Final Assembly

Bob Evans

Grumpy Old Admin
Staff member
Setup of valves and valve springs:
Now that we have the short block assembled we need to install the valves and springs. Prior to this you should have lapped the new valves into their seats. This will allow you to clean everything before final assembly.

Using new valves, you will first need to cut the valve stem to give you the clearance and thus the proper open and close numbers you decided upon back when profiling the cam. All cam makers will give you recommended clearance numbers but these are very general and will vary from motor to motor based upon the actual block, crank and cam. While you can obtain a tool for cutting the valve stem from most kart shops you can also make one from a 1” piece of mild steel bar stock. Simply obtain a piece about 6” in length and drill a 1/4” hole through one end. You will stick the valve through this hole. Be very sure to do this on a drill press so the hole is parallel to the side of the bar stock. After drilling the 1/4” hole drill a smaller hole for a 5/32 screw into this hole on 90 degrees from the original hole. After drilling the hole tap it for the 5/32 bolt/screw. This will be used to lock and hold the valve in the 1/4” hole.

Now you can put the valve through the hole and let the amount you want to cut hang out one side. Lock the bolt down with the 5/32 screw. A simple way to set the amount you want to cut is to lay a feeler gauge of appropriate thickness under the tool and not touching the valve stem. Take the valve and cut off the stem by laying a file on a flat surface and running the tool back and forth cutting off the stem sticking out. Go slow in the amount you cut off and test it often in the motor for it’s proper clearance. You can always cut more! Measuring the amount of clearance is done with the valve installed and a bit of pressure applied to it insuring it’s seated against it’s seat. Then take a feeler gauge of appropriate thickness and try it between the valve stem and the lifter. Keep cutting carefully until you get the desired clearance. Feeler gauges can be obtain from any auto supply house. I have cut my valves using the above tool on a bench grinder but this takes a bit of experience to cut the right amount and not over heat the valve stem(causing it to loose it’s hardness). It’s very important to make the cut square!!

WKA and IKF currently allow you to back face the upper portion of the valve spring pocket area to help stabilize the valve spring and more importantly adjust your spring pressure. Tools to accomplish this back facing are available from most kart shops or EZ-Bore.(see photos)

Spring pressure is the key to getting the new Slapper style of cams to float the intake valve at the upper RPM range and keep them in some sort of control. Bottom line on valve springs is to have just enough pressure to float the valves in a somewhat controlled manner and yet not have too little or too much pressure. Excessive spring pressure is just wasting HP due to the added resistance. A spring whose installed height is greater will have less installed spring pressure than one installed at a smaller height. Also used springs will exhibit less pressure due to their being heat cycled many times in a motor. New Springs from Briggs will typically lose a couple lbs. of pressure after being run the first time.

An engine which is floating the intake valve will normally show the valve just ‘kissing’ the head on the intake side. I personally do NOT float the exhaust side as I believe this makes tuning the exhaust system impossible.


On most stock class motors today, you will be using a new exhaust valve spring on both the intake and exhaust side(WKA legal). For the intake side it will have too much pressure if installed without back facing. While this does take a bit of experimentation, back facing the intake side around .040 will get you in the ballpark. This when combined with cutting the valve seat down will lengthen our installed height and reduce the installed pressure. On the exhaust side around .020 - .030 back facing will do fine to start. All you want here is to cut enough to stabilize the spring. Most cam makers today will offer a coil bind length recommendation for their cams. This coil bind number will be for a new exhaust valve spring. For the Dyno 95-3 and 99-3, try around .380 on the intake side and .350 on the exhaust. What is coil bind??? Well that is nothing more than the length of travel of an installed valve/valve spring before it binds up the spring and will not travel any further. A simple way to get you to an installed height or spring pressure.

The way to measure this is to install your valve with it’s spring and retainer. Next install and zero a dial indicator over the valve. Take a screwdriver and raise the spring up as far as it will go. The reading on your indicator is your coil bind number! Just as with installed height, more coil bind length would give you less seat pressure. Personally I’ve used actual installed spring pressure as my measurement over the years. I’ve used an old valve with an eyebolt threaded into it’s face. We install this valve with it’s appropriate spring and then use an electric fish scale to measure spring pressure just as the valve pulls off the seat. I install a dial indicator to show me when the valve just starts to move and note the weight on the fish scale. Around 14 lb. on the intake is right for most Slapper cams for stock classes. On the exhaust side look for 14 - 17 lbs. These numbers may vary a bit for you depending upon your scale. I use an electronic one(STREN) obtained at WalMart but the less expensive spring style should be fine. The trick to achieving consistent readings is to bolt the block down and have a method of pulling the scale with steady pressure such as with a drill press(my method).

On some restricted motors(purple plate), you can use intake valve springs on the intake side as we don’t turn these motors as hard as stockers so we will need less pressure at those RPMs. If you are building a restricted motor with an intake spring don’t back face as much on the intake side. Only enough(.020) to hold the spring in place. I like to use around 10-13 lb. on the intake valve depending upon the class(purple to gold). I always installed a used exhaust valve on the exhaust side of these motor(less pressure). Don’t go too light on the exhaust side pressure as the high cylinder pressures of a restricted motor during the intake cycle can actually open the exhaust valve(big problem). Never less than 14lbs. For gold plates(575), we normally use an old exhaust spring and backface to a greater depth(380-400) to obtain the correct pressure.

To install the valves take your spring installer and place it with the spring and retainer into the pocket. Retainer is on the bottom with the small indent facing outward from the block. Briggs makes a very nice hand tool to install stock springs that is much less cumbersome than the traditional C style compressor. This tool has a round cut out for the end of the spring/retainer and a slot so it will go by the valve stem. Once you have the spring and retainer in place with the hand tool still on the retainer, drop the valve down into it’s guide. The valve will stop as it bottoms onto the retainer. Now with the tool apply a bit of upward pressure and pull back a bit. This allows the valve stem to slip into the bigger portion of the retainer(offset from center). Now push the retainer and spring up and forward with the tool. This will slip the retainer over the valve stem and center it. This takes a bit of practice but will become second nature after a couple of engines. Make sure the valve spring is centered into your back face cut and you’re good to go. Recheck both valve clearances after you install everything under spring pressure.


Installed spring height is a key to consistent performance of the exhaust springs. We like somewhere in the neighborhood of 1.030 to 1.050. It is this range where the springs seem to perform best. We sort our used and new springs by pressure at 1.040. This way we can cut the backface looking for a given installed height and then go pick a spring for that height. Easy way to find your installed height is to compress a spring in a vice to it’s fully closed position and measure it’s length. Now install the spring/valve/retainer in the block and zero a dial indicator on the valve top. Compress the spring to it’s fully closed position(coil bind) and then add what you have on the dial indicator to your pre-measured length. = ** installed height **

EzBore has a new valve spring pressure gauge that uses a small air cylinder with a pressure gauge to push the valve up with a lifter to measure the pressure. Chapter 16 will tell you how to build one for yourself. This is the tool I use to measure all my springs today. It’s very easy to use and gives accurate readings. The key to any method you choose to use is to be consistent and develop your own numbers!!

Installing the head and head gasket:

Installation of the head and head gasket is fairly straight forward. I personally like the new Fel Pro # 1004 gasket, but the Standard Briggs gasket is fine. Either the older style Briggs or the newer graphite one works well. The older style has two metal surfaces and can be re-used several times. The newer graphite style seems to seal better but almost always will tear up upon disassembly. The Fel Pro has two metal surfaces surrounding a graphite interior. Before installing the gasket lay it on the head and check for any areas that might over hang and mess up the air flow. Cut the gasket with a Dremel tool and sanding disk in these areas.

Lay the head gasket over the block and then carefully lay the head and head cover on top of it. Next gently hand install the front head bolt and it’s rear counterpart. These are the two in the middle of the cylinder. Do not tighten these just yet. Depending upon your motor Briggs has made two styles of head bolts over the years. Originally they came in two lengths (1 3/32 and 1 15/32”). The longer ones only were used on the three holes surrounding the exhaust valve. All other bolts were the shorter design. On the Raptor series of engines all are long bolts due to a change in the block design.

After hand tightening the two bolts push the head back toward the intake valve and tighten the two bolts enough to keep the head from moving around. This will give you the most area around the backside of the intake valve for best flow. Now install all of the remaining bolts by hand. Next take you torque wrench and 1/2” socket and tighten the bolts in the pattern shown(pictures), to 160 inch. Lbs. I like to torque the bolts to 100 in lbs. And then move up to the 160 in 20 inch lb. increments.

Installing the carb:

After bolting the carb to it’s tank(use two gaskets!) you’re ready to install it onto the block. We use 1/4” X 20 Allen headed bolts for all carb and header bolts. These are very inexpensive and can be obtained by the hundreds from MSC for very little cost.


Install the two bolts through the carb holes and place the intake gasket on these bolts. For stock motors we like to use the larger intake gasket so we don't have any potential of blocking the intake passage. Next install the carb/tank assembly onto the block and run the bolts up till they are hand tight. Now take a look at the bottom tank bolt hole that bolts to the block. It should line up perfectly. If not, see if you can loosen the carb bolts a bit an move the tank around to line the hole up. Very often you will need to enlarge the hole so this bolt(1/4” X 20) will install with NO pressure at all. You don’t want to force this installation as you will put undue pressure on the carb and run the risk of breaking it! Very often restricted motors will require a washer behind the brace to take up the slack created by using the restrictor plate and two gaskets.

After getting this hole correct go ahead and install everything and run all bolts up tight but.... keep in mind you are dealing with aluminum and you don’t want to strip the bolt threads. If you do run across any stripped holes use a thread repair product such as a Heli-Coil. These are very easy to install and the instructions come with the tools. They are available from MSC or your local auto parts store. I would recommend you have them in the common sizes(1/4 x20, 10/x32, 5/16x18) used on a Briggs.

I also recommend that you always use a carb and/or tank brace on any Briggs. Cheap insurance for that special carb, as once you break one they are almost always toast. The new style that bolts to the carb and head is very good and readily available today. Tanks can also be braced by welding a strap from the bottom of the tank to the bottom support or you can also purchase one of the bolt-on tank braces that use a large hose clamp.

One last comment on assembly. Be sure and check all parts before assembling them for any specific tech requirements such as exhaust spring min/max height. Hate to go to all this trouble and get tossed for a part that is out of spec. Just because the part came from Briggs does not make it legal!
 
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