buttdud1122

I just got a free 25cc homelite weedwhipper engine. I want to build some sort of rc car, and I want to raise the compression and grind out the exhaust bridge. I need a centrifugal clutch, and I want to raise the copression ratio and reach some higher rpms. Where can I get a piston ring kit and the centrifugal clutch? Anything else I should do to get the most I can out of this little gasser? Any help is appreciated! Thanks!

purenitro33

Don't push it too hard or it will just blow up, ebay may have the rebuild kit but it's not a commonly rebuilt engine due to the lack of quality. I have seen them put into boats but as soon as you bump the rpm up, durability goes out the window.

buttdud1122

makes sense... Any place where I can find a clutch?

purenitro33

Your best bet would be to ask in the gas boat section, they use them more for that application then land based and may have more info on which clutch might work.

proanti1

My Feedback: (2)

A trick for raising the compression and advancing the port timing on weed eater engines is to remove the base gasket, then use a little RTV in its place. These engines have a flywheel on one side, and a pull start on the other... not really anywhere to mount a clutch.

1QwkSport2.5r

About the only place you can use a 25cc engine is in a 1/5th scale or a custom scratch build.

Many guys use converted weedy engines in airplanes as well as boats, but compared to a chainsaw engine, they're not as powerful. Most homelites have the clutch on the flywheel side because they usually have a closed backplate on the rear. No shaft sticking out.

Grinding the bridge out of the exhaust port could cause the ring to catch the edge of the port. These engines can be ported to turn 12,000rpm, but don't last long at that rpm. 10,000rpm is the safe limit. Tuned pipes help, but without running gas/glow or glow fuel, power gains will be limited. More compression will make more power, but you have to see how much clearance you have between the piston and spark plug to know how far you can go. If running premium gas, keep it under 13:1. If using methanol, you could probably go up to 14.5:1 provided you don't use nitro.

Just a few thoughts.

purenitro33

K, I don't want to argue but lowering the jug will increase the compression "but" it will also lower the timing duration. You have to raise the ports in order for the open duration to increase.

I also have to point out that a properly tuned pipe will show big gains on a gas engine as well. Here is an original stock baja 5B with a completely stock 26cc CY engine that I modified. I also designed a tuned pipe for it and here are the results, take the pipe off and it would lose a pile of that downhill wheelie pulling power.

http://www.youtube.com/watch?v=_bpTkF669_g

1QwkSport2.5r

Im not trying to argue, or contradict you. As I see it, the port duration will not change. The point when the ports open will change though. The ports will open later which may cause a loss of power but it's a common way to adjust the powerband. Generally, the earlier the exhaust opens and the longer it's open lends to being able to take better advantage of a pipe and make peak power at higher rpm. Of course there are other variables to consider. One cannot just drop the jug and file the exhaust port. The transfers and boost port( if there is one) need adjustments too.

But I'm just a RTR basher guy. What do I know.

purenitro33

If you put a degree wheel on it and time it, with the jug being lowered by removing the gasket, the ports will open later and close earlier, this will reduce the open duration, albeit a small change, it is a change none the less.

8MILLSNIPER007

I know this is a few months old, but lowering the jug will actually increase your intake duration and lower your exhaust duration.  Set your intake around 150* Exhaust 170-180* Stuff the backplate in order to keep your volume up.  And set your squish @ .020 (you will have to remove the squish band inside the cylinder in order to get to .020  With these numbers you will make great power and it will live as long as you run 20-30:1
You can set your squish down to .010 which should be right around 180psi.  But with the crankshaft only supported on one side it wont last long, you will either shear the rod pin or if it has a 3 piece crank you will shatter the axehead (counterweight).
Also in order to remove the bar in the exhaust port you need to pin the piston ring, Pm me if you want a good write up on how to go about that!
Lastly, you will never see the kind of power a new Zenoah makes, the homie has 2 transfer ports and the Zens have 4 trans ports.

purenitro33

I stand corrected, the statement above is true. I was thinking nitro engines as the ports all open above the piston, the gasser's intake is drawn into the case below the piston skirt, my bad and apologies.

8MILLSNIPER007

Ahhh yes I do see how that could be confusing, I did see an 80cc two stroke once that was an ABC style that had all the ports above the piston and boy did that thing make some power...

8MILLSNIPER007

I know this post is a few months old but honestly for a car engine you would be way ahead of the game buying a Zen or RCMK that is built for a car. Not saying the homelite wont work but it will be a challenge. If I cant talk you out of it and you still want to convert the homie then you can pm me and I will give you all the info you will ever need to get that homelite screaming and be reliable too!