Install Cylinder on Norton Commando Engine
Article by Mark Trotta
This article describes two ways to refit the barrel on a Norton Commando engine. If you're a one-man shop like me, method #1 works best.
With Motor In Frame (One Person)
Without a helper, this method is easiest - install pistons in cylinders, hang cylinder over motor, slowly turn crank with a wrench until connecting rods line up in pistons, slide in gudgeon pins and install outer circlips.
Sounds easy? It is, once you get set up.
Getting Started
The bracket is a piece of 1/8" scrap metal with holes drilled 1-3/8" apart. A hand-held drill will work, but they spin fast and take too long to accurately drill through metal. A drill press provides much better control and precision.
The threads in the barrel are 5/16" SAE. Whatever length bolts you use, make sure at least 1/2" are threaded into the barrel.
Before getting to the final steps of attaching pistons to connecting rods with the gudgeon pins, now is the time to test the pins for fit. Most (not all) will slide into the piston with a finger or two. If yours don't, you'll have to apply a little heat to the pistons.
At this point, install inner circlips with snap ring pliers.
Ring Gap Orientation and Spacing
Follow the manufacturer's instructions when installing rings. On this set of Hepolite R26730 (+020), top and 2nd rings are marked and face up.
Like all internal combustion engines, ring gaps should be evenly spaced around pistons. This is done to minimize the possibility of gases blowing down past the rings.
The factory service manual recommends positioning top ring gaps to front of piston body and the 2nd ring gaps to rear. The scraper ring expanders should face to the side.
One ring clamp is required. Squeezing the rings by hand also works, but the clamp method works quicker and with less hassle.
With the inner circlips pre-fitted, install pistons with rings in the cylinder bores.
NOTE: On 850 models, there is no piston orientation. On 750 models, pistons have a left and right.
The base gasket was adhered to the bottom of cylinder with a light coat of Hylomar RTV clear sealant. Before hanging, the pistons were pushed down into the bores until the gudgeon pin holes were clear.
I'm using coat hanger wire to hang the barrel from the frame. Note the foam and tape so as not to scratch the new paint!
Temporarily install rotor nut on the left/primary side crankshaft.
With a 1/2 Whitworth spanner, slowly turn the motor clockwise, which raises the con rods into the pistons.
If needed, lengths of wood may be used to help stabilize.
CAUTION: Before attempting to install circlips, stuff rags around connecting rods, so that if a circlip drops it doesn't fall into the crankcase!
Installing the outer circlips was easy because I have a good set of convertible snap ring pliers.
Before pushing the barrel all the way down, install the two rear nuts and washers.
They will not clear the bottom fin once the cylinder is flush with the cases.
By using this method of hanging the cylinder above the connecting rods, a single person can refit the barrel without drama.
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Cylinder Over Pistons
The procedure described in the factory manual is to mount the cylinder over pistons and rings. This method works best with engine out of frame.
Before I thought about hanging the barrel over the engine, I used this method (always with a helper).
If you're using ring clamps, tighten them as much as you can until you can just slightly move them side to side on the pistons.
Support Bars
Scrounge up several sections of wood (or plastic) of appropriate size to hold the pistons up. In the example below, a pair of rubber bands are holding the rear piece in place.
Some prefer gluing the base gasket onto the cases, others prefer gluing it to bottom of cylinder. Either way works, but be careful not to rip it.
Carefully lower barrel over pistons and rings, pushing the cylinder over the clamps smoothly and quickly.
If resistance is felt, STOP. Do not force it. Pull the barrel off and check clamp tightness.
Once the barrel is past all the rings, remember to start the two back nuts (with washers) before pushing it flush to the cases.
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Final Tightening and Torque Specs
With the barrel installed, double-check the base gasket all the way around. If all is well, tighten bottom nuts and top bolts evenly.
Torque the upper cylinder bolts to 30 lb/ft. Bottom 3/8" nut torques to 25, and the 5/16" nuts to 20.
"A man who has installed a British-Twin cylinder knows significantly more than one who hasn't." - Mark T
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