Valve Train Technology
For Kart & Jr. Dragster Racing
camshafts and engine components have been aggressively developed
on the dynamometer and on the race track to provide you with the
most competitive products on the market.
your hi-performance 5 HP Briggs and Stratton engine, we recommend
that you read these instructions completely to familiarize yourself
with the necessary tools and the preparing a high quality racing
engine. We also recommend you have a copy of the Briggs and Stratton
factory service manual for reference purposes. Use of hi-performance
engine components will not improve your racing chassis handling.
The quality of your chassis handling is as important as the quality
of your engine.
If you have
any questions concerning installation or proper use of your Go-Parts
hi-performance components, call us toll-free at 1-800-976-9376.
Complete Engine Disassembly Instructions For Briggs & Stratton
5 HP Engines
that your goal is a hi-performance racing engine, it is in your
best interest to follow these instructions precisely. Clearancing
issues are dealt with and should not be ignored. Skipping steps
will reduce horsepower, efficiency, and the performance of your
1 - Warm the engine at an idle. Shut the engine off and
remove the blower housing, spark plug and attached hardware.
Next, perform a leak down test on your engine to test the sealing
condition of the engine. You can perform a leak down test while
the engine is on the chassis or on the bench. Either way, you
must be certain that the engine is warm, that the flywheel is
held stationary during the leak down test and that both valves
are closed. The flywheel can be held stationary by attaching
a flywheel holding tool onto the flywheel. If the leak down
test indicates a leak percentage higher than 10%, you will need
to inspect and possibly repair the valve seats, head, head gasket
and piston rings. If you listen closely to the engine during
the leak test, you can pinpoint the source of the leakage. Overlooking
the sealing condition of your engine can cause inaccurate performance
potential from your new camshaft.
Tip: Go-Parts offers a
leak down tester
(part #GP301010) that is an accurate and dependable tool
for this application.
2: Remove clutch, clutch guard, header, straps, carburetor,
tank, all hardware and brackets. When removing these components,
check the condition of the fasteners and engine block threads.
Replace or repair if necessary.
3: Drain fuel and oil/lubricant and dispose of properly.
4: Remove the cylinder head and valve cover. Remove valve
springs and valves. When removing dual valve springs, use Go-Parts
Valve Spring Compressor
(part #GP351018) for safety and ease. Stock class springs can
be removed with a stock spring compressor or two screwdrivers.
Inspect valves, retainers, valve guides and valve seats for
wear. Replace or repair if necessary.
In stock classes, replace stock valve springs every three to
If using Go-Parts dual springs in modified classes, replacement
is necessary every eight to ten races.
For stock classes, check the Go-Parts application sheet
for the proper valve spring for your camshaft.
For modified classes, check the Go-Parts application sheet
for the proper spring for your cam. Go-Parts offers two
different dual valve spring sizes to fit all modified engines.
Part #GP959-Kit is designed for use on modified engines with
camshaft lifts up to .380". Part #GP960-Kit is designed
for use on modified engines with cam lifts over .380".
5: Remove the side cover and side cover gasket from the
engine. Remove PTO bearing. PTO bearing should be a slip-fit.
If PTO bearing is not slip-fit, you will need to completely
disassemble the engine to install your new camshaft or use a
"puller" to remove the PTO bearing.
If you use a "puller" to remove the PTO bearing, you
must have the crankshaft journal "turned down" to
allow the PTO bearing to slip-fit upon reassembly AND must replace
the PTO bearing.
If your engine is not equipped with a PTO bearing, you must
inspect the clearance between the bushing inside diameter and
the crankshaft journal outside diameter.
If clearance is excessive or bushing quality is poor, replace
crankshaft and/or repair bushings.
Note: If you choose to leave the PTO bearing pressed on the
crankshaft, you will have to remove the piston and connecting
rod; remove the crankshaft and camshaft; and reinstall the crankshaft
simultaneously with the new camshaft.
6: Turn the engine upside down or deck surface down, line
up the crankshaft and camshaft timing marking dots and remove
the camshaft. When removing the camshaft be careful not to "knick"
the camshaft lobes on any internal engine components.
7 - Remove and inspect the lifters for wear pattern.
If your engine is a modified class engine, we highly
recommend replacing your lifters with stronger & harder Go-Parts
lifters regardless of the existence of any wear patterns.
If your engine is a stocker or restricted stocker, and
has had a "fast-rapid" lift or a "fast-ramp"
camshaft previously, you must install new lifters.
stock class lifters
(GP8250-2), which will allow the cam to "degree in"
every time. These lifters will also pass tech inspection.
Fast lift camshafts have been known to break weaker lifters,
valve spring retainers, valve guides and consequently ruining
some engine blocks. Overlooking this fact can cause severe engine
Inspect for excessive clearance in the lifter bore. If the lifter
appears loose in the lifter bore, installing a sleeve in the
lifter bore area may be necessary. It will also be necessary
for you to inspect the quality of the valve guide bore. If excessive
clearance is present, you will have to replace the valve guide.
If you install a new valve guide, you will need to "lap"
the valve or cut the valve seat with the proper seat valve cutter.
Note: All valve lapping and seat cutting should be performed
with a "torque-plate" attached to the top of the block
and torqued to spec.
Note: If you are not familiar with the type of camshaft that
you are removing, replace the lifters for safety.
Note: Check sanctioning body legality before cutting valve seats.
Note: If reusing a lifter, make sure to mark the lifter during
disassembly and reinstall the same lifter in the same lifter
bore originally installed in.
Note: Inspect the entire valve train for faulty components
and for faulty valve sealing. Installing a new camshaft without
inspecting the quality of all internal components may lead to
poor performance and possibly engine failure.
8: In modified class engines you must now inspect
for proper internal components-to-crankcase clearances.
The main areas to inspect are:
1. Connecting rod to camshaft intake lobe clearance.
2. Connecting rod to camshaft "barrel" (area between
3. Camshaft to crankshaft clearance.
4. Connecting rod to crankshaft clearance.
5. Lifter head to lifter bore clearance at max. lift.
It may be necessary to remove material from the bottom of the
lifter bore, the camshaft "barrel" (center section
between both camshaft lobes), the sides of the camshafts lobes,
the crankshaft "pin" area and the connecting rod.
A .030 clearance between internal components is acceptable.
Clean engine parts with a clean cloth. Install (with a light
film of oil) the crankshaft, camshaft, piston (with no piston
rings) on the connecting rod, lifters and PTO bearing. Be sure
to line up the timing marks on the crank gear and the camshaft.
Turn the engine over very slowly and with a flash light, look
through the Go-Parts billet camshaft gear face and view
where material needs to be removed from the engine block or
any internal engine components. After removing the necessary
amount of material and cleaning all parts, recheck the tolerances
with crankcase cover and crankcase cover gasket installed and
torqued. This can be done by listening closely for internal
noise while you are slowly turning the engine over in the direction
Note: It may be necessary to hold finger pressure down on the
lifters while checking for internal clearances. See Go-Parts
lifter installation instructions for further details.
Note: Firing and running the engine without checking clearances
can be fatal to engine life.
Note: Go-Parts billet modified camshaft installation numbers
match the cam card when the cam gear tooth marked as "0"
lines up with the crank gear marking dot (as shipped). If you
change the location of the cam gear to the crank gear by advancing
or retarding the cam gear on the camshaft, you will need to
re-check clearances before running again.
now be ready for re-assembly.
you have any questions, call us toll-free at 1-800-976-9376