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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, evenMP Port work 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. Crank Pin Welded 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 Inner Cases Assembled 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.

Dave Custom Shipping CrateNow 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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