Need help on mods

[glens]

Tzed,

I didn't do it, but very many did, and that was to thrash the bejeezuz out of the thing and sell it at the end of the season for a grand more than they'd paid (since Harley, after having essentially put over 100 domestic motorcycle manufacturers out of business, went crying to Uncle Sam for protection).&nbsp; I'd placed my order in Feb. and paid the "full" $3498.<u>^oo</u> for it.

2nd gear was good (not just adequate) for anywhere between 15 and 85 mph as I recall.&nbsp; But the bike wouldn't outrun a Motorola worth a ????.&nbsp; Now I miss my youth in the Rockies...

Glen

 

[Tzed250]

Days of old

At the same time that I had the V45, my brother had a CB1100F. It had mad power for the time and we had fun throwing parts at it to get more. I now have a ZRX1100, which is very much like the 1100F, but smoother. I have started to throw parts at it too.

 

[Jwoods]

Bruiser:

Making your own mods will get you a better understanding of saws, and the performance capabilities thereof. -More so than just reading the book and spouting off knowledge. I posted the same kind of question a while back, and got the same kind of response. I rebuilt my 066, and took .013 off the jug base without touching the transfer ports. I think it's a definite improvement. Next time I might try .020. What you will find are a lot of people talk about mods, and very few people actually do them.

Later,
Joe

 

[bwalker]

Jwoods, Do you actually know what you did by milling your head and not touching the transfers? You must understand theory before you remove metal.

 

[Jwoods]

Mods

bwalker,

Understand? I should have increased torque theoretically. In reality, I know I have a great running machine that I believe runs better than stock. I think theory is great.

Does or does not Stihl sell two different thickness base gaskets for an 066?

What's the worst that could happen?

 

[bwalker]

BY milling your base you did two things. 1 you raised your compression and lowered your squish clearance . 2 you retarded the timeing on all you ports. Increased compression tends to help lowend torque, but may negativley effect peak hp beacuse of increased pumping losses. Retarded timing has the effect of shifting the power band lower and decreaseing peak hp. So in a basic sense you have deacrease the amount of peak hp you are making in exchange for a wider low rpm power curve. There is a very good chance you now have a slower cutting saw as high rpm power is paramont in a saw.

 

[Jwoods]

What percentage change is necessary to slow a saw down by taking material off of the jug? I took a very, very small percentage off the total height with the removal of .013".

-Maybe it's just the placebo effect for me??

If you replace a thick base gasket with a thin one (Factory replacement I think- correct me if I'm wrong) Does Stihl recommend you to change port timing?

Joe

 

[glens]

Jwoods,

I don't have a two-stroke book in which to look up the resultant characteritics changes, but perhaps you'll consider this simple idea:

For our immediate purposes, say the stroke is 36mm (just a wild guess, and all the following dimensions are based on that value).&nbsp; The <i>average</i> movement of the piston in the bore is .008" per degree of crank rotation ((36/25.4)/180).&nbsp; However, the first and last degree from the top or bottom of the cylinder account for .0001" of piston travel each, while the two degrees either side of the midpoint account for .012" of piston travel each (the math for those values is somewhat more involved, but I'd be happy to go over it with you).

On the average, by dropping all cylinder openings .013", you've changed all the (start/stop) timing values by 1.6&deg;.&nbsp; To the extent that any of those openings start or stop nearer an end of the piston travel, the number of degrees the change represents is multiplied greatly, hence the timing has been changed just as greatly.

It's not the same thing at all as "shaving the head" on a four-stroke engine.&nbsp; The equivalent would be doing that, <i>and</i> changing the shapes of the cam lobes, <i>and</i> the orientation of the cam lobes on the camshaft.&nbsp; Kind of scary when you think about it that way, don't you think?

Of course, we're just talking theory here

Glen

 

[Jwoods]

Glens,

I understand the math.

Here's my angle. Let's say I polished the ports without touching the jug base. It wouldn't take long with a pin grinder to remove .013" in a clean-up procedure. What if I put different radii on the ports on the cylinder side? It's not much material, but can change the timing to what appears dramatic on paper. -And I can still do all of this. One variable change at a time right?

Is it a noticeable change on the top end, if any? Probably not in my case. Does it keep the engine at a higher horsepower level when it comes off peak? Did I remain the same, or reduce max horsepower slightly, while increasing the bottom end power? That's what I want to find out. This is a woods saw (no pun intended), and not a racer.

Joe

 

[bwalker]

.

Let's say I polished the ports without touching the jug base. It wouldn't take long with a pin grinder to remove .013" in a clean-up procedure.

Polishing is mostly for mental hp. If your removing that much material by polishing you are meesing up your ports flow chrachteristics.

What if I put different radii on the ports on the cylinder side

changing the discharge angle of the ports can have a prfound effect on cvanging. Changing this without knowing exactly what you are doing is detrimental.

Two stroke engine tuning is not just grinding ports larger. Bulk flow is seldom a issue. Its the very complex relationships between ignition timing, exhaust, and port timing. If you dont know what you are doing its very easy to end up with a motor that makes less HP than when you started.

 

[Tzed250]

Squish

Jwoods, what you mainly did was change the squish clearance. Some setups are very sensitive to proper squish. To little squish clearance can create excesive turbulence. This does not let the flame front act as it should. You may have helped. Got a saw dyno?

 

[Fish]

Squishing clearances??! I am blushing!!:blob5:

 

[Jwoods]

Tzed250:

No, Wish I did. The only way I have to test is by cutting timber. The saw works extremely well for that purpose.