RB Designs LLC
Machine Shop Services ~ Motorcycle ~ ATV ~ PWC ~ Small Engine ~ Custom Parts Machining
Squish Band Clearance Testing
This test is to determine the actual piston to head clearance called "squish band clearance" of your engine. Each engine is a little
different and this is why you need to do this test so we can properly set-up your head for optimum performance and reliability.
easy way to measure this clearance is by using common solder that you can get from your local auto parts store like NAPPA and Auto
Zone. A leaded solder with a rosin or acid core is best for doing these tests. You can also use a low lead solder as long as
it has a core. The core allows the solder to smash more easily and give a more accurate smash without overly binding the engine. Do
not use "lead free solid core solder" used for plumbing from the local Home Improvement Store as it will not smash properly causing
binding in the engine and not give a accurate result.
Most European and some Japanese bikes will need .125" (1/8") solder NAPA
Most Japanese and some European bikes will need .093" (3/32") solder NAPA PN 31-406
Smaller bores 125 cc and smaller may
need .062" (1/16") solder Radio Shack PN 6400013
If your test solder smashes more than 50% of its diameter you should use a small diameter
It is important to follow our instructions and do these tests with great care as these test solders are our only look
inside your engine and are used to determine how much to re-cut your head.
Preforming these tests do require good mechanical skills.
note: When doing these tests make sure to use the same make and brand of piston that will be used in the finished engine. Also make
sure to use the same thickness base gasket or base gasket stack thickness and use the same thickness head gasket if it uses
one as well.
If you have a water cooled engine, drain the cooling system first and remove the cylinder block drain plug if it has one.
Next remove the flywheel cover, this will allow you to turn the engine by hand. Now remove the head and save the old head gasket if it uses one, some engines use o-rings and this does not apply. With the head removed clean any excess carbon from head and the top of the piston.
Preparing the test solders:
You will need to cut your self several pieces of solder about 1.5" to 2" longer than the bore diameter (you will need at least 3 of these). Now take a cut piece of solder and bend it in half with a nice U shaped bend (not a sharp bend). Next make a sharp 90 Deg bend to one of the legs of the solder about 1/2" from the U shape, then do the same thing to the other leg in the opposite direction of the first leg. Make sure both legs line up with each other in opposite directions making a straight line and it should look like a straight piece of solder with a 1/2" hump in the middle. See pic's below.
Now you will need to trim the ends of the test solders and file them flat so the test solders just fit inside the bore of the cylinder. It is very important that the ends of the test solder are blunt and flat. You can use a finger nail file to remove the sharp pointed end of the solder where it was cut.
Time to do the test:
Using the flywheel, rotate the engine and position the piston about 1/4" to 3/8" below TDC. Note: Do not move the piston more that
1/2" below TDC while doing these test. If you lower the piston down any farther you run the risk of the test solder falling into one
of the ports and then it can be sheared off and fall into the lower end.
DO NOT use the kick starter to rotate the engine!
your test solder across the top of the piston placing one end at the 3 O'clock position and the other end at the 9 O'clock position
(through the center line of the wrist pin). Make sure both ends of the test solder touch and rub against the cylinder wall. Make sure
the solder and hump shape lays flat on the top of the piston. You can use the hump shape to shrink or lengthen the test solder ends
by pulling the ends apart or by pushing the ends together so they touch and drag on the cylinder wall.
You should add small dab
of heavy grease to the hump shape as it will help hold the test solder in position while doing the test.
Now install the head and tighten it down. If your engine uses a head gasket, you will need it for this test (you can use your old one). Now carefully turn the crankshaft by hand using a wrench on the flywheel nut. You want to rotate the the flywheel making the piston go over TDC and then stop. You will feel a slight binding and this is normal. You will want to rock the crankshaft back and forth over TDC several times until you feel very little restriction assuring the solder has completely smashed. Do not allow the piston to travel any more than 1/2" below TDC.
Now remove the head and you will see the area where the solder has been smashed and this is your actual squish band clearance, it should look something like the pic's to the right.
You will need to do this test 2 more times and send at lease 3 of these test solders with the head to be modified.
Please feel free to Contact Us
for more information.