Spuds Porting and Tuning Thread

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5 hours ago, spudulike said:

Nope, nobody has posted on it.....that's all. No conspiracy, just that the thread hasn't been used!

So what, you been on holiday or somethin' ? ?

 

Thought I'd seen some posts on here during the summer,  but in hind sight I must have been searching some old posts. ... on the XP395, they're still there of course,  yonks old.... Brains going,  going,.... going ... and gone. 

[spudulike]

Mmmm, had a few family things going on that were of major concern but now pretty much sorted, backed off work a bit during the summer and am looking at keeping work at a manageable level from now on rather than taking on everything that comes in.

You have to keep the work life balance in perfect balance when you get to this time of life. Winter months are easy enough but summer is summer and holiday is holiday!

[spudulike]

I just wanted to make it clear that porting a saw is best on a good well working saw. 

Porting will not fix a crap running engine with issues.....a SERVICE.....yes I repeat.....A SERVICE will!!!!!

Just had a 357XP in, "down on power" wanted porting......wanted a new bloody crankshaft as the big end had 1.5 - 2mm of play in it.....completely shot!!!!

Porting is not a silver bullet, it enhances a decent saw and doesn't bring the dead back to life!

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Weird timing... picked up a 357xp yesterday, non runner - described as having low compression. Expected piston trouble but its free enough, cylinder 😩 looks like this: 

 

 

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I price checked Meteor and Hyway top ends before buying, need to check rod width as its '04 model then time to order....

Needs the inlet clamp update and carb rebuild.

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The same, cheapest of the cheap.

So turns out it was piston trouble with mine, not a lean seizure but heading that way ....

[Stubby]

2 hours ago, frammo said:

back to bench with this one,cocked up timing numbers or 359carb aint up to job🤣🤪

Cherry ?

[spudulike]

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 grinding the crown exhaust 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.............

Edited March 7, 2021 by spudulike

[spudulike]

Here is my more commercial view on what I call porting: -

Most of the saws I get in for porting are anything from knackered to new....mostly "Well Used". Most need a good 45 min clean and an hour service. Things like the fuel system and pressure and vacuum testing of the saw are important if you are going to get more out of it and failure to do this will result in the saw not lasting.

In my world, I look at £200-250 as being what the general fella with a saw for porting will spend, most will accept this as being acceptable on a MS200T up to a MS880, small MS150s and MS201s are different in so much as a muffler mod and ignition advance make such a big difference, I don't do a full port but do a muffler mod and ignition advance/service for around £100.

So, what I do is clean the crap of the saw and get it as clean as I can. I strip it down, inspect its bits replace what is needed, make sure the fuel system can provide what is necessary and then do a muffler mod. This can be a simple increasing of the outlet hole area or letting in a secondary outlet port but always look for a "Rorty" sound and increasing flow rather than an ear splitting row likely to piss the owners customers off.

I then try to increase compression and widen/reshape ports and do piston work to improve flow in the engine then finally tune the carb to keep the saw close to manufacturers limits but not to exceed them. This won't give max power but will ensure safety of the owner and the saw. The chain brake and chain catcher are cleaned and inspected and on all top handle saws, the cover is stripped, cleaned and all components inspected to make sure it works as the manufacturer designed it to do - those that have had me do your MS200T/MS201s will have seen this!!!

My modifications give at least 25-35% increase in performance and I avoid changing port timings as it is time consuming for the reasons in my previous post and I tend to aim for getting the 80% of relatively easily achieved gains rather than spending hours achieving timings that will give a relatively smaller increase in performance compared to the simple modifications (simple in my world) that I do that make a real difference.

I don't tend to measure the performance from what I do but I did have a customer who was competing in timber-sports with a 372XP. He was all over his saw and sport and already had a jungle muffler on the saw. My mods to ignition advance and ports (without taking the jungle muffler increases) gave him another 30-35% increase in performance.......his figures not mine.

In short, when I mod a saw,  I aim to get the easier 80% and avoid the difficult 20% gains so my customers get a good working saw with enhanced performance, that is safe and will last.

Call it what you like, that is what you get!

 

Edited March 6, 2021 by spudulike

[Ratman]

Here is my more commercial view on what I call porting: -
Most of the saws I get in for porting are anything from knackered to new....mostly "Well Used". Most need a good 45 min clean and an hour service. Things like the fuel system and pressure and vacuum testing of the saw are important if you are going to get more out of it and failure to do this will result in the saw not lasting.
In my world, I look at £200-250 as being what the general fella with a saw for porting will spend, most will accept this as being acceptable on a MS200T up to a MS880, small MS150s and MS201s are different in so much as a muffler mod and ignition advance make such a big difference, I don't do a full port but do a muffler mod and ignition advance/service for around £100.
So, what I do is clean the crap of the saw and get it as clean as I can. I strip it down, inspect its bits:blushing: replace what is needed, make sure the fuel system can provide what is necessary and then do a muffler mod. This can be a simple increasing of the outlet hole area or letting in a secondary outlet port but always look for a "Rorty" sound and increasing flow rather than an ear splitting row likely to piss the owners customers off.
I then try to increase compression and widen/reshape ports and do piston work to improve flow in the engine then finally tune the carb to keep the saw close to manufacturers limits but not to exceed them. This won't give max power but will ensure safety of the owner and the saw. The chain brake and chain catcher are cleaned and inspected and on all top handle saws, the cover is stripped, cleaned and all components inspected to make sure it works as the manufacturer designed it to do - those that have had me do your MS200T/MS201s will have seen this!!!
My modifications give at least 25-35% increase in performance and I avoid changing port timings as it is time consuming for the reasons in my previous post and I tend to aim for getting the 80% of relatively easily achieved gains rather than spending hours achieving timings that will give a relatively smaller increase in performance compared to the simple modifications (simple in my world) that I do that make a real difference.
I don't tend to measure the performance from what I do but I did have a customer who was competing in timber-sports with a 372XP. He was all over his saw and sport and already had a jungle muffler on the saw. My mods to ignition advance and ports (without taking the jungle muffler increases) gave him another 30-35% increase in performance.......his figures not mine.
In short, when I mod a saw,  I aim to get the easier 80% and avoid the difficult 20% gains so my customers get a good working saw with enhanced performance, that is safe and will last.
Call it what you like, that is what you get!
 

Fair play mucker, wasn’t really needed imo for you to go to this extreme but hey ho. Good reading [emoji106]