[Timberwolf]

These are piston ported motors. A few guys have tried to put reed valves on them with hit and miss success. The reeds have only worked on the larger motors run with tuned pipes.

For the most part cases on these little motors are quite tight and given they are super short strokes with with bore to stroke in the 1.4:1 plus range even before overboring it's not hard to achieve lots of base compression. The cranks in these motors are lobed, so that brings up another welding topic welding these lobed cranks into full circle cranks.

Problem with reeds though on the small motors is the plenum volume after the reeds that becomes part of the base volume. Also given the desire is just for maximum power at high RPM there is little advantage using reeds in the conventional sense, however some designs using a hybrid of reeds and piston porting have shown to work.

 

[zapster]

Here is a CHAINSAW.

http://media.damagedreality.com/V8ChainSaw.avi

...zap!

 

[deadman1474]

Here is a CHAINSAW.

http://media.damagedreality.com/V8ChainSaw.avi

...zap!

Zap are you back for good?

I can't speak for everyone but I can say that you are the ones with the most post, And the one that has been the most helpfull to everyone on this site that ever asked a question. Oh yea and sorry for Hi Jacking you'r thread

 

[zapster]

Zap are you back for good?

Nope.

...zap!

 

[cranest]

Timberwolf, been a few months npow. Just wonderted where you are in your "season" and how your mods turned out. Understand that none of this is a static situation, always finding out more and continually modding.
I sent you the Wiesco link.
Stew

 

[Timberwolf]

I have not really tested out the welding yet need to put some hours on it and see, looks promising though in the little bit of testing I did. Did do some welding on a cast cylinder though and it worked pretty well.

Right now been playing more with ceramics and coating on the pistons.

One thing I want to try is to fill in the lower ring groove. Not sure if it would be best to try to fill the square groove as it sits or notch it out on Lathe and then weld into a more "V" or "U" shaped groove.

 

[Rojodiablo]

I understand welding the piston dome for compression.

What is the purpose of welding the piston skirt?

Craig, if the skirt is shorter, there is less frictional loss. Buuuttt...with a 2 stroke, the skirts are often grooved, to carry some lubricating oils on them. Too short a skirt can lead to a lack of oiling on the cylinder walls.
Also, if the skirt is too short, you can get some nasty piston slap, especially in a single cylinder motor. It already vibrates, regardless of the amount of counterweight on the crankshaft. The single firing pulse shakes the motor, and at certain rpm, the shaking plus piston slap will be fatal.

OP- use 4043 for the build up on the piston, or 4047. The 5356 is not a good filler choice for very high service temps. You will see too much embrittlement on the piston crown in an oil cooled motor. A water pumper, it would be more acceptable, but probably not recommended.

 

[Craig in Denver]

Rojo:
Thanks for the reply. Unless it's at a factory level, I'm still thinking that welding on a piston is a bad idea. Instead of welding the second ring grove shut, why not just leave the ring out? There would be less reciprocating weight and less piston distortion??

TIA, Craig

 

[Rojodiablo]

I personally would not be eliminating rings. You need 2 of them for sealing/ wiping the cylinder wall. Plus, thew 2 rings tend to help with centering the piston in the cylinder so there is not galling on the sides of the piston.

I have to admit, this thread is a lot of fun to watch; we all love R&D, and destructive testing!!!

 

[littlefuzz]

What kind of chains to those things run?

 

[Timberwolf]

I'l see if I can find a couple pics of chain, they are just as modified as the engines. In some cases each link dissasembled machiened and put back together. Possible to have 20-40 hours into a chain, though most just get 6-8 hours of filing.

As for the rings on these motors only one is needed. Pretty much anything running over 8,000 RPM need very little sealing and the second ring is nothing but drag on the cylinder wall scaping oil away and weight. These racing motors are never asked to produce power below 10,000 and in most cases run more in the 14,000-18,000 range. Many production saws only have one ring, the only time the second ring really works is when the first wears out or gets stuck. Also removing the lower ring makes more room for ports. The rings are pinned with locator pins that get in the way of where I would like to add ports. Having a single ring piston is an advantage there too.

I have left rings out and that works ok, but there is some short circuiting of charge from the transfer ports out to the exhaust port and reverse flow of exhaust back to the transfers through the empty ring land. Blocker pins can be added in the ring land, but if a ring is left out portions of the piston lose support and can fracture.

As far as building up the skirts, it is just to get more width on exhaust and intake ports. Rings can survive with ports a hair over 70% of the bore diamiter, but often the skirts on the pistons limit the port width to 60% or less. Skirt need to full seal the port, so port will always be a couple mm narrower than the skirt If there is not enough port width then high RPM power suffers as there simply is not enough time to get all the charge/exhaust trough the narrow port.

Here are a few chains, a couple wrecked pistons (one went off pretty good when a steel washer came loose and droped into the engine at full throttle) and a cylinder where the two rear transfer ports were added, in this cas a single ring piston is being used, the ring end runns between the rear transfer ports (lower middle of the picture)

 

[Craig in Denver]

Timberwolf:
Thanks for the detailed answers to the multiple questions. As Rojo said, this has been fun to follow and learn.

OBTW: yer knutz. :drinkup:

Craig

 

[Rojodiablo]

Thanks Timberwolf. I knew the bare basics of the piston sealing the ports, but all my 2 stroke experience is with reed motors. So, I am learning a good bit about these motors.

I like the idea of them basically being a WFO style motor!!! Who needs midrange when 12,500 is the basement, and 16,000 is the ceiling!!!!

 

[jimmys]

Never seen a piston like that mushroom-shape guy upper right. Not much friction in the bore, but how does it seal the ports? Except for the ring land it doesn't look damaged. Or is that for a reed valve engine? Wow, and thanks also for the education.
Jim

 

[Timberwolf]

Just about all the saw engines are piston port, a few older saws had reeds, but these were most often steel reeds and motors that never saw more than 7 or 8 k RPM. Making the ports is a matter of working around the limitations of the skirts that too is where it is nice to have custom pistons, no extra metal where you don't need it and enough skirt width to cover as much port as can be put in within the limitations of ring life.

Piston with ring blow out was a wierd one, ring blew out exhaust side no dammage to the cylinder. If you look at the very top of the crown you can see it's rubbed and even slightly crushed. Problem too was just too much heat too quickly and the crown was expanding and getting squeezed in the bore before the bore had fully expanded. The replacement I made for it I turned dow the crown edge so there was more room for expansion, but also more blowby till it reaches full temp. Thats why I'm working on the ceramic coating part. Most rings in these are cast iron, some of the low quality ones are not ductile and can fail when RPM is pushed, ductile are beter but the steel rings if they can be found are the one that hold together for racing.

I have a performance reed block from a kawasaki dirt bike I'd like to put on a saw some time, with reeds the intake durration can be made much longer and yet the saw still will run well enough at low RPM to get to full speed in 1/2 a second or so. Problem with piston ported design and long intake durration is the low speed gets affected and the saw will stumble on spooling up. In races where the saw is on the ground and turned off time is lost. Seen a couple 120-140cc chainsaws that do quite well on reeds.

 

[351MOD]

To Timberwolf, you've inspired me to go ahead and modify my husky model 351 which is based on the 346xp and 353 crankcases. To start I got a 45mm updated cylinder off a newer 350 with the removeable transfer port covers, the 351 was solid and 44mm bore. I chucked the new jug in the lathe and removed the crap cast in head and made a nice machined raised edge. Then gave the ports a little cleaning up. The piston was releaved in 4 spots around the intake ports and polised to alow full flow. The head was made from billet aluminum on the lathe I used a 10mm plug to alow for less combustion space. I used lapping compound to seat the head to the cylinder and it seals perfect. The carb is stock, the clutch has been lightened, block was studded with 1/4 28 studs and it runs good but I have a Question for you, all I have right now is a stock junk muffler and it runs like crap with it on. When I removed it the engine idled great and the throttle responce went through the roof. I had to richen up the carb and lower the idle down. So that sounds like the motor is being choked out by the exhaust. Would an expantion pipe slove my issue? Like I'm thinking of a pocket bike pipe their around 50cc can you think of any other good ones? Thanks,` Jim

 

[351MOD]

This is the 351 now a 353xp mod pics

 

[Hammer]

Is this Timberwolf from TCU and The Fix? This may not make some of the the welder here happy but Ive used this stuff in the past. Its not alumiweld or the other older rods. Check outHTS2000. Its got a higher tensile and its great for dirty welding. I havent used it on pistons, but Ive fixed a couple loonyum exhaust heads with it. Very machinable and should have a high enough melting point to handle this.

 

[Ultrachop]

Is it necessary to modify these homelites to keep up with the Stilh's? (just kidding)
Great thread! Thanks,

Tim

 

[eyeball engineer]

all of these tricked out saws, I started checkin out you tube and found this

http://www.youtube.com/watch?v=E9x8rBKC4BE

:cool2::cool2::cool2: