is a design issue where there is no head bolt in that area at all so clamping pressure on the gasket is reliant upon the head bolts at 1 o'clock and 5 o'clock.

That's a lot to ask for a simple compound head gasket to deal with. Inevitably, yes, it will happen again.

The telltale indication of trouble is when you begin to see oil on the area around the vacuum fuel pump at the rear of the engine cowl. In addition to the crankcase breather the additional excess pressure in the crankcase is relieved by blowing through the pulse line to the fuel pump. Eventually you begin to see oil on the chassis in the area near your left foot. (Below the fuel pump)

At that point, where oil is on the chassis you know your head gasket is a goner.

The upside is that it's a relatively simple repair in-situ. An hour, (in the field even) , at most.

The downside is that if you miss the oil-on-chassis-signal (Red Alert!) you will lose the engine through "insufficient lubrication".

Easy monitoring involves checking the dipstick every time before mowing. It's that simple.
(Most operators, however, don't bother.)

If you notice a drop in oil level on the dipstick - Where has it gone? Look for the oil on chassis...

Second - look on the crankshaft pulley in-case the lower crankshaft oil seal has failed.

When refitting the cowl to the engine take care to correctly align the 'finned edges of the dipstick tube with the grooves inside the cowl. (Practice upside down on the bench first so you can see how it sleeves together.)

Also that air-duct shield you mentioned above has two tabs that fit on the cowl.
Another pair of hands can be useful when refitting this together with the dipstick tube and a keeping it all aligned.

Thanks for the info and I agree it's a poor design with no head bolt in that area. The intake runner goes right through where it needs another one.
One Youtuber suggested giving the head gasket a coat of copper gasket sealer, which doesn't sound like a bad idea. We used to use it on some of the old engines in construction equipment that really needed the heads milled or the block decked, just to get them through the season and get fixed over the winter.
Yes, I know about the dipstick tube and shroud that goes around the cylinder, and was able to get them in place when I had the flywheel cover off before.
I got everything cleaned up this afternoon, and deglazed and crosshatched the cylinder bore. The is no wear in it that I can detect, which is amazing considering the lack of maintenance it has had.
I bead blasted and painted some parts that were pretty rusty, especially the flywheel. I looked like water had been setting on it a lot, it was rusted pretty badly but cleaned up pretty well. Even the mag coil was rusted badly and the metal got blasted and painted.
Drilled out the broken screw on the under side of the cylinder and had to tap it 10-24 to get it cleaned up.
When I ordered parts for the engine, I couldn't read the engine model number off the rocker cover because it was rusted so bad. I could see a few really vague parts of a couple of numbers, but that was it, but it looks like the LA125 only used a few models that had the same internals.
One thing that I cant believe on the engine is that the only lower thrust surface on the crank is the toothed side of the gear that drives the camshaft. there is so little surface there. I know that's the way it goes, because I can see the witness marks on the other side where it presses against the eccentric that the balance weight runs on.
I think after I get back together and give it back to my niece, I'll make it a point of checking on it a couple of times in the summer, and pick it up every fall and check it out and service it. I've put too much time and money into it to let go to pot again.

 

[tomplum]

They really should have a fire ring style gasket on these. They have increased the torque to 250 inch pounds and updated the torque sequence a while back. You shouldn't use a dressing of any kind. Clean up is king. I do them all the time and it takes me an hour and a half.

 

[BravoXray]

They really should have a fire ring style gasket on these. They have increased the torque to 250 inch pounds and updated the torque sequence a while back. You shouldn't use a dressing of any kind. Clean up is king. I do them all the time and it takes me an hour and a half.

Okay, that's good information.
What's the tightening sequence, I haven't been able to find a diagram that shows it.

 

[Richard001]

I hate to disagree with tom P, but you really should use a gasket sealant on that. They make gasket sealant for a reason.

Also run a file over the head and cylinder mating surfaces to make sure that they are flat. Check the head carefully. If you run the file over the head in the area where the gasket failed and the file does not pick up the surface in that area, I suggest that you use a metal flat plate with sandpaper on it to get the warpage out of the head.

Richard

 

[BravoXray]

I hate to disagree with tom P, but you really should use a gasket sealant on that. They make gasket sealant for a reason.

Also run a file over the head and cylinder mating surfaces to make sure that they are flat. Check the head carefully. If you run the file over the head in the area where the gasket failed and the file does not pick up the surface in that area, I suggest that you use a metal flat plate with sandpaper on it to get the warpage out of the head.

Richard

I have a big flat mill file I might try on the head

I was thinking about using a flat plate and some sandpaper on the head and block mating surfaces to make sure they are flat.

Anyone know what the torque is on the case half bolts?

 

[beenthere]

I wouldn't use a file.
I'd put some wet/dry sandpaper placed on a glass plate. And use light oil or water with 220 grit paper.

Something like this video shows.

 

[tomplum]

I have a big flat mill file I might try on the head

I was thinking about using a flat plate and some sandpaper on the head and block mating surfaces to make sure they are flat.

Anyone know what the torque is on the case half bolts?

220" #s

 

[tomplum]

I hate to disagree with tom P, but you really should use a gasket sealant on that. They make gasket sealant for a reason.

Also run a file over the head and cylinder mating surfaces to make sure that they are flat. Check the head carefully. If you run the file over the head in the area where the gasket failed and the file does not pick up the surface in that area, I suggest that you use a metal flat plate with sandpaper on it to get the warpage out of the head.

Richard

It would be interesting to hear your take on this. What would you use? Bear in mind that this is a grafoil head gasket. I saw someone somewhere was making them out of copper? Is this a better idea ?

 

[BravoXray]

While pondering the head gasket sealing problem, I remembered how some racing engine builders o-ringed the tops of the blocks and laid a soft copper wire in the groove to help clamp and seal the head gasket. Sounds like a possible solution for these engines unless someone comes out with a real head gasket with a fire ring seal instead of just stamping them out of a sheet of material.
If I had a mill, I would seriously consider making a fixture to hold the block to do that. There are also grooving tools available, but at over $300 I'll try something cheaper for now.

 

[tomplum]

The OEM gasket has a slight embossment, but yes an actual fire ring should do the trick.