Hi,

Posted a while back on this, got some serious vibes unable to solve and only getting back to it now.
Was recommended to check flywheel forward for the source, so far, found the following:

With my shiny new DTI, I measured the following:
Engine shaft runout at tip: 0.07mm
Adaptor bolt runout at tip (bolts over the engine shaft): 0.3mm

Flywheel on the 25cc is a Phelon (45?)
Flywheel on the 30cc is a Walbro (G62)

The Phelon has been machined down but seems much more out of balance than the Walbro (unmachined).

Questions:
1) Is the runout sufficient to cause significant vibrations? I think not as I used the same crank/flywheel/shaft on the 25cc without disturbing it (just changed the piston and conrod) and it was fine, no vibes.

2) Should the flywheels balance or is there an offset to counteract part of the piston assembly weight?

3) If there is an offset built in, is it possible that there is a variation according to the piston used? If so, one would expect the Walbro to have greater imbalance, not less!

4) Is the crank web the same across capacities? I was told that it is interchangeable but I dont see how a bigger piston (and therefore heavier) can be effectivly counterbalanced then.

5) Can I eliminate the runout by tapping the end of the shaft with a hammer once its all screwed together?!

Im going to try running the Walbro flywheel on it without the prop conversion (if I can work out how to start it) to home in on the vibes.

Any help greatly appreciated!

Thanks
Mark

This I gotta see, a Walbro flywheel...I have the latest Walbro parts catalog, there are no flywheels listed..
The Zenoah G23, 26,45,62, and GT74 and 80 all use the same rotor, source coil, and spark coil..The G23 and 26 rotors are the same iexcept for the smaller diameter taper where they fit on the crank...

If you've gotta see it, go down to Lowes and buy yourself a new Bolens (Ryobi) weedeater. I just turned one down yesterday. Definitely a Walbro flywheel.

I just remembered that w8ye mentioned a walbro flywheel in reply to my question on a 33cc homelite. He might have some info.

The flywheels on both my Homelite 25 and the one on my 30 are both Walbros. But the one on the 30 came from a chain saw. The one on my Ryobi is a phelon and it was a long ways out of balance originally.

Back a few years ago, the last time I looked in the Homelite catalog, there was no mention of what brand either the module or the flywheel was. The dealer assured me that you may see either brand on the weed whackers or the saws. The brand for each flywheel brand was marked on the back side.

I looked at the Walbro catalog too and found the ignition modules but no flywheels. Maybe the Walbro flywheels are O.E.M. propietary?

Ralph, I can send you a long shaft one if you want to see the brand?

Enjoy,

Jim

Nope, just never saw one....Must be proprietary....I wonder where you buy one if necessary ?

Can anyone answer my original questions pls?

In a nutshell:

1) Does anyone balance their flywheel on a high point after turning down, or should they be left with an imbalance to counteract the piston assembly?

2) Is nearly 0.1mm runout at the shaft tip too much?

Thanks,
MArk

Did you check the balance BEFORE the machining was done? I removed the fins on my Ryobi 4 cycle flywheel, but only after cheching to see where it balanced. Then rebalanced it to the same point after the trimming.

No unfort not. I can try that when I get the Walbro turned down, if it runs smoothly. I shall find out soon if it runs smoothly before turning down the flywheel, if I can just work out how to start it from the shaft. Im thinking an electric drill and socket on the shaft...

Squid, I use a Skil reversible drill ( 2250 rpm ) on my 31cc ryobi and a 33cc homelite. I cut the big end off of a short 1/4" drive extension and chucked that in the drill motor, with the appopriate socket. This set up will start my engines immediatley. Hope this helps.



Ron

Thanks Ron,
I ground a 5mm square on some 8mm rod stock, chucked it in a normal 500w electric drill, and stuck it in where the weedwacker shaft normally goes in the original nut. Worked well but unfortunately vibration broke the sidewalls of the nut socket before the motor started so maybe I'll try your idea, or maybe just grind enough of the post flange on the new flywheel to be able to mount a spinner/backplate.

Hi guys,

Tried balancing the Phelon flywheel instead. Did a rough balance on the high point to see if it helped. Ran it up with the prop/hub etc and boy what a difference, that was obviously the problem. Well, now im gonna spend some time perfecting the balance and hopefully thats problem solved. BTW getting 7k rpms on APC18X8 on a new (1/2 tank) piston/cylinder, not too bad I think!? (sea level, 24 deg C)
Cheers
Mark

Ya gotta remember that these flywheels are from an engine that sells for less than $50. It is not a precision part. They are out of round and out of balance. Machine then round and then balance and you will be much happier.

just checked the notes for my homelite 30 and got about .001 @ the prop hub . Your s at .1 mm = .003 seems a tad excessive. But once you come into balance might be ok. Might be you need a new front bearing. 6-9 bucks at your local bearing shop. If you want smoooth.
And yep I also have a flywheel with Walbro stamp!!!
Aloha, Les Ward

Only engines with a purposely unbalanced flywheel have only one crank web, Q35, 42, Sachs 2.4, etc...The old Homelite Super Hustler II had a single counterbalance crank just like a Quadra..There was no flywheel, the engine had points and a battery..The steel hub was ground away almost to the crank on one side, same as a flywheel made purposely out of balance.....The Super Hustler II turned a 20-10 Master Airscrew about 6000 rpm, got way smoother at that rpm....
Dario Brisighella sold "overbalanced" flywheels for the old Quadras, made 'em smoother...
Seems like the cost was about $10...[8D]

Well, I spend most of an afternoon perfecting the static balance on a high point balancer, and guess what, there is now more vibration than before!

RCIGN1, there is only a single web on the crank of this motor so are you saying the flywheel should actually be unbalanced?

Les, my bearings are brand new, but could have a manufacturing defect, runs smooth though and no end play [] I dont think the runout is an issue because it ran smoother before I tried to balance the flywheel, and I havent looked at fixing the runout yet.

tkg, how would you machine the flywheel? The magnets stand proud compared to the opposing side, are you suggesting turning down the magnet area, or just the front and back sides of the flywheel?

Im thinking maybe dynamic balancing is the answer, IF, the flywheel is meant to be in balance and does not have a built in offset.
Can anyone answer this categorically please?

RCIGN1 it looks like you are indicating that this is so, but then, how come the popular electronic ignition add ons do not require the ground hub to balance?

The only other thing I can think of is that the crank web is different between the 25cc and 30cc (im using the 25cc web on the 30cc jug/piston). Im told there is no difference here, but maybe the flywheel balance was then modified to counterbalance the extra piston weight?

Anyway, thanks for all your responses guys, great forum.
Regards
Mark

I always wondered about the unbalanced flywheel, so I never converted a Q35..I have a US 41 coming (I'm now a dealer) to convert and see what happens..Reid's sells a US 41, called a Cheetah, with electronic ignition....Will be interesting....