combatpilot

Ok so from what I am seeing is the pistiondia from the small dia crankcase engine measures 1.306. what is the dia of the piston from the engine with the large dia crankcase?

if you have the crankshafts out try and measure the stroke.

If the stroke and the dia of the piston is the same the cc is the same.

You may be able to measure the stroke with the crank in the engine measure with the depth part of you caliper from the cylinder base to the rod journal at tdc and then again at btd. the difference is the stroke.

I think what is happening is with the Larger dia crankcase set up it has a longer rod. It has to as now the cylinder base is higher in relation to the crankshaft center. the enngine with the smaller crankcase has a cylinder base that is lower in realtion to the crankshaft center than the other engine and therfore needs a shorter rod. the original rod must be used with this engine and cannot be interchanged between the two crankcase sizes.

Ok so look at the pistons. Are they the same? is there a difference in the rod lentghs? Take the piston you want to use and install the short rod from the small crankcase engine to this piston. This should now work but i dont know for sure as I dont have the parts in front of me.

Ajonr I see your in hutchenson KS. I can come get the parts and it will give me a chance to look through what you have and we can also do some comparisons with what you and i have. My brother lives in andale and I would love to come visit him to.

I will be intersted to see what you find on this crank and rod set up

Twin Star

Combatpilot
Did you get my PM.

TwinStar

combatpilot

Yes I did didnt you get my reply i sent it this morning? let me try again ok.


It says it sent and it should be from [email protected]
I used your yahoo adress.

let me know if i need to send again ok

aj0nr

[:-]All the rod,pistons,top of pistons to wrist pin are the same.All of them can change out.The only head that is more differant is the 2 slot with comp releif cuts.The small case hits , but the large case none of them hit.
All rods are the same.The 3 rods that are differant are the same lenght.The WEIGHT are. Some are 66 grams,the others are 78 grams.For refrance- the 2 ring I beam style rod is 78 g. The other rod type with 2 rings is 68 g.The same rod with 1 ring are 68 or 78 g.
The crank throw is +/- 26.50 mm or 1.043 in. Small or large case.Didn't matter.

If the rods were NOT the same The "PARTS STORE" would have two rod type piston assemblys available.

I went parts hunting just this past Tuesday.I was asking around for pistons for these hoping to score some more 2 ring types.I did ask if the parts book showed 2 differant rod lenghts,and they didn't. ??? The last place I was at I was noticeing that there are Ryobi type(by the rear intake/exhast kind) motors with 28cc,30cc,31cc,33cc. ???
I did get me some 4 stroke 26.2 cc, but that is another project..Then he offered me a job,I seemed to have known more about them than he did.

To everybody. If you have a motor tore apart and can measure the parts, all the info would help.
I have looked at other engines that are set up like the Ryobi.There is several for r/c-airplane engines that are pumping out 2-3 +hp in the 8000+rpm range.To think that these engines can only do about 1.5 hp is wrong.

I have so many people say that covnersions are " to heavy, not worth it,cant make the same power,and so on" They are the out of the box kind.10 years ago the gas engines were expensive, and they still are.Now there are some less expensive ones out there,but if I or any one of you can make a hot running Ryobi that can work better and for less $$ with parts that you can get anywhere, thats the goal I have.I bought my JAGGs kit back in '03 and wanted to go EI with it was too expensive,but now aftermaket EI kits are 1/4 the price.To get the Ryobi running well for less than $80 ,thats what I want,not $250+.They all can hit the ground[] and they all sound the same when they do.

Racinrc14

My Feedback: (7)

Here's what mine measures... its a large crankcase, single wide ports, single ring piston, bolt-on mag shield, non-recessed reed mount.

1.285" stroke
1.378" bore
.313" crank pin dia.
2.208" dia. inside the crankcase at the backplate mounting area
2.352" rod length, both pistons (old single ring and new two ring).
.400" wide x .950" deep, single, wide, ports, one on either side in the head.
2.135" diagonal measurement of bolt spacing for the backplate holes.

Twin Star

I'm curious, what kind of static thrust are you getting @ 7400 RPM w/ the 18 x 8 prop. That would give some indication what airplane would be suitable.
Also have you tried a velocity stack on the carb to see what if any benefit that might give to performance. I've noticed on many of my carbs, that the screw that holds the throttle butterfly to the shaft, the threaded end sticks way out into the venturi. I would think this might restrict some air flow. When I do my conv. I plan on grinding it back flush.

combatpilot

All the differences in these motors is gona make me pull my hair out lol. thats to bad cause i aint got much left.

from racing rc from ajonr this dont make sense to me.

Are you using the gasket when you put your cylinders on ajonr? When i took mine out and installed my old cylinder on my new crank housing it also hit the piston into the head. I had to have a min of a .010 gasket in it to keep it from hitting. when I put my new cylinder on the same engine I didnt need a gasket at all and it would not hit.

If there is no difference in the rod lenght of the small case engine and the large case engine and the stroke is the same on the large and small case engine then the cylinder base has to be cut the same height from the centerline of the crank. meaning the cylinder base mounting surface to cranks center is the same on all the engines no matter large or small case.

I have to agree with the power output ajonr. I think we are getting pretty close as i think we are exploring areas that i have never seen talked about anywhere till now.

I have no way to know what hte thrust output is and i just dont want to take the time to build a way to do this yet. No i havent tried a velocity stack and to be honest i really cant belive this will do much good. any increase would be very small at best. I could be dead wrong though.

I am certian this would restrict flow. anything placed in the path of the air/gas flow would be a restriction. Again do i think this is going to yeild a noticable gain in power? Probably not but it very well may be worth a try.

Ok so on to something new. I am convinced the way to go from here is trying to reduce the crankcase volume. I had a backplate that is junk as the carb holes are stripped so i decided its a good experimental piece. this is what I came up with. I think this does a good job of reducing the crank case volume and yet does not require a great amount of machinery to do. most anyone can do this. I will describe this mod in future posts in great detail with pics and all but you will just have to be patient for now. anyhow here are the pics of it. this unit is not the one im gona use but just a test to help me develop my method of this mod

aj0nr

Combatpilot-
racingrc14 is correct on the total stroke length. I had a typo.I was trying to measure the crank pin center to piston pin center to see if there was something I was missing.

aj0nr

Has anybody has looked at the DA-50cc ,rear intake.Look closer,very small crank case. ??? Just makes you think.

aj0nr

If anybody is trying to find bigger carbs,try looking for them on Homelites and McCulloch.The ones I have are a little bigger than those on the Ryobis'.I have a really big one from a Stihl chainsaw (17mm)

aj0nr

Does anybody know which carb are the " magical one" is? Walbro or Zama , if there are # you have that could help.

aj0nr

I found a web site on the walbro carbs that is a good read.

http://tech.flygsw.org/walbro_tuneup.htm

combatpilot

Now thats going in my favorites file for sure. Theres some pretty damn good info there and a reall good find. thanks ajonr.

As far as a magic carb. I dont know I have only seen the walbro. they all pretty much work on the same principle though. I dont know that specific numbers will do you any good as its gona be very hard to find that specific number. they are all pretty much the same within the venturi size ranges for each size. the only real differences are gona be little thing like throttle arm configuration and choke style or configuration or fuel inlet port direction some even have an integral fuel primer but again this is all secondary differences to the primary operating principals of this carb.

What i would do is look at the walbro site i had posted erlier for information on a specific carb you are looking at to identify the venturi size. this is gona be the only real operational difference in this carb.

Man im gona read that walbro tunning site a few times for sure lol. In browsing through it i now see why when i open it up full throttle and hold it it leans out and reduces rpms and no amount of richening the needle will help and now whatt to do about it.

aj0nr

I have some zama and walbro that are larger than what you have talked about.

Inlet 8.25 mm,Outlet 13.92mm . This is a zama.
In 8 mm, out 14.25 mm -Walbro WT57 10/86
Some others smaller and larger,too.These all came from weedeaters.

I need to say that I have not run any of the motors.I have only blueprinting these to understand what I have and to pass the info on.I have built a test stand today to start helping in the running info that some of you have been helping with.

aj0nr

Has anybody messed with the intake runner ?
In race cars,they change the runner lenght and/or volume to increase the Hp or torque band.

I seen an ad for a 26cc 2-stoke set up for marine raceing boats turns 19,000rpm and 6.5 hp !!!! That is some serious modifications going on there.

Racinrc14

My Feedback: (7)

Hey Combat, what if you used muffler pressure to pressurize the crankcase to 'fool' the crankcase into thinking it's a lot smaller?

combatpilot

Racincr im not sure I follow you but sounds interesting please describe a little more.

I had thought about messing with the runner lenght like you say. I dont know that making it bigger would help or not but lenght may have some tuniing relavance.

a 26cc making over 5 hp. thats kind of hard to belive but i guesss its possible at that rpm as hp is a mesurement of how much work can be accomplisehed over a matter of time.

That wt 57 carb you talk about is unfrtunatly not listed in walbros archive so i cant get any info on it.

Racinrc14

My Feedback: (7)

Drill and tap the muffler for a fuel nipple, then drill and tap the crankcase in a handy spot for another. Then connect the two with a piece of fuel tubing. The impulses from the exhaust (not the actual exhaust) would be fed into the tubing, and maybe with a check valve of some kind, the negative (scavenging) impulses could siphon off a little pressure out of the crankcase. Similar to how us glow guys pressurize fuel tanks, but kind of in reverse. I dunno, sounded interesting. Easy enough to cap off if it doesn't work.

combatpilot

Thats an intersting idea. I had thought about putting in ports on the crankcase to see about testing crankcase pressures anyhow.

diceco

Did the mod on the reed. Bent the reed so that it fit the curve of the back plate and adjusted it so it just barely touched the seat. Bent the stop plate so it only contacted the reed at the very end where it clamps the reed. Did NOT cut waist in reed valve. Radius-ed the intake tube to a sort of bellmouth shape. (There's hardly any contact area around the edge of the hole so the radius was pretty small.

Not much gain. About 60 RPM. All this with an 8 mm venturi carb.

What's the consensus on the best carb size?? There has been a lot of talk about 11.1 mm venturi. Also heard of 12.2 mm (although I can't find that exact size in the literature. There's a 12.7mm)) and some thought that that might be too big. I'd like to hear from you all before I go out and buy another carb!

Thanks for the advice, diceco

combatpilot

I was wondering about doing that bellmouthing mod to. Like you say there isnt much contact area anyhow.

When you say bent the reed valve how did you do this. I found when the reed stop was bent to where it clamps out on the end like you did it held it to the plate pefectly without having to put a bend in it anyhow. Pressure will also help it seal.

All of my tests have been with a 12.7 mm carb. i really would like to find a 11.11 mm carb to do a comparision. I am temperarily out of money so it may ba a while on this test.

When i did the experiment on modifying the backplate i used a common polyureathane resin that i got at autozone. there was some left at the end of the pour and it set up in the mixing cup. I really like those plasit cups for mixing this stuff when it hardens it pops right out and you can mix another batch in it again. anyhow i poped out what was left and i had this nice little plug. Wondering if it was gas proof i placed it back into the cup and covered it with gas and let it set overnight. It was totally unaffected by the gas. i think this resin is gona work wonderfull for backplate experimentation. I was gona try and do my final backplate modification this week. I may take a small break from posting for a while so dont get impatient. my wife is getting a little peeved how much time im spending on this post and on the computer as we only can get dial up out here. Besides i want to post my backplate modification procedures and testing all in one shot so it makes more sense anyhow.

Here is a pic of the resin puck after a nights bath in gas

aj0nr

check out the MODIFIED boat motors

www.redlinemotors.us/#

aj0nr

I have been seeing that the Walbro WT-257 is the one for boats.

Is it overkill for the planes ??

tkg

My Feedback: (1)

Sounds a bunch like EGR and it lowers the quality of the intake charge.
TKG

combatpilot

A wt 257 carb has a 12.7 mm venturi. this in all effect is the same carb im using.