I have the engine on a test stand. I noticed some excessive vibration at 7600 +/- on a balanced APC 16-10 backed off some (500/600) and vibration disappeared. Upon inspection both upper and lower port mount bolts had snapped off! The bolts were installed with Locktite less than a week ago. They were both clean fresh breaks. Total run time on engine is less than 3 hours.


Is this a common occurance with these engines? OR did I possibly miss something in setting it up? Any thoughts appreciated.

what is the size of the bolts? You might try larger bolts or harder bolts such as #8. Is it rubber mounted or bolted solid?

They are the factory Ryobi bolts that hold the 'fiberous end cap (with the carb mount)' to the alum case. Duhh.., hunting for proper descriptive word and have no idea what it is..
The bolts are the triangluar self tapping, Tork heads;estimate them as #8-24 x1" but the thread may be non-standard. They appear to be a hardened bolt.

The engine is hard mounted to the alum engine mount.

Mike I used allen head bolts in the Ryobi. Im pretty sure they were 10-24. I changed them because I didnt think there was enough length after the mount was installed. I would guess that the factory bolts are probably the cheapest available, plus on the weedeater they are not designed to hold the entire engine.

I remember you were having problems with the bolts loosening up and what probably happened was the bolts loosened a little and the vibration sheared them off.
Adam

You are correct on the prior loosening problem. I totally disassembled, brushed & cleaned threads and holes with acetone and locktite every bolt before reassemble and test operations.

Bolts are 10-24's Mount is .135" thick so lost 3.25 threads (22% of grip length) It will be interesting to see any difference tightness of broken stubs to remaining bolts.

Are all allen head bolts created equal? No but how are they marked for grade/strength? A reference site would be quite helpful.

Initially, my thought was that probably the self-tapping bolts would be of a higher quality/strengh. You cost / lowest bidder has its merits as well.

This article is devoted to fasteners. Design, application, materials, failures, fastener pre-stressing and other considerations. High vibration applications - motorcycles engines and frames

http://www.engineeredracingproducts.com/art/art1.htm

The problem continues.
Since last post the mount holes had a tap run in them, cleaned with acetone, and the bolts replaced with allen heads of proper length ( 90% of available hole thread) and both hole and bolt had locktite.
The #2 Ryobi has been on that mount for about 3 quarts of fuel. This morning while running a tank I heard a slight 'pop' over engine. Shut down for inspection and found not only lower port side mount bolt head sheared off but 3 cracked areas on the mount itself.
The site of sheared bolt shows no fatigue cracks.
The mount is 3/16"+ thickness on front plate.
This has me more than just scratching my head! Could sure use some input as to causes and solution(s).
Pics if they will help

Is your flywheel running true? I can see from your picture that you made a pretty good cut on the backside of it. How did you turn it? Just mounting the flywheel in a 3 jaw chuck and facing it does not guarrantee that the hole for the crank is centered or that the taper is straight, most of them won't be. I turn all my flywheels while mounted on an old crankshaft and they run dead true. You can carefully move your finger up against the backside of the flywheel while the motor is running and get a feel of how much runout the flywheel has. How about your prop hub? Have you looked at the prop from the side with the motor running to see if the prop tips are running true? Most of the time I run a 18x6 or 18x8 on mine to get the rpm down a little, but I have run the APC 16x10 and it worked well. As long as your crank is straight, there's not much else that can cause excessive vibration.

What mount is that? Is it possible the mounting face in not completely flat, concentrating stress in that area? That is about the only thing I can think of that would cause that kind of damage.

Not knowing any better, I balanced my Ryobi flywheel. Before I ran it, I happened to read about the imbalance in Ryobi flywheels and the many opinions. So I carefully tried the engine on the test stand with a 16-10 and the engine has little vibration. That was four years ago.

Enjoy,

Jim

If I'm not mistaken that portion of the backing plate is indented and needs to be shimmed so it will not create stress in the motor mount or the backing plate....

I'm using the original bolts that came with the motor and haven't had a problem with any snapped bolts or backing out with no Locktite at all..
Just another suggestion...debur the edges of the holes to keep them from having sharp edges to keep stress cracks from starting at the edge of the holes.

Also using CH ignition...Puttety, puttety...

My Ryobi has a vibration problem about the same rpm as yours . Rebalancing the fly wheel didn't help the problem.I just reproped to keep the rpm below the harmonic prone area.Ryobi's like big props. IMO. Dennis 18x10

flipflop: Took 5 of them to local (& best equipped) machine shop to have them definned; owner advised that he wanted to face back as well to assure everything was true, and he indicated he had a 'mandrel' for the taper to face off square.

I'll check backside as suggested or maybe a pencil.

Prop hub was made from a hole cut-out from a 1"sheet of VHMW and the hub nut from 1.5" G-10 ( a high density FG shaft material). I did not check or balance them. :stupid: But I will before it runs again.

I have looked at prop and it appears to run ok no wobble other than below about 1800 when engine runs rough. The long shafts are all used.

Used Ryobi weedies are plentiful for less than $15, so may have to pick one up for a crank to have FW turned on.

BigBird1 You are correct about one of the plate mounts needing a shim. It is the mount hole starboard top, directly above pictured one. Inspected to make sure it was installed.

rob10000 Mount was fabricated from used rowing machine. one of several and it I get the shearing solved before I wuse all the stock for mounts part of it should serv as a mount for a roller base for a thrust scale.

This pic bit is new to me how do you get just a thumbnail size vs. the large pic?

I just looked at the original picture you posted with the crack in the mount...
Is that a slot machined at the edge of the bolt?

If it is..that's probably where the crack originated..

BigBird1
No. The dark vertical is a mixture of fuel oil and whatever. I'm not sure how that much gets past the gasket and residual locktite.

No. The dark vertical is a mixture of fuel oil and whatever. I'm not sure how that much gets past the gasket and residual locktite.


Something might be wrong around that area...that's a lot of oil...
I get some oil spray on the firewall and some on the mount, but nothing like that...it looks like it's blowing up past the bolt..
Ever checked for a cracked back plate or case?
A air leak might cause a lot of things to happen.

Just two more cents worth.

BigBird1

The case and plate both seem fine.
There is only about .040" between mount holes and the part of the plate going into the case. The gaskets on the new engines were cut without any attempt to seal that area. The older enginge had gaskets that had material in that area. I made new gaskets in the 'old' style and the engine had one of those installed.

Is anyone else getting this much 'blow by'? Never messed with 2 cycles much before, just knew they were messy and thought that crud was just part of their nature. Could put some hardening Permatex but did not figure it was necessary as manuf used nothing.

After pulling the engine 3 of the 4 mount holes had cracks from the mount hole going in towards the center cut out hole as well .

Could anyone using the mounting plate and stud columns furnish the column diameters, bolt sizes, and spacing pattern for the columns? Have some .25" 6061 Alum. that would make a H... for stout plate? Is this overkill?

I had the same problem with the bolts. I simply pulled the milled flywheel off, and balanced it true on my high point prop balancer... all the probs went away. (drill holes in the back to remove weight.)...

Sounds like you are setting up a standing wave along the axis of the crank.... I would check the balance... if this fails; try simply changing props t see if you can move the node of the wave behind or in front of the mount. If the bolts are sheering... you can bet a killer wave is being set up with your exact config (you just got lucky:-)

OR

Your steel bolts are gouging the aluminum????... put one steel and one nylon washer on each... you could be simply wearing down the aluminum during the first few mins of running which causes them to come lose , in tern, cause the vibration and a this wave.


OR

Is that a plastic four stroke prop (Dynatrust???) This prop could be flexing at higher RPMs (around 5K) and givening you this problem as well...

food for thought...
Tim