Tzed250
Addicted to ArboristSite
Is it two of the 6763 and one of the 6816?
Building a SP125C / 101B Kart Saw
- Thread starter blsnelling
- Start date
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No. You cannot use two of these seals on the flywheel side. They are too thick. I used the original outer seal. The outer seal isn't used on a cart engine, and this saw will not have points. I could have actually left it out. The purpose for the outer seal was discussed some pages back.
Tzed250
Addicted to ArboristSite
I gotcha. The NOS points box I have has a new seal in it anyway. Thanks!!!
MechanicMatt
Cut Split Stack Burn
Hey Brad, If I were you Id throw that rod bolt on a scale weigh it then grind the other bolt to match the weight. Im not sure what you other fellas think about it but I would like to learn. When building small blocks for my buddies we start with the lightest rod then shave the rest down to its weight. Just helps them hold together. Does it matter on such a small engine? The only thing is in the back of my mind I know what kinda off speed Id be trying to get out of that engine. Ill stop babbling now.
Anthony_Va.
XPW Fan Club
I don't think there's any way to really balance a chainsaw engine. I may be wrong though.
Correct. That's not an issue on these single cylinder chainsaw engines. We sometimes remove a fair amount of material from the piston when doing a port job.
Right. You don't balance a single-cylinder engine unless you're balancing it on your chin.
MechanicMatt
Cut Split Stack Burn
Hmm, I didn't think of that guys. I forgot you boys sometimes remove the skirt. But the skirt isn't spinning it's only going up and down. Just a thought fellas. I get what your talking about JJ there is nothing in there to balance it. No 2nd rod. Hey Brad you gonna have it running by this weekend? Seems your back on track.
Tzed250
Addicted to ArboristSite
IIRC most singles are balanced at 60% of the recip. mass. Another no free lunch deal. Everything you do to counteract the motion of the piston ends up shaking 90° from that axis.
I doubt it. None of the other parts have been cleaned or painted yet. Also, starting Thursday, I'll be tiling my master bathroom.
Tzed250
Addicted to ArboristSite
Here is a single with perfect primary balance. Ducati Supermono engine. Notice the second rod 90° from the main rod and piston. The balance rod is toggled to a rocker which dummies a second piston. This engine revved to over 10,000 RPM which is quite high for a 500cc single. The engine had a slight secondary imbalance. A rocking couple induced because the rods sat side-by-side on a common crankpin.
That is freakin' cool. I actually had a saw vibrate a lot once after I put a piston in it that was too light. It was around 60% of the weight of the stock piston.
So I went back in and lightened the flywheel and crank and got it back to where it needed to be. It did lose some torque after that, but the acceleration and
chain speed was ferocious.
Brad, it's looking like another winner but I wanted to comment on the seals on the flywheel side. The old Homelite EZ, EZ6, 5-20, etc. used two seals per side - one with the lip pointing in an one pointing out. Since these are single lip seals, I had always assumed this was to seal against the vac and pressure pulses as the saw is running. On the flywheel side of my SP125Cs, the parts manual shows the same seal config. The inner seal goes in with the flat side out/lip in but the outer seal goes in with the flat side in/lip out so the single lips are facing in opposite directions. Again, I assumed that it was to seal against the + and - pressure pulses. The crank seal is much heavier and has a double lip. You picture shows both of the flywheel seals with the flat side out - I don't know how the seal lip corresponds to the face of the seal.
Maybe I totally misunderstand the design, just wanted to throw out a little caution base on my experience.
Anyone - feel free to correct me.
Not really correct Buzz. On the Mac's i have rebuilt and thats many.
Both seals go in the same way. There is a hole drilled in the case
that goe's in between the two seals. The idea as i understand is if
the inner sealed had any weepage the second seal would prevent
the weepage from getting into the points but let it exit out the hole
into a felt block that is held in place by one of the points cover lock tabs.
Lee
Both seals go in the same way. There is a hole drilled in the case
that goe's in between the two seals. The idea as i understand is if
the inner sealed had any weepage the second seal would prevent
the weepage from getting into the points but let it exit out the hole
into a felt block that is held in place by one of the points cover lock tabs.
Lee
Tzed250
Addicted to ArboristSite
So are there three different seal part numbers?
Correct.
This is straight from Terry Ives.
"The magneto side McCulloch engines ran a pressure seal next to the crank case, they also ran a dust seal next to the ignition side. That was to keep saw dust and engine oil out of the ignition. Since we use the engines for karting, you do not need to run the dust, oil seal."
"The magneto side McCulloch engines ran a pressure seal next to the crank case, they also ran a dust seal next to the ignition side. That was to keep saw dust and engine oil out of the ignition. Since we use the engines for karting, you do not need to run the dust, oil seal."
husq2100
Addicted to ArboristSite
would the balance the saw to a specific rpm area, ie where it would be at cutting speed in wood???
Thanks for clearing that up - makes sense and I wondered how it would seal against pressure with the hole.
Here's the drawing I referred to from my manual. This is how both saws were when I tore them down. This is looking at the inside of the crankcase cover. Looks like the flat sides face each other - or maybe just a bad drawing that was revised in a later version? Since the outer seal doesn't seal against pressure, does it really make a difference which side goes in or out?
the centrifugal force produced by the inertia of the flywheel is strong enough it would be best lighten the wheel and cut a piece of lighten flywheel fins would have less weight which can go faster and with less inner strength she explained centrifuged my father from certain rpm it produces many internal forces in the motor and just destroying everything.
