ryan_t888

A friend of mine did this with an old .15 from O.S. and it would never throw the rod. We were dying laughing cause we were expecting a piston through the roof but it ran a full tank of fuel at peak rpm no load without any destruction. It must have been around 4-7 minutes of consistant screaming. From this I kind of feel it is impossible to over rev an engine with no load.

I can't remember what ended up happening with this engine but I know it isn't around.


As for the mods, I find the biggest difference in botom/top end if the cylinder sleeve channels and the channels in the block are ground down. I have never touched the crank as I am concerned about the balance of it. Any opinion?

Ryan

jkulhanek

I was curious about the balance, but since my piston and rod are lighter it doesnt seem to affect it, you just can't balance a single cylinder engine anyway, they will aleays be out of balance.

ryan_t888

I re-read all of the work you have done to your engine and was wondering if you got another carb for it? Maybe a .15 or .18 carb would work since the engine is demanding more air and fuel.

Ryan

poseyracing

My 2 cents-
unless you know how to rebalance a crankshaft correctly, just port the sleeve and call it finished. Knife edging the rod isn't required either. Just the humble opinion of a card carrying ROAR racer and 23 yr R/C veteran who's been to a race or two over the years.

www.rbmods.net

ryan_t888

It is impossible to completely balance a crankshaft. The unbalanced forces acting upon it also don't help.

Ryan

SManMTB

What you can do to balance it somewhat and get a so called balance factor of 50-60%. Do this if you got plenty of spare time. You will need a very good scale, a digital if you got one.

Disassemble your engine and clean the parts (always nice to work with clean parts).
Remove the conrod and weigh the bottom half and then the top part of it, write down the numbers.
Weigh the piston/clips/wristpin as one assembly. Add this weight to the weight of the top half of the rod (conrod). Now you take a pecentage of this (between 50 and 60%, let's say 55%).
Add this 55% to the weight of the bottom half of the rod and machine a piece of brass or steel of this weight to fit over the crankpin.

Now you assemble the crank with this weight and balance it on the ballrace surfaces on two knife edges. If it rotates you will need to grind the heavy side until it does balance. You now have an engine that's balanced to a balance factor of 55%.
The factor is rpm dependant and I don't know what factor is best for a specific rpm, I'm just writing this up from memory. I saw it on a site somewhere.

Any material you can remove to reduce the reciprocating mass, that is the piston/wristpin/top half of rod, will make an improvement on engine performance especially at high rpm. It will also reduce overall stress.

I haven't spent any time on this myself since I don't have a good scale and a lathe.

poseyracing

My post was mainly intended to keep newbies from trashing their engines by trying to duplicate other experimenters. The main gains to be had on a sport engine are on the sleeve and crank window. Keep the dremel away from the connecting rod.

FYI- most of the Italian built engines already have good porting. The cheaper sport engines are the ones who gain the most from port work.

But...to make things clear to those who browse this board, being as I am a third generation dragracer(our legacy began in the 1950's), I believe I know just a bit about porting and balancing an engine. And yes you CAN balance/rebalance a crankshaft. That's what the counterweights are on there for in the first place. However I don't recommend the home porter to attempt to do so.

And... we have been tuning RC nitro glow engines since the early 1980's.

My intent is not to come on here for arguments sake, but I'd be amiss if I didn't share some wisdom from years of engine tuning and building. Good useful information abounds on the net concerning this hobby and I'm just glad to be a part of it.



Everyone have a great weekend and be sure and introduce someone new to RC!

SManMTB

You just can't balance a single cylinder engine.

hpi apollo

ok i've got a few questions on this matter, i ported my stock (rather crap) HPI 18ss engine, i ported every port on the sleeves, skirtd the piston, ground down the conrod to a finer edge, and rounded off the head button to get more flow into it, this all really helped and it nearly skipped to second gear, but i wanted a better engine, so i got my os 18cv-rx.....has anybody ported one of these engines? i know it has plenty of power alread but i was considering some light modding and was curious as to the outcome on this particular engine, and about grinding the crankshaft, what kinda bits are you guys using, i tried to grind down the crank on the 18ss and it chewed up my hardened steel bit......

ryan_t888

Yes you can virtually balance the mass of the crank/piston/pin/rod ect. while it is not running.

For a vertical 1 cylinder engine:
Counter weights are used to balance the mass of all the moving parts. This in turn helps with the changing momentum of the engine, reducing vibration. But the mass of the piston/pin and upper part of the rod only travel in a vertical direction and the counter weight on the crank rotates 360 degrees throwing weight around in all directions. Thereby eliminating vertical vibrations and introducing horizontal vibrations.

Through the mid-stroke of a piston the piston speed is at its greatest. At TDC and BDC, forces and the mass of the piston/pin/top of rod, completely change direction. This changing direction happens up to over 60 000 times a minute. It is extremely hard to balance this out and 100% cancellations of these forces are never achieved no matter what is done.

Lastly, the unbalanced forces acting upon the crank
Vibration are produced by the simple fact that a single cylinder 2 stroke engine is only producing power during the power stroke. This will create a frequency for every power stroke.

I’m not arguing either but trying to make it clear that single cylinder engines can not be completely balanced.

Ryan

jkulhanek

I agree ryan, single cylinder engines will always be out of balance.

I have had no problems with modifying counterweights, piston skirts and conrods, no signs of excessive vibration, and lots of performance gain.

jkulhanek

UPDATE:

My dear little O.S. .12 and I had a great time, but alas it had to come to an end...lol

A 5 hour continuous bash in mud, dirt and sand dunes and negelcting to change the air filter meant it sucked in a load of dirt and lost all it's compression [:'(].

The piston and sleeve fit was so loose that the piston would actually slide all the way through the sleeve.

So I ordered a new duratrax ABC piston/sleeve and rod, and also a new backplate.

Before cleaning and reassembling the engine I decided to modify it more. Some of the mods are the same as the worn out piston/sleeve/rod.

-Cut port channels in the new sleeve with angled cuts to help the scavenging.

-Removed the skirt on the piston and left just enough to make sure the exhaust port was always sealed off from the crankcase. The original modified piston just had bits removed to de restrict the transfer ports.

-Knife edged the new rod.

-Enlarged the port channels on the crankcase, and ground a channel out for the boost port, which never had one originally, now the boost port is fed like a normal transfer port.

-The inside of the crankcase has been contoured and smoothed out and has channels angled to help direct the fuel/air into the transfer channels.

-The top edge of the backplate has been sculpted to direct fuel/air up to the 270 degree transfer channel, the old one had lots of sharp edges and corners which I didnt like.

-I also polished the intake to mirror finish and matched the venturi to the carb a bit better than before.

-All components (apart from piston/inside of sleeve) were polished to mirror finish and the engine put back together.

I began break in of this engine and it was immediately apparent that it had more authority than before, had more torque, and towards the end of break in it had noticeably more power than ever.

Unfortunately, the pull start one way bearing died and I have been unable to start it. But stay tuned for updates.

ryan_t888

Addictive, right?

Sounds good, keep us posted.

Ryan

jguitarsandcars

OK, so from what I see, these are done mostly on an OS, or Kyosho motor...Can you use the same basic techniques on any motor, say a Team infinity .18, or the CVX taiwan engine that comes with the engines in the cheaper entry level cars?

ryan_t888

You can do most of the mods to almost any engine out there.

Ryan

jguitarsandcars

Cool, thanks Ryan

ofnaliebregts

What would someone recommend to an owner of a hyper 21 8 port. I've wanted to change the ports for a while. Maybe polish everything. What would you guys recommend to be done?

ryan_t888

Take it apart and look at how much material can be removed from the cylinder sleeve. Just the area leading up to each port on the cylinder sleeve. There are many pics of sleeve material removal all over the web.
The most power gain will be from this simple mod.

Ryan

stevehickey6

hi all hope someone can help me i have a kyosho gx15 engine i need to replace the piston and liner but can not work out how to get the old one out

i have removed cooling fin pull start and crank faceplate

i can see conrod think it is called and also can see top of piston but see nothing that undoes to get either of them out

can someone please tell me how to dismantle this engine

many thanks steve

ryan_t888

Stick about 3 plastic snap ties through the exhaust when the piston is at BDC. Then rotate the crank to push the liner out. Once the liner/sleeve is out the piston almost literally falls out.

Ryan