So here are some photos of the teardown from last night. I have to admit, it was a bit nostalgic for me dismantling this engine. When I was 15, the first snowmobile I ever bought had this same engine ( but it wasn't correct for the chassis). I ran it anyway and put countless hours back in the woods exploring unmarked trails, getting stuck, cruising the trails at a maximum of 40mph ( on the really long, straight and smooth stretches). I ran that old JLO until it just didn't have the compression to get me around anymore. Well, anyone who wrenches on JLOs is aware of the "quirks of disassembly" ; how much you have to take apart to get at this and that, hard to remove things etc. These all came flooding back and I had to get out the special JLO tools I made for these occasions all those years ago. But I digress, here is the disassembly:
As with just about any engine, the recoil was the first item to come off. I was pleasantly surprised to find the old foam dust seal was still stuck on the recoil hub. When engines are wrenched on frequently, these are usually the first things to go which makes me think this thing hasn't had too many visits the small engine shop. Unfortunately, it wasn't salvageable and disintegrated as soon as I touched it, literally.
The starter cup was removed next and again, I was pleasantly surprised to find all of the proper shims still in place, untouched. Often, these are forgotten upon reassembly.
The next step is to remove the fan shroud and here is the first of the "quirks" I mentioned. There are a series of bolts that secure the fan housing to crank case half and in order to remove one of them, the carburetor has to come off. Anyone who has wrenched on any JLO equipped a Tillotson HD, is aware of how difficult it is to remove the mag side carburetor bolt. These are a thin 17mm nut. So many of these are chewed up along the edges from the tips of screw drivers "chiseling" on them in order to tighten them up. Well, here is the solution to that issue. The very first tool I made for the JLO. It's nothing fancy, but it works wonderfully.
With the carburetor off, you can now remove the fan housing cover as well as the cylinder head shroud. The 297 is the only JLO single that used a one-peice cylinder head shroud and to remove it, you need to remove the exhaust manifold, carburetor and intake. You can see the bolt I was referring to earlier, the one that you needed to remove the carburetor in order to get access to, on the right side of the photo below. The engine has the insulating intake adapter which is a good thing. JLO singles can get pretty warm when run hard and I have had a few in the past vapor lock on me due to the intake adapter being aluminum rather than an insulating material like this one.
All clean inside and only very minimal signs of our favorite furry friends ever being in there.
One bolt was missing on the shroud which is the first sign I have had that someone might have been into this motor before.
The flywheel nut is 28mm and after removing it, I set up to remove the flywheel. There is a right way and a wrong way to pull a JLO flywheel. The wrong
was would be to throw a harmonic balancer puller on the three starter cup bolts and pull. The result is a broken flywheel everytime or damaged ignition components from threading in the bolts too far. This is the right way:
Remove the flywheel nut:
Grease up the puller, both threads and tip:
Install the puller and remove the flywheel:
The flywheel is nice and clean inside:
Like the flywheel, the stator assembly is nice and clean and appears to be all original. I will investigate the wire splice and verify originality when I get into the stator to freshen it up later on.
Once the stator is out, we're in all the way on the magneto side. The magneto side crank seal looked good and felt nice and soft but since we're in this far already, it will be replaced.
The next step is to remove top end and it's time to remove the head and see what lies within. Only 5 nuts secure the head in place and when properly seated, they require a gentle rap on the side to pop 'em loose. The properly installed head, as this one was, has a spacer and locking washer between the head and nut.
Well now we know that this old engine has been to the shop at least once. Originally this head gasket would have been copper but this one is a composite style. I can see some lettering on the underside of the head as well with a clear letter "W" implying a "Winderosa" brand head gasket. It appears as though some one has scraped some of the buildup from the piston crown as well.
Now I can remove the cylinder and have a peek but this is another one of those "quirks". The cylinder is held on by 4, 17mm nuts on each corner. The stud they use is too tall to fit a conventional open end wrench between the end and the cooling fins so again, use the same homemade wrench as was used on the carburetor to loosen them up. Access to the magneto side bolts is gained through the opening in the magneto side fan housing. Hopefully, now it becomes apparent why I disassembled it in this particular sequence. I was a little negligent in my photo taking during this particular step but hopefully, can get the idea from the picture below:
The cylinder showed some signs of moisture and rust had set in. I am going to attempt to hone this out but we'll see how it turns out. I am cautiously optimistic and we'll deal with it if it ends up needing a fresh bore.
I removed the piston next and in most cases, a piston puller would be used here. After removing the circlips, you'd install the puller and draw it out of the PTO side of the piston. Sometimes, if you're feeling strong, you can push it out with your fingers and when you can no longer reach it, installing a socket that is slightly smaller than the pin can allow you push it the rest of the way out. That's what I did here. I could move it with my fingers so I figure I could remove it entirely without the puller. JLOs use spacers on each side of the wrist pin needle bearing so you need to be aware that they'll drop once the pin is out. You just have to have your other hand there ready to catch them when they fall. Also note that there is a recess on one side of the spacer. The recess is meant to fit against the needle cage bearing. If you have them flipped around, they won't fit back in the piston.
This piston is pretty gummed up. Seems the mixture was pretty rich but the piston looked great except for a little discoloration from ring blow-by. Very little if any scoring. I am hoping it's re-useable but I won't know until I clean it up. If not, we may need a piston for the old bird.
There isn't much left to it from here. From the magneto side now, the next step is to remove the socket head capscrews that hold the two halves together. These require a 6mm allen wrench. After removing these, I re-installed the flywheel nut on the magneto side of the crank until it was flush with the end. A couple of raps on the end with the rubber
mallet and you'll see a gap open up between the cases. Once the gap forms, I used a plastic wedge to gently wiggle the PTO side free from the crank. Once the PTO side was free, a few more raps on the crank end, and the crank pops free from the MAG side case. If these were stubborn, applying heat with a heat gun to the case halves with a heat gun directly onto the exterior of the crank bearing seats, expands the aluminum cases enough to let the bearing slide loose. When I go to re-assemble this engine, I will probably heat both case sides like this and also leave the crank in the freezer over night to contract the bearings a little more yet. This just ensures an easier assembly since once the crank is trued, I don't want to be rapping on it at all during assembly.
Since I did rap the end of the crank, something I try to do very, very sparingly, I will check the runout on it before I re-assemble. JLO engines are built quite beefy as you can see. Big bearings, big counter weights, big pins, big bolts,,...just heavy duty stuff. It's no wonder they're considered workhorses rather than speed demons. So considering the strength of the rap, and the mallet material, I doubt I have induced any issues to the crank alignment but it's always better to be safe than sorry.
So we're completely dismantled at this point. My next steps are to clean everything up. Stay tuned for further updates.