3120 Gone BAD

Disclaimer: I did not do the port work on this saw!!!

A quick history here. This 3120 was bought brand new back in '04 by another forum member. It was ported, muffler modded, and the timing advanced. Shortly there after the offset keyway sheared. It hasn't run right since that time and has just sat all these years. I have it to sort it out and get it running good. I pulled a compression check and only got 110-115 PSI. However, the rings still look like brand new, with the little machine lines still in them. This saw never even got broken in.

None of the ports were widened. However, the exhaust was raised A LOT. The transfers were also raised considerably, and the intake lowered. I will be putting a degree wheel on it to see where it sets.

What happened to this saw? Notice all the odd markings in the cylinder and piston. Did this saw get real hot at one time, but not enough to seize? You can see the shape of the exhaust port roof on the piston skirt where the piston is at TDC. Was the port not deburred and beveled after porting, and marked the piston? There's one line to the right of the exhaust port on the cylinder wall that I can feel. Why is the compression so low? Exhaust too high?








It was only raised at the cylinder wall, and not tapered out to the flange.


Not widened at the cylinder wall at all. You see some finish sanding marks towards the flange. It was not widened.




Markings above the intake.

The intake was not widened at all either.




But it was lowered considerably.


Check out these transfers!

Have at it guys. Tell me what went wrong to cause all these markings and loss of compression.

Better check the timing and jetting for the new piston and cylinder.

brncreeper said:

Better check the timing and jetting for the new piston and cylinder.

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I understand a standard key is back in the flywheel, but I have not pulled it yet. I have not taken the carb apart yet either. If the port timing isn't just way crazy, I'll try to save this P&C. The piston isn't really hurt.

uuuhhhhh...first of all, everything is left pretty rough, and by the looks of it they didn't realy even do the numbers it sounds like....i'd say turn it into a cup holder and buy a new jug.

Brownpot Deaton said:

uuuhhhhh...first of all, everything is left pretty rough, and by the looks of it they didn't realy even do the numbers it sounds like....i'd say turn it into a cup holder and buy a new jug.

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A degree wheel will answer that. The roughness can be cleaned up. BTW, the muffler and exhaust gasket weren't even port matched.

S********?

Looks like that saw got ran hard and too hot. I have seen similar slugs and jugs. Usually they are too lean or have been rode hard for years.

epicklein22 said:

S********?

Looks like that saw got ran hard and too hot. I have seen similar slugs and jugs. Usually they are too lean or have been rode hard for years.

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But this one is virtually new!

The numbers aren't near as bad as I feared. The transfers are higher than I'd like but I think it should be able to be made to run well.

Exhaust 96° - 168° Duration
Transfers 117° - 126° Duration
Intake 81° - 162° Duration
Blowdown - 21°

I'm still really curious about all the strange markings on the P&C. I'm suspicious that the ports were not deburred and beveled after porting, and consequently scrathed the piston. I see no bevel on the ports at all. The piston is not really hurt though. Pictures make things look worse than they are.

I think the markings in the cylinder are due to extreme heat. I suspect a good oil was being used and prevented seizure. Or, it was just shy of melting temps.

I'm stumped on why the compression is so low. The oil on the piston was really gooey and sticky. It may have been years since it ran. I'm thinking I'll clean things up, hone the cylinder, and put it back together and see what happens.

blsnelling said:

But this one is virtually new!

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don't s'pose ya'd wanna tell us who did this would ya ??

I am failing to understand why anyone would port such a new saw.

showrguy said:

don't s'pose ya'd wanna tell us who did this would ya ??

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No I wouldn't. He's no longer porting saws. I'm really just looking for clarification of my hunches.

Kwdog75 said:

I am failing to understand why anyone would port such a new saw.

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I do it all the time.

I wondering if by raising the exhaust port, the saw no longer had sufficient torque. Then the operator lugged it to it's death.

brncreeper said:

I wondering if by raising the exhaust port, the saw no longer had sufficient torque. Then the operator lugged it to it's death.

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96 ATDC is higher than I like, but should have killed the torque. We'll soon find out.

Kwdog75 said:

I am failing to understand why anyone would port such a new saw.

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dog,
don't be silly..
you port a saw because it makes it lighter !!!!!!!

really, think about it !!!

raise the exhaust a little more and lets pipe it!

breymeyerfam said:

raise the exhaust a little more and lets pipe it!

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That crossed my mind Transfers are too high for a pipe though, at least from what I've read.