Haynes' World is a regular feature that takes a look at what the staff at Haynes are doing with their cars, bikes and other vehicles. This time, Martynn Randall has an update on his Soviet-era motorcycle project.
Bike: IZH Planeta 350
Owner: Martynn Randall’s son
Getting the 1967 IZH Planeta 350 running properly didn’t quite turn out as I thought it would…
I stripped and rebuilt the motorcycle's carb, replaced contact breakers, checked the compression and fitted a new spark plug. It was still reluctant to start and would only continue running with the choke partially on. It definitely felt like a fueling issue.
I decided to keep it running to get the engine up to normal operating temperature. As the centre stand wasn’t working, the bike was on the side stand leaning over at quite an angle. With the engine quite hot, the exhaust note suddenly changed and clouds of grey smoke started belching from the silencers.
Eureka! I instantly knew what the problem was.
Motorcycle crankshaft repairs
The motorcycle's crankshaft oil seals had failed and gearbox oil was being sucked into the crankcase and burnt. It would also be sucking in air, which would cause the weak mixture.
Unfortunately, as with most two-stroke engines, in order to change the oil seals, the crankshaft must be removed.
A couple of hours later, I had the engine out and completely stripped. This revealed that the left-hand oil seal was indeed the problem. The rubber was rock hard and cracked.
However, I also found that the connecting rod big end bearing in the crankshaft (shown below) was quite loose and had excessive play, and both main bearings were worn.
The right-hand main bearing was not happy, and hadn’t seen any lubrication in a long time.
The wonderful Russian manual (translated poorly to English) advised that the crankshaft was ‘not repairable’, although a well known internet auction site does list new connecting rod repair kits from Eastern Europe. However, my son sourced a ‘reconditioned’ crankshaft assembly from a trusted seller in the UK for £65. Result!
So I rebuilt the engine with the replacement crankshaft, a Russian oil seal kit (£11), and a Ukrainian gasket set (£18).
Above is a pic of the ‘new’ crankshaft in place, waiting for the right-hand crankcase.
The official method of tightening the crankshaft sprocket bolt: a wooden rod through the exhaust port to jam the piston!
With the engine refitted, it was time to see if it was worth the effort.