captinjohn

I would like to learn all the best ways to enlarge and contour ports in 2 cycle engines of 25cc-50cc. Can you please post links and photos. The tools used would be of great interest. Also if some of this can be done more accurate on a Mill , I would like to know that. Is stoning the sharp edges after cutting a good way to keep liner from cracking /flaking or wearing piston rings. Of other interest would be good port timing limits. I think a lot of data in one thread would be of interest for a lot of others. Thanks Very Much Capt.n

tstotts

Great idea Cap. Would sure like to see that.

captinjohn

I sure hope some guys like Pe Reivers, Dick Hansen, RCIGN1, AV8TOR, Brillie Brothers, tim220225, and others that know where this data can be found will from time to time add anything in the art of porting. Basically the tools used. The right tool means everything some time. Thanks Very Much. Capt,n P.S. I will post a photo of a 25cc Homelite cyl that I modified the webb to keep piston ring intact...into a wedge shape. May not be the best.???

tim220225

My Feedback: (4)

Here you go. Check this link out and you will find tons of very good information. There are others but I need to look more in the hard drive. I know Scott at Brillelli changed the ports on the 2 barrel Toro's he was doing. I have played with it some but have always been pleased with the performance of my favorite conversion engines, those being Echo. You can use an end mill or a Dremel tool depending on what you are doing.

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

captinjohn

Tim220225: I read in the 2 cycle tunners hanbook you gave the PDIf files here...is that files reshaped for porting may be the best for newbies doing this work. Far more accurate and easy to use. That was worth reading for sure. Got to go read more!!! thanks Capt,n

BillS

Porting is both art and science much like painting.

I trace the port profile on a piece of cardboard placed inside of the cylinder to assist in maintaining the profile of the port while cutting.

To determine the duration for a change prior to cutting I use a degree wheel and a feeler gage. On a cylinder that I am looking at now 1mm (.039”) represents 12 degrees of exhaust duration and 8 degrees of intake duration. Read the degree wheel angle at exact port closing and then with the feeler gage in the port and of course multiply by two for duration.

Aluminum cylinders can be easily cut with a tile cutter and Dremel tool. After cutting the sharp edges should be broken. I use die files and then Emory cloth. When finished there should be no sharp edges.

Recently I measured a G-62 that had a finger port that was 3/32 high by 1/4 wide on the exhaust. The benefit of finger porting as opposed to simply changing the duration has been forgotten. It is probably are related to an attempt to achieve longer power pulse. On motorcycles we sometimes cut the top of the piston to change exhaust timing.

Bill

captinjohn

Bills; Thanks for the data. How to you hold the carboard pattern in cyl? Duct tape maybe? Do you place edge of cardboard a few thousands above port, then cut to edge of cardboard? Thanks Capt,n

Pontiac_40

My Feedback: (3)

Cap, here's some illustrated info on a Homey being ported...good stuff

http://testfly.0catch.com/homelite/e...lindermod.html

BillS

The cardboard is only used to get the original port shape and as a profile checking tool while cutting. I hold the cardboard by hand to the cylinder wall and trace the port with an ink pen. The cardboard is then removed and used as a reference to the original port outline.

With a degree wheel and feeler gages determine how many degrees the duration is to be changed. In a current case 1mm represents 12 degrees duration or 6 degrees difference on the degree wheel with and without feeler gage.

Measure the port height. Something round will usually just fit into the port. In this case a 25/64” drill. Find something else round that is drill size (25/64”) plus 1mm. In this case a 27/64” drill will be the first go gage while cutting.

Cut the port with Dremel tool until the first go gage fits but occasionally check the profile with the cardboard template. Repeat increasing the size of the go gage until finished.

You originally guessed at the amount to increase the duration. Accuracy is subjective but I like for the end result to be accurate within two degrees of target.

Bill

captinjohn

Thanks Guys...thats the kind of data that helps everyone. A win, win Deal. Best Regards Capt,n P.S. KEEP IT COMING!!!!!!!!

BillS

Stihl 57cc blower engine unmodified. Designed to turn 8,000 rpm.
Intake – 130 degrees
Exhaust – 144 degrees

G-62
Intake – 162 degrees
Exhaust – 186 degrees with 3/32” high by 1/4” wide finger port

Bill

captinjohn

Bills: Nice data for sure. I bet if you redo the Stihl 57cc to match the G62...it will really wake up!!!! TX Capt,n

av8tor1977

My Feedback: (6)

I'm surprised the G-62 has such aggressive port timing. It would do well with a tuned pipe.

AV8TOR

BillS

Don’t know. The Stihl already turns 7100 with a 22 X 10 prop. I am planning to increase the duration by 1mm on both intake (10 degrees) and exhaust (12 degrees).

The G-62 had an in cowl Pitt’s muffler and probably less than an hour run time. The port duration is likely to be too wild to be effective without an expansion chamber. It would not be surprising for the G-62 to produce less power than the Stihl. Port timing alone is not the route to HP. Hope you have the Jennings book dissected and understood.


Bill

BillS

I was also surprised and doubt if it was matched to the 29% Extra that it was in. Judgment about the port timing is withheld until it is bench run with a few mufflers that I have available. More is not always better.

Bill