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Bikernet - JIMS Double Barrel Pump Up


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I guess we'll just have to find something to keep the guys down in JIMS R&D occupied. When most folks would rest on their accomplishments JIMS just keeps breaking new ground, and this time it's a 95 inch barrel kit for twin-cams. This kit contains barrels, pistons, rings and gaskets, everything you need. The cylinders are made of aerospace quality 356-T6 aluminum, with high-grade cast iron sleeves. The pistons are made by Arias to JIMS exacting standards, and use a compression ratio of 10:1. JIMS tells us you can expect your horsepower to increase to between 85 to a 100. The kits are available in either black or plain aluminum finish.

We met up with Tom, at JIMS brand new R&D facility, and he managed to pull himself away from the hectic development pace long enough to go through this unbelievably easy install with us.

As with just about any engine modification, the seat and exhaust comes off first, (Photo 1) and, for safety's sake, disconnect the negative battery cable from the battery. 


Once the fuel line to the carb is disconnected and the tank bolts removed, the tank can be raised, and a block of wood placed in the tank well to hold it out of the way. This can be done with the crossover still attached, if you're careful. Be sure to use a small bungee cord to stabilize the tank (Photo 2). 

Photo 2

The carb comes off next, remove the cables (Photo 3) and set the carb aside.

Photo 3

Unbolt the manifold retainers and carefully remove the connector to the MAP sensor (Photo 4) before removing the manifold.

Photo 4

Now it's time to get down to business. Tom recommends marking the rocker boxes (Photo 5) because, even though they're interchangeable, it's best to re-install them on the heads they've run on. 

Photo 5

The rocker covers are now removed, and we're ready to pull off the rocker arms. Always pull the breather bolts out first (Photo 6), this is VERY important. 

Photo 6

These bolts extend into the heads, and, if taken out last, will strip the bolt holes in the heads. The rocker stand bolts are now removed, along with the rocker assembly, and we're left with the lower rocker boxes (Photo 7). 

Photo 7

Pop the rest of the lower box bolts and the head bolts are exposed (Photo 8). The four head bolts on each head come out and the heads can be laid on the bench.

Photo 8

You're now ready to pull off the old cylinders, but you've got to watch out for anything falling into the case. In order to keep foreign material out of the case, ease the cylinders up, part way, and stuff a couple of shop towels around each rod (Photo 9). 

Photo 9

Once that's done, go ahead and pull the cylinders the rest of the way off (Photo 10).

Photo 10

The old pistons can now be removed. The pistons use full floating pins and, once the snap rings are taken out (Photo 11).

Photo 11

JIMS pin tool can slide them right out (Photo 12).

Photo 12

The new Arias pistons can now be installed on the rods (Photo 13). 

Photo 13

Making sure not to slam the new pistons against the head studs, install the piston rings (Photo 14). 

Photo 14

New o-rings are included with JIMS kit and are installed now (Photo 15). 

Photo 15

Place the new base gaskets on the new cylinders (Photo 16) and then the new cylinder o-rings (Photo 17). 

Photo 16

Photo 17

We used a Snap-On detachable ring compressor to get the slugs into the cylinders (Photo 18). With both cylinders in place, it's time to get the heads back on.

Photo 18

With the heads in place, lightly coat the case bolts and bottom face of the cylinder head bolts with clean 20W50 oil. Start the head bolts onto the studs, short bolts on the left side, long bolts on the right. Tighten the four cylinder bolts with the left side rear first, then the left side front, next the right side rear, then the right side front to 7-9 foot pounds. Following the same sequence tighten each to 12-14 foot-pounds. Finally tighten each bolt, in the same sequence, 90 degrees (Photo 20).

Photo 20

The rocker boxes go on now. Replace the gaskets and set the lower box on and tighten the bolts (Photo 7) in a cross pattern, starting with the right front first. 

Photo 7

Be sure to use a small dab of medium strength Locktite on the bolts first. Tighten the bolts to 10-14 foot-pounds. The push rods and tubes are now put in place and the rockers are installed and torqued down using the Snap-On wrench shown (Photo 21). 

Photo 21

Make sure to replace the o-rings before the shaft assembly in put in place. The rocker arm shaft assembly bolts are tightened, a quarter turn at a time, using a cross pattern, until they are at 15-18 foot pounds, The breather bolts are tightened, also to 15-18 foot pounds. The rest of the rocker boxes can now be installed, remember the front and rear (Photo 22) and the bolts tightened in a cross pattern, starting with the middle bolts and torqued to 9-12 foot-pounds. 

Photo 22

Put the push rod tubes in place, replace the manifold and carb and spiff up your work, as we see Tom doing here (Photo 23) and you're done. 

Photo 23

You've now got 95 inches of serious v-twin power (Photo 24). 

Photo 24

Now it's time to take this puppy out and thrash it around a little. 

Later, Oz.

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