MCCULLOCH The official McCulloch thread

[Al Smith]

Regarding the piston taper and ovality .It was once done using a type of machine that used a taper ramp to cut the taper which goes from the bottom of the skirt up to just below the bottom ring .The ovality used a spining tool holder the cut on an elipse (angle ) more narrow over the pin wider at 90 degrees to the pin .I've worked on one piston line at Honda and 5 or 6 at Ford .All this is done by CNC machines these days .

 

[Mastermind]

If I'm reading that chart correctly.....

.007" clearance?

 

[Al Smith]

If I recall correctly they said any thing up to 10 thou is good to go .My old buddy Louis B who was number two in the AKA during the late 70's would know running 101's with Wiseco pistons would know .Most of those old farts are dead by now .Louis is one day older than me ,another old fart .

 

[Bigmac]

If I'm reading that chart correctly.....

.007" clearance?

Ya. 006-.008

 

[Mastermind]

I'm at .004" skirt clearance now.

 

[Mastermind]

I'm at .004" skirt clearance now. View attachment 456479

Went on to .005" Calling it good.

 

[sawfun]

I'd like .005 - .006, especially in an air cooled non-race engine. .003 scares the hell out of me.

 

[Bigmac]

I'd like .005 - .006, especially in an air cooled non-race engine. .003 scares the hell out of me.

The key is warm up, a cold sieze happens when the piston grows faster then the cylinder, and it is rapidly wormed up. Give time to warm up the iron bore will grow to match the clearance. The blaster, air cooled 2t is speced a .002 clearance from wiesco. For years I would set things up a little loose just in case, and fear. It’s safe to have more clearance, to a point. But at the sacrifice of engine life and performance. I have talked to weisco about air cooled clearances vs water cooled, plated bores and they state, it’s the same, no extra clearance, just different warm up times. Some of the plated bores can take more abuse, but also transfer heat better making warm up times faster. Almost never have any issues with the plated cylinders, have had a few problems with people on big bore Honda, put temp gauges on their bikes and zero issues since, all of my build now have temp gauges with warm up instructions, and no problems even with large bores. Up to 15mm over bore cylinders at .0045 clearance. Water cooled takes even longer to warm up compared to air.

 

[Al Smith]

Some of the plated bores can take more abuse, but also transfer heat better making warm up times faster. Almost never have any issues with the plated cylinders, have had a few problem

That's another situation .I've had so far two plating failures on late 70's Macs .I don't know if it was a qualty control problem or the use of inferior soft chrome .That was the same time period of "apartheid" and hard chrome was hard to come by.Which is why I sleeved the Mac 125 c,chrome peeled .Types of cylinders,plated,cast iron .4140 steel has long been a bone of contention.Saying that what ever works,works .

 

[Al Smith]

Now the engine .There's a lot you can do to it .One variant can have two additional boost ports cut in on the back side of the engine .Multiple carbs can be installed . The double reeds can be replaced with pedistall reeds .Mc Bob RIP had the charts but weather you can still find them I have no idea or if McDizzy is still around .That stuff is way above my pay grade so to speak .Just keep in mind usually that that runs extremely fast does not run extremely long . McBob did send me a CDrom that had some of the charts I'll have to see about .If I can find them I'll copy and post some of the more important ones .

 

[Mastermind]

Now the engine .There's a lot you can do to it .One variant can have two additional boost ports cut in on the back side of the engine .Multiple carbs can be installed . The double reeds can be replaced with pedistall reeds .Mc Bob RIP had the charts but weather you can still find them I have no idea or if McDizzy is still around .That stuff is way above my pay grade so to speak .Just keep in mind usually that that runs extremely fast does not run extremely long . McBob did send me a CDrom that had some of the charts I'll have to see about .If I can find them I'll copy and post some of the more important ones .

Mine has 6 transfer ports, and two boost ports.

 

[Al Smith]

You've got runner there .

 

[Al Smith]

I dug out the Mc Bob cd and didn't find as much as I thought it contained.However are three charts on pistons rings etc .This I did find directly from McCulloch .Max taper or ovality is not to exceed 5 thou .Piston to cylinder chainsaws 2.5 to 5 thou kart engines out to 7 thou .But I think as much as 10 thou as it isn't real clear about that . That said I never claimed to be an expert on McCulloch or any other brand .I just know more than most but not as much as some .

 

[Al Smith]

Now as to the above that was all with OEM McCulloch cylinders and pistons .Using aftermarket like Wiseco the thermal rate of expansion could be slightly different .Also the cylinder especialy if it was relined with say an LA sleeve,grade 50 cast iron or 4140 steel which aircraft air cooled engines use .So not as tight as a mouses ear nor loose as a two bit 'toot .

 

[edju1958]

I finally picked up some kerosene yesterday & put that in the oil tank of the PM800.It puked out at the oil pad like it should,then I let it sit overnight with the kerosene in it & pumped it a few more times,then drained it.I mixed some kerosene with the bar oil & put that in,put a 24 in.bar & chain on & it seemes to be oiling as it should.The saw started on the 1st pull today,so all is good there.Here are a couple of pics.

 

[Al Smith]

Good old kerosene is the cure for a lot of things besides lighting off a brush fire .

 

[heimannm]

I picked this up today, 4 HP McCulloch air cooled outboard based off the 80 cc cylinder.







Mark

 

[Mastermind]

I picked this up today, 4 HP McCulloch air cooled outboard based off the 80 cc cylinder.

View attachment 456941

View attachment 456942

View attachment 456943

Mark

That's cool.

 

[cinci5]

Mark @heimannm do you have one of these I've never heard or seen one until now.

 

[Mastermind]

Mark @heimannm do you have one of these I've never heard or seen one until now.View attachment 457061

That has to be a rare unit.