McCulloch Chain Saws

[IdahoMac]

Hey all, I’ve got a 790 with a w1 welder block in it and I’ve got a few questions. I tore it down to deep clean and do new gaskets and seals, and I see the D port block between the tank and cylinder has a gasket to block off the port. However the inside of the port is functional and goes through to the inside of the cylinder. I’m curious as to why it had the blocked off gasket.

 

[bob kern]

Ed, I go on a sabbatical and come back and your all banged up. What happened? You know the PO has those prepaid boxes that take up to 70 pounds. Just ask and we can start sending you wood from all over the world. You can do a study of which burns best?

Now there's an idea lol!

 

[heimannm]

Preparation is the key.

Mark

 

[edju1958]

Lookin' good Vinny!

 

[edju1958]

Joe,it's just arthritis taking it's toll on my decrepit body.Doc says 3-4 months to be pain free.I'm pretty much pain free right now,but the bandage & splint haven't come off yet either.
My son & I went out for tacos tonight & we were greeted by the owner of a auto repair shop & he asked what happened.I told him I cut my thuimb off with a chainsaw,Lol.Stop & think about it,how could I possibly do that?

 

[heimannm]

Idaho - McCulloch eliminated the "3rd port" design on later big saws after some kart guys figured out that by filling the third port space (typically epoxy) they could reduce the effective crankcase volume and thereby increase the pressure and velocity in the crankcase during the transfer event. It is possible that someone was trying to accomplish the same principle by simply blocking off the third port on that saw.

On the previous page I show a photo of a Mc40 kart engine that has the 3rd port filled with epoxy (and other areas filled with epoxy due to a significant connecting rod failure). In the case of that engine a creative porter added some holes in the piston to help the transfer operation. On some of the later saws without the 3rd port feature, there were boost ports built into the engines to facilitate the transfer.

Mark

 

[IdahoMac]

Idaho - McCulloch eliminated the "3rd port" design on later big saws after some kart guys figured out that by filling the third port space (typically epoxy) they could reduce the effective crankcase volume and thereby increase the pressure and velocity in the crankcase during the transfer event. It is possible that someone was trying to accomplish the same principle by simply blocking off the third port on that saw.

On the previous page I show a photo of a Mc40 kart engine that has the 3rd port filled with epoxy (and other areas filled with epoxy due to a significant connecting rod failure). In the case of that engine a creative porter added some holes in the piston to help the transfer operation. On some of the later saws without the 3rd port feature, there were boost ports built into the engines to facilitate the transfer.

Mark

Thanks for the info! I keep learning new stuff about these saws and it never fails to amaze me. I may finish the previous persons job and block off the port with epoxy. Would a guy fill the port on the cylinder or just the block that separates the cylinder from the reeds and fuel tank?

 

[heimannm]

I am definitely no expert, but on the one that I have (AWOL did the work) the opening is filled with epoxy but the ports are still open. I am not sure how far the epoxy goes down that 3rd port opening.







Mark

 

[IdahoMac]

I am definitely no expert, but on the one that I have (AWOL did the work) the opening is filled with epoxy but the ports are still open. I am not sure how far the epoxy goes down that 3rd port opening.

View attachment 1107082

View attachment 1107084

View attachment 1107085

Mark

I may give that a shot then and finish the previous guys work. The 790/w1 I’m working on was found in a dumpster and then given to me. Definitely makes me wonder what the previous owners story was. Thanks Mark!

 

[heimannm]

Max the Mac Man was here for a visit this week.



We traded a few parts, had a nice visit, I even put him to work helping me rearrange the display a bit so I could put the Blue Streak out for all to see.

Max presented me with a new McCulloch banner so we put it up in the hallway.



Mark

 

[matt_lamb_160]

IdahoMac, if the ports are drilled, I see covering the port as a negative only (unless is is to mask another issue). As Mark said they fill the port to lower crank-case volume and sometimes to replace the third port with a boost port (kind of like Mark has shown) to improve performance. But none of that that is happening with the port drilled in the cylinder and the gasket blocking the top. The crank-case volume stays the same, you're just missing out on the extra cylinder filling from the third port.

 

[matt_lamb_160]

For saws with the ports drilled the first kart porting approach was to gulley port.

If the port isn't drilled you can boost port either via the third transfer port (high case volume and poor flow path) or fill the port and add a boost port like later kart engines (if you use an appropriate piston)

 

[IdahoMac]

Man that’s super interesting. Not entirely sure what my plan is now. Kinda just want to get this saw running good again so I may unblock the port and use the correct gasket

 

[piglosi]

I think this is what you need.

View attachment 1069914

Mark

Hi Mark,

Would this spring work on a spring-less SDC 3 carb? I was thinking of putting that carb into service in a newer 10–10 replacing a SDC 37. Carbs look darn close besides maybe throat dimension. Or is that a bad idea? Apologies for re-opening an old thread with my issue.

 

[heimannm]

Based on the IPL's I looked at, the SDC3 did not have a throttle return spring so I don't know if it is designed to accommodate one.



Mark

 

[flatsfisher]

this seems unusual...

 

[heimannm]

Looks like a 5-10, same basic airbox as the saws with the bullfrog carburetor but fit with an SDC.

There were also conversions available to change the airbox from the bullfrog type carburetors to the SDC.



Mark

 

[flatsfisher]

didn't know about the conversion kits. he says he thinks it's a 2-10. says it was running when the PO passed away.

 

[heimannm]

The round fins on the cylinder does reflect the 2-10. There were 1-10 and 2-10 models that came with the cube carburetors.

Mark

 

[Rocker59]

My vote is a right hand start 10-10. Tank may have been replaced at some time as I thought all the RH start 10-10s had yellow tanks.