Short Block Assembly

Bob Evans

Grumpy Old Admin
Staff member
In this chapter, we’ll go through the final assembly of our “Killer Tiller” block. The very first thing to talk about is cleanliness of ALL parts. I really cannot over emphasize this step. Make sure everything clean and you have a clean work area. I have two separate benches in my shop and one of them is used strictly for assembly. No dirt or aluminum chips laying around. The second thing I’ll mention is to take you time and make sure everything is right. If something does not feel right it most likely is not.

First thing to insure is that the block is clean and the bore has no honing residue in it. For most of the block, a spray bottle of “purple” cleaner and water pressure will do a very good job in attacking all of the grime on old motors For the cylinder, use Carb cleaner and clean white cloths to insure the bore is spotless. Keep wiping the bore down until the cloths come out clean. Also spray the area around the lifters and cam boss with the carb cleaner as a lot of honing oil seems to settle there.

Once you have all of the parts clean and you have a clean area to work in, we can begin.

You will need some way to bolt the block to your work bench. I have used everything from fancy mounts that allow you to turn the motor every direction possible to simply using a combination bolt that has one end like a lag bolt and the other a 5/16 X 18 threaded screw. This allows you to screw these bolts into a wooden table and then bolt the block down using nuts. This works very well.

OK, the first thing is to gather all of the tools you will need to assemble the block. Oil, 1/4 or 3/8 “ drive torque wrench, sockets, ring compressor and your side cover gaskets. The crankshaft should be installed first, but be sure to oil the flywheel side bushing and the areas on the crank that will come in contact with the bushing ,as well as the journal itself. While you have the oil can out shoot some oil into the cam boss on that side.

Rotate the crankshaft so the journal is in it’s most downward position. Now gather up your piston, rod and rings. If you have not previously installed the rod to the piston do so now. Be SURE both the wrist clips are installed and in their proper position. I like to rotate them in their grooves to insure they are properly installed and seated. Now carefully take your gapped rings and install them on the piston. I like to install the oil ring first from the bottom of the piston followed by the scraper ring and finally the top ring. On the scraper ring the side with the recess goes down. If you happen to have a top ring that has a recess on one side it go up.


Proper installation of the rod is as follows. If you look at the top of the rod you will notice a tit on one end. When installed this will point toward the Flywheel. As noted previously, on the new RAPTOR III piston the arrow on top of the piston will orient the wrist pin offset.

Lot’s of opinions on where to set the gaps when installing the rings, but here is what has worked for me for many years. The oil rings gap should point at the valves. The scraper ring (2nd ring)gap points toward the PTO side of the block and the top ring gap points toward the Flywheel. You will note that no gap points toward the front of the motor.

With the rings installed properly, oil the entire piston and the journal portion of the rod. Now take your ring compressor and carefully place it over the piston and rings so you will not disturb the positioning of the end gaps. Carefully tighten up the compressor. Be careful here as it’s easy to bend some of the new RAPTOR III rings at this point. They tend to jump out of their piston lands during this operation. What you want to end up with is a bit of the bottom portion of the piston hanging out of the compressor. This will help to guide the piston and rings into the cylinder. A point here on guiding the rings into the cylinder. On new Briggs blocks you will notice a chamfering to the top of the cylinder. This is to help guide the rings into the cylinder. If you have decked the block or had the block line bored for an oversize piston, this taper may not be there. Be sure your machinist puts this taper back in. You can do it yourself with the use of a deburring tool available from MSC or most any supply house. It’s simply a sharp edged hand held cutter that you can rotate around the cylinder cutting this taper into the top portion. They are very inexpensive (<$5) and also work well to debur the sharp edges found on most new blocks from Briggs.

Now install the piston and compressor into the cylinder letting the pair rest on the edge of the compressor. Push down on the center of the piston with your thumb firmly and in a fairly quick mode. This should slip the piston and rings into the cylinder. If it binds or stops during this operation STOP and pull the piston back out the top. Start over with the entire process. Making sure the compressor is fully compressing all three rings. Be sure to have oiled the cylinder prior to this operation.

Next slowly rotate the crankshaft up and guide the rod end onto the journal. Take the dipper end(cap) of the rod and install it onto the rod with it’s two bolts. You should be able to run the bolts up by hand. When properly installed, the dipper should point back toward the valve side of the block. Now take your torque wrench and a 5/16 socket and tighten the bolts in an alternating pattern to 100 inch pounds. I recommend you do this in 20 - 30 inch lbs. increments. Be careful here that you use a socket and extension long enough to insure you will not hit the dipper and potentially break or weaken it. Remember a broken dipper will wreak all of this work in short order.


Now you have the piston, rings and crankshaft together in one piece we’re ready to install the cam and lifters. I like to mark my lifters as to whether it’s an intake or exhaust lifter. This help insure that you put them back in their correct guides if you choose to reuse them during a later rebuild. I do this with an engraving tool. Billet lifters are now legal in WKA and should always be used on any Slapper cam! These are available from any of the Cam builders(Dyno, Competition, Precision). Good insurance.

Oil the lifters and cam with any good oil. Slip the lifters into their bore and install the camshaft. This process can be tricky unless you simply turn the block upside down. This will keep the lifters from falling out while you install the cam. You should not have the crank gear on the crankshaft at this point. Now install the crankshaft gear onto the crankshaft lining up the keyway with the small key on the crank. It’s a bit tricky to do this and guide the gear past the camshaft gears but wiggling the camshaft will facilitate this. Now you will need to align the cam and crank gears. Notice in the accompanying picture that both have alignment point(dots). They MUST line up to have the correct cam timing. It’s easier to slide the camshaft out a bit and rotate it to line it up. Again this can be easier if done with the block upside down.

Next we want to slide the bearing onto the crankshaft and install the side cover and gaskets. Slide the bearing and butt it up to the gear. Prior to installing the side cover shoot some oil up into the cam lobes and around the crankshaft journal area.

Now we are faced with selecting the proper sidecover gaskets to use. These gaskets come in various thickness’ to enable you to obtain the proper crankshaft end play. This end play is simply the amount of movement of the crankshaft(side to side) when everything is installed and the side plate torqued down. This is a bit of trial and error to get the proper end play. I recommend on single bearing motors .012 - .015 end play. On dual bearing motors use a bit tighter end play of .005. If you have a bushing only motor use .020. The only way to do this is to install the side cover with a standard .015 thick gasket(black), torque the bolts and measure the end play with a micrometer. You can clamp your dial mic used for degreeing the camshaft on to the crankshaft and push/pull the crankshaft to determine your end play. Adjust the play by adding or subtracting gaskets or thickness of gaskets. Gaskets come in .020,.010 and .005. For WKA a maximum of three side cover gaskets in any combination are legal.

On the side cover bolts I like to torque them to 80 inch pounds and do it in a pattern starting with the top two bolts. Then tighten the bottom two and finally the middle bolts. Never stripped a bolt or had one come loose using the 80 inch Lbs.

With the bottom end all buttoned up we’re ready to move on to installing the valves and setting the valve timing for the camshaft we have selected.
 
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