MAICO engines
MAICO engines.
Much of the maico fame is due to their engines and power output. The open class 440 and 490 engines have a reputation for having the best and most usable powerband of all bikes all times. Maico actually has several engines but we will focus on two: the old engine of the 70's and early 80' with a chain primary drive and therefore one shaft more than most bikes. And from 1983 the smaller compact more conventional engine that however never gained the same fame. It's an excellent engine though.
OLD
ENGINE
The older engine design has been called the best powerband ever, slickest shifting
mechanism ever made and everything from good to bad. This engine is easily recognized
by it's shape. From the ignition (right) side the engine case is long
but very thin. This engine has a few special features that makes it both durable
and easy to rebuild but there are a few drawbacks to. We start up front. These
engines are air cooled. The huge radial shaped fins with their rough casting
generates a whole lot of sound. There is no head gasket, only a copper ring
that can be used over and over again. The trick is to heaten it up on the stove
and put it in cold water fast. This makes it softer and as good as new. The
cylinder has no reed cage intake until 1981 (250cc) and 1982 (490cc). The piston
controls the intake timing. The cylinders have a steel sleeve that can be rebored
several times. The piston is a forged Mahle single ring. It's famous for beeing
expensive but worth every single dollar. The piston is a quality unit that should
last for a long time. There is a forged steel connecting rod with needle bearings
on each side. The first problem area is the needle bearing and wrist pin in
the crank. The big bores produces and enourmous pressure on the wrist pin. Therefore
the lubrication in the pre-mixture is crutial. Normally a two stroke motocross
engine can very well operate on 2-2.5% oil ratio. This is not sufficient for
the 400,440-490 engines. The problem is not the cylinder but the lower bearing.
They require high quality oil with 3-4% ratio. The crank rolls in two huge hefty
main bearings that simply cannot wear out from riding. Remember that these bearings
cannot deteriorate from the mechanical forces created by the engine. This is
unique in two stroke history. On the right side is the ignition which is a Motoplat
electronic unit. We won't discuss them more at this moment. On the left side
is a sprocket wheel with either two or three rows. This sprocket can wear out
if the chain is worn and the owner doesn't perform regular oil changes. This
is however not likely to occur. The wheel should be ok even if there is some
visible wear. The 250cc normally has a duplex (two row) chain whereas the 400,440
and 490 has a triplex (three row) chain. This chain is the main problem with
this engine design. The chain has to be changed now and then and requries fresh
oil at all times. Once the chain has strechened a bit it will hit the clutch
cover and produce a crack in it. Newer engines has a nylon piece in the cover
that can withstand this problem for a short while. The primary gearing ratio
makes the clutch rotates at a very high speed compared to practically all other
engines on the market. The clutch basket has a small diameter but is made of
steel and therefore stronger against wear. The clutch basket filing shouldn't
be necessary as it often is with aluminium baskets. The sprocket on the clutch
basket can wear just like the front one but can almost always be reused with
a new chain. The clutch has spring washers instead of normal springs. This is
a bit complicated but works once correctly adjusted and mounted. There are normally
20 spring washers that should be mounted like this: (())(())(())(())(()). In
pair of two against each other. This will result in the correct pressure to
prevent the clutch from slipping. The gearbox is in some perspective different
from most other engines too. First and foremost there are mostly needle bearings
instead of roller bearings for the shafts. The gearwheels are constantly engaged
which is called constant mesh. Once moved sideways the blocks on the side of
the wheels hooks into each other and locks that particular gear. The shiftforks
are good quality pieces but like most others they wear out. This is something
one can expect to change if the oil changes has been neglected. The shift forks
are guided by a flat steel plate instead of a drum with grooves like most engines.
The shifting mechanism is somewhat complicated when it comes to transfer the
shift lever movement to the guide plate. Keep an eye on that in order to achive
a good working gearbox. All in all the gearbox is made of good quality steel
and should last a long time. Like always the important thing is to give it clean
oil since the sintered clutch plates contaminates the oil turning it to an effective
grinding paste. And the next problem is wear on the bearings which allows movement
on the shafts and can damage the gearwheels and shiftforks. All bearings in
the maico engine is standard sizes and can be bought in any hardware store.
Problems:
BEARINGS, SEALS & CHAIN (1980 model)