Nikasil Plating And Porting Concerns

[blis]

Another option, not ideal, but easier to do.

Remove some material from the piston crown where the transfers come in, this effectivly raises the transfers. You don't want to leave much less than .100 of piston crown above the ring. Doing it this way if you dont like it, it is just a new piston not a new jug.

It is a work arround, call it hack, but it will work. What it does structurally to the piston and dynamically to the balance and squish velocity is another question.

it will lighten up the piston a bit, therefore making it accelerate faster and loose a bit of torque (which shouldnt be such big matter in chainsaw)... just dont remove the whole skirt of piston, long as its within sensible amounts it wont even interfere with integrity of piston...

 

[timberwolf]

Talking about the top of the piston, not the skirt. Maybe I was not clear.

It will ligten the piston a little wich if anything would increase output as the piston would eat up slightly less wasted energy starting and stoping at tdc and bdc. I would think torque would be unaffected by this. and given that the piston is only a fraction of the rotated mass is should not effect inertia.

Compression will be lost very very slightly due to the increased head voulme, squish velocity will be reduced over the transfer areas, likely not super criticle. The piston may be structuraly weekened a bit. But as you say Blis if it is within reason should not be an issue. The issue of piston balance and harmonics uneven forces of squish compression on the piston are unknowns.

 

[amdburner]

Timberwolf,
Currently the base gasket is installed. I took the time to check the squish both with the gasket and without to see if it would be OK without the gasket. I had remembered though that the tranfers would be affected by removing the gasket so I opted to leave it installed since I do not have an angle attachment for my dremel and would not be able to raise the transfers to offset the difference. I have done what you mentioned to do to the piston crown years ago on an old Kawasaki 125 I used to own when I was a teen. I simply made sure that the cut I made matched the same angle as the transfers. I will try the saw first as is though.

 

[blis]

Talking about the top of the piston, not the skirt. Maybe I was not clear.

It will ligten the piston a little wich if anything would increase output as the piston would eat up slightly less wasted energy starting and stoping at tdc and bdc. I would think torque would be unaffected by this. and given that the piston is only a fraction of the rotated mass is should not effect inertia.

Compression will be lost very very slightly due to the increased head voulme, squish velocity will be reduced over the transfer areas, likely not super criticle. The piston may be structuraly weekened a bit. But as you say Blis if it is within reason should not be an issue. The issue of piston balance and harmonics uneven forces of squish compression on the piston are unknowns.

ahh, sorry, my overactive imagination took over :monkey:

 

[amdburner]

I finally was able to fire the 920 up today. It runs excellent. Even with the new rings I was able to start it without killing myself. Without having reduced the squish the saw runs well and there is a noticable increase in RPM's compared to before the ring job and minor porting. I slabbed up a log with it today and had no problems. I appreciate everybodies input. I do feel that there is a lot of power to be made with this saw and at some point I may dig into her again and decrease the squish and retime the transfers. Thanks again all.

 

[buck futter]

I think you would be better off slightly retarding your timing for the gain in compression. you will also gain some intake duration. you may lose some transfer duration but it will increase the pressure for when it does open.

You also have nothing to lose by glueing the cylinder on. you can always reinstall the gasket.

 

[RiverRat2]

Sounds like it should go pretty good????

 

[amdburner]

BF and RR2,
I have been running this saw without incident since my last post to this thread. I use it for milling and it runs fantastic. I tried my cousins 394XP and it didn't appear to cut any faster than my 920. I know I don't have the HP of the 394XP but with what little porting I did do it appears to have been of some benefit. Unless I need to take it apart for rering I do not intend on running it without the gasket. I do have another 920 that I have put new rings in and used a thinner gasket that I had made for the first one. Though I haven't put a compression guage on it I can tell you that the compression is unreal. I have to put my foot into the hand grip and my right hand on the top bar to pull it over without throwing the whole saw. I started it up and it to runs excellent. The second 920 is for my Alaskan Mini Mill. The first one is on my Alaskan MKIII mill. I have a 930 on the way as well. This new hobby is just as bad as my others!!! One rifle isn't enough and aparently one saw isn't enough either!!! :biggrinbounce2:

 

[amdburner]

Buck,
I forgot to mention that retarding the timing on the 920 can only be done by elongating the mounting holes in the primary coil.

Dave

 

[RiverRat2]

You Poor Ba$z Terd

BF and RR2,
I have been running this saw without incident since my last post to this thread. I use it for milling and it runs fantastic. I tried my cousins 394XP and it didn't appear to cut any faster than my 920. I know I don't have the HP of the 394XP but with what little porting I did do it appears to have been of some benefit. Unless I need to take it apart for rering I do not intend on running it without the gasket. I do have another 920 that I have put new rings in and used a thinner gasket that I had made for the first one. Though I haven't put a compression guage on it I can tell you that the compression is unreal. I have to put my foot into the hand grip and my right hand on the top bar to pull it over without throwing the whole saw. I started it up and it to runs excellent. The second 920 is for my Alaskan Mini Mill. The first one is on my Alaskan MKIII mill. I have a 930 on the way as well. This new hobby is just as bad as my others!!! One rifle isn't enough and aparently one saw isn't enough either!!! :biggrinbounce2:

Your just as hosed as the rest of us

 

[amdburner]

Where do I sign up for SA? Is it a twelve step program?

 

[buck futter]

I wasn't talking about the ignition timing but the port timing.
pm me your email amdburner.

 

[amdburner]

My bad Buck!!! PM on the way.