OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines Split the crankshaft

Hello. Can someone point me to some instructions on splitting the crankshaft on a victa 18 (125cc). I want to replace the big end bearing. Are spares available?

Is this topic taboo?

hey man , ive got a few books around with detail on crank service just got to find it , as far as i know you should still be able to find a suitable replacement bearing

If you require big end bearings I would suggest contacting the online store as they still have a few parts available for the 125cc engines including the rebuilt crankshafts.

They have an alloy conrod with bearings for a 160 but dont say if that is a torque flight or full crank. If it is for the full crank, is that the same as the 125? IE has the 160 the same stroke as the 125?

Jack,

The conrods are different on the 125cc and 160cc engines. If you post a picture of your crank shaft it will help.

Hi Jack, and a warm welcome to the forum.
It's nice to have you aboard, as we all like to learn new things and tinker here.
Instructions for posting pics using our inline uploader and be found HERE

Once again Jack, to OutdoorKing.

Ok Bruce, here is a photo of the crank. It is mounted on my lathe because i was milling the output shaft to take a variator. The project is to use the motor on a 1950 french motobecane mobylette. Since the whole crank fitted on the lathe I no longer need to split it. Out of interest, here is also aphoto of the original Moby engine. It is a similar design and even uses the same size main bearings (availab

le from SKF). Maybe Victa and the Motobecane copied the Villiers design.

Jack, I'll make the obvious comment in case someone sees this picture and isn't aware of the limitations imposed by that setup. I recognise that you know about the issue, but others may not.

Because this is a built-up crank made out of multiple pieces pressed into each other, aligning the two sides of the crankshaft (flywheel side and output shaft side) is done very carefully with V blocks and indicator, to get the two sides into alignment so they can run in the engine's main bearings. Consequently any torsional load applied to the tailstock side while the crankshaft is held in the chuck, might twist one or both ends of the crankpin where it is pressed into the webs. This would cause misalignment of the flywheel shaft relative to the output shaft. That could be corrected by setting up the crankshaft again with the V blocks and indicator, but any machining you had done in the meantime on the tailstock side of the crankshaft, would then run out of true. With this type of setup you can only perform conventional lathe-turning operations on the side of the crankshaft that is held in the chuck.

Thanks. I understand your concerns. In my case the old lathe is driven by a leather belt that slips as soon as anything bites. I saw on youtube a guy splitting a two stroke motorbike crank by cutting througt the big end with an angle grinder then pressing each side out. Then i guess you could mill a new crank pin if they are no longer available.

I haven't actually taken an old motorcycle built-up crank apart, but I'm told the crankpin was a simple turned bar, and the webs were shrunk onto it, then the unit was aligned under a press. That is certainly how they looked to have been made: the visible ends of the crankpin were round. Some of the modern bike engines are still made that way.

Jack,

To separate the two half's of the crankshaft is fairly simple. You just need a press to push the pin out and then replace the pin and bearings. Once that is done all you need to do is realign the two haves so that they are about .001 out. I have done a few in the past and they say that you can be anything up to .003 out.

Thanks Bruce. Im going to look around for a junk crank and practice on that first. Do you heat the counterweights?

Jack,

The answer is NO.

how many tons will you need a shop press to be to remove the the pin of the crank shaft that goes through the connecting rod.
thank you,

Sorry dmtr, never pushed one apart, but I have done buckets of Enfield single cylinder cranks. The crank pin in these has a shoulder on it so that once pressed back together the wheels come up against the shoulder and this gives the correct spacing of the wheels and the correct clearance on the conrod. I have a jig that holds both wheels in place so it is true once pressed back together. After that I check them in the lathe for trueness. I don't know if the Victa pin is the same but if it has a shoulder each wheel has to be pushed outwards to split it. I think a 12 ton press should handle it

G'day folks,
There's a description of the procedure in this Repair Manual excerpt; https://www.outdoorking-forum.com.au/pages/V...icta%20Workshop%20%20Engine%20Manual.pdf - pages 9-10.

Victa used to offer the crankshaft jig pictured, but the job can be done without it. It's just more time-consuming; the Victa crankpin doesn't have locating shoulders.

Victa suggest that a screw press could be used, so any 5 tonne or above hydraulic press would do the trick.

Thanks Gadge, I guess you just press it together and center the pin in the wheels and the thrust washers give the rod the clearance it needs. Cost wise it is not something I would probably ever consider, I still have full crank motors under the house I picked up about 35 years ago and with a set of rings they would probably run, might need a couple of seals maybe