I am Looking for info on how to do some slight mods to my Force .26.....I do some machine work so I have a small bit of knowledge on how to do it, but what to do is a different story.....Any info would be great.

What I do for all my engines is tear drop the side ports and chamfer the boost port on the cylinder sleeve. Remember to Keep the swirling effect on the side ports. (away from exhaust) You may also open up the channels in the engine block as well. Once I did this I threw on a larger carb and got a bit more power and RPM's out of it.

I also do some work on the crank and rod.

Ryan

Thanks Ryan.....I have heard that if you take too much out you can throw off the timing of the engine....is this something I should watch out for....I am thinking of in-larging the exhaust and intake ports....Right now the intake port is 2 smaller ports separated by a thin wall and the exhaust is not even as large as the exhaust in the case opening....I am also thinking of balancing and polishing the crank and piston and con rod....I would assume a dremel is the best tool to use for these mods?? What sort of attachments are the best to use??....I know this seems like alot to do on a stock .26, but I figure if I screw it up I won't try it on my Nova...

Don't do what you plan on doing. Enlarging the exhaust without knowing anything is just going to screw up the engine.
If you increase the height of the ports you are completely changing the way the engine works. Raising the exhaust port will give a lot of top end power but you need to know how many degrees you are changing it. The more you raise it the less power it will have at low rpms.

Do you even know how to balance it? No? I thought so.... Just FYI it's impossible to balance a single cylinder engine.


Doing these random 'mods' will just turn your engine into a nice looking paper weight. You need to know what you're doing.

I meant to only take material away from the path to the port on the sleeve. Not the actual port itself.

Balancing a single cylinder engine is extremely hard. Typically they are designed to resonate at a low RPM. If they resonated at a higher RPM there is more of a chance of them coming apart.

I just used a very small grinding stone, then I used high grit wet sand paper.

Ryan

I guess I know less about this then I thought I did.....So actually making the ports larger is a big no no...If I am understanding this right only remove material from the outside or the sleeve without inlarging the ports...won't this thin the wall of the sleeve and create a hot spot in the sleeve??

Thanks Again for the help because I can see that I was heading in totally the wrong direction....This is kind of a spare engine and I don't mind screwing it up but I would like to see it run after the mods are done..

Oh and Sman...I asked these questions to get info not to get talked to like a jackass so if you can't reply in a respectful way keep your non-informative comments to yourself.....ASS!

As far as a hot spot in the sleeve, not a problem. It will make the sleeve much thinner, I did remove quite a bit of material. The point is to give more of a pathway for the fuel/air. The biggest power improvement is from this mod.

I would try this first and if you see a difference then move on to more modding. It is fun and very addictive once you see the results!

Ryan

Ryan thanks again, your info has been most helpful....any other info you can give will be much appreciated!!

You're very welcome.... ASS
I told you what not to do.

Sman...I'm glad you told me what not to do...I just wish you would have done it in a more adult way then making me think you are a Jerk with nothing better to do then give people advice in a condescending way...So now why don't you give me some advice on how to do it the right way.....since I'm sure you know or are you keeping you knowledge a secret..

Some easy and safe things you could do (if it's not already done on your Force):

Cut away some of the skirt on the piston to allow for better flow from the crank case to the transfer and boost ports.
Knife edge the lower part of the liner also to allow better unrestricted flow to those ports.
Check how the ports in the liner mates up with the ducts in the case. If you can see a mismatch you could grind the case to get a good fit and better flow.
Take out the sharp edge on the lower part of the transfer and boost port so there is a smooth transition.
Some people recommend to polish the outside of the liner, I'm not too sure it actually helps but I've done it and it didn't hurt anything.
Make sure yoy clean everything very carefully afterwards.

Those things are safe and easy to do and doesn't change any timings in the engine, it just improves the flow. I've done it on a few and I got a bit better fuel consumtion and for some weird reason it ran cooler too (can't verify that 100%, too many variables)

If you like to experiment you could play around with the width of the ports. It actually helps but be careful.
I widened the transfer ports (there are 2 in a 3 port engine) and the boost port (the one opposite the exhaust) by close to 1mm each. Make sure you are not raising the timings, just make it wider and keep all angles the same as they were. It's pretty tedious. You need to firmly secure the liner in something and use a good cutting tool for the Dremel. A magnifying glass helps too.
I felt this mod improved overall power. It was noticeable in the low to mid range. The track wasn't long enough to see how much it did on top.
Like I said, be very careful. If the timings are changed it can end up being bad and the engine won't run right.

Widening the exhaust port also works. It will give a bit more top without sacrifising bottom end. Raising the exhaust timing by 5-6 degrees will also give more power on top but you will loose some torque. By increasing exhaust timing you are effectively moving the power band up in the rpm range. The engine breaths better at high rpms the higher the port is but the torque down low is decreased.

A 'low power' engine like the OS RG has a very moderate exhaust timing of 160 - 162 degrees which makes it easy to tune and not super sensitive to weather conditions. It also has a lot of torque but will not have as much power at high rpms.
A top end engine like the MAC.21 (for example) has an exhaust timing of around 180 degrees. It makes gobs of power up top but it's weaker down low.
Both the MAC and OR RG are 3 port engines (as is the OS V-Spec) which is a 'classic' design. More ports is not equal to more power like some people say. The benefit of more ports is that you can actually use a bigger area of the cylinder wall that way.

What I mean by that is this:
You can always make a port wider but only up to a point. If they become too wide there is a risk of the piston actually tipping on its side a bit and get stuck. Instead of making one wide thransfer port you can then make two and have some support for the piston. At the same time the are of the two can be made bigger than the single port. This is (one) of the reasons some engines like the C5BB has 3 exhaust ports.

Phew, I'm tired of writing. I need a smoke

If you have access to a milling machine you are golden and can make very precise cuts.

Exactly! There will be a definite gain in power with all that. The only thing I have not done is chenge the dimensions of the ports. I wouldn't recommend it either, unless the appropriate tools are used.

After all the mods listed so far my fuel consumption has gone way up. I burn a lot more fuel than I had used to.

Ryan

Yeah, that's what's so confusing. Just doing the basic mods my consumtion dropped. I would expect it to go up. [sm=confused.gif]
A big part of the fuel consumtion formula has to do with what pipe you use.

Well I thought it would go up because you are increasing the amount of fuel that will enter the cylinder(using more fuel) thus making more power.

Anyway it works very well either way!

Ryan

It's only fuel.

Thanks Guys.....You two have been a big help in getting me going in the right direction.....I know one of you mentioned add a larger carb once all the mods were complete...What carb would be a good replacement?? Also how will these mods affect tuning this engine....( I know every Engine is different but just in general )

Just doing the basic mods will not change much. You might have to slightly adjust the needles.

In my really old boat engine I went from a stock .12 carb to a .21 carb. But I ran it on 60% fuel. (Requires a much richer setting making use of the larger carb)

I am currently trying to find a larger carb that will fit on my Tower Hobbies .15X.

Ryan

just got done knife edging the intake of the crank and doing some work on the counterbalance like friction relieving the rh side and relieving the center hole, also angled the front side of the crankpin and then polished all the marks out and rounded all corners.... this is my first time for modding a motor and uploading pics.... so i hope it works !!!!!!! This motor is an os .25 fx airplane motor but i havent changed any actuall timing yet..... still pondering that part.... comments welcome.......... ok i give up how do i upload pics???? lol....... not as easy as i thought.

click this reply ---------------------------------------------------------------------^^^^

Then upload files is on the bottom of the messaga. Above the notify me box


Ryan

ok here goes.......[img][/img][img][/img][img][/img]

try #2..... lol........

sweet !!!!!! ok. now i have to get back to the shop to finish a piece for a buddy so i can get back to modding this motor
like i said b4 comments welcome good or bad !!!!

Hey guys. let me put some input here.
First of all-any polishing or massaging on crank will not give anything at all. if you think that after polishing edges your engine went up in power-it just in our heads.
For off road engines I will sugest as follow-check and/or aler induction timing to open @ 38 ABDC and close @ 52-53 ATDC, second thing is check transfer and exhaust timings-transfer should be somewhere between 120-124 and exhaust 156-158. Never ever put piston or liner to any metall working machine as lathe or mill. To fix them secure you will need apply a lot of force and it will defenetly bent out of original geometry-then it will be paper weight. I can sugest to change anglr on transfer ports (use only dremel and your stay hand) to more steep angle, let's say originaly most of engines is about 15 degree, if you can do it to 20 will be very good result. One more thing-it will be very helpfull prepare engine before first time start-I mean piston needs to be lap in to certain size. Usualy it is head button deepnes + 1.5 mm. It will save a lot of tiem and fuel for brak in and it will make your racing life of engine about 30% longer. This thing can be done by using lapping tool and lapping compaund ( which I know it will be hard to get) or by using very fine sand paper (2000 grid) and lap piston to desired size (which will be very hard to do and don't scrw up piston). Any way if samobody will try to do that, please remmeber-first clean piston and sleeve and make sure there is no oil at all. then put piston to the sleeve and push it till stops on the top. Mesure the distance from top edge of sleeve. Ddeterminate what size you will need (mesure head button part which goes insdie sleeve ). Next step is cut piece of sand paper wide as lenght of piston, wrap ones around the piston as clamp and with slight pressure turn piston arround 2-3 times, clean it very well and put piston to sleeve again and mesure-do it till you got piston to size you want to. It sound that it is easy to screw up with sand paper, but not really. First of all I can assure you i did many many times for over 25 years I am in hobby, second is that real size will decreas just by couple of microns on diameter. It doesn't mean that it is impossible to scew up-there is great chance it might happened, but if to be very carefull, prepare yourseld very well (never be rush work on motors), try first on dead pistons.
if you have any more questions please fill free to ask and I will be happy help.
Oh one more thing-please to mean people don't start bushing my english-I am not native born american and english is my second language.
Edward