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By: Pete
Clyne
Let
me start off by saying this will NOT be a normal review.
This review will be a little longer than most due to
having substantially more information to talk about.
Back in December when we here at ATV Source.com contacted
Dave Moore at MP
Racing , we had intended to do a review on a
cylinder ported by him. This is when the fun
started for me. Dave informed me that if we were
going to do a motor for review, he wanted to do a
complete engine build, that way he can look at
absolutely everything and make sure its done his way.
This worked out rather well for me, because just a week
prior to talking with Dave, I blew my 250R's bottom end.
The 2nd main and countershaft gears exploded, throwing
shrapnel out of my case half, and ruining the case.
Dave suggested I send him my cylinder, crank, flywheel,
counter balancer, head, and some other misc. parts that
he would need while I looked for a bottom end. I
finally located an '85 bottom end and had it shipped to
Dave.
Dave first went to
work porting my stock '88 cylinder. As you can
see, his attention to detail is unmatched. Each
full race or methanol cylinder takes about 4 hours to
port. All done by Dave himself. The porting my cylinder
received is pretty radical porting and many find it
hard to believe that it can be trail ridden. Well,
it can, even
with a TT pipe. I trail ride every weekend with
the R. There
are a few tricks involved that allow this. One of
them is running extremely high compression, along with
some other small tricks that MP uses in their bikes.
Dave is the first motor builder I have seen that
actually takes his porting into the sleeve. This
makes sense if you look at the picture. An '86
head was used (the '85 and '86 heads used a better
quality aluminum than the later years). It has
been cut, re-squished, and o-ringed for the use with silicon
o-rings. The o-rings used cost about 2 dollars
each, rather than the 20 dollar o-ring kits you find for
most other popular aftermarket heads. It also
utilizes a custom Wiseco piston modified by Dave (cut
round boost port into piston skirt). The piston
and rod kit was generously supplied by DTR
Cylinder polishing was performed by David Welborn (phone
# 503-363-1957) at the cost of about $150. You
will also notice by looking at the ports that they have
been bead blasted, which really gives everything a nice
clean look.
My
250R's bottom end was also looked at and modified by Dave.
My OEM '88 long rod crank was getting a bit tired and
worn out after 13 years of service, so the crank was
split apart using a custom jig that Dave created, which
allows the tin cans that go around the crank pin to
remain intact. 
The OEM rod was replaced by an IMS Hotrod
unit. The bearings
were also replaced with new ones and the crank pin was
welded in to prevent it from ever backing out and
causing a catastrophic failure. My flywheel was
lightened from about 1068 grams stock to
968 grams. This provides for a faster
revving engine. My stock counterbalancer had some
damage due to a prior bearing failure. It was repaired
and also lightened. The bottom end was also thoroughly
inspected and a few minor parts that were worn were
replaced (mainly a shift fork). The cases were
bead blasted and painted OEM gray.
Now
that most of the machine work was done, it was time for
assembly. First, in went the '87 tranny into the '85
cases (yes my motor is a real mutt with different year 
parts). Then the shift forks and drum, crank, and
everything else that is needed before putting the case
halves together were installed. I previously sent Dave my '89
clutch update parts, my aftermarket clutch basket,
stator, and a few other parts that he would need.
All of this went in as well. On went the piston
and topend. Then the o-ringed head and exhaust flange.
It's a good idea when installing o-rings in this sort of
situation to lubricate the o-rings with Vaseline,
grease, or some other sort of lubricant. After assembly,
the engine was leak-down tested.
 Now
that the engine was done, Dave had a couple of small tasks
left before he shipped out the motor. One, of course, was
packaging and sending the engine. The other was
setting up the new Mikuni 38mm TM carburetor. It was prejetted with a 460 main, 65
pilot, Q8 passageway, and a 6F4J1 needle, and a custom
#2 slide (requires some machine work). With all of
this packed into a custom crate which is complete with
motor mounts, it was time to ship it out on its journey
to me.
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