Porting Question!

[Farley9n]

Had a friend bring his Husky 371xp over to be tuned up-checked out as it hadn't been run in some time. I didn't try to start it but pulled the plug and took a compression check. It showed 125lbs which I felt was low and since the muffler was already a bit loose I went ahead and pulled it. It has a 2 ring piston and shows both rings at BDC. At TDC the bottom of the skirt is at least 1/8 above the bottom of the exhaust port. Some one had really hogged out the exhaust port. That seemd like way too much to me so I went ahead and pulled the cylinder. Intake and transfers are also huge but seem more in keeping with what I have been thinking would be an improvement. I also have a stock 371K cylinder to compare it with and the changes are massive!
Friend claims the he got the saw from reservation Indian who had done some logging with it. He has run it and felt it had lots of power but his experience is limited. It's equiped with a 28" bar and skip chain.
I guess my question is: Should the pistion be sticking up above the bottom of the exhaust port and should the skirt ever raise above the bottom of the exhaust port?????? I have both cylinders and a spare piston here and can post some pictures if needed. THANKS.......Bob

 

[Mr.]

Had a friend bring his Husky 371xp over to be tuned up-checked out as it hadn't been run in some time. I didn't try to start it but pulled the plug and took a compression check. It showed 125lbs which I felt was low and since the muffler was already a bit loose I went ahead and pulled it. It has a 2 ring piston and shows both rings at BDC. At TDC the bottom of the skirt is at least 1/8 above the bottom of the exhaust port. Some one had really hogged out the exhaust port. That seemd like way too much to me so I went ahead and pulled the cylinder. Intake and transfers are also huge but seem more in keeping with what I have been thinking would be an improvement. I also have a stock 371K cylinder to compare it with and the changes are massive!
Friend claims the he got the saw from reservation Indian who had done some logging with it. He has run it and felt it had lots of power but his experience is limited. It's equiped with a 28" bar and skip chain.
I guess my question is: Should the pistion be sticking up above the bottom of the exhaust port and should the skirt ever raise above the bottom of the exhaust port?????? I have both cylinders and a spare piston here and can post some pictures if needed. THANKS.......Bob

Sounds a little nasty to me. Post some pics.

Definately doesn't sound like something I would carry to work with.

Fred

 

[timberwolf]

Freds on the money, no sense being gentel about it, it is FUBARd. Likely run better with the stock jug.

 

[Farley9n]

The Pictures!

Here's some pictures. I used a stock single ring piston as a helper to show what the exhaust port looked like with piston at T&BDC. Cylinder base has not been cut and it was assembled without a gasket.
The two ring piston is in good shape and the rings are not worn. I'm thinking of reassembling the saw with the stock 371K cylinder. Is it the same as a stock 371xp?
THANKS for your answers.......Bob

 

[Farley9n]

The Rest

Someday I'll learn to put them right in the text......Bob

 

[timberwolf]

That is ugly. Shameful! Nice photos though!

Don't run that jug, very good chance the rings will fail on the piston and cause dammage to the lower end.

It's junk, no saving it. Who ever did it has no clue at all on what they were doing, anyone who sold that knowing what it was is a crook.

 

[weenieroaster]

Those photos are like looking through a medical text book.

 

[Blowncrewcab]

Who ever ported that had Not a Clue what they where doing. Porting the exhaust port floor like that gained Nothing, other than a great chance for a hung ring and major damage. Chuck it, or keep it on the "what Not to do shelf"

 

[drmiller100]

pretty amazing it runs at all.

 

[Danger Dan]

It's my understanding that builder has a "no open" policy! :smoking:

 

[drmiller100]

Those photos are like looking through a medical text book.

so, an opportunity for me to learn!

lets knock what we see. goal is to point out things in hopes we can all learn a few little tricks.

the easiest. porting below where the piston goes does absolutely no good, and can do harm. the pics of the bottom of the exhaust port show the guy went waaaay to far down. on the one hand going a LITTLE too far doesn't help, but doesn't hurt. on the other, if you go so far as to open the exhaust port at tdc, you are losing major power and taking chances of blown up saw.

likewise, transfers, cutting those transfers down that far do no good. worse, it hurts power. I believe a goal is to have the same cross section the entire length of the transfer. so, start at where it opens into the cylinder, get the area, then build back on the transfers to keep the same cross area.

where the guy ground huge holes on the transfers, it will totally screw up the velocity and cost some major power at WOT.

exhaust port. as the piston goes down, i imagine the first .040 as the port opens does 90 percent of the work. so, square off the tops of the exhaust ports as much as you can. This is balanced by if you make it TOO square, you can chow out rings lands in a big hurry and catch a ring.

 

[Farley9n]

Plus one on the above. I like doing more matching & smoothing of the ports than changing their timing. A compression increase, a little piston work and a cleaning up of the ports coupled with a muffler mod in my (Some but limited experience here) opinion makes for a fast clean running dependable saw.
The 371 is still apart waiting for some decisions on it's fate........Bob opcorn:

 

[romeo]

Ported with a 90 pound jack hammer


I guess that would be an attempt at a race saw. I have noticed that people on their first port jobs will go a little overboard but that is ridicules. Dropping the bottom of the exhaust port that much wont do anything. They started to have the right idea on the intake but there is no purpose in going that much bigger than the carb that feeds it, it also has a pretty nasty nick in the bore but where it was probably didn't hurt it. It looks like it would have eaten up rings quick since there was no chamfer. From what I could see of the transfers, they were as ugly as a two buck whore. I suspect no thought was put into the port timing at all. I would bet a bone stock 372 would walk all over it, there is no way that saw was quicker or had more power.

I like modded saws, but if you are flying blind, fly a little lower.

 

[timberwolf]

Good points Sean.

It's not about bashing the builder, I am sure the even first MVP saw was not what his later ones were. No one builds things perfect, esp not the first time. However, what is done in this jug is bad in a lot of ways, there is no candy coating that.

Getting things nice and symetrical side to side is importaint. Looking after the rings with ports that are not to flat, too big or sharp and have not had the edges beveled... One major misconception that many people have is that the manufacturers and engineers designing saws have absolutely no idea what they are doing, the result then is makinging radical changes in porting to atempt to build a better mouse trap. Reallity is manufactures know how to build saws, and with the exception of the low end junk saws they are designed pretty well.

For building a good ported work saw it does not require major diviations from the original design. Just slight enhancements on what is already there. Smoothing out casting flaws, widening the ports out a little, matching ports up, gaining a little compression and improving flow is all that is needed. Some times slight timing changes of a few degrees, but that is about it. Also in some cases there are limitations due to the design or parts used and then swaping out or modifying parts can work too in more advanced porting jobs.

 

[Farley9n]

Just a Little more

In the first post I didn't mention that the muffler was gutted and has both a top and right side exit but is in poor shape. As you can imagine with the way the exhaust was done this was badly carboned. The whole intake I took off as one piece and didn't look to see if anything had been done to it other than the needle stops removed. I should know by tomorrow what the fate of this saw will be. I'm hoping he will sell it to me. If I get it I will go with the big bore set from Baileys cleaned up a bit and a good muffler.
Current project is a 281/88.......Bob :greenchainsaw:

 

[troutfisher]

More is Better!!! Right??

 

[spankrz]

in my completely non expert but still slightly experienced opinion,

THOSE ARE HORRIBLE
ahahaha

a stock saw would rip that one in half

 

[Farley9n]

End Of The Story!

This 371xp has been in a box in my way for just about a year. When I last wrote about it I had thought the owner ( a good friend ) might be willing to just sell me the damm thing and I would end up putting a big bore kit and some minor porting into it before it joined my Husky pack! Didn't happen! I ended up cleaning it up and replacing the cylinder with a good used one. I was also able to reuse the piston and rings from the previous build. Once back together before running the cranking compression was just over 145lbs. so I felt that it should run. I had been through the carb and replaced fuel lines so there shouldn't be any good reason for it not to run. Wrong!!!! About all I could get it to do hit a few times and then die! What a pain in the a$$! Well since the owner had been complaining about it being really hard to start I got a coil for it but just threw it into the box with the rest on the saw. Until today that is! Owner said he was going to come by so I told him come on! We can change the coil together and if that didn't work out the next step would be to split the cases and do bearings and seals. He came, we went to the shop and I handed him the saw. It fired and died in three pulls. I told him that that was all I ever got it to do! Next couple pulls it started again, he blipped it a few times and it settled into a steady idle. "What the HELL". How do you figure that? To make a long story just a bit shorter......I replaced the bar & sharpened the chain then headed to the cookie works. Leaned it a bit and reset the idle. It runs good, sounds good and cuts good.
I told him, "Get it out of here! No Charge! It was worth it to finally be free of that saw!..........................Bob

 

[Meadow Beaver]

It's good you replaced that cylinder, what was it ported with a keyhole saw? :jawdrop:

 

[buck futter]

I think the piston you used was a 268 non-xp open port piston and they are shorter then a 372 piston and would exacerbate the result of that horrific porting.

the 372 design is one the better and is fairly well optimized as it is. If you increase all flow components to scale but an equal percentage on all ports the saw will come to life.