piston do I need?
If you are just replacing the piston, then you
need to first know the bore of the cylinder. This can be done by using a bore
gauge to find the diameter or by reading the owner’s manual to find the bore
specifications. Ultimately, the bore should be measured for the best possible
results. After the diameter is known, then you can pick which size piston will
work best in your cylinder. Remember to maintain about a 0.05mm (0.002”) piston
to cylinder clearance, depending on application. If you are having a cylinder
re-plated, then you will want to choose a piston of the OE bore size (an A or B
size is probably best). When you send the piston and cylinder away to get
re-plated, the plating facility will match the cylinder bore to piston
diameter. If you have a cast iron bore cylinder and you are sending the piston
and cylinder off to a machinist to be bored out, then you will want a piston
that is oversized from the current diameter. For example: If your current bore
is 64.00mm, then you will want to choose a 64.50mm or similar oversized piston.
The machinist boring the cylinder will bore and hone the cylinder to match the
pistons cast or forged?
Vertex pistons are both cast and forged. Vertex
casts their two stroke pistons because of the ability to incorporate higher
silicon content into castings as opposed to a forging. This gives the piston a
lower thermal distortion characteristic and higher wear resistance. Vertex uses
castings and forgings in its four stroke pistons depending on application. Low
rpm, low performance four stroke engines can use cast pistons. High
performance, high rpm engines (like today’s race bikes) use forged pistons for
strength. Vertex has the ability to manufacture its pistons to suit each need.
Vertex offer A, B, C, and D piston sizes and what is the difference between
Vertex offers A, B, C, D, sizes so that the
customer can properly fit each piston to the cylinder. The difference in the
sizes is 0.01mm (0.0004") increments with A being the smallest and D the
biggest. When a cylinder wears, the customer can choose the next larger piston
size to regain the proper factory fitment.
Which rings go
where on a two stroke piston?
On a two stroke piston the rings are generally
the same and it does not matter which ring groove they are installed in.
However, some rings can be L shaped. If you have an L shaped piston ring, this
one goes in the top ring groove. The most important thing to note on a two
stroke is that if there are any letters stamped on the ring, by the ring gap,
these letters face up. Some rings have a wedge shape and if these letters are
not facing up, the ring will not fit all the way into the ring groove. It is
also important to note that the rings compress properly into the ring groove of
the piston and fit properly around the ring locating pin. And always remember
to point the arrow on the piston dome towards the exhaust port.
2 Stroke Piston Kit
Which rings go
where on a four stroke piston?
In four-stroke applications Vertex offers both
two-ring and three-ring pistons. Three-ring pistons will have two compression
rings and one oil ring. A two ring piston only has one compression ring and the
oil ring. The oil ring on both types of pistons is a three piece design,
consisting of two rail rings and one expander ring. On three-ring pistons, the
two compression rings will go into the top two ring grooves and the oil ring
will go in the bottom ring groove. The two compression rings may be different from
each other. If this is the case then it is necessary to look at the profile of
the rings to ensure they are located in the proper groove. Often one ring will
have a taper to its profile. If this ring is installed into the wrong ring
groove, it will not compress properly. It is also common for the second
compression ring to be darker, because it may be made from cast iron. Ensure
that any letters located at the tip of the rings are facing up. This is the
same for two ring pistons except there is only one compression ring. When
installing the oil ring, first install the expander ring and make sure the ends
do not overlap. If you look closely at the expander ring, it has a shoulder/lip
on both top and bottom that prevents the rail rings from seating completely
against the piston groove. It is important that when installing the rail rings
you do not allow them to sit on top of this should/lip. If the rail rings are
not seated correctly on the expander rind then the oil ring will not fit in the
groove properly. After all the rings are installed on the piston, make sure
that each of the ring end gaps is about 120 degrees from each other.
4 Stroke Piston Kit
What is the
life of a two-stroke and four-stroke piston?
Piston life is relative to the operating
conditions of the engine, so no exact life expectancy can be given. In a
perfect world, about 20hrs is the max usage you want to try to get out of a
piston. Again, this is all relative to use, maintenance, and operating
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