365/372 kit builders thread

[Maintenance supervisor]

I was googling some and at this point I just wants to understand a little more about 2 stroke engines, I know the basics alright - but exactly why does people do what they do to their cylinders in their quest to make them run "better" than what the educated designers and engeneers who originally made them have concluded with.

I am not going to change any timing or do changes to my cylinder other than making the transitions and channels smooth. I am not going to remove material that would make the air/gas flow at a reduced velocity, or that might reduce the vacuum and compression below the piston because of a larger volume as a result.
I just like to be on the safe side of things, doing modest changes that cannot be negative in any way.

But I am still qurious obviously, so I found this thread using google and I think it was really interesting.
https://www.arboristsite.com/threads/the-myth-of-high-compression-in-2-strokes.320432/

That thread is a little misleading, motorcycle Engines and chainsaws might be similar in design but they are using a totally different band of power.
I also have a motorcycle 2 stroke builder book from the 70s that basically contradicts most of those posts. The book covers specific engines and oem part numbers to add more compression for racing, so were they trying to make people lose the race? on their equipment.

 

[link]

That thread is a little misleading, motorcycle Engines and chainsaws might be similar in design but they are using a totally different band of power.
I also have a motorcycle 2 stroke builder book from the 70s that basically contradicts most of those posts. The book covers specific engines and oem part numbers to add more compression for racing, so were they trying to make people lose the race? on their equipment.

Also this thread is about "hot" engines, so my guess is much of it wont apply to a basically stock engine anyway.
But I think the points of view is interesting though, and those all adds to the puzzle pieces and that too much of anything is probably not good.
My thoughts of compression is without being an engine engineer that it's a good thing on a stock engine if you want torque as far as I understand it.
And also what you do if you remove the base gasket, lowering all the ports and in effect you actually make the stroke longer. Perhaps at the expense of High rpm and HP, but the saw dont run at 13k rpm in the cut anyway. And perhaps those ports are related to the ignition chamber more than to the base initially.
Not sure I will be able to do that since I have levelled the crankcase base and removed a small amount of surface though, I have been thinking about making a copper base gasket if I need to because I can make it at any thickness.

 

[link]

Another thread I want to have as a reference, all you ever wanted to know about porting - its all there:
https://www.arboristsite.com/threads/best-porting-instructions.358732/

 

[link]

It seems I never will get to the finish line with this build, but its just because I have so much fun with it I never want it to end.

I have levelled the ports at the opening position/edge, carefully not to elevate them and to maintain the angles.
I used a small diameter slightly cone shaped very fine milling bit/burr, the standard ones from Ali is sharp but way too coarse.


And I have made a template for the exhaust opening, the left tracing is the Farmertec and the right is the Hyway.
I have cut it using a straight edge and a scalpel and used a fine mist spray adhesive, this is mounted a tad too high to get the top surface of the port.

 

[9050lx]

About the O-ring yes I think so too, and it is supplied with the kit, even though I already ordered an OEM one since it was reported missing.
I have two carbs for my 038 and they both performs perfectly, but for this one I have a new original Tillotson HE-18A carb on the way too so I actually have an alternative to the aftermarket one that came with the kit.
The Tillotson carb is actually quite affordable, they are still made and you can buy them directly or through a dealer. The inner venturi is 16,5mm and that is the same as the aftermarket kit carb. I'm not saying its any easier to adjust but if you have problems with the one that came with the kit it might be worth checking out.
https://tillotson.ie/shop/he18a-carburetor/

The Dolmar/Makita 6401/7300/7900 carb bolts right on and is very smooth.

 

[link]

The Dolmar/Makita 6401/7300/7900 carb bolts right on and is very smooth.

That is a good advice, not too expensive and it have a bigger venturi too at 17mm it seems.

 

[link]

I don't expect anyone to actually use this template but I might as well leave it here as an example of how I did it anyway.
When I tried to print from the PDF file the result came out too small, so I have embedded the DXF file as well. I have added reference measurements.

 

[link]

The Dolmar/Makita 6401/7300/7900 carb bolts right on and is very smooth.

How about the linkage, throttle wire and choke, any modifications needed or tips you could share about this, or is it just "plug and play" ?

 

[9050lx]

Plug play

 

[9050lx]

when using the farmertec carb I had to set the high at 1/2 turn out to run.at one turn it was pig rich.

 

[cuttinupferalivin]

Also this thread is about "hot" engines, so my guess is much of it wont apply to a basically stock engine anyway.
But I think the points of view is interesting though, and those all adds to the puzzle pieces and that too much of anything is probably not good.
My thoughts of compression is without being an engine engineer that it's a good thing on a stock engine if you want torque as far as I understand it.
And also what you do if you remove the base gasket, lowering all the ports and in effect you actually make the stroke longer. Perhaps at the expense of High rpm and HP, but the saw dont run at 13k rpm in the cut anyway. And perhaps those ports are related to the ignition chamber more than to the base initially.
Not sure I will be able to do that since I have levelled the crankcase base and removed a small amount of surface though, I have been thinking about making a copper base gasket if I need to because I can make it at any thickness.

Deleting base gasket doesn’t increase stroke of crank in effect or in theory. It does have its benefits but to increase crank stroke the cylinder volume must increase.ie:be lengthened/made taller,not shorter.

 

[cuttinupferalivin]

It seems I never will get to the finish line with this build, but its just because I have so much fun with it I never want it to end.

I have levelled the ports at the opening position/edge, carefully not to elevate them and to maintain the angles.
I used a small diameter slightly cone shaped very fine milling bit/burr, the standard ones from Ali is sharp but way too coarse.
View attachment 974208 View attachment 974209 View attachment 974210

And I have made a template for the exhaust opening, the left tracing is the Farmertec and the right is the Hyway.
I have cut it using a straight edge and a scalpel and used a fine mist spray adhesive, this is mounted a tad too high to get the top surface of the port.
View attachment 974211 View attachment 974212 View attachment 974213

On am cylinder upper transfers are almost always off size and lower in spots causing interference with piston crown Egan they are supposed to be fully open
While this will surely be debated I did come to find as a fact that by beveling the edge of the piston Crown in the place of interference that it makes the saw wake the -:;/ up.
Main issue with these engines is air fuel mixture escaping through exhaust port as the transfers and exhaust ports are simultaneously open.
By beveling the crown it shoots the flow of fuel straight past the exhaust port to top of cylinder, into the chamber, leaving no room for escape. If done correctly it also directs the mixture towards the front on chamber where the spark will be waiting, providing your timing is on spot.
I could not believe what a difference this made, unbelievable and like I said, it is true to the form and basic physics. The so called squish band is trivial to the method mentioned here

l
It has such an adveantage that I do it on oem cylinders once I found am were not worthy of using in mop

 

[link]

Deleting base gasket doesn’t increase stroke of crank in effect or in theory. It does have its benefits but to increase crank stroke the cylinder volume must increase.ie:be lengthened/made taller,not shorter.

Well, I guess what I meant was that by removing the base gasket - all ports are lowered about 0,5mm compared to the piston.
The distance/stroke from the piston crown top position to the start of the exhaust and transfer ports will be elongated about 0,5mm, so the stroke that inherits compression will be longer. And, the exhaust and transfer ports will open about 0,5mm less than if a base gasket is used.

 

[link]

Main issue with these engines is air fuel mixture escaping through exhaust port as the transfers and exhaust ports are simultaneously open.

Perhaps, but as long as you still get enough fuel/air mixture in to the cylinder that does not matter to the engine performance, it does however matter to the engine efficiency conserning fuel consumption and inviornmental impact.
The ports are already angled for best performance in a reasonably modern 2-stroke engine, the primary transfers are angled backwards away from the exhaust, and the secondary transfers is angled backwards and upwards towards the ignition chamber. Together this should create a vortex circulating away from the exhaust port and up to the ignition chamber and then down again at the exhaust side of the cylinder.

I do think what you are suggesting is interesting indeed, but I have not seen any porting gurus recommend doing this other than for testing purposes.

 

[link]

Well, it's taken some time before I was ready to do some cutting at my sawbuck/horse with this saw.

What I learned is that this is what happens if you're too greedy porting your exhaust opening too wide and too flat:

The rings will grab the edge.

I was just finishing adjusting the carb and it was getting good and warm, it was at idle just come down from max when I heard a "ching" sound and it took about a second and it stopped. I didn't try to pull the starter again because I new something had happened.

Other than that I was using the Farmertec carb that came with the kit and it was extremely easy, defined and responsive to adjust both at max and at idle.

I already have a new Hyway 76,5cc cylinder with a popup piston to replace it, and I know already I like this saw !
The best way to learn is the hard way

 

[Maintenance supervisor]

That's why these things are great, you "didn't" FUBAR a 200.00$ oem piston and cylinder.

 

[Sierra_rider]

Well, it's taken some time before I was ready to do some cutting at my sawbuck/horse with this saw.

What I learned is that this is what happens if you're too greedy porting your exhaust opening too wide and too flat:
View attachment 1010282 View attachment 1010283 View attachment 1010284
The rings will grab the edge.

I was just finishing adjusting the carb and it was getting good and warm, it was at idle just come down from max when I heard a "ching" sound and it took about a second and it stopped. I didn't try to pull the starter again because I new something had happened.

Other than that I was using the Farmertec carb that came with the kit and it was extremely easy, defined and responsive to adjust both at max and at idle.

I already have a new Hyway 76,5cc cylinder with a popup piston to replace it, and I know already I like this saw !
The best way to learn is the hard way

It's always hard to tell from pictures, but looks like you could've beveled the port edge more on certain areas of that port. It is a fine line with beveling...too little and you can snag a ring, too much and you're effectively changing the port timing.

I aim for a very slight arch across the top of the exhaust port. In theory, you want the entire width of the port to open up ASAP without getting to the point of snagging a ring. With this in mind, I'd rather have a port that opens up quicker(the width that is,) and gives up a little overall width...rather than a very wide port that has to have a more arched roof. My understanding is most of the flow happens immediately when the port begins opening.

Disclaimer: I'm not a professional saw porter by any means...more just like an educated idiot in the matter. lol.

Regarding the FT techs, I've found varying quality between the kits. The Husky cylinders I've seen all looked very nice...the Stihl kits were another matter. I've got multiple 044 cylinders, you can tell that they came from different castings and don't even look like they're from the same manufacturer. Some were very good quality, with even port heights and ports that were pretty clean. Others had a very poor hone and had ports that were a mess. Also the squish bands have been very rough on most of the Stihl kits...not a big deal as I mill them on the late.

That's why these things are great, you "didn't" FUBAR a 200.00$ oem piston and cylinder.

This...I gained most of my limited porting experience by learning on FT cylinders. I've got some that I came up with the right recipe on and were awesome...one still lives on one of my saws, it was so good. Others I made into complete dogs and I learned what not to do. If the only options were OEM cylinder kits or even $100+ Meteors, I doubt that I would've ever bothered getting into modding saw cylinders.

 

[link]

It's always hard to tell from pictures, but looks like you could've beveled the port edge more on certain areas of that port. It is a fine line with beveling...too little and you can snag a ring, too much and you're effectively changing the port timing.

I aim for a very slight arch across the top of the exhaust port. In theory, you want the entire width of the port to open up ASAP without getting to the point of snagging a ring. With this in mind, I'd rather have a port that opens up quicker(the width that is,) and gives up a little overall width...rather than a very wide port that has to have a more arched roof. My understanding is most of the flow happens immediately when the port begins opening.

Disclaimer: I'm not a professional saw porter by any means...more just like an educated idiot in the matter. lol.

Regarding the FT techs, I've found varying quality between the kits. The Husky cylinders I've seen all looked very nice...the Stihl kits were another matter. I've got multiple 044 cylinders, you can tell that they came from different castings and don't even look like they're from the same manufacturer. Some were very good quality, with even port heights and ports that were pretty clean. Others had a very poor hone and had ports that were a mess. Also the squish bands have been very rough on most of the Stihl kits...not a big deal as I mill them on the late.


This...I gained most of my limited porting experience by learning on FT cylinders. I've got some that I came up with the right recipe on and were awesome...one still lives on one of my saws, it was so good. Others I made into complete dogs and I learned what not to do. If the only options were OEM cylinder kits or even $100+ Meteors, I doubt that I would've ever bothered getting into modding saw cylinders.

It was beveled but very small, like 0.2mm - mostly just the plating. And I was using Caber rings that also have a slight bevel.
I think you are right I should try to make a compromise in the width and perhaps an arch. Slightly less width and perhaps a slight arch of some sort. I'm a little worried that a bigger bevel at the center of the exhaust port will only expose the soft aluminum behind the plating and perhaps the plating will be peeled off the cylinder in time.

Yeas the FT cylinders looks like they are all made at a different factory, some ok and some not so nice. This particular BB cylinder was quite nice in port shapes but needed to be cleaned up some, what worried me the most was the very coarse honing/plate finish, because while the piston rings might polish it up in time - the rough sanded surface at the plating in the very hard Nikasil might wear down the soft aluminum piston skirts quicker.
I will be a lot more careful with the Hyway cylinder, it has rough port shapes with a lot of excess beveling at the ports, but a very nice/fine honing/plating finish.

 

[link]

I had a second FT BB cylinder I got as a reserve when I ported the first one that failed, it was a cylinder only and it came without a cardboard box and in one corner the fins where bent severely so I planned not to use it.
But now as then I have examined both the 50mm cylinder that came with the 365 kit and the Hyway BB and the FT BB cylinder, and I only comes back to the same conclusion that I would prefer the FT BB cylinder.
I used my propane torch and a couple of pliers and I corrected the fins on it.

I have a Hyway on my 038/381 and I simply love it, despite the short stroke it has tremendous grunt for its size with a 20". And it has eventually turned out to be a dead solid reliable and simple work horse - its the easiest saw I have to start ! Spent a lot of money and work on it though...
I am building a 460 as well - super deluxe with lots of OEM parts including an OEM crankcase, on this one I have chosen the Hyway BB cylinder at 82,5cc because I just basically wants a bigger version of my 038/381 for milling spruce. Actually its not Hyway but its made in Taiwan and it looks exactly like Hyway with the same distinct features, but I think the brand name is New West. I have not ported this one, only cleaned and polished because the cylinder was so nice to begin with and I just wants it to be solid and long lasting. The Hyway cylinders are notably tuned for torque and mid rpm power.

But for this 372 I want something different for the sawbuck/horse, and more as a reserve for milling.
And what would I learn if I only fail without even trying to correct my faults ?
And so since I have an accurate template drawn in CAD (as in computer aided drawing - not the chainsaw bug), I have a perfect opportunity to make a new exhaust port template based on my old template and my new knowledge.
That's what I will do, it might take some time but I will report back.

 

[link]

I did prepare the second Farmertec BB cylinder and it turned out alright.

I have placed a spacer down in the cylinder so that the piston is at where the transfer ports opens and I have secured it in place with some tape too, then I have beveled/rounded the piston/cylinder transfer port entrance a little;



Beveled and polished the inside of the cylinder afterwards, barely visible;


Cylinder comparison;


The intake is adjusted to fit the intake boot perfectly, and the exhaust is adjusted to the muffler/gasket;


Since I have made the exhaust port window symmetrical inside the cylinder it have become a little wider, and it does not have an entirely flat opening as I made a very slight arch and the opening is raised about .040 in the middle of the port. But eventually it is quite wide and flat, so I have beveled/rounded slightly the upside of the piston rings about 1/2" at the center of the port to prevent the ring from catching the cylinder wall at the upstroke. I use a black marker pen to color the metal so that I see exactly where I grind/polish;