Railridr

I am in the process of converting a few Homelite 25cc motors that I picked up for free. One of them has been run a lot and is low on compression compared to the other Homelite 25's that I have. I have plugged the EGR hole above the exhaust port which helped, but I was thinking of replacing the piston ring. Would a stock Homelite 25cc ring perform as well as a ring from Frank Bowman? I know that on the Ryobi motors with a single ring, performance is greatly increased by using a Bowman ring. This is mainly because the Ryobi ring on these models do not seal well. Would I see the same benefit from the Bowman ring on a Homelite motor? or is the design of the stock Homelite Ring good enough that I would not really see much of a difference?

w8ye

My Feedback: (16)

There are some variances in the Homelite's for they have been made for a few years in various models. As a general rule, the 25 has a conventional ring but every once and a while, there will be a pinned one. You can identify which kind it is by looking in the exhaust port. The conventional ring has a divider in the exhaust port whereas the pinned one has a single large exhaust port.

If you can pick up a ring locally very easily and inexpensively, you should get that one. Other wise get one from Frank Bowman.

Enjoy,

Jim

av8tor1977

My Feedback: (6)

I just put Frank's rings in my Homelite 30cc and I am super pleased with them!! His service and support are the best I've seen in many years. He answers all e-mails and questions promptly, and I had my rings two days after I ordered them. I would go with his rings, and will be doing so on any engines of mine that I decide to replace the rings on. His rings broke in within a tank of gas or so, and the engine has much more power. If yours is a pinned ring, I would definitely go with Frank's ring(s), as he uses a notched design that fits over the pin and allows a tighter ring gap for more sealing. I can't say enough good things about Frank and his product.

Take care,
AV8TOR

Railridr

Thanks for the information. All of my motors have a conventional ring and an exhaust port bridge. It is interesting that you mention that there were some 25cc motors with a pinned ring. Do you have any idea of what type of equipment that is came on? String Trimmer, Blower, Chain Saw? Any Idea on how long ago the pinned ring was produced? I am interested to find out because If I could find the part, I could install the piston with the pinned ring and mill out the exhaust bridge, and the little nub in the intake port. I was planning on experimenting down the road with with installing my own pin, but if I could get a factory part it would save me some time.

If you don't mind me asking, what did you pay for the ring for your 30cc homelite av8tor?

av8tor1977

My Feedback: (6)

The rings from Frank are $9.50 each, but I think they are worth it!

Check this site: http://www.shark-racing.com/Ingles/T...acaoMoting.htm

In one part it shows how a guy installed a pin so he could do away with that bridge over the port. (Be patient, that site loads very slow.)

Good luck,
AV8TOR

Railridr

Thanks Av8tor. The Shark Racing site is what gave me the idea to pin the ring and mill the intake and exhaust port. I was planning on doing it down the road, but I was thinking it would be really easy if I could find a factory 25cc part that already had a pin installed.

Railridr

Something I was thinking about Av8tor. On your 30cc you mention that the Boman ring is a notch design to fit over the pin. In the picture on the Shark Racing site the ring is butted up to the pin. I am assuming by your description that the pin on your 30cc is not flush with the side of the piston like on the Shark Racing site. I was trying to think of how I could do a recessed pin and an overlapped ring. I suppose I could just recess the pin in the groove instead of making it flush with the side of the piston. I was also thinking how much compression would I really loose if I just butted the ring up to the pin instead of recessing it. Would recessing the pin and notching the ring really be worth the extra effort.

av8tor1977

My Feedback: (6)

With Frank Bowman's rings for pinned pistons, they are already notched. It wouldn't work to notch a stock ring, as you wouldn't gain anything. The ring has to be longer to begin with, and notched to go over the pin as well. What Frank has you do, is either tap the pin in until it is half way down into the ring groove, or carefully grind it down with a cutoff wheel or tiny carbide bit.

AV8TOR

platero

You can make the pin in the ring, it is easy and work well, so you can to eliminate the bridge in the exaust port
Take a look to my web site is in spanish but lot of photos
Good luck
http://cablemodem.fibertel.com.ar/ci...lite_25_cc.htm

Railridr

Thanks for the link Platero. I went ahead and ordered rings from Frank Bowman for my 25cc Homelites. I decided to use the bowman rings instead of the stock rings after discussing this with Av8tor, a friend in my club, and Frank Bowman. I also decided to pin the rings in place and use a notched ring design. This will require drilling a hole in the ring groove at a location on the piston that is never exposed to an open area. One possible location is between the intake port and one of the transfer ports. A piece of stainless steel rod is inserted into the new hole and cut to length. The pin is then fixed in place with a small amount of JB Weld. The pin is then ground down to allow the notched ring ends to lock in place on top of it. Attached is an illustration of what I am talking about.
Because I am pinning the rings in place I will be able to mill out the exhaust port, and the little nub in the intake port to help the engine breathe better.

Rupurt

I have a 25 with the pin and no bridge in the exhaust.
It came on a zip start trimmer fortunatly i still have the manual it refers to models zr20760 and zr20772 hope this helps

Railridr

Thanks Rupurt,
Do you know what the UT number is on your engine? The number is usually on a little sticker that is on the backplate of the motor. Also do you know the serial number from your motor?

Rupurt

Sorry I cut that off and threw it away. There are other problems with this engine its got one of those compression release things as a result the carb insulator is huge compared to the one on a normal 25

Railridr

Rupurt, I figured out that model numbers that you have, zr20760 and zr20772, correspond to the homelite UT numbers of UT-20760, and UT-20772. The specifics of each model are:

Trim N' Edge String Trimmer UT-20772
TrimLite String Trimmer UT-20760 before before S/N MB0850000
TrimLite String Trimmer UT-20760 after S/N MB0849999

Each one has a 25cc motor.

I compared the part numbers of the piston assembly on each of your trimmers to the part numbers of the piston assembly for each of my trimmers and blowers. They should be different since your rings are pinned, but they are not. All of your trimmers and my trimmers and blowers use the same part number of UP00768 for the piston assembly. BTW UP00768 was superseded by UP00768A. UP00768A was then superseded by 984544001. 984544001 is the current part number for the 25cc piston and ring assembly. This piston assembly currently sells for $29.84 at http://www.ordertree.com, and for $10.35 at http://www.outdoordistributors.com/

I was thinking, maybe your string trimmers were a special 30cc model? That would explain the pinned ring, and the lack of an exhaust port bridge.

w8ye

My Feedback: (16)

Homelite's parts system is rather generalized. If you need a coil, there is one part number. But on Homelite's, some have Phelon magnetos and some have Walbro. They force you to use a Phelon coil on a Walbro flywheel? Phelon coils are real weak compared with the Walbro.

Its also the same story with the carbs. You never know whether you are going to get a Zama or a Walbro.

Jim

Rupurt

Ok, I will check the serial number on the engine itself this weekend. I dont think it is really worth looking for this engine specifically its probably more worth while looking for a 30cc.

w8ye

My Feedback: (16)

Some dealers, that don't know Homelites very well, will not even start to look up the part without the UT number.

Other dealers will genralize what you want and come up with the correct part (using their own UT numbers from memory I guess?). There are several dealers around where I live but, anymore, I just go to the one that doesn't demand the UT number. My 30 doesn't have any numbers on it and never did (at least on what's left of it?). It was a replacement short block. The only number was on the John Deere box it came in. I bought it from the knowledgable dealer.

Enjoy,

Jim

Railridr

w8ye, I understand your point about Homelite's part system. They will have a part number for a carb and they may have 2-3 different carbs from zama or homelite that are functionaly the same. However, it would be a mistake if they generalized an internal engine part such as a piston assembly with a free floating ring, and a piston assembly with a pinned ring. As an example, can you imaging if Rupurt ordered from Homelite what appeared to be the correct piston assembly for his converted trimmer, only to discover that the ring is not pinned. Can you see the problem if they were generalizing these two parts? My point is that a pinned ring and a free floating ring are different enough mechanically, that they should have their own part number. That is why I am looking for a different part number for a 25cc piston assembly that has a pinned ring.

Rupurt

Maybe it's not he right manual. The people who import them had put their stamp on everything and removed pages from the manual. I will phone them tomorrow and see if they know whats going on. There is also a number on the cylinder under the exhaust i will check it and tell you what it is.

Rupurt

Ok, I phoned today the dude says that the part number for the piston and ring the one with the pin is 0634729d, I hope this makes sense to you.

Railridr

Thanks Rupurt. I am going to try and hunt down this part.

Rupurt

I was just curious but did you find these parts if so was it the right stuff.

BTW the number on the cylinder is ps03429(sorry i took so long to get back)

MickMolloy

How did you engine come out ???
for parts info look at www.ordertree.com

Railridr

Rupurt,

I tried looking up the part number that you gave for the cylinder (ps03429), and it does not show up in any of the online parts vendors databases. I did find a new model of 30cc Homelite Blower that is currently available here in the US. You can see my post about it here.

http://www.rcuniverse.com/forum/New_...2492708/tm.htm

Mick, I have not finished building the engines that I have yet. I am working on converting 10 of them, and have just received the last 5 from club members. I need to clean them up before I can start on them. I am planning on doing some porting, and lowering of the cylinders for more compression, and cut off the casting from the crankcase. We are going to setup to do the machine work all at the same time. If time permits I may also try to machine a new backplate that will take up more space in the crankcase, rather than install an aluminum plate onto the existing backplate. I think I can make a new backplate that will take up more space and uncover the rear transfer port.

Rupurt

I feel like an idiot, i found another homelite trimmer manual that refers to model #UT20805 the other manual was obviously for my other trimmer.