RE: Doesn't look like it can be converted
 

Looks like we have all reached near identical solutions - makes me feel better!

BTW, I'm no Guru, - (Dave and Mike can speak for themselves of course:D). - generally though we seem to agree on most engineering ideas.

Just another idea, - my thoughts on the extended bolts, - Leave the threads in the crankcase as well as using the threaded spacer, ( I may seem to have suggested on the mail I sent you, that you use only the spacer as a nut), they will have to be threaded on to the bolts first before being attached to the plate.
Aluminium box section (RHS) could also be used, - I have some 100mm x 50mm which looks like it could be a good solution for mounting, - allowing the exhaust to protrude into it, also using short spacers as necessary.

RE: Doesn't look like it can be converted
 

Brillant people !!!!:D
You guys make it easy for a newbie like me at this !!!:D
cheers torp.;)

RE: Doesn't look like it can be converted
 

That's a better flywheel :;)

RE: Doesn't look like it can be converted
 

Looks better for a solid base for the hub.
Is that a Corsair in the background?

RE: Doesn't look like it can be converted
 

Yes, GP40.:D

RE: Doesn't look like it can be converted
 

Prototype spec's :
torp;)

RE: Doesn't look like it can be converted
 

Wow, cool drawing. Nice work.

Good luck,
AV8TOR

RE: Doesn't look like it can be converted
 

thanks av8tor1977,
torp:D

RE: Doesn't look like it can be converted
 

Any suggestions how we can hold on our new prop shaft after we turn one up ???
Pic is a wacker product.
cheers steve;)

RE: Doesn't look like it can be converted
 

Pic worth 1000 words!;)
What size are the threads on crank? What size bore do you want on prop? bolt threads to match.

It is a bit of a bummer to have props reamed a different size than the 2nd engine particularly oversized. ( If they last that long!)

RE: Doesn't look like it can be converted
 

Hi mikenlapaz,
Is this correct.
Thread new prop hub { 5/16 24 }
Screw to crank tight against flywheel.
Then pin with 3 socket head bolts tapped to flywheel ?????
Use a 5/16 24 for prop bolt as well in same threaded hole ??
thanks torp.;)

RE: Doesn't look like it can be converted
 

Hi all ,moving through the problems that are poping up nicely:D thanks to all:D
Next : What do you suggest for a muffler. Not limited to a Dba rating over here.
simple header pipe curving sraight out the side{look pretty cool] or a box muffler with a couple of stacks srewed into it poking out the bottom ???
your thoughts please .......[8D]
torp

p.s if you see this wildo my 11mm x2 outlets and 16mm x1 look close.

RE: Doesn't look like it can be converted
 

i say go with the short header. this will also keep the cowl area behind the engine much cooler. i like to use a tube with at least the same cross sectional area as the exhaust port....you can also flare the end for a megaphone effect:D


dave

RE: Doesn't look like it can be converted
 

I'm not yet really knowlegable about small engine mufflers, but I do know (from motorcycle experience) that mufflers and pipe dimensions can be quite critical, and if not designed properly can result in poor performance.

If someone can come up with the best layout and some concrete (as opposed to airy fairy) dimensions, or a formula, I'm prepared to have a go at making one. ;)

PS, that last statement applies to everything else too!

Why am I up at 4.30am?- I'm crook, that's why! ( that means "sick" to our foreign friends.[&o] )

RE: Doesn't look like it can be converted
 

"as opposed to airy fairy"
where did that come from:eek:
I will take care of muffler Wildo:D
torp

RE: Doesn't look like it can be converted
 

Cheers Dave, will go with short header. :D
That pic above of one came off a 31cc ryobi on this site.
it worked real good.
Will track down the designer tonight and get info on building one if possible.;)
thanks for help , torp;)

RE: Doesn't look like it can be converted
 

I mean that I'm not clued up enough on exhausts, and would rather not risk guessing off the top of my head! I think maybe Dave has a bit more experience in this department.

RE: Doesn't look like it can be converted
 

torp: I'm not an expert but the idea is similar to this:
taken from http://www.fujiengines.com/manuals/fjig0087-manual.pdf
Manual for their 50cc Check it out.

Consider full required bolt length and allen head driver when you design overall length.

RE: Doesn't look like it can be converted
 

cheers Mikenlapaz, some good idea's and details in there.
torp;)

RE: Doesn't look like it can be converted
 

if you make the hub like that it should be considered permanent because if taken apart you'll never get the three holes in perfect alignment again. drill/tap the holes only after you're confident that everything is right.
with the fuji the hub is held only by the three screws and does not thread onto the crank.



dave

RE: Doesn't look like it can be converted
 

Hi all, have decided to go with alloy backplate ,shorter standoffs and a ply box.
Wildo:Dis going to take care of prop hub for us.
might use header pipe for exhaust , just have to find some 16mm i/d alloy tube or 11mm i/d somewhere ????? Wildo ??
Will keep posting pics as project moves along.
cheers torp.;)

p.s pic shows exhaust port .good base for headerpipe with those three mounting screws.
making of header looks hard now though.Big port !!!!!!
looking like using a box muffler now........[&o]

RE: Doesn't look like it can be converted
 

Dave,
You're right , It would be impossible to get those three bolts to line up again if the hub is used as a nut, to tighten up the tapered flywheel boss on the shaft.

No matter how it's done, the bottom line is, the crankshaft nut is what holds the prop, prop driver and the flywheel to the engine, and that's all, so it'd better be secure! ( the taper does too, but not without that crucial nut).

Steve,
That is a big exhaust port outlet, - it's 475 sq mm, and that would equate to a 25mm ID. pipe, and with a right angle bend, it would take up a bit of room!
Maybe something resembling a squashed bend ( with the proper cross sectional area ), fabricated from sheet?

Probably no decibel limit, but there will be someone complaining! - some people love to find an excuse! ;)

RE: Doesn't look like it can be converted
 

Gidday.
Have a look at my prototype muffler.
Main box made from 40x25x2 and stack from 19.05x1.42.
1 - cut box section to lenght
2 - Drill bolt pattern
3 - Cut out side to match port
4 - Make 3 spacers for bolts inside muff
5 - Cut hole for stack [19mm}
6 - Cut 19.05 tube to lenght
7 - Make 2 end caps
8 - Find some one who can weld alloy !!!!
Could also have 2 stacks like a pitts,this config is to avoid my plug.
As Dave suggest work around std exhaust area {196mm2}
This works out as 16mm i/d
My 19.05 tube has a 16.21 i/d.
Right on i reckon, suck it and see !!!!!!
your thoughts please.
cheers torp;)

Wildo, think this will be easier for us ??
Header too big a job.Above will be quieter too.

Ullrich Alloy UA1979,UA1232

RE: Doesn't look like it can be converted
 

Mike posted some excellent ideas and pics for a no-weld exhaust diverter. would probably be doable with the same 40x20 alum profile you specified above...cap one end and then run the other end out the side. not as elegant as your plan but a good option if you can't find someone that welds aluminium.


dave

RE: Doesn't look like it can be converted
 

Steve,
Which part of the port are you working from? - the hole in the cylinder, or the outer hole where it joins the muffler? - maybe this is where the discrepency between our calculations lies! - as I see it, there's no sense in making it a smaller area than where it exits the barrel.
Of course it is possible that my engine could be a little different to your's!

Possibly 2 small stacks would be better than 1, ( much more clearence for the plug). - maybe even splayed a little.

I'll have a go at the welding, - I have the equipment, but it's been a long time, - no charge for ridiculous times or botch ups! :).

However, I still don't know about dimensions - your method of fabrication is ok. of course.

All I have been used to was racing motorcycle exhausts, and they were very critical for dimensions, and the size of the tailpipe was deliberately much smaller than the than the header pipe, - but if too small, could contribute to piston overheating.

However, for these lower powered engines, thinking this way may be a little bit over the top, and it may not matter so much, as they don't have the wild port timing of the competition bikes.

Maybe somebody else can enlighten us on this. [8D].