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Joined: Jan 2016
Posts: 7,861
Likes: 184
SENIOR TECHNICIAN
So Max,
why do I have massive kickback problems with my PT's on 24 bases. They need at least 1kg added to the crank to prevent them kicking back and near breaking my fingers

Joined: Sep 2015
Posts: 2,432
Likes: 191
SENIOR TECHNICIAN & HISTORIAN
G'day Norm,

I thought we talked about this on a lot of occasions , that was why I made the PT video to show you don't need a lot of weight
on a PT to stop it kicking back under normal circumstances.

As we know



Flywheel Mass and Engine Dynamics:
The flywheel on an engine serves several important purposes: it helps smooth out the delivery of power from the engine, maintains momentum during the power stroke, and provides mass to aid in starting. The larger the flywheel mass, the more inertia it has, and the smoother the operation of the engine can be.

Direct Crankshaft Connection:
In a mower where the blade plate is directly attached to the crankshaft, the flywheel mass is effectively utilized throughout the starting process. The engine and blades are directly linked, meaning that when the engine gains momentum and starts firing, this momentum directly translates into rotational speed for the blades. The inertia of both the engine and the blade plate works together, making starting smoother and minimizing potential kickback.

V-Belt Drive System:
In a V-belt drive system, the engine's rotation is transmitted through the belt to the blade plate. This means that the mass of the blade plate does not contribute effectively to the flywheel effect because the load (the blade plate) is not rigidly connected to the engine.
When starting, the engine is attempting to overcome the resistance of the blade plate, but the V-belt tends to absorb some of the energy required to start the blades turning. As a result, the effective flywheel mass is reduced because some of the energy that would be contributing to inertia (as seen in a direct connection) is dissipated through the belt system.

Added Flexibility and Loss:
The flexibility of the belt system means that not all the rotational force generated by the engine is transmitted immediately to the blade plate. Slippage or tension variations in the belt can further reduce the effective mass that contributes to inertia during startup.
Additionally, if the blade plate has a significant mass itself, it requires more energy to start moving. The V-belt drive can cause a lag or delay in how effectively this mass contributes to the overall inertia during startup.

A V-belt drive system separates the engine's power delivery from the blade plate, which diminishes the effective flywheel mass during starting. The inertia and benefits of flywheel mass aren’t fully realized because the engine's energy isn’t transferred directly to the blades, leading to a potential for increased kickback and reduced starting efficiency compared to a direct crankshaft attachment.

I suggested adding mass to the crank on the PT crank with a v belt drive to overcome the kick back problem but that's not
the only way to overcome the kickback problem.I've suggested other ways before but because you had the weight working
you weren't interested in trying something else ,which is fair enough.



Retard Ignition Timing:
Retarding the ignition timing can help reduce the likelihood of kickback. If the ignition fires later in the compression stroke, it allows the piston to move down before the combustion pressure can push it back up, minimizing the abrupt force on the starter mechanism. However, this may also affect engine performance, so finding the optimal timing is essential.

Adjust Decompression Mechanism:
Decompression Timing: Modifying the decompressor to activate later can be effective. A decompressor helps relieve cylinder pressure during starting, making it easier to turn the engine over. If you delay its activation until the engine is at a point where it has started turning over, the compressive force can be reduced, effectively lowering the likelihood of kickback.
Automatic vs. Manual Decompressor: Consider utilizing an automatic decompression system that engages during starting but only releases after startup. This allows maximum assistance during start without affecting operation once the engine starts running.

Starter Engagement Mechanism:
A more sophisticated starter engagement mechanism can help manage the initial load on the starter. A system that smoothly ramps up the tension in the belt or utilizes a soft start can reduce the kickback effect.

Using an Anti-Kickback Starter:
There are starters designed specifically to minimize kickback. These starters can incorporate features like a ratcheting mechanism that allows the starter to disconnect under certain load conditions, preventing the rotational forces from being transmitted back to the starter cord.

Improved Belt Design and Tensioning:
Review the design of the V-belt drive. Using a belt with different material properties or improving tension management can help ensure a tighter grip and reduce slippage. Proper belt tension can minimize energy losses and allow for better power transfer, also aiding in smoother starts.

Flywheel Design:
If you cannot add weight, consider designing a flywheel with a different configuration. A flywheel with more mass towards the edge (increased rotational inertia) can store more energy and provide smoother power transmission, to help eliminate kickback.


Cheers
Max.

Joined: Jan 2016
Posts: 7,861
Likes: 184
SENIOR TECHNICIAN
Yes Max,
Adding weight to the crank is the way to go, but it is very time consuming for me on my little lathe. I did have a full crank Tilta -Cut that suffered violent kickback and I ended up adding weight to the crank and that solved the problem. Once they have this additional weight they start easier and have more power because of the extra spinning mass

Joined: Dec 2024
Posts: 14
Novice
Hi All,

Day 3

With Kill Swicth bypassed, Primed 5 times and now in the cold position it fired on the 3rd pull. Did some lawns for half hour and now similar to before will not start even though I let it cool down for an hour.

So I don't know what to do next. I started my green base 2 Stroke it started first go runs at 4100rpm. I can leave it rest for an hour and it will start in the run position first pull. It might rev a bit high , but I might need to do the brass washer trick to slow it down a bit.

I might do a heart transplant and use this motor on the newer base.

Joined: Jan 2016
Posts: 7,861
Likes: 184
SENIOR TECHNICIAN
Nothing new about any of this Hazzaman, I think with worn rings the bore expands slightly and the worn rings just can't create enough compression.

Hi Max,
I had a GCV160 Honda that was giving me big kickback problems on a 24 just as bad as the PT's do. I'm not sure if they lightened the crank on the GCV's but all I can think of. I fought it for a few days trying to add weight to it but couldn't hold them tightly enough in position so ended up pulling the motor off, put it on a standard Victa base and out the door. The bloke sent me a text a few days later saying he was happy with the mower and how well it ran. What I don't understand is why I don't have kickback problems with the Deutschers apart from the bigger ones with the cam issues

Joined: Sep 2015
Posts: 2,432
Likes: 191
SENIOR TECHNICIAN & HISTORIAN
Hi Harry,
It could be compression too low when hot but you really need a compression tester to check that .

Ignition Coil: If the ignition coil is getting weak when hot, it might cause intermittent starting issues. You can test for spark when the engine is hot.

Compression and Engine Condition

Compression Check: Use a compression gauge to ensure the engine has adequate compression. .

Air Leaks: Check for air leaks, particularly around the intake manifold or carburetor gasket. An air leak can lean out the mixture and make it harder to start.

Possible Considerations

Overheating Issues: If the mower is overheating, it can lead to "heat soak" issues, where it gets hard to start after being turned off briefly. Check for blockages in the cooling fins and ensure the engine is not excessively dirty.

Cleaning and Maintenance: Regularly clean the air filter and ensure it's not blocked, as a dirty air filter can affect performance.

I'd check fuel flow when it won't start as sometimes the fuel cap breather doesn't work ,also when you turn the mower off turn the
fuel tap off that will rule out over fueling.

Hi Norm,

I'm sure you would have Deutscher kickback problems if you used a Powertorque or the Honda motor.

When you look at my video of starting the Powertorque without a blade plate the engine spins fast from the starter cord
but I remember starting Victa 24's with the side pull starters and they were so much slower to spin over as you just end up getting
drag from the v belt drive turning the blade plate,this just adds to a kickback problem.

You can't compare one motor that doesn't kickback to another that does unless you know all the specs and condition of the motors as there
are a few things that contribute to kickback.List below of specs that can be changed so the engine can suit other applications.


Compression Ratio: Higher compression ratios can lead to stronger kickback. A higher compression means that the engine requires more force to turn over, which can cause the starter mechanism to experience sudden reversal when the ignition occurs.

Ignition Timing: Incorrect ignition timing can significantly contribute to kickback. If the spark plug fires too early while the piston is still rising (before top dead center), it can lead to a violent reaction that causes the engine to kick back.

Flywheel Weight: A heavier flywheel tends to smooth out the rotation of the engine, helping to prevent sudden changes in momentum that can lead to kickback. Conversely, a lighter flywheel may exacerbate kickback.

Crankshaft Design & Weight: The design and weight of the crankshaft can influence the inertia during startup. A heavier crankshaft may absorb some of the shock associated with kickback, whereas a lighter one may not.

Starter Type: The type of starter (manual pull starter, electric starter) can also affect the experience of kickback. Manual starters can provide less mechanical advantage than electric starters, potentially leading to more noticeable kickback.


Fuel Mixture: The air-fuel mixture can affect engine performance. A rich mixture may lead to lower temperatures and incorrect combustion timing, which can contribute to kickback.

Engine Condition: Worn components, such as valves, piston rings, and bearings, can lead to inefficient combustion and increased likelihood of kickback.

Cold Engine Effects: Starting a cold engine can change its dynamics. Increased friction and oil viscosity can contribute to the behavior of the engine when it first starts, potentially increasing the chance of kickback.


Factors Affecting Kickback Due to Cam Design

Camshaft Profile: The shape and design of the cam lobes influence the timing and duration of valve opening and closing. A more aggressive cam profile can result in quicker valve motion, potentially increasing the likelihood of kickback if the engine is not designed to manage such forces effectively.

Timing of Valve Events: If the camshaft timing (when the intake and exhaust valves open and close relative to the position of the piston) is not optimized, it could lead to back pressure during the compression stroke. This can create resistance when attempting to start the engine, leading to kickback.

Compression Ratio: The cam design can influence the effective compression ratio of the engine. Higher compression ratios can lead to increased resistance when starting, resulting in more potential for kickback. Camshafts designed for performance often increase compression at specific points in the engine’s cycle.

The design of the decompressor in a small engine can play a significant role in reducing or eliminating kickback during starting.

Yes the Honda 4 stroke crank doesn't look to have much weight out from the main shaft ,the early Victa full crank has a lot more
outer weight on the crank ,If adding weight to a powertorque is time consuming why not just fit the full crank 2 stroke motors
to the Victa 24 mowers.


There are a lot of different specifications a factory can change on a motor to stop it kicking back when starting when used in
other applications .

I see a lot of people that have an original working mower from the factory then when the engine is worn out they just take an engine
that is not to the factory specification to suit their mower and fit the wrong motor then it kicks back when starting.

Then you end up with people selling cheap mowers that don't run.

Cheers
Max.

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Joined: Jan 2016
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SENIOR TECHNICIAN
Hi Max,
fitting a full crank motor to the later 24 bodies is not straightforward, I have drawn up a sliding plate that should allow me to fit F/C motors on the later bodies but I would need to get them laser cut and it all ads to the costs and at this stage I am not 100% sure it will work

Joined: Sep 2015
Posts: 2,432
Likes: 191
SENIOR TECHNICIAN & HISTORIAN
G'day Norm,

Looking at the pic below it just looks like you get a flat 1/4 inch plate and drill the holes to fit the PT holes in the base then
drill 4 holes for the full crank motor and drill a centre hole then make the adjuster for belt tension.



Cheers
Max.

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Joined: Jan 2016
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SENIOR TECHNICIAN
Yes Max,
I was thinking of going the other way putting PT motors on the F/C bases. The PT motor is great on the 24's once you get past the weight problem on the crank and I have a lot more PT motors here than full cranks. I have a lot of 6mm plate here but the only way I can cut it is with a grinder as I don't have a plasma cutter. Think I will have to get one

Joined: Sep 2015
Posts: 2,432
Likes: 191
SENIOR TECHNICIAN & HISTORIAN
There was a Victa collector not long ago selling off his full crank 2 stroke mowers for $5. each Norm except they
were interstate.

May as well use up some PT motors if you already have good ones.

The 6 mm plate isn't too difficult to cut with the 9 Inch Angle Grinder ,it's just the cutting discs don't last that long.

Joined: Jan 2016
Posts: 7,861
Likes: 184
SENIOR TECHNICIAN
It is cutting the round hole in the plate for the motor to to sit through is the problem. Hole saws will do it but it is hard work

Joined: Sep 2015
Posts: 2,432
Likes: 191
SENIOR TECHNICIAN & HISTORIAN
A 30mm hole cut with a decent hole saw like Sutton through 6mm plate tales about a minute and a half if you drill a clearance hole first
Norm.

Mark the hole with the hole saw then drill a 10 mm hole or bigger on the edge of the circle this will remove the swarf ,I also use an
oil can for cooling and Lubrication.

You can use this method to drill through 2 inch thick steel .I usually use an old Sher 2 speed drill set on slow speed with a 1/2 inch chuck.

Cheers
Max.

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Joined: Jan 2016
Posts: 7,861
Likes: 184
SENIOR TECHNICIAN
Yes Max,
The hole to fit the bottom half of the crank through is about 80/90mm in diameter. I do all that sort of drilling in my drill press but plasma for that stuff is so much easier. Problem is all this stuff adds up and as you know there is no money in fixing mowers. I need a plasma, a bottle of migshield gas and a bottle of oxy and a bottle of acetylene all ads up and it is hard to justify when I am nearly 80 years old

Joined: Dec 2024
Posts: 14
Novice
Hi All


As I have an older 2 Stroke Green Base Rapier 2 Blade Lawn Mower. What I might do is use the 4 Blade System from the newer Lawn Mower on my older 2 Stroke Green Base Rapier 2 Blade System Lawn Mower.

This way I can keep cutting the lawn without worrying about not being able to start it after turning off for 10 minutes.

Thus, this will allow me, plenty of time to pull it all apart, clean everything and source a new Throttle Cable and G4 Carby as I am now thinking the issues stem from there. If i pull everything apart, I can do the Large O-ring replacement and also see if I can borrow a proper Compression Tester to check compression.


I will persevere, it might take me months, but I will try to remember and post what happens

Joined: Dec 2024
Posts: 14
Novice
Hi All,

A small update.

I purchased a cheap Compression Tester from Ebay. So I can test it's compression.

With the Decompressor in place , I get 25psi.

Without the Decompressor and the hole plugged, I get 35 psi.

Is these figures correct for a Powertorque Victa 2 stroke lawnmower.

Also I pulled off the Carby and noticed I have quite bit of dirt inside the Carby air intake. It looks looks very dirty from dirt being sucked in. It seems the clamp that goes around the hose and Carby does not Seal enough or it is getting sucked in from the top of the hose.

I am hoping for advice from someone that knows what should the psi of these lawn mowers should be. If it is too low I can pull it all apart and replace the O-rings and Piston Rings.

Thanks
Harry

Last edited by Hazzaman; 15/02/25 12:30 PM.
Joined: Sep 2015
Posts: 2,432
Likes: 191
SENIOR TECHNICIAN & HISTORIAN
Hi Harry,

The lowest compression that I would use is 50 psi with the comp tester on the end of a flexible hose without the hose compression
probably is around 65 psi.

It's usually cheaper to buy a good mower at a tip shop for $10 to $20.or gumtree ,garage sale etc

Cheers
Max.

Joined: Dec 2024
Posts: 14
Novice
Hi Max,


Thanks for the advice.

Good point about a Tip Shop or Gumtree.

Let's see what happens.


The moral of the story is I should of bought the cheap Compression Tester at the start it would of explained a lot.

Last edited by Hazzaman; 15/02/25 02:11 PM.
Joined: Dec 2024
Posts: 14
Novice
Hi Max,


Can you please have a look at the below pictures and advise if I purchase the below kit from Ebay will it work or am I wasting my money.





Thanks

Harry

Attached Images
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Pict 2.jpg (392.04 KB, 28 downloads)
Pict 3.jpg (441.17 KB, 28 downloads)
Last edited by Bruce; 17/02/25 08:08 AM.
Joined: Sep 2015
Posts: 2,432
Likes: 191
SENIOR TECHNICIAN & HISTORIAN
G'day Harry,

That bore looks worn enough to at least need honing ,but it depends after the bore is honed and the piston is measured as well as measuring the bore wear then the maximum clearance should be no more than 11 thousandths of an inch to be suitable for new rings.

A new piston should not be used in an old bore.

OutdoorKing have a rebored engine for $80.https://www.outdoorking.com.au/clearance-items/victa-power-torque-rebore-err1352n

PowerTorque manual https://www.outdoorking-forum.com.a...del/Power%20Torque%20Engine%20Manual.pdf


As your 2 stroke mower engine was so low in compression I wouldn't spend time fixing it as a replacement mower is
cheap on FaceBook Marketplace ,Gumtree ,eBay

I've seen piston ring sets for around $15. online but depends how worn the engine is.

That 11 thou clearance sounds a lot from the manual as usually motors are about 2.5 to 5 thou maximum piston to
bore clearance

Cheers
Max.

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Joined: Sep 2015
Posts: 2,432
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SENIOR TECHNICIAN & HISTORIAN
A full crank 160 cc Victa 2 stroke maximum clearance between piston and bore for new ring replacement is 8 thou.

There's always people giving away mowers.




Cheers
Max.

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