A shim in time…
Ed resorts to lathe work to improve his Izh
I’ve owned a lathe and a milling machine for more than 10 years. I’ve very seldom used them and often wondered about selling them. But I’ve always concluded that if did, I’d instantly regret it. In Staff Car Sagas (PC, August 2022), I described how I unbunged the blocked oil pickup and crankshaft oilways of my 2003 Izh Oda – which had suffered repeated oil pressure failures. Previous work after importing the car in 2016 had ironed out rusty brake pipes, an uncooperative ignition advance unit and a host of minor niggles.
The only problem left to address was a clonking and grumbling sound from the rear axle. I expected to simply adjust the crownwheel setting to reduce excessive backlash between it and the pinion. However, the gears were perfectly adjusted and the noise stemmed from the differential itself. It had been insufficiently shimmed, allowing the sun wheels to cock themselves on the driveshaft splines and in the differential cage.
There was, luckily, no wear or damage. Surprisingly only a single, standard size of shim is listed in the parts manual, so maybe the wheels or cage had been incorrectly machined. They’d certainly been very roughly machined, leaving a fairly shonky surface. I approached two firms to make custom shims.
The first interrupted me to state a minimum charge of £150 + VAT. The other described a rather laborious process that would take at least three or four hours at £50/hour + VAT and then told me it didn’t want the job anyway. After some thought, I decided to buy some shim steel via ebay and make two packing washers to supplement the existing ones.
Getting a feel for it
Placing feeler blades behind the alreadyshimmed sun wheels, I measured the combined end float (which was 0.3mm, but should be zero) then ordered 0.1, 0.125 and 0.15mm steel to hopefully cover all bases. I marked out the shims using dividers and cut a square out of the steel using tailors’ scissors. This I stuck to a flat block of aluminium using double-sided tape. I placed this in a four-jaw chuck in the lathe, and centred the cutting tool on the centre dimple that was created by the dividers.
‘All in all, an interesting job, and I learned a thing or two along the way’
A quick spin later, I took the block and its precious cargo back inside, flooded it with thinners and used a kitchen knife to gently lift the steel off the aluminium substrate. The only thing that remained to do was to dress the slight burrs around the edges using a fine, diamond knife sharpener. The 0.15mm shims fitted, but they gave difficult, lumpy rotation of the sun wheels, which were now too tight against the teeth of the planets. Next I made a 0.125 set. This was slightly ‘clicky’ unless the suns were pressed firmly against their seats, whereupon rotation was almost perfectly smooth and silent. That would allow for the running-in of any remaining burrs, I thought.
I reassembled the differential cage, bolted on the crownwheel and inserted it into the axle. The axle is a mix ‘n’ match of Volga, Lada and Moskvich designs and the differential cage is fixed directly to the axle casing. Thus, the crownwheel-pinion mesh has to be adjusted on the car, not on the bench. The technique, after loosely tightening the bearing caps, is to screw in the left-hand bearing stop to give a backlash of 0.07 to 0.10mm. Then you force it back the other way with the right-hand stop to give a slight preload to the bearings, stopping when the correct backlash of 0.15mm is achieved. The bearing caps are then torqued-up and the backlash rechecked.
I filled it with oil and took the Izh for a test drive. The clonking was gone, but an obstinate grumble remained when driving under load at higher speeds. Confident that the axle was (probably) not to blame, I changed the propshaft joints. These are the same as those on the Moskvich 412, spares of which I already had in the Museum. There it was: an arm of one joint, despite plenty of grease, had a corrugated bearing surface.
All in all, an interesting job – and I learned a thing or two along the way. The Izh has covered about 3000 relatively mellifluous miles since and I’m pleased to report that it hasn’t given a moment’s bother. And the lathe paid for itself twice over. Onwards and upwards!
■ practical.classics@bauermedia.co.uk