I came into a Briggs and Stratton Animal engine some time ago and it has been on the shelf since. I had always wanted to get into karting, and I had just sold my monster Miata so I thought now would be a good time to start tinkering with it. To start I was told on a forum to Blueprint the engine, still keeping it in a stock class. I think I've made every newbie mistake in doing this that is possible. I've even done stuff wrong where I knew better. I will be sure to point those shortcomings out along the way. The goal was to lap the valves, hone the cylinders, and install a new set of rings to an exact gap. I also got an electric starter to install.
I started by removing the two cowling covers and the top plate, then the ignition coil. I marked everything with a Sharpie and blue masking tape, labeling each part with the numbered order that I took it off. I also used the tape to tape the bolts to the pieces they belonged to. Next I took the cylinder head off. Before you attack the head bolts, you need to loosen the valve lash adjusters and take out the push rods, just turn the loosened rockers to one side or the other. Be sure to label the exhaust push rod and the intake push rod, you want to replace them (and every bolt if you can) in the same place they came from. Once you have pulled the push rods out, the head can be safely removed. There are four bolts holding the head on, I loosened the bolts in a star pattern, cycling to each bolt a few times before the bolts were completely loosened. I don't know if that was necessary or not, but better safe than warp the head.
With the head removed we can now work on the valves. Take the adjuster nuts off, then pull the rockers up. Set them aside keeping the exhaust set separated from the intake side. To remove the valves you can buy a special spring compression tool. I however, just made my own, makeshift valve remover. This trick has probably been used since they valve itself was invented. Take a cheap 6-point spark plug socket and use an angle grinder to grind off two of the faces, about an inch up. Put a balled up rag under the valves so they have something to push against, then take the socket and press the valve spring cap down, you can do this with your hand. Next, take a small magnet and take the spring retainer halves out through the hole (the one you just cut in) in the socket. After the retainers are out you can take the spring cap, the spring, and the valves out. Be very careful not to gouge, scratch, or mar the valves, valve guides, or the valves seats while you are doing this.
With the valves out you can take the valve plate off, you don't need to take the rocker studs out, just the two bolts on either side. This will make the head easier to clean later. I put the head in a vice upside down, being careful not to mar it in any way. Look up a bunch of videos on youtube on lapping the valves. I say a bunch because ANYBODY can post on youtube, and some of the videos are just documentation of people destroying engines. Of course, for all I know, I'm doing that too. First I used some of the Napa water-based stuff for about a minute, then I completely cleaned that out. Next I used some 600 grit lapping compound from E-Z Bore, I used the 600 for about another minute. I then cleaned out the valve seats with a rag and some brake cleaner then painted the valve seats with some red layout fluid (also from E-Z Bore). This is great stuff; it is red acetate that dries within 5 minutes into a very thin painted surface. I then coated the valve and the valve seat evenly with another application of 600 grit lapping compound and worked the valves for another 30 seconds a piece. The red dye will show you if you have any low spots or scratches. If you have any, throw on some more 600 and start again. When the valves are properly lapped in (a healthy looking, think, contact surface is all I was looking for) take the valves out and clean them thoroughly. By clean I mean clean the heck out of them, brake cleaner, followed by dish soap and water, then dry them off and hit them with some more brake cleaner to make sure they are completely dry. Then I hit them with some Breakfree CLP, to keep them from oxidizing. Next, take the head and do the same. IT CANNOT BE CLEAN ENOUGH. Use brake cleaner, dish soap and water, compressed air, clean rags, then do it again. Any amount of lapping compound will destroy your engine if it is left in there.
After everything is clean and dry, re-attach the top valve plate, and apply assembly lube to the valve guides, valves, and valve seats, then reassemble. Push the valves through, ball up a rag underneath them again and use the makeshift valve tool you recently made to reinstall the keepers. Take time to make sure they are fully seated. The valve head is now finished.
With the head finished we start on the short block. I bought a 5/8 and 2-3/4 inch animal bore (and wrist pin) brushes to finish the piston and connecting rod wrist pin holes and the cylinder bore. Again, from EZ-bore. These bore brushes are not designed to take very much material off, more they are designed to create the proper cross-hatch in the bores and holes to retain oil. They are not a set grit, but I mixture of different grits for a particular purpose and oil, so be sure to specify that you are working on an Animal for the correct brush.
The mantra in the race world is "a loose engine is a fast engine". This may be true, but I aimed for a "tight" engine because I knew I would end up with a loose engine anyway. This is another reason I torqued everything to the middle of the torque ranges.
To start I took the flywheel off. You need to buy the Animal flywheel puller, and the flywheel holder from Briggs and Stratton. If you refuse to, you can take a large flat head under the flywheel, between the case and tap the crank with the nut screwed to the top (to prevent damaging the threads) the get the flywheel off the hard way. Then take the side cover off. I loosened the bolts in a star pattern with multiple passes to prevent warping. With the side cover off notice the cam gear and the gear on the crank. It takes two revolutions of the crank for one revolution of the cam (4-cycle of course). The natural direction of output for any motor or engine, is always made to be counter-clockwise for some reason. For instance the electric starter motor for this engine, if you were looking at the starter output gear will turn counter-clockwise, turning the flywheel clockwise, this means if you were looking at the output shaft side of the Animal it would be turning counter-clockwise. Thus if you want to know which way the cam will be turning imagine the electric motor turning counter clockwise, turning the flywheel gear, turning the cam gear. Or just look at the output shaft (counter-clockwise). Carefully take the cam out, being careful not to mar the camshaft in anyway. Also be careful not to loose any shims. Make sure the lifters do not fall out while you are doing this. If they do, just be sure to know (and mark) the exhaust one and the intake one respectively. Some people scribe an 'X' into the top of the exhaust cam so they forever know which one it is.
Next you need to take the connecting rod bolts out, just use a _ drive socket wrench and be careful to mar anything. Take the cap off the bottom and push the piston out through the top of the cylinder. DO NOT let the crank roll down freely when you take the rod cap off, it could damage something. When you push the piston out the top, hold the rod so it does not scrape the cylinder wall. I then take all the oil plugs and drains out of the block so it will be easier to wash later. Use the bore brushes on pipes of similar diameter first, 60 seconds at 600 rpm with the same motion you will be using on the bore should do it. This will break in the brushes and cause any epoxy and aggregate spurs from manufacturing (that may damage your bore) to be knocked off. Next follow the directions to bore the cylinder (I did it for around 45-60 seconds with a good cross hatch), I did not want to over do it because I wanted to use the original size piston (the same one). I will give all the tolerances at the bottom of this page. After you have put a good 45 degree cross-hatch on the cylinder wall, its time to CLEAN the block. First spray the bore out with brake cleaner, then use dish soap and water and a sponge to clean the bore and the block, soak and scrub and scrub again. Dry the bore off and run a very white cloth or a q-tip down the bore, if there is ANY discoloration, clean again. Dry the block off and spray some brake cleaner around just to make sure it is completely dry. Then I take some Breakfree-CLP and coat the bore lightly to prevent it from rusting (it will rust in an hour or two if its humid) or you can just use your assembly lube, which you have to put in there anyway. Next lube the cylinder with Assembly lube if you have not already, a take out your rings NEW set of rings. There is an upper ring, Middle ring, and an oil ring (lower) the animal oil ring. I first got a standard sized set, and cut them ALL to short. So I bought some .010 oversize rings. I was going for .004 end ring gap on the top and middle rings. You check the end gap by lubing the ring with assembly lube, compressing it with a ring compressor then pushing them into the cylinder. Carefully take the old rings off the piston and use the piston to push the ring down 1/2 into the cylinder. Then take your feeler gauges to feel in between the gap. I Used a Drimmel tool I mounted in a vise to cut the rings from both sides. I used a course stone wheel and a fine stone wheel. Make sure to take the burrs of between test fits. When all was said and done I .007 on the top ring, .012 on the bottom and .016 on the middle. I also took 3/8 of an inch off the oil expander ring (inside the oil ring). The forums say your safe until .018 but we will see, I did a shameful job, but it was my first time. Carefully install on the piston, compress the rings and push back into the cylinder. (this is after you have bore brushed the piston and wrist pin and wash thoroughly before reassembly) guide the rod back down the bore to not scratch anything. Apply assembly lube EVERYWHERE. The piston needs to have the arrow pointed to the flywheel, the rod needs to read "mag" facing the output side and the rod cap need to have the oil dipper facing the lifters. Reinstall the cam and bolt the side back together.
I purchased a "heat deflector" kit from Briggs and Stratton, to use it you need to drill and tap the head bolt hole closest to the exhaust port. I drilled then, in a fit of newbieness, a tap the hole crooked. This only became apparent when I put the head back on and found that the bolt holes didn't line up. So I drilled out the hole and took the heat deflector assembly off. People on the forums said they had never even used it so I assume I can live without it. As for the over-sized bolt hole I now have in my head, I'll let you know if that's a deal breaker and I need to buy a new head when I run it.
This would also be a good time to point out how I treated the torque specs. I've included the torque specs for the Animal from Briggs in this page. They are always in a range. An example would be, the given torque specs for the blower housing are 60 to 110 inch-pounds. I use the middle number. To get the middle: take the high number and subtract the low number from it. Then divide by 2, then add it back to the low number. So 110 - 60 = 50 then 50/2 = 25 then 25 + 60 = 85, the center number. I do this because the literature that came with my torque wrenches, tells me to have them calibrated every six months, uh, I do not. I also do not have the "touch" of a pro.
Next I installed the electric starter by cutting the crescent on the block with a hacksaw. After, I used a pair of vise grips to lightly wiggle the pieces off, then I took a Drimmel tool to finish the block. I installed the flywheel and the ignition leaving a .035 inch air gap. Then I installed an external breather from Briggs and Stratton. Be sure to measure twice and cut once on the valve cover. I should have done a leak down test before I tore into the motor but I did not. Live and learn. I will do that next.
Another note: I took off the stock momentary push-button ingition-pull-to-ground from the top plate. I replaced it with an ON-OFF-(ON) DPDT switch from allelectronics.com , that's on-maintained, off-maintained, and on-momentary. The first pole (pole is the separate circuit, the throw is the position in that circuit) pulls the ignition to ground in the on-maintained position. The second pole connects the starter solenoid to +12 volts with the switch is moved to the on-momentary position. This gives the switch a label: STOP-RUN-START.
Here are some of the specs I've picked up so far:
I set my valve lash at .001
You want .004-.006 end gap for the top/middle ring.
You want to use FHS Hurricane Lite race oil.
You want to use new gaskets when you rebuild your engine. (self explanatory I know)
You want your EGTs usually in the 1100-1200 deg. area.
For crank to rod gap, use Plastiguage to measure, and never use anything over .0035.
Leakdown of over 5% means you need a rebuild.
Spark plug gap (not air gap) = .030
Ignition air gap (not spark plug gap) = .35
Piston to cylinder wall gap = .002" to .003". Measure the piston across the thrust surfaces at the bottom of the piston.
Description |
Wrench / socket size |
Torque |
| Air Guard | 7mm | 40-50 lb-in. (4.5-5.6 Nm) |
| Blower Housing | 10mm & 3/8" | 60-110 lb-in. (7-12.5 Nm) |
| Carburetor (to manifold) | 10mm | 80-110 lb-in. (9-12.4 Nm) |
| Connecting Rod | T27 | 115-120lb-in. (13 Nm) |
| Cylinder Head Bolts | 10mm | 200-220 lb-in. (20-27 Nm) |
| Exhaust Brace Screws | 10mm | 95-125 lb-in. (11-14 Nm) |
| Exhaust Stud | 10mm | 95-125 lb-in. (11-14 Nm) |
| Flywheel Nut | 15/16" | 55-75 ft-lbs. (74.5-101 Nm) |
| Flywheel Fan | 10mm | 180-240 lb-in. (20-27 Nm) |
| Intake (to cylinder) | 5mm Allen | 70-90 lb-in. (8-10.2 Nm) |
| Oil Drain Plug | 3/8" | 100-125 lb-in. (11-14 Nm) |
| PVL Module | 7mm | 20-35 lb-in. (2.3-4 Nm) |
| Rocker Arm Stud | 7/16" | 90-120 lb-in. (10-14 Nm) |
| Rocker Arm Plate | 10mm | 70-90 lb-in. (7.9-10.1 Nm) |
| Rocker Arm Set Screw | 1/8" Allen | 50-70 lb-in. (5.6-7.9 Nm) |
| Spark Plug | 5/8" Deep | 95-145 lb-in. (11-16.4 Nm) |
| Side Cover | 10mm | 95-125 lb-in. (11-14 Nm) |
| Starter Gear | #2 Phillips | 35-53 lb-in. (4-6 Nm) |
| Top Control Plate | 10mm | 70-90 lb-in. (8-10 Nm) |
| Valve Cover | 10mm & 3/8" | 30-60 lb-in. (3.5-7 Nm) |
When the smoke had cleared, this is what I had bought:
