TECH

Perspective on the New 750cc Ural Engine
by Sidney Pollard
photos by Michael Mardis
(click photos for larger view)

The new 750cc Ural motor is the best thing yet to come out of Irbit Russia and should make others sit up and take notice of Ural and IMZ.

The first one notices about the new engine is it's size, it is almost 3" wider than the 650. Also, the cylinders heads are rectangular in shape apposed to the old oval ones, the cylinders are square and aluminum apposed to the round cast iron ones used on the 650. The valve covers look a bit odd at first, but soon grow on you. Did I say the cylinders were square? Well, that is correct they are 78mm X 78mm, where the 650 was what is called over square 78mm X 68mm. A square design implies that the bore and stroke are equal but, yes the cylinders are square as to there outward appearance, and the bores themselves are some of the roundest ever to be produced by IMZ.

Improvements over the 650 are as follows for the,

750cc MOTOR and TRANSMISSION:

Much improved relibality.

HORSE POWER RATING 41 SAE/45 DIN.

TORQUE = 50 FT/LBS English, metric - a pile of Fig Newtons.

Cast iron cylinder liner, cast into an aluminum finned jacket for better heat transfer.

3 piece press fit crankshaft, designed to eliminate past failures due to web cracks.

Larger crank main bearings to spread out and reduce the stress/load on the main bearings, for longer life.

Redesigned valve rocker assembly for longer life with light weight alloy push rods.

New pistons with 8.8:1 compression ratio and chrome rings.

IMZ has reused the same crank case but, made some modifications to accommodate the new cylinders and crankshaft.

The over all machine work is so much improved that Ural no longer requires the strict 2500k break-in period. What is required here is that you drive it with much care at first, allow the motor frees itself up and don't lug the motor. The same as with all modern built motors.

Drive train improvements are as follows:

Higher output ratio gearing on 3ed & 4th gears allowing a higher cruising speed of 65 for the standard 4.62 FD.

Better machine tooling through thus once again reducing the break-in time.

A new drive shaft with course splines to reduce the chance of stripping out the drive coupling.

The tooling has improved so much at the plant in Irbit, that when I changed the break-in fluids I noticed that there where no metal particles to be found in the fluids. I even went so far as to tear apart the oil filter looking to see what it had collected, just a few specs nothing more.

What needs improvement is the alternator and they know this and are working on this. The unit itself should be replaced with a better quality product. The plant now assembles the alternator in house to assures better quality of the units used on Urals. The timing gear noise is always an issue with the Ural and can be eliminated with the use of a fiber cam gear. The cam gear is what drives the alternator therefore a fiber cam gear would isolate the alternator drive noise. It's true that fiber gears have a shorter life than metal gears but, it is not a big job to replace the gears and they should last for several riding seasons and many, many miles. This too is something IMZ is looking into.

Ural/IMZ is not only the largest builder of sidecar combination rigs, with better than 3.2 million units sold, they are now the best! The new 2002 Ural 750 is what Ural should have been when it was first introduced into the American market back in 1993. IMZ has worked hard to better it's product using the input it has received from the American's who love this old style classic boxer pulled sidecar. The Dnepr plant has closed and the CJ is now in very limited and soon to be discontinued production, so IMZ has the road to itself. I hope they can move ahead as fast as they can and still be able to keep it within the white lines, and not drop the classic sidecar from their production line-up.

Sidney Pollard