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| Batavus Laura Head
Shaving |
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| This is a 'HOW TO' on shaving the head on a Batavus
Laura M48 engine. If you find errors either in the text or content please
email me with the details. It's involvement and input from fellow Batavus
owners that will make these pages a great source of information for others.
Click on photos to enlarge. WARNING: These modifications are experimental.
I take no responsibility in the accuracy or damage this information or
modification may cause to you Bat. |
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Updated: 9/06/01
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The engine illustrated for head shaving is the Laura M48
engine that is found on the Batavus moped. These engines are under powered
and really respond well to increasing the compression. I've broken it down
into a three part series. The first part is how to make a lathe arbor that
will work with most moped heads. The second part is initial measuring of
the critical components and figuring how far you can go. The third part
is the actuarial shaving of the head. This procedure can be applied to
other moped engines. In fact I shaved .015 off the Avanti head using the
same procedure.
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Laura M48 engine
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PART 1
Lathe Arbor
The first thing to figure out is how to physically hold the head to
machine it. It can be done in either a milling machine or a lathe. I chose
the lathe for the simplicity of the set up. Once an arbor is made you can
do various types of heads with the same set up providing the spark plug
hole is centered in the head.
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| Turning a 5" long by 3/4" diameter shaft. |
The first thing to do is find a 5" long by 3/4" diameter piece of CRS (cold
rolled steel). Of course you never have the right stock for the right job
so I had to turn my shaft from larger stock.
Next, turn 3/4"(.750") of the end down to the diameter of 14mm or (.544")
which is the size of the spark plug. (Yes 14mm is .551" but you need some
thread clearance of about .007" so .551 - .007 = .544)
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| End turned down |
Before turning the treads, I cut 1/8" relief at the shoulder and end of
the arbor at a diameter of .480. This relief at the shoulder allows the
head to thread tight against the shoulder of the arbor. The relief at the
end of the arbor gives it a nice finished look and makes it easier to thread
into the spark plug hole.
Now comes the fun part, thread turning. The standard moped spark plug
is a 14mm by 1.25mm pitch thread. For anyone that doesn't like changing
their lathe over for cutting metric threads here's an observation. 1mm
= .03937 inches. Take the pitch of the tread we are trying to make and
covert it to inches. 1.25 * .03937 = .0492 The English standard 20 TPI
(treads per inch) is .0500 in pitch (1 inch/20). That's only .0008 difference
between the 1.25mm and 20 TPI thread pitches. I cut 20 TPI on my arbor
and it fit in the head like a dream. Don't let this little secret out of
the bag and your friends will be amazed that you know how to cut metric
threads on an old English lathe.
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Treads turned on the arbor to match the spark
plug.
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The arbor in use. |
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