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Ryobi differences... Comments??

Old 01-03-2009, 01:41 PM
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av8tor1977
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Default Ryobi differences... Comments??

I have found some Ryobi differences I didn't know about until now....

I have a Ryobi that had excessive vibration, so I pulled it apart. I also got out my supply of Ryobi miscellaneous parts. I found that there are two different style backplates, (carb mount/reed valve), and two different crankcases.

The engine I was working on had a backplate with the reed valve recessed into the plastic about 1/4". This would highly impede flow. I had another backplate on hand, and it is a much better design, with the reed valve unshrouded, and with a taper where the flow goes into the transfer ports instead of a sharp edge. Much to my surprise, when I went to fit this better reed/valve carb mount to my crankcase, it wouldn't fit.

Upon measuring my other crankcases, I found that one style case has a crankshaft area diameter of 2.220", while another has a diameter of 2.070". This is a difference of .150", and while the bolt holes are the same for the reed valve/carb mount, the better reed valve assembly will not fit into the smaller crankcase. It's o.d. is too big.

I do not know if this is where the difference comes into play, but the smaller diameter case happened to be a short shaft engine, while the larger ones were all from long crankshaft engines. Once again, I don't know if that means all long shaft engines have the larger case and better reed valve setup. I would like to know if any of you know for sure.

Since I was originally looking for a severe vibration problem, I then checked the balance. The short shaft engine was WAY off. It was nowhere near in balance, which makes me wonder if it originally had an off balance flywheel that helped to balance the engine. (I was not running the magneto, I was using electronic ignition.) The long shaft engines I have balance perfectly. 1/2 of the reciprocating weight perfectly balances with the counterweight on the crank with those. Remember that there have been questions about whether the Ryobi had a zero balanced flywheel or not?? I now think some models do and others don't!!

In the pics you can see the differences. Look at the space between the edge of the crankcase and the mounting holes for the backplate and you will see the crankcase i.d. difference.

My brother has a Ryobi with the better style reed valve, and it runs very well. With no mods other than a free breathing muffler and a slightly larger carb, it turns an 18 x 6 at 7700 plus rpms, and has very good torque. It will loop a 14 lb. airplane at half throttle without slowing down. This one of mine with the crappy reed valve was down 500 rpms in comparison, which was another reason why I had pulled it apart to inspect it.

What style reed valve do you guys have, and what's the scoop on these differences? Is there a certain model that has the better reed valve?

Thanks,
AV8TOR
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Old 01-03-2009, 02:37 PM
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av8tor1977
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Default RE: Ryobi differences... Comments??

Here are some better pics showing the differences in reed valves I'm speaking of....

(I've just got to dig out that camera manual and learn how to take better close ups!!)

AV8TOR
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Old 01-03-2009, 03:50 PM
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trumpetman
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Default RE: Ryobi differences... Comments??

My only Ryobi conversion had the smooth flow reed backplate and is a short shaft version.
So, it must be the larger backplate. It is not disassembled or I would measure it for you.
As I remember, the crank counter looked like the large one.
Jack
Old 01-03-2009, 04:27 PM
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Default RE: Ryobi differences... Comments??

I got a long shaft I can take the back off and measure & potograph it. I will post my findings soon. Capt,n
Old 01-04-2009, 12:27 AM
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Ram Jet
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Default RE: Ryobi differences... Comments??

Don't know but it would be a very good idea to Locktite those reed retention screws.

Bill
Old 01-04-2009, 11:47 PM
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rangerfredbob
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Default RE: Ryobi differences... Comments??

you'd have to use thread sealant or glue or something as loctite breaks down plastic
Old 01-05-2009, 02:21 PM
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pe reivers
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Default RE: Ryobi differences... Comments??


ORIGINAL: av8tor1977

Here are some better pics showing the differences in reed valves I'm speaking of....

(I've just got to dig out that camera manual and learn how to take better close ups!!)

AV8TOR
If you look at the reeds and port, you will observe they are pretty much the same. Power can be gained by trumpet shaping the port to the very near edge of the reed. More power can be had by fitting a larger reed and even more trumpeting.
Look at my [link=http://home.wanadoo.nl/pereivers/home.html]Ryobi hop up page[/link] for more details.
Old 01-05-2009, 07:11 PM
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scott h
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Default RE: Ryobi differences... Comments??

this has always caught my intrest (engines with reed boxes and others dont ) such as my poulan 46 cc doesnt have one why is this. does it make for more power . i would be glad to know the difference. thankyou scott h.
Old 01-05-2009, 09:06 PM
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Default RE: Ryobi differences... Comments??

AV8TOR looking at the Pic's the outside Dimensions of both Crankcases appear the same. Bore / Hone the smaller inside case to fit the larger/better Reedplate/carb if the Vibes are really bad take a long crankshaft cut it down to size or just use the longer Crank in the Engine and check for Viberation. If you chose to do any/all of these Sugestions post the Results Please. Doug.
Old 01-05-2009, 09:28 PM
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av8tor1977
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Default RE: Ryobi differences... Comments??

Oh I'm not stuck. I have other Ryobi cranks and crankcases here to use. I am just curious if the smaller case and the crappy shrouded reed valve came on a certain model, older engines, or what.

I did check, and the larger counterweight crank won't fit in the smaller diameter case. If I ever want to use that small diameter case and reed valve for some reason, I will have to use the original crank. The problem with that is I will have to add weight to the counterweight on that crank, as it is way out of balance as it is, and the engine vibrated terribly.

If I ever really needed a crankcase and didn't want to use the unbalanced crank and shrouded reed valve, I could just chuck that small i.d. crankcase in the lathe and machine it out to the larger size. As you said, the o.d. is the same.

PE Reivers Yes, I have reviewed all your web info on Ryobis. Interesting info.

Thanks,
AV8TOR
Old 01-06-2009, 10:41 PM
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Flathead
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Default RE: Ryobi differences... Comments??

The more you look, the more you find. I have found both of the variations you describe, but the one that you describe as "being caged" is found in a trimmer called a "TRIMSALL" amoung others. If you look close, the bottom of the cylinder is not slanted as in regular RYOBI,s. There is another variation that carries the name of "STIHL" and was sold by them, probably under contract with RYOBI. The name STIHL is inprinted on the plate of an otherwise WALBRO carb. The REED VALVE plate is decidly different, and usually of a ligfht colored material with a flat interior plate, but what I have seen of this production run, they are all long shaft Ryobi sngines. All of the TRIMSALL's I have seen are short shaft engines. I am sure there are other names out there I have not seen. I have two of the "TRIMSALL" versions that I have on electronic ig, and have not experienced the vibration you indicated. I am interested in these particular engines because of the "STUFFING" possibility. (decreasing the amount of open area in the crankcase) Cold weather set in, and my work area is not heated, so have not really had the oppoprtunity to explore these engines, but the one I have running was turning a 18X8 wood prop over 8200 RPM. It has a larger carb, but not much else has been done, I did add additional material to the back plate to futher decrease the open area. I will not run it again without a bigger prop because of the potential con rod problem. I will keep any info I gather posted in the forum. Also, if I can figure out the picture capability of computers, I will try and send some pictures. FLATHEAD 4
Old 01-06-2009, 10:52 PM
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Flathead
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Default RE: Ryobi differences... Comments??

Another item I didn't mention, the backplates you describe as be the best for you can be found on either short or long shaft engines, and neither one will fit the smaller case. Keep looking, and you will eventually find a "BEEFED UP" con rod if you fine enough engines. That may be my next exchange to go to a higher RPM range. FLATHEAD 4
Old 01-07-2009, 12:13 AM
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av8tor1977
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Default RE: Ryobi differences... Comments??

I've thought about machining a rod for a Ryobi out of aluminum to replace that stamped steel stocker. Lot's of ideas, not enough time.... I don't really think the crank would be an rpm limiting factor, just that connecting rod.

Got a Frank Bowman ring coming for this one; should arrive tomorrow I believe. When I finish it up and get the big Tiger Moth biplane back in the air I can go back to work on my "stroker" BME twin Echo 23.6cc project.

AV8TOR
Old 01-07-2009, 07:46 AM
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pe reivers
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Default RE: Ryobi differences... Comments??

I found other differences as well, mostly to comply with CARB rules (California Air Resource Board)
like compression reduction slits on top of ports and like 7000 rpm limiter in ignition. The last one was a tough nut to crack. The engine just would not go past 7000 rpm, until I fitted an electronic ignition.
I then checked the patent pending number at USPTO.gov and found out that there were integrated electronics in the ignition coil that regulated the timing and max rpm.
Old 01-07-2009, 11:34 AM
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av8tor1977
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Default RE: Ryobi differences... Comments??

Do you really think that is what those slits are for? Seems like if they wanted to reduce compression they could have done it by increasing the combustion chamber size, increasing the deck height, etc. Those slits extend upwards from the transfer ports, and I just am not sure what their function might be. I was pondering that again just yesterday.

As the piston ring uncovered those slits, it would send combustion pressure and exhaust gases pulsing into the transfer port. Then when the exhaust port opens, that would stop and internal flow would be as normal. I keep wondering if it isn't a form of exhaust gas recirculation. Maybe some of the exhaust gases that enter the transfer ports never get exhausted, thereby giving "EGR".

I would like to know for sure why they are there. My brother has a Ryobi that runs quite well. When I pulled it apart to clean it after a crash, I was quite surprised to find that it had the slits. Has anyone done a controlled comparison to find out if and how much power they cost????

AV8TOR
Old 01-07-2009, 03:23 PM
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pe reivers
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Default RE: Ryobi differences... Comments??

The slits have two functions.
In high rpm they hardly influence the compression ratio, but they very much do so for starting.
They also cause exhaust gas blowdown into the crankcase. If about 10% spent exhaust gas is mixed in with fresh charge, combustion will be a lot cleaner and burning will be with blue flame. This very much reduces carbon and carbon monoxide pollution.
You could also make the slit on top of the exhaust port. In that case it provides easier starting and less exhaust noise.
Old 01-07-2009, 09:21 PM
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av8tor1977
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Default RE: Ryobi differences... Comments??

In other words; "EGR". Exhaust Gas Recirculation. The introduction of exhaust gases into the fuel/air mixture lowers the combustion temperature, hopefully to the point where Oxides of Nitrogen, one of the contaminates in smog, won't form.

That's what I thought.

This need to lower combustion temps for smog reasons is also why we are stuck with low compression engines, and low octane gasoline.

The last thing I want in ANY engine of mine is an incoming mixture contaminated with exhaust gas.

Thanks,
AV8TOR
Old 01-08-2009, 09:07 AM
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pe reivers
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Default RE: Ryobi differences... Comments??

You can fill up the slots with a small aluminum plug filed to shape, and use the cylinder.
Old 01-08-2009, 12:31 PM
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Default RE: Ryobi differences... Comments??

Most of the ones I have seen are full of carbon anyway.

Jim
Old 01-08-2009, 12:45 PM
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av8tor1977
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Default RE: Ryobi differences... Comments??

While I wouldn't personally set out to build a Ryobi with a "slitted" cylinder, I have to admit that the one my brother has with the slitted cylinder runs well. It turns an 18 x 6 prop at 7700 rpms or so.

I measured the exhaust port width and came up with an approximate dimension of 62% of the cylinder bore. That should be small enough not to cause ring problems if you ground the bridge out of the exhaust port. Does anyone here have experience with doing so? Pinning the ring and then grinding out the bridge in the Homelite 25cc engines helps a lot.

AV8TOR
Old 01-08-2009, 02:56 PM
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Default RE: Ryobi differences... Comments??

I've been watching this Ryobi thread with some interest. There are quite a few differences in Ryobi engines even though they seem alike from the exterior. Here are some pictures of a cylinder I think I sent to Avator some time ago. Note the absence of the bridge and the much better shape of the transfers......Bob
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Old 01-08-2009, 03:06 PM
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pe reivers
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Default RE: Ryobi differences... Comments??


ORIGINAL: av8tor1977

While I wouldn't personally set out to build a Ryobi with a "slitted" cylinder, I have to admit that the one my brother has with the slitted cylinder runs well. It turns an 18 x 6 prop at 7700 rpms or so.

I measured the exhaust port width and came up with an approximate dimension of 62% of the cylinder bore. That should be small enough not to cause ring problems if you ground the bridge out of the exhaust port. Does anyone here have experience with doing so? Pinning the ring and then grinding out the bridge in the Homelite 25cc engines helps a lot.

AV8TOR
Leave the bridge attached to the upper port wall, but grind it narrower, and detach it from the lower port wall. Exhaust gas heat will heat the bore side of the remaining lip mor than tha downstream side, so the lip bends away from the piston slightly and guides the ring nicely back into the bore on the upstroke.
Make the exhaust ports wider towards the scavenge (transfer) ports, but only the portion above the transfer ports, so the exhaust port gets a mushroom shape.
If you want to fit a tuned pipe, increase port height by milling the central 1/3rd width port section upwards.
Old 01-12-2009, 08:29 PM
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av8tor1977
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Default RE: Ryobi differences... Comments??

Well, I got it all back together, but this time with the larger crankcase, the long shaft crankshaft that balanced well, and the good reed valve setup. Before, besides the vibration the best it would do was 7200 rpms with an 18 x 6 prop. Now, it turns the same prop a surprising 8500 rpms. Looks like I better "prop it up" a bit. I am pleasantly surprised. It also doesn't vibrate now, as was expected. The short shaft I have that is out of balance is not out of balance just a little bit, it is WAY out. Some day I'll have to go through my box of old flywheels and see if I can find the one that came on that engine and see how it is balanced.

As far as mods on this one:

Base gasket left out and sealed with Yamabond (Lowers cylinder about .035" )
Exhaust port raised to provide a timing of 152 degrees
11mm carb
Dual outlet after market muffler
CDI ignition set at 28 degrees
Good style reed assembly with reed stop set to 1/8"

farley9n Yes, I still have that cylinder. I bought an extra Ryobi ring from Frank Bowman, and if/when my brother can find me another donor engine with the good style backplate and a useable piston, I am going to build an engine using that cylinder. It will be interesting to see how it runs. I haven't cc'd it to see what the compression difference is, but that cylinder has a larger, almost full hemi style combustion chamber in comparison to all my other Ryobi cylinders. I have a couple of good crankcases, bearing sets, cranks, and cylinders here; just don't have a piston/rod nor a good reed/backplate.... []

AV8TOR
Old 01-13-2009, 04:59 PM
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pe reivers
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Default RE: Ryobi differences... Comments??

I just fished a ryoby Y-branch manifold out of my scrap box. With my Ryobis long gone, you can have it for the shipping cost.
Crankcase diameter needed is 56mm. The manifold seals to the case with an O-ring. Carb bore is 17mm, each branch has 10mm bore.
Two reeds are needed. It now is fitted like the picture, with just one reed.
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Old 01-13-2009, 05:27 PM
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av8tor1977
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Hey, I'll take that offer! I wonder how much shipping would be from the Netherlands???

I'll pm you my mailing info.

Thanks!
AV8TOR

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