OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Victa Lawn Mower Frames Victa 160cc mystery crankshaft drive side taper.

After much fighting and clawing to get my inch of progress (no thanks to Victa's tech support), I appear to have finally found the actual listed taper of the said drive shaft.

I learned from restoring OLD Harleys with "proper sprockets" that didn't quite fit the crankshaft taper, that obtaining a correct fit with correct preparation - makes an enormous amount of difference to the amount of power that can be transmitted through the connection.

OK pre Victa rapp.

For maximum taper joint strength.

Wash the said crank and gear in petrol - scrub and wipe with brushes and paper etc... rinse. Wipe clean. Removes all crap from parts - leaves slightly oily film.

Wash and clean parts in mineral turpentine (only need a bit of it) to remove oily film from petrol.

Wipe clean from wet with unused toilet paper.

Cleaning may be repeated with acetone or acetone used as the second wash.

Use recommended thread - locking CLEANER / PRIMER compound.

(the fumes from these will tend to eat your lungs out)

Use HIGH STRENGTH shaft locking compound - apply a THIN film to each surface, all over with applicator - cotton bud etc..

Make sure all parts are in alignment - eg. shaft key etc.

Make sure all parts are braced for tightening.

Make sure all tools are at hand.

Join parts - tighten nut to required torque specification - perhaps a wee bit more (not recommended on specialist components).

Leave to set.

AN exceedingly clean tapered joint, with a high strength bonding agent will easily impart a very high strength to the joint - that is capable of passing about 3 to 5 times the power that a slapped together slightly dirty / oily joint is capable of passing.

OK the Victa specs.

http://bluemm.blogspot.com/2005/11/specifications-for-early-125cc160cc.html

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Friday, November 11, 2005
Specifications for early 125cc/160cc Victa 2 stroke mower engines
Bore:

* 125cc .............................. 53.975mm (2.125")
* 160cc .............................. 61.493mm (2.421")

Stoke ...................................... 53.975mm (2.125")
Piston taper:

* Bottom of Skirt -
o 125cc ......................... 53.848mm (2.120")
o 160cc ......................... 61.366mm (2.416")
* Top ring land -
o 125cc ......................... 53.721mm (2.115")
o 160cc ......................... 61.239mm (2.411")

Piston rings:

* Numer .............................................. 2
* Size -
o 125cc ...... 2.381mm x 53.975mm (0.093" x 2.125")
o 160cc ...... 2.381mm x 61.493mm (0.093" x 2.421")

Big end bearing type:

* Early models ......................... 15 steel rollers
* Late models ...................... Caged roller bearing

Little end type:

* 125cc .................................... Bronze bush
* 160cc -
o Early models ........................ Bronze bush
o Late models ............... Needle roller bearing

Connecting rod material ................ Hardened alloy steel
Crankpin material ...................... Hardened alloy steel
Crankshaft type ........................ Alloy steel forgings
15 deg taper on drive end
0.5 in B.S.F thread both ends
Crankshaft main bearings:

* Type .................................... Ball bearing
* Size -
o Magnet side ................................ 20mm
o Drive side (early models) .....20mm inner 17mm outer
o Drive side (late models) ..20mm inner 20mm L.D. outer

Crankcase oil seals:

* Drive side (early models) ........................... 17mm
* Timing side (early models) .......................... 20mm
* Both side (late models) ............................. 20mm

Ignition timing .............................. 3mm (1/8") btdc
Breaker point gap ............................ 0.50mm (0.020")
Spark plug gap .............................. 0.635mm (0.025")
Spark plug type ............ Contact your nearest Victa dealer
Fuel requirement ......... 2 stroke petrol-oil mixture (25:1)

RPOO DPOO, you have supplied some excellent information there - I haven't seen it before. A couple of points/comments:
When preparing to assemble a tapered joint, begin by ensuring the parts fit together with a very high contact area. This means no burrs or dents on the parts (dents are always surrounded by raised up areas: that is where the displaced metal goes). When both parts are smooth and you think they fit, paint the male one with bearing blue (texta if that's all you can get), assemble gently and disassemble. Look at the blued area to assess the contact percentage, and find out where it does and doesn't fit. Damaged areas are repaired by localised fitting (scraping or filing). Poor overall fit may require lapping the parts together, or throwing one of them away.
Your information says the crankshaft uses half-inch British Standard Fine threads in both ends. This is a thread that has been obsolete since before the Second World War, and you have little or no chance of getting taps or dies for it, let alone bolts, except at a swap meet or flea market.
You have said ignition timing is one eighth inch BTDC. Do you mean measured by the piston position (1/8" below its highest position) or the flywheel position (1/8" rotationally before TDC)?
If someone can answer these questions, I think this post will be very useful in the Outdoorking archive.

In relation to the BSF nuts, you can still buy these brand new from most nut and bolt suppliers, I purchased 10 nylock 1/2 inch BSF nuts not long ago.

Prettu sure the crank case bolts are BSF as well, as I had trouble with any imperial or metric nut fitting at one point.

Yeah the properly lapped and mated joint faces is THE business... sorry forgot to mention that - Twas 3am-ish.

Lapped and ground with a No 10. Cornish winding engine balance beam bearing OLD beach pumice lapping compound - that is the gear...... I have cans of it at $11.99 per 250 grams.

Ummmmm the 3 millimeters BTDC timing point..

I'd say given the machinations of a nice hot engine, running at say 2/3 maximum RPM, the bore diameter and stroke, the mixture turbulence, the flame speed, and my general knowledge of the timing of mixture ignition of infernal combustion engines etc., etc., etc.. I'd say that it refers to the piston location BTDC and not the crankshaft position.

Ignition timing for optimum power - well 3mm before TDC, on the piston, that I think would relate to about 10 or 12mm on the flywheel radius - which also sounds about right.

Tho I do not know if the 3mm BTDC is right either.

Basically the suck it and see approach is to fit a water brake to your engine such as a part submerged marine propellor in water or a generator with load, or spray a fixed solid stream of of water into the rotating mower blades at a shallow angle etc., and to run the motor at say 2/3 maximum speed and find the point by adjustment of the points - where the motor pulls it's hardest and does not slow appreciably.

This simple test is "the way" to figure out the most efficient settings for the engine.

Kind of like running a lathe - it all comes down to the amount of metal you can removed in Kg per hour. It is calculated by the amount of electricity going in and the amount of metal going in the waste. The complex algorithm is all the things like feed rate, depth of cut, surface speed / RPM, cutting tool materials, coolants and surface finish etc..

The issue with motor mowers is how much physical material can be sheared off and driven through the output chute, at a specific blade speed, at a given feed rate, for a specific quantity of fuel, in a specific time interval.

This is it in a nutshell.

Although the standard 2 stroke engine really is a piece of.... has much room for improvement; a properly set up engine will cut more grass for less fuel, in less time, than a clapped out engine running worn down blades, with worn engine seals, bearings, rings and piston, a far too rich mixture, and with incorrect timing.

(toss in oil viscosity - deposits in the cylinder, head and exhaust ports etc.)

It's not ONE specific item, it's the combination of all the events that determine the most efficient conversion of chemical energy into kinetic energy.


I did not write the article - the main issue in (lifting) re-posting that Victor Specifications information, is that it has the drive side shaft taper listed on it - whichI am interested in.

And given the transitory nature of life and the web, thought it best to "copy and past it" here - before the webpage submerges never to be seen again.

Other than that - I have NO idea about the validity or otherwise of any of it.

Not like I am a fool - but I have not cross checked any of it, I don't have the factory blueprints and engineering specifications....

The only Victor manual I have - is a few pages of a shitty Haymes (?) manual photocopied from a pubic library.

BUT - in an overall sense; most of that information APPEARS to be correct - though a touch limited for my liking.

Speaking of grumpy old men.....

Someone was selling 49cc engines online - cheap.

So I thought I'd ask a former buyer IF he thought the engine was a decent product - like so; and have a LONG slow think about the answer:

With the little 49cc engines, I gather that it may have a centrifugal clutch and a single speed reduction gear box.

What is it's peak power output, and what is your impression of it?

Does it appear to be a quality product or just chinese junk?

Would you buy a second one?

The answer:


(Note: the motors do come with a manual)

It does have a single speed reduction gearbox and a centrifical clutch it is not a piece of Chinese junk. And i most certainly would buy another one because it also looks BEAUTIFUL! and i havent put it on my gokart yet so i dont know the power! Hope that answered your questions.


OH good.....

The ignition timing of engines that don't have speed-dependent timing (either centrifugal advance or computer-mapped spark timing) is usually determined by the need to be able to start them without kick-back on the starter. If the flywheel is heavy enough, 10-12 degrees BTDC is usually achievable. That is insufficient for maximum power at high speed, unless the engine has a very fast-burn combustion chamber: 4 valve hemispheric for example. For a side-valve mower engine, the appropriate timing for maximum power would be around 35 degrees BTDC - but then you couldn't start it. Similar outcomes happen for crude 2 stroke engines such as are used in lawnmowers. The burn rate is not as slow as for side-valve 4 strokes, but it's pretty slow due to poor scavenging. Poor scavenging has the same effect that a large dose of EGR (exhaust gas recirculation) has on an emission-controlled car engine at part throttle. If you've ever driven a car with a stuck-open EGR valve, you'll remember the experience.