Spuds Porting and Tuning Thread

[Rich1911]

Husqvarna 359 porting  Number 5 of 6

 

 

Setting the squish.

I don’t have access to a lathe, as such I don’t remove any material from the bottom of the cylinder or top of the piston and I don’t get into the realms of timing, degree wheels and resetting the woodruff key on the flywheel etc. I’ll leave that to those with more skills and experience.

I simply put on the piston, four dabs of grease and four pieces of soldering wire 1mm dia (at this stage the piston ring is not installed). I then offer up the cylinder with no base gasket and tighten the four screws. I then rotate the crankshaft until the solder has been crushed against the top of the cylinder. Then remove the cylinder and measure the thickness of the crushed solder. I use the thinnest measurement and cut out a gasket from gasket paper either 0.15mm or 0.25mm thick or a combination of both so the overall gap (squish) between the top of the piston and the cylinder is near 0.6mm but no less than 0.5mm. The squish measurement on this 359 with 0.15mm gasket paper is 0.57mm after I’ve added 518 sealant the final squish will be very close to 0.6mm.  When porting 357’s I usually end up using 0.15mm gasket paper.

 

Installing the cylinder

First the intake boot, plastic partition and clamp need to be put on the cylinder. I have my own way of doing this as I’ve come across dozens of intake boots in the past that have been installed incorrectly where the male intake tube has been crushed or misshaped.

I first offer the intake rubber boot to the cylinder without putting on the plastic partition surround and metal clamp, this way I can tell visually with 100% certainty that the male tube is inside the cylinder impulse hole. I’ll then push on the plastic partition over the intake boot and finally the metal clamp. No special tool for the metal clamp just long nose pliers a screw driver and a raised block of metal to rest the cylinder on whilst fixing the metal clamp. These can be a pig to attach my trick is to hold the clamp in place with a wire ring whilst I bringing the ends together with the pliers and pushing the bottom of the clamp into place with the screwdriver. I’ll then put together the rest of the intake items, impulse hose etc.

Once the piston ring is put on the piston I’ll add a smear of Loctite 518 to the cylinder base then add the gasket paper then another smear of Loctite 518, oil the inside of the cylinder and piston ring and slip the cylinder over the piston and I add medium strength thread lock to the bolts before I install these. I don’t put on the top or brake handle at this point as it makes putting the cylinder on a lot easier without them.

[Rich1911]

Husqvarna 359 porting.  Number 6 of 6

 

I then pressure test and vacuum test the saw to make sure everything is sealed and holds pressure/vacuum and also check the fuel tank vents properly. Then assemble the saw as normal adding new fuel hose  and fuel filter, one further job is undertaken and that is to smear gasket sealant (Hylomar Blue) around the base of the chain oil pick up pipe before it goes in the saw body. I also modify the chain plate by depressing slightly the area which sits on top of the chain oil feed pipe. When the chain bar is fitted and tightened up the depressed area of the chain plate squeezes the chain oil feed pipe against the oil pump. Both these mods I find will stop any chain oil leakage when the saw is stored.

 

Carburettor

A few options here, Walbro HDA (199 or 198 or 197) or Zama C3 EL42

I’ll always opt for the Walbro first as it delivers more fuel than the Zama but the Zama is a more reliable carb and seems to idle better.

I’m happy to use the Zama on ported 357’s but not on the 359 without first modifying the Zama main fuel jet as it just doesn’t deliver enough fuel to pull the chain when the bar is buried full length in wood.

As you’ll see the Zama feed hole (Zama is the silver jet on the right) to the main jet is considerably smaller than the Walbro. I tried a trick I picked up from the US web sites, if you drill through the Zama feed hole all the way through to the other side of the main jet it increases the fuel delivery. I use a 0.5mm drill. Don’t try and use a bigger drill thinking a bigger hole will be better, it won’t work. It simply bogs down the saw with too much fuel when revving hard. Also I found this doesn’t work on the 357 even after porting but it worked a treat on my first 359. I’ve put a Walbro 198A on this 359 but will probably change it to a modified Zama later.

The compression of the saw when built was 175psi. I expect there will be a further increase to this when fully bedded in. I’ve set carb to run rich the rpm at 12900 for the time being and I’ll check and increase this to around 13600 after about 10 tanks of fuel when it should be bedded in.

The saw accelerates hard, there are no flat spots or delayed pickup when squeezing the trigger. I’ve not cut any wood yet but it will get a full day’s work this weekend.

You may be asking why bother with the 359 and just use a 357XP instead? The difference between the two are the 357 has 46mm cylinder and 359 has 47mm, the 357 has stuffers on the crankshaft and the 359 doesn’t and the 357 max revs 14000 whereas the 359 max is 13600.

Well I’m fortunate enough to run both saws, both 357 and 359 are ported, both scream and are fantastic to use but the first 359 seems to accelerate more aggressively and certainly pulls better in the wood which I put down to the modified Zama carb so it’s always the saw I pick up first….

Time will tell if the one I just built works as well.

I hope this may be of help to anyone thinking of porting saws it’s good to share information.

 

 

[Lillywhite Timber]

Well Steve , the stone cutter arrived yesterday ... Sounds perfect ! . The 357 is pulling like a train and superb acceleration after the adjustment you suggested the other day  .

Thanks very much for the work on both . 

 

[spudulike]

1 minute ago, Lillywhite Timber said:

Well Steve , the stone cutter arrived yesterday ... Sounds perfect ! . The 357 is pulling like a train and superb acceleration after the adjustment you suggested the other day  .

Thanks very much for the work on both . 

 

Glad you are happy PJ, I hate those stone cutters but worth repairing in the end. Glad the 357 is working well, thought it would after having a new piston and they often need a tweak once they have a bit of fuel through them - just glad the courier could tell the difference between Birmingham and Eire

[kcstevens]

What size hole is best in the 201tcm exhaust Mr Spud?

[spudulike]

On ‎14‎/‎03‎/‎2018 at 11:38, kcstevens said:

What size hole is best in the 201tcm exhaust Mr Spud?

Sorry, missed this, usually 10mm although I don't drill holes nowadays, have a neater solution!

[Wonky]

On 11/03/2015 at 22:22, spudulike said:

The saga of my ported 066 Red Eye continues, a very old coil gave an ignition advance of 20 deg with no change on revving it. In the cut it had as much go as a bog standard 50cc old saw on its 20" bar so pretty crap. Technically a two stroke with a set advance should be around 25 - 27 deg which will make full power but lots of kick on start up.

 

The lack of power I assumed was lack of ignition advance and the following backs this up.

 

I have tested a standard MS660 and it has circa 30 deg at idle and 22.5 deg around 7-8k revs so this coil has a built in advance and retard circuit which I already knew but wanted to find out what and when it kicked in.

 

I have now fitted a MS660 aftermarket coil to my saw and it is now idling with 22.5 deg at idle and this drops right down to 5-10 deg flat out. This sounds a lot but having done a lot of research on the subject, a good curve will be near zero for ease of starting, rising vertically to around 29-32 deg at idle and then down to 20 deg in mid range and dropping at max revs to 0 -15 degrees to protect the engine from pre ignition, the curse of ignition modification.

 

Soooo - the answer is to take the flywheel off and position it ten degrees clockwise of where it is now giving a few degrees extra advance on standard to give the engine extra wallop but not enough to cause pre ignition.

 

Anybody still following the train of thought:001_rolleyes:thought not......guess I do too much thinking:lol:

 

In laymans terms - I now know where I need to be, why the saw isn't right and what I need to do:thumbup:

 

Oh - I have learn't a lot about ignition timing advance as well!

Umm I guessing I’m a bit late to your porting thread,, but it’s an everlasting/ongoing thread, and I’m learning,  learning lots..   but what you say here is just can’t understand what your sayin, to what I’ve read. Else where,

,I think it’s pprolly time for a picture as it’s is a 1000 words and it’s. Better than me trying to ask the teacher the question

 

cheers

[spudulike]

On ‎23‎/‎04‎/‎2018 at 23:44, Wonky said:

Umm I guessing I’m a bit late to your porting thread,, but it’s an everlasting/ongoing thread, and I’m learning,  learning lots..   but what you say here is just can’t understand what your sayin, to what I’ve read. Else where,

,I think it’s pprolly time for a picture as it’s is a 1000 words and it’s. Better than me trying to ask the teacher the question

 

cheers

That graph pretty much says it all and is a curve from a relatively modern coil/saw. Earlier than that, the coil had a fixed ignition advance, no "soft" ignition start like on most modern machines so the manufacturer set them to around 27 degrees as a 30 - 34 degree advance would probably break bones on start up!

Two strokes need an ignition that advances rapidly and then falls off mid to high revs unlike a four stroke that advances more and more through the rev range! 

Anyway - the saw is set to just over 30 degrees which is slightly more than a standard 660 - been some time since I did it but that is where I believe it ended up!

[spudulike]

Interesting conversation with one of my customers today. I had recently ported his 395XP, he had taken a big tree down and had a 28" bar on the 395XP and a 30" on the MS880 which was standard. He was somewhat surprised to find the 395 outperforming the 880 with ease on ringing up the same timber - not bad considering the weight and engine CC difference!

It is good to get a bit of feedback as it is rare I get the chance to run the big saws I port through big wood and it gives me good information about the improvements my adjustments make.

[spudulike]

Lets say that someone decided to do a muffler mod on a 560XP but didn't comprehend where the hot gas would end up, this may happen.......