What's the deal with transfer finger ports?

[WHSH]

Hi,
I am a working saw modder and have a small saw shop. I do compression work, and all of the other usual modding stuff. I had a saw shipped up to me from CT to look at and rebuild and port. The owner said it was done by a guy in the north west who just dropped off the map. I got the 460 and it was really cooked down, melted piston crown, molten bubbles in the squish band. The modder had a AM big bore on it, ok quality, and he did finger ports from the lower transfers, the work look good. I had a .015 pop up, a base cut, no real timing port changes no widening other than the from the base cut, no polishing but only the finger ports. I have seen these in MX form and have heard of them on saws. Other than more fuel what is the point. It would seem that with no increase in time area with the intake or exhuast it would just act to decrease the speed of the transfers. Some one have some experience or knowledge whey one would want to make these on a working saw?

 

[mdavlee]

That saw came from Dean at Washington hot saws. I had one just like it an wasn't impressed. Finger ports gives more transfer to feed on too of the piston. I've done some sets in 288s and liked the results. I will be trying a set in a stihl before long. You have to turn the piston around backwards or relocate the ring end pins. It will take more intake to feed them.

 

[WHSH]

Its a small world, and how did you know who did it from the description? The customer said that the builder dropped of the map and could not find him nor any shop would touch the saw, so he looked me up on the internet. I am right down the middle with my porting, meaning I leave a lot on the table for durabilty and longevity. I want the saw to be very strong, but I rely on return customers and referals, so doing fringe race saw stuff, its not part of the plan. There were a handful of questonable things done with the saw, one was the carb still had its limiter caps on it, second was that the muffler heat sheild was stock, never matched the to exhaust port or the muffler, so it was a point of restriction. The base was cut to thin for a high compression big bore saw, the quality of the AM jug was, so so, the exhaust and intake time area was not touched. I say this not as and attack on some one who do I don't know, that is unfair, but just a statement to the problems I found. Anyways I'm glad to have the business and sorry that the customer has such a bum saw.

 

[WHSH]

The video is slow to start bit this is the saw after I got done with it. No finger ports, final comp 190 psi, timing changes suited for a 24" bar in North Eastern hard wood. These cuts are in fozen white pine, folks like strong saws in weak wood.

 

[CanadianCarGuy]

What was the squish set at? If it is too tight there is not enough room for the flame front to pass and it starts to melt things (aluminum begins to melt at constant exhaust gas temps over 1400 you expose it up to 1600 for short periods). Too much ignition timing advance (to the point where it detonates) will do this as well. Do you have pics of the damage? If the ring pin locations are wider than the piston skirt than turning the piston backwards should be ok. I used to use finger ports for better scavenging of the exhaust gases from the combustion chamber, but find chainsaw cylinders to be too thin these days to make em big enough to move enough intake charge to really be effective. 190psi is good for a work saw that you want to last. I like em 170 to 185ish, with a big bump in ignition timing.

 

[Moparmyway]

The video is slow to start bit this is the saw after I got done with it. No finger ports, final comp 190 psi, timing changes suited for a 24" bar in North Eastern hard wood. These cuts are in fozen white pine, folks like strong saws in weak wood.

"Still 4 stroking @ 14,400" ???
Are you sure, it sounded like it didnt 4 stroke at all ........... sounds lean on the high side

 

[Trx250r180]

one of my 440 stihls has fingers ,and my 066 has bridge ports ,they helped the rpms pull higher loaded in the cut

 

[WHSH]

"Still 4 stroking @ 14,400" ???
Are you sure, it sounded like it didnt 4 stroke at all ........... sounds lean on the high side

It was, I found it by testing it two ways, saw was hot and free rev out of wood listening to the transition, and also the sound in an out off wood based on cut pressure when the saw was hot. I can understand why you would think this but if were in person with the saw in hand, you might have a different perspective.

 

[WHSH]

My porting is not that exotic to be putting finger/boost ports in them. I like the ring support of leaving the transfers to close to orginal time area. I want to send a saw out knowing that it well with its limits structually. Most folks don't take care of there saws, even if they tell you they do, so I try to cover my rear end as much as possible. If a saw is amazing but only lasts a year, they will never remember or talk about how fast it cut but rather how it blew up and who did the work. The last guy to touch the saw gets the blame, regardless of what happend.

 

[WHSH]

What was the squish set at? If it is too tight there is not enough room for the flame front to pass and it starts to melt things (aluminum begins to melt at constant exhaust gas temps over 1400 you expose it up to 1600 for short periods). Too much ignition timing advance (to the point where it detonates) will do this as well. Do you have pics of the damage? If the ring pin locations are wider than the piston skirt than turning the piston backwards should be ok. I used to use finger ports for better scavenging of the exhaust gases from the combustion chamber, but find chainsaw cylinders to be too thin these days to make em big enough to move enough intake charge to really be effective. 190psi is good for a work saw that you want to last. I like em 170 to 185ish, with a big bump in ignition timing.

Its an honor to have you respond to my post, I like your work and vids. I don't mess with the ignition timing, to worried about involuntary fly wheel shift. 190psi is the max on a big saw like that. I figure that out threw mistakes, broken cylinder bases, and lower crank bearings. I do .025 to .030 squish on big saws and nothing below .020 on any saw. Its just not a risk I want to take. No finger ports for me, more time than I want to spend and to much risk for a work saw. below is the video of the dead saw