Spuds Porting and Tuning Thread

[spudulike]

8 hours ago, topchippyles said:

Really good read spud and very interesting. Might be asking a daft question but your saying that you get 30-35% more performance out of the saw so does this mean the manufacturers are producing under powered saw units or is it a case of enhancing and modifying a standard engine like you would a racing car so to speak.

Pretty much so. Manufacturers work with EPA regs (that is a BIG part of it), they have to make less than 118db noise and will work with a much narrower set of parameters on port size, shape, opening. 

Motorcycle manufacturers were getting 20hp out of a 125cc engine back in the late 80s.......the MS880 makes 8.6 Hp so chainsaw technology is a fair way behind. Even the NEW fuel injected MS500....Bimota did that in the 80s as well on motorcycles, it finished the company but that is another story.

[Retired Climber]

6 minutes ago, gary112 said:

Good point,also if you had a new saw done i guess your warranty would be out the window

I honestly don't know if it's a good question or not. I'd imagine your insurance company would bend you over as well if they found out a modified saw was involved in an accident (once the HSE had a go). 

 

Edit. Anyone know enough about PUWER to know if it's relevant?

 

Edited March 7, 2021 by Retired Climber

[bmp01]

11 hours ago, spudulike said:

In response to various comments on porting,

Porting is viewed in different ways....here is perhaps a purist view and will follow this post with what my more commercial business take is: -

You take a two stroke engine, you put a timing wheel on the crankshaft, many use a drill chuck as it makes it simple. You affix a pointer to the engine that points to the outer part of the timing wheel. You insert a piston stop, you rotate the engine clockwise and anti clockwise moving the timing wheel until you match the degrees in either direction meaning that when the pointer points to zero degrees, you have TDC (Top dead centre).

From this point, you can measure the important parts of the engines timing....these being "blow down timing" - the timing between the top transfer ports top and the top of the exhaust port - shorter is perceived as more aggressive and found on higher revving saws plus the higher the transfer port is, the longer the fresh fuel charge is entering the combustion chamber. Followed by exhaust port timing - the point the exhaust port opens (where the top of the port lies in regards to TDC. The higher the port is usually means the saw revs higher but it has less compression due to the piston having less travel up the bore to make compression. And finally, the inlet port duration, that is how long the inlet port stays open thus charging the crankcase with a fresh fuel charge.

So, for the purist, you have blow down time, exhaust port timing and inlet duration. You then try changing these figures by ...getting figures used by other tuners or developing your own figures and get to them by grinding the top of the transfer ports, top of the exhaust port or bottom of the inlet port to achieve them. Some machine the squish band of the cylinder and the base of the cylinder to allow more compression and greater scope of changing the port timing of the engine. Then there is the "pop up piston", the outer part of the piston machined as is the base of the cylinder where the middle part of the piston goes higher in to the combustion chamber making much more compression with 220 psi being pretty much the most you would want as more will slow the combustion process.

Some motorcycle tuners used to port the piston rather than the cylinder as it was easier and cheaper to test timing figures by changing the timing by grinding the lower skirt of the inlet side of the piston and the crown inlet side of the piston and then try different pistons rather than scrapping cylinders if it didn't work out.

So to meet a set of pre determined port timing figures you have to sort out your compression/gasket/squish first of all and then keep fitting your cylinder, measuring your timing with the wheel and then removing, grinding and repeating until correct to your figures. This is time consuming but it is an effective method of modifying an engine to achieve the exact figures you have developed or "borrowed" and know will work.

One set of figures will not work on all saws....it doesn't work like that and all tuners will have their own approach to these figures, what they mean and we haven't got on to the general basics of modification yet!

More to follow.............

 This ought to be a Sticky at the start of the thread.  

Quick edit of '...crown inlet side of the piston...' maybe ?

[spudulike]

Just now, Retired Climber said:

Is there an issue letting employees use modified saws? If there was a kickback or trousers not stopping the chain quick enough related injury, I'm thinking the HSE would be all over the fact that the saw had been modified to make it more powerful than the manufacturer intended. 

 

 

That is one reason I don't push the revs beyond the manufacturers maximum recommended specification. An air leak or just a well used engine can also peak out of this specification and have had to pull many limit caps to get the saws back in to the black but the safety reason is one area I am careful about.

In answer to your question - ported/modified saws should only be used by the owners of the saw and in no way would I recommend or condone giving a modified saw to an employee.

As an employer you have a duty of care to your employees health and safety so it isn't wise to give them a ported saw.

In my world, my customers ask for a saw to be ported, I don't sell it to them, they ask for their saw to be modified. When it is done, I check out the safety devices on the saw, cleaning, lubricating and servicing them. 

I have asked many when their saws were last serviced.....I usually get a blank look on that one. Coming from an engineering based manufacturing past, we used to have to check all heavy plant safety devices at the start of each shift, carry out preventative maintenance, training etc and log the lot. 

If the H&S get involved in a serious accident, I would imagine they would question when the saw was last maintained and by whom........now that is probably a big grey area judging by the state of most of the chain brakes on the 200s I get in!

[spudulike]

11 minutes ago, gary112 said:

Good point,also if you had a new saw done i guess your warranty would be out the window

Yes, correct and I always ensure the owner knows this and really prefer at least 10 tanks through the machine first.

[spudulike]

Just now, bmp01 said:

 This ought to be a Sticky at the start of the thread.  

Quick edit of '...crown inlet side of the piston...' maybe ?

I meant that some bike tuners cut the front edge of the crown of the piston where it interacts with the exhaust port thus giving a very similar effect to lowering the exhaust port. I also recently found it on a Wiseco Dominant piston I was asked to fit to a 372XP.

[spudulike]

12 minutes ago, Retired Climber said:

I honestly don't know if it's a good question or not. I'd imagine your insurance company would bend you over as well if they found out a modified saw was involved in an accident (once the HSE had a go). 

 

Edit. Anyone know enough about PUWER to know if it's relevant?

 

They are good questions and can't say one way or the other. Many would say that the modification allows the user to complete a more forceful and accurate cut with less chance of it splitting and then there is using a smaller saw to do heavier work giving less fatigue on the body.

All are the reasons most like a modified saw and were the reasons many of the yanks started porting......046, 2.5' bar, semi skip chain, ported instead of lugging a 066 or 084 about all day!

I guess H&S would ask if it was a contributing factor or not!

[Retired Climber]

10 minutes ago, spudulike said:

That is one reason I don't push the revs beyond the manufacturers maximum recommended specification. An air leak or just a well used engine can also peak out of this specification and have had to pull many limit caps to get the saws back in to the black but the safety reason is one area I am careful about.

In answer to your question - ported/modified saws should only be used by the owners of the saw and in no way would I recommend or condone giving a modified saw to an employee.

As an employer you have a duty of care to your employees health and safety so it isn't wise to give them a ported saw.

In my world, my customers ask for a saw to be ported, I don't sell it to them, they ask for their saw to be modified. When it is done, I check out the safety devices on the saw, cleaning, lubricating and servicing them. 

I have asked many when their saws were last serviced.....I usually get a blank look on that one. Coming from an engineering based manufacturing past, we used to have to check all heavy plant safety devices at the start of each shift, carry out preventative maintenance, training etc and log the lot. 

If the H&S get involved in a serious accident, I would imagine they would question when the saw was last maintained and by whom........now that is probably a big grey area judging by the state of most of the chain brakes on the 200s I get in!

Thanks, that's interesting. I agree, letting employees use a modified saw is asking for trouble. It's one thing a saw unintentionally being a bit more dangerous than stock, but to intentionally make modifications to make it more of a risk to use would be bloody difficult to defend in court. 

 

Equally, making a saw louder than standard has health and safety implications too. 

[spudulike]

My first saw I ported was my own 346XP, I was on Arboristsite at the time and spent a little time talking to Brad Snelling (well known US tuner) about it. In his words - don't change the stock port timing and don't hog the lowers out too much. 

Interesting point on the port timing as this was the reason it all kicked off. Seems the 346 port timing is pretty much bob on and the guys on Arboristsite still call their 346s "ported".

Mixed up world we live in!

[bmp01]

6 minutes ago, spudulike said:

I meant that some bike tuners cut the front edge of the crown of the piston where it interacts with the exhaust port thus giving a very similar effect to lowering the exhaust port. I also recently found it on a Wiseco Dominant piston I was asked to fit to a 372XP.

I know. But its skirt trimming on inlet side as you said and crown trimming on exhaust / transfer sides (not crown trimming on inlet side, which is what needs editing...).

STICKY..... STICKY..... STICKY..... 😀