Iam about to start moding a 25cc, it is the one peice forged, non clutch short shaft version.
I will be using it in a future boat build.

I took apart the motor today to clean it and start cutting the plastic housing off.

Istarted gutting the muffler which I will be drilling two half inch holes in and silver soldering stacks.

I will be posting pics along the way.

We are looking forward to seeing your posts

I got most of the plastic housing off that Ineed to, and tried to finish gutting the muffler.
The baffle box where the exhaust goes out from the muffler is stuck on there extremely well and I am having trouble getting it to come off.

Ibent the seam a little bit getting the 2 peices out that are in the middle, one of them came out very easily.
The other one not so much, I had to cut one of them to get it to come apart.
It is nothing I can't fit with a little tlc when I put it back together.

I will be posting some pictures tomorrow of my progeress so far.

Here is some photos of the motor, muffler and plastic housing.

As you can see the baffle is still in the muffler it is very hard to get out, not sure how I am going to get it apart.
Any help would be appreciated.

The plastic housing with the peices beside it that I cut off, still need to cut a little bit off the crank case cover.

The motor looks good it doesn't have any scoring and looks to be in good condition.

to get the last part of the inner muffler out, drill out the little spot welds carefully so that you don't go through the other side, that's how I've done it before.

you're going for an air cooled boat engine I'm assuming? one the one I set up a year ago that I haven't finished yet (got my airboat going instead) I trimmed the pull start housing similar to what you did but I left more of the ducting for the cylinder but it'll probably be fine.

For the baffle in the muffler I used a small die grinder and ground the spot welds down until the baffle came loose. Sort of like what the previous post said but he used a drill.

If it is a cad plated muffler, the cadmium will have to be removed where you are going to weld. I did two. one was black and the other was cadmium.

Yeah I plan to keep it air cooled for now.
I might eventually water cool it at moment I am keeping things simple and then go from there.
This is just my spare motor as the one you saw before is going in my mono and this motor it just to learn on and maybe make a boat out of later on.

Thanks for the tips on how to get the rest of the baffle out, I will give it a try and see how it goes.

I'm not sure if it is cadmium or not but I plan to strip it down to bare metal and then silver solder it back together.

The cad plating is silver looking. That muffler looks like it is black oxide coated to me but it may be dirty is the reason I mentioned.

Yeah it is black oxide coated and has some dirt/grease still on it as well.
Appreciate the heads up. either way I will ge grinding it down to bare metal and either leaving it like that or painting it with hightemp auto paint.

Well i decided to drill them and did it carefully but still managed to drill through 2 of them. OOPS... Guys I have some patching to do.
Also I have to grind down the edge of the other side where the extra material was left over from pulling the middle baffles out because it is stopping me from putting them back together smoothly.

Today I took apart the other engine that Ihave which Ipurchased from someone else and found out it has more modifications then Ithought.

The piston looks like it has been machined down on the top and on the bottoms? I am assuming this is done to lighten it as well as make the squish clearance adjustment needed for the top. Also it raises the compression?

The crank case has been milled down I am assuming to make the squish clearance smaller?

Does it look like a decent job has been done? I did not do the work myself and this is the first modified motor I have seen.
I have not yet had a chance to check the timing but I plan to in next few days.
The engine still has the bar between the exhaust port but both ports have been modified as well.

The cut on the piston doesn't look completely like the book to me?

I remember there being a squish band cut around the perimeter with this being blended in a dome radius back to the center. i guess there are many ways to do it?

The skirt on the exhaust side is critical because of sub piston induction possibilities because the cylinder base or the case top surface was cut?

The skirt on the intake side controls the timing/duration of the intake port from the carb

As a result all the timing intervals need to be rechecked? Seems like we talked about all this on the other engine?

The book?

You tell me I am only guessing on these mods. I am still new to all of this. I am sure the things you are saying are correct seems from what I have read....

Ihaven't checked the timing on this motor yet I plan to.
This is the first time I have had it apart since I purchased it.
I will post my findings as soon as I have some numbers.

I was hoping to use this motor as a sort of guide to help me with my stock motor I plan to mod.

I have started the motor once and everything seemed to run fine I only had it running a very short time though....

Yeah, check the port timing numbers to see where they are at. Seems surprising someone did this much work to the engine and didn't do the "Pin the ring" mod. I imagine you have read about that. You send the piston to Frank Bowman, and he puts a pin in the ring land and makes a special piston ring for it. Then you grind the bridge out of the exhaust port. It is a worthwhile mod.

I am wondering why they cut the piston skirt. Lowering the cylinder raises the intake port timing. Cutting the piston skirt raises it even more. Not necessary usually for our applications. It is possible this engine was intended for very high rpm operation for a car or a boat. Checking the timing of the ports will tell more...

AV8TOR

This motor is a boat motor, it is also water cooled.

I thought the same thing strange they didnt pin the ring and take out the bridge.

I will check the timing tonight and post some more pics.

Oh yeah... the boat guys run those things 10,000 rpms plus! I'm betting you find quite high timing numbers.

AV8TOR

All these Homelite mods were popular 10 years ago but is hard to come across now

I put all the jibberish together as you cut the edge of the piston down to leave 100 thousandths between the edge of the piston and the top of the ring land. This cut goes in 400 thousandths. Blend into the uncut portion taking into consideration the shape of the dome in the cylinder .

Now place solder in heavy axle grease in one quadrant of the piston. Assemble the jug and pull the engine through a few times. Measure the thickness of the solder. Repeat for the other three quadrants. You want to cut the cylinder base to get .020" squish band clearance.

Then onto port correction?
I = 140
E = 160
Transfer = 124
Blow down = 21 <style type="text/css">p { margin-bottom: 0.08in; }</style>

It is the difference, in rotational degrees of the crankshaft, between the opening start of the transfer port and the opening start of the exhaust port.</p>

Crankcase back plate volume reduction? to .020" clearance with crank

Interesting reading http://bbs.homeshopmachinist.net/showthread.php?t=39737

http://www.edj.net/2stroke/jennings/
http://www.edj.net/2stroke/jennings/...rshandbook.pdf

<hr size="1" style="color: rgb(209, 209, 225);" /><! / icon and title > <! message ><div id="post_message_421098">Ok so I checked the timing and here's what I got.
148 intake
164 exhaust

I tried to check the transfer timing but not sure I was doing it correct.
Blow down is 21

Here are some pics of the exhaust and intake ports.

I am not sure if the crank case has had any reductions, it definitely hasn't been stuffed.

Thanks for the thread I will have to read it all the way through.......</div>

I have a Homelite 30cc that I did with similar port timings as yours. It turns a 16 x 8 APC wide blade prop at 9400 rpms. Also has electronic ignition, stuffed crankcase, all port interfaces smoothed, squish clearance set at .020", larger carb, etc.

AV8TOR

Sounds like that motor goes pretty good.

I want to make sure I have the piston ring in the right position I think it was off when I got the motor. Should the opening be perpindicular to the ports?

Do you think it would be a worthwhile thing to remove the bridge?
I have been told it would be a worth while mod. I am wondering if I can do it myself.
Iaslo was told I would need to radius the edge does this mean to just smooth it out a bit as well as pin the piston?

Another question I have is what numbers should I shoot for with them motor Istarted this thread with that I plan to mod?
Intake 130 range and exhaust 156 range or should I go higher??

I am going to practice on a mac motor that Ihave a spare head to which is scored and get the hang of things then dive in on my stock homie....

If you have a free flowing muffler, the engine will benefit from removal of the exhaust divider.

You must pin the ring

Be careful about the Nikasil coating on the inside of the cylinder that you do not flake it off

Iplan to probably pin the ring in the future, for now I will leave it and see how it runs.
I have a template for making a tuned pipe from chipbreakr and plan to try to make one so when I do that I will probably take out the bridge.
For now I have a gutted can muffler.

I checked my clearance and it looke like it is about .025-.03

Pinning the piston, grinding out the exhaust port bridge, and using a new Frank Bowman ring are the FIRST things I do when doing a Homelite 25cc.

The ring gap on these little engines should be really, really tight. Spec. is .003" for the ring gap, and that is about the thickness of a sheet of paper. I'll bet if you check, your ring gap is several times that big.

Hop ups go like this:

1. Make the engine like new in all sealing, including ring.
2. Then start modifying other things.

Always start with a freshened engine, never with something that could gain power just by a simple overhaul. The new ring is only like 10 bucks...

AV8TOR

Iam scarred Imight mess up the piston if I try to pin it myself.
Iknow you can use a welding rod as the pin, anything else that can be used?
What size drill bit would I use to drill out the piston and would Ineed to use a dril press?
Obvioulsy Idon't drill all the way thought just enough to seat the pin.

Iplan to get a ring from him when Ipin the piston.