McCulloch Super Pro 125c build thread

[jacob j.]

Just a note on post #406; two of the six holes for the crank case cover are tapped 1/4-20 so you can use your same puller to remove it. I have used the tap, tap, tap method but the puller is actually quicker and easier.

Mark

Great point Mark - but that's not always the case. None of the holes in the backing plate for this saw are tapped and a CP-125 I went through a few years ago didn't have any tapped holes in its' backing plate either.

Luckily the replacement backing plate I'm going to use in this saw does have the tapped holes and it is a Mag plate vs. the Alum plate the saw came with (the Mag plate will save several ounces of weight).

 

[heimannm]

Interesting - I have never come across one that was not tapped. The CP-125 I put together was tapped...McCulloch...



Mark

 

[Al Smith]

To interrupt or rather add something .One of my 125's swallowed part of the clip on the choke linkage that broke .To pull the flywheel believe it or not the threaded holes were for number 12 screws .Try and find them. I did but pulled the threads trying to pull the flywheel .I tapped them out to 5/16" which solved that problem .
I think the flywheel was just a freak thing that made it out of the factory undetected some how . At some time however I knew it had been off because somebody had disconnected the points and were using a POS "Atom Arc". Which I promptly discarded once I found the points were intact . That one BTW has an off set key to give it a little more spark advance .

 

[jacob j.]

I'm sure all of the old McCulloch crankshafts are forgings, but yes, the only one I've seen with a "modern" three piece style crankshaft is the PM8200. All of the vintage saws use loose needles and a split connecting rod. Use a little grease to get the needles to stick to the rod during assembly.

Use some grease to stick the needles to the cap when you assemble it as well.

I am told the kart guys used to leave one or two of the needles out when building an engine to allow a little more clearance on the crankshaft end of the rod. Most McCulloch service manuals remind you to count the needles as you put them in and inspect the crankcase for any lost ones before the engine is buttoned up.

Mark

Yes sir, And there should be 24 needles in all of the big saws, correct?

Re-using needles has been a point of contention - I'll re-use them if it was a low-hour saw that I fairly well know the history of.
I think it's safer to re-use rod cap bolts, provided they're in good shape and were previously torqued to the correct setting.

 

[jacob j.]

To interrupt or rather add something .One of my 125's swallowed part of the clip on the choke linkage that broke .To pull the flywheel believe it or not the threaded holes were for number 12 screws .Try and find them. I did but pulled the threads trying to pull the flywheel .I tapped them out to 5/16" which solved that problem .
I think the flywheel was just a freak thing that made it out of the factory undetected some how . At some time however I knew it had been off because somebody had disconnected the points and were using a POS "Atom Arc". Which I promptly discarded once I found the points were intact . That one BTW has an off set key to give it a little more spark advance .

I know there's several different flywheels available Al, some with a timing advance. I have two here that are supposed to be a five degree advance and I've seen one on ebay that was supposed to be a 7.5 degree advance.

I think there was also some variation in McCulloch's manufacturing line - not as much as Homelite, but a fair amount.

 

[jacob j.]

On the intake, I make sure the reeds lay good and flat against the manifold, and I check the lap edge with my fingernail to see how much wear the reeds have.



This is the new engine I have for this saw - good condition 125c cylinder, new piston + rings, new connecting rod, new bearings, new seals. Someone did some mild porting on
the intake and it looks pretty good. Exhaust and transfers are stock (which is a good thing).

 

[p61 western]

Yes sir, And there should be 24 needles in all of the big saws, correct?

Re-using needles has been a point of contention - I'll re-use them if it was a low-hour saw that I fairly well know the history of.
I think it's safer to re-use rod cap bolts, provided they're in good shape and were previously torqued to the correct setting.

I have a extra set of new rod bolts if you need them Jacob.

 

[Lightning Performance]

Those rod bolts look exactly like an inline marine four cylinder rod bolt or a ujoint strap bolt. Both are of very high quality with a nice radius on the shoulder.

 

[Bigmac]

Those rod bolts look exactly like an inline marine four cylinder rod bolt or a ujoint strap bolt. Both are of very high quality with a nice radius on the shoulder.

The Mac splined rod bolts are extremely high quality!! Stronger that’s arp bolts in the same size.

 

[Bigmac]

Yes sir, And there should be 24 needles in all of the big saws, correct?

Re-using needles has been a point of contention - I'll re-use them if it was a low-hour saw that I fairly well know the history of.
I think it's safer to re-use rod cap bolts, provided they're in good shape and were previously torqued to the correct setting.

I have talked to terry on several occasions and he is saying to visually inspect and measure the rod bearing, the supply is drying up and I don’t believe replacements are available yet so if they are clean and measure correctly run them

 

[jacob j.]

I have a extra set of new rod bolts if you need them Jacob.

Thank you Mike - I think I'm good to go for this project. I'll PM you about something I have though.

Those rod bolts look exactly like an inline marine four cylinder rod bolt or a ujoint strap bolt. Both are of very high quality with a nice radius on the shoulder.

The Mac splined rod bolts are extremely high quality!! Stronger that’s arp bolts in the same size.

I've never seen any documentation that the rod bolts are torque-to-yield, so I think it's ok on the saw engines to re-use them if they look good.

 

[Bigmac]

To interrupt or rather add something .One of my 125's swallowed part of the clip on the choke linkage that broke .To pull the flywheel believe it or not the threaded holes were for number 12 screws .Try and find them. I did but pulled the threads trying to pull the flywheel .I tapped them out to 5/16" which solved that problem .
I think the flywheel was just a freak thing that made it out of the factory undetected some how . At some time however I knew it had been off because somebody had disconnected the points and were using a POS "Atom Arc". Which I promptly discarded once I found the points were intact . That one BTW has an off set key to give it a little more spark advance .

Al the offset key doesn’t advance the timing on the 125 with points, it would with the chip, just to clear that up

 

[Lightning Performance]

Both the bolts I described are NOT torque to yield but you can probably spot a stretching one prone to failure if you use the right yield gauge to check them before and after. I put 3 rods out the side of the 125 in line so ask me how I know

Then I switched to new power wagon driveshaft bolts.

Those crappy stretch bolts would launch the rod imo.

 

[Bigmac]

Thank you Mike - I think I'm good to go for this project. I'll PM you about something I have though.




I've never seen any documentation that the rod bolts are torque-to-yield, so I think it's ok on the saw engines to re-use them if they look good.

I agree, the bolt should be fine if the history is known, as long as they aren’t over torqued or over reved it should be fine.

 

[jacob j.]

I have talked to terry on several occasions and he is saying to visually inspect and measure the rod bearing, the supply is drying up and I don’t believe replacements are available yet so if they are clean and measure correctly run them

Terry is the man, so I'll go with whatever he says. Dave Bonbright said it was ok to re-use rod bolts and bearings on the WB820 industrial engines but not on the kart engines if they've been run hard because the rod expands a lot
under full temps & load.

 

[Bigmac]

Terry is the man, so I'll go with whatever he says. Dave Bonbright said it was ok to re-use rod bolts and bearings on the WB820 industrial engines but not on the kart engines if they've been run hard because the rod expands a lot
under full temps & load.

On the kart motors terry was saying it was ok to run the Allen head mc91 or 100cc kart rod bolts in single use, and throw them away, and he hasn’t had a failure yet, the Allen head kart bolts are 190,000psi bolds with the splined bolts being 230,000 psi, 210,000psi is the best arp bolts, I have seen bonright has some killer rod bolts for the west bend kart motors!!

 

[Bigmac]

So just as something to bring up, on the flywheel removal, I have heard the the hole in the points box
And the notch in the flywheel
Were for removing the flywheel, simply take a round file or round rod and tap from the back side, I have used the method and it works really well, but it also seems odd. Wasn’t sure if it was to hold the flywheel for some other purposes?

 

[Al Smith]

Al the offset key doesn’t advance the timing on the 125 with points, it would with the chip, just to clear that up

It does if you "maverick" the points .

 

[Al Smith]

What happens is the key just shifts the flywheel so in theory the points can be set to open at the top of the sine wave where the voltage is highest .Fact you can get some advance just by the points setting but it won't be as high of voltage . In my case I doubt I have much more than 2 or 3 degrees of shift on the 125 however on a 610 it's 4 or 5 with no offset key .BTW those two saws are the only ones I've ever shifted.

 

[Al Smith]

On those splined bolts .which I find to be a pain in the buttocks a #10-32 grade 8 socket head will work but the heads need turned down so they clear the stuffer .It's not a big deal to do .You just leave a flange like the splined heads .As general info in case somebody doesn't know the pressure cracked rods ,which are used on just about every auto engine these days was first used by McCulloch .Too bad old Bob went bonkers ,hard to say what else he could have dreamed up .