OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Victa Two Stroke Engines Engine rebuild - Crankshaft float

I have just rebuilt my 160cc 2-stroke engine (70's series)
- Cylinder rebored / new piston (+020) new crankpin and rollers / new gudgeon and needle bearing / new crankcase seals and bearings.
My concern is that I've noticed that I have a variable float on the crankshaft and this worries me a bit!
E,G:
- With the piston at top dead centre, the crankshaft does NOT float in the crankcase - its nice and firm with no lateral movement.
- BUT with the piston at bottom dead centre, the crankshaft floats within the crankcase by about 1.5-2 mm (i haven't put a dial indicator on it as yet to make a precise measurement but there is a distinct kock when I force the crankshaft back and forth in the crankcase.
My queries to the forum are as follows:
1. Is a bit of crankshaft float permissible and if so, are there limits.
2. If crankshaft axial movement in the crankshaft is not permitted, what is the best way of removing it (Eg. Refacing the crankcase faces to obtain a tighter fit / installing shims behind the crankshaft bearings or spacer sleeve between the two drive end bearings?
Any feed back would be much appreciated.
I don't want to launch into recommissioning the engine after I've done all this work only to destroy the bottom end due to excessive crankshaft float.

- BUMPS

Hi Bumps,

This below is the workshop manual that should be able to help answer your questions. it covers the 125cc and 160cc engines.

THx Bruce, I've taken a careful look at the manual but cannot find any reference to permissible crankshaft end float tollences or any instruction on how to adjust the end float. As mentioned in my original post, I reckon I have end float of 1.5 to 2.0 mm, sufficient to make a distinct clunking noise as I hand force the crankshaft in and out of the crank case....... Just doesn't seem right?

Agree with you. Been trying to fathom why your motor has no crank float at TDC yet has a couple of mm at BDC.

Thinking maybe the conrod is bent so the axis of the big end isn't parallel with the little end axis but that doesn't explain it. Or the flywheel edge is kissing the crankcase at TDC but there's nothing to kiss against at BDC. Or ???

I worked out that if I put a 0.8 mm thick shim (washer) between the Crankshaft and the bearing on the NDE (Magneto end) and pulled up all the crankcase bolts then the end float was eliminated. I used a set of feeler gauges between the crankcase halves to determine the shim thickness. All good now. I guess Victa's manufacturing tolerances were to blame but its a pit the subject wasn't covered in their repair manual that Bruce kindly sent me. If i seize the bottom end on start then I'll repost.
P.S: The end float variation between TDC and BDC may have been due to me not having the crank case bolts not fully torqued.

Hi Bumps,

I suggest that you check your crankshaft alignment because if it is out more that two thow you will have issues.

We used to split the crankshaft and replace the conrod bearing and pin and then realign the crankshaft so that it was only out less than one thow out.

Hi Bumps,

Just a warning about the shim , it should be on the pto end of the crank and not the flywheel end.

You shim the PTO (blade) end instead of the flywheel end because on a vertical shaft 2 stroke.

The major thrust loads and wear happen at the PTO end
The flywheel end is relatively stable and lightly loaded axially
Shimming the PTO side keeps the crank positioned correctly under real working load

When spinning, the blade creates:
Downward axial load (from gravity + airflow lift effects)
Up/down thrust from cutting impacts
Gyroscopic and vibration forces

All of that pushes and pulls on the crankshaft at the PTO end, not the flywheel end.

Over time, this causes wear on the lower crank face and bush/bearing surface.

When you shim the PTO end:

You take up the slack right where the wear occurred
You re-center the crankshaft in its natural running position
You maintain correct:
Bearing/bush alignment
Oil film clearance
Crank stability under load

A lot of the motors I have, have so much end float the flywheel starts to rub on the coil plate , see image below.

So it always pays to lift the crank back up a bit to compensate for wear.

Make sure the round shim is a fair bit smaller than the bearing.



So why still not full size?

Even though it’s a ball bearing, lubrication still matters because:

The inner race isn’t sealed against the crank
Oil/fuel mix still needs to:
Get between shim, crank, and bearing surfaces
Prevent fretting and galling at contact points

If you used a full-size shim that completely matched the bearing face:

You could trap oil out of that interface
Create dry rubbing surface between bearing and shim
Increase heat and wear on:
Crank face
Shim
Bearing inner race side


You want the shim:

Slightly larger than the crank shoulder, but smaller than the bearing inner race

Inner diameter (ID):
Close fit on the crank (not sloppy, not tight)
Outer diameter (OD):
~1–2 mm larger than the crank shoulder
Still clearly smaller than the bearing inner race

I had a damaged crank the other day, flywheel side , worst one I've seen on a victa that's still together in one piece, they
must have run the motor with a loose flywheel.


Cheers
Max.

Excellent reply Max and totally understood.
I did drill 8- 1/8 inch holes in the shim face for bearing lubrication purposes.
I'll move the shim as suggested.
I guess Mr Victa never imagined in his wildest dreams that we would still be using his engines 50 (+) -years down the track so shaft facial wear was resulting and float was never envisaged so was never added to the repair manual.
Again, brilliant reply mate! - It perfectly addressed my issue,

- Bumps