Mac saw engines

[Terry Bentley]

Mac Saws

Lets just jump right into the different models of saws that are compatible as kart engines.

In 1958 the first standard series saws appeared. All of these were 4.9 cubic inches with the same 2.125" bore and 1.375" stroke.

Two styles of crankshafts were available on them. For the direct drive models, they came with a stepped crankshaft. A 5/8 " diameter pto that steps down to a 7/16-20 left hand thread. The other style is a 9/16" pto that tapers down at a 10 degree angle with woodruff key slot and 3/8-24 right hand thread.

All of these blocks with removable cylinder heads measure approx 5 47/64" in height. The center line of crankshaft is 1-1/2" from bottom of cylinder block.
The center line of exhaust port opening is about 4.450" from bottom of block. Exhaust ports can vary in height +/- approximately 0.010". Each exhaust port is drilled out to 33/64". Intakes are drilled to 7/16".

The first of this series saws introduced were the models D-30, followed with the D-36. Unique to these particular saws was the recoil starter used. It is a pinion style gear driven to a ring cast on back side of flywheel. The pull start rope was on top of saw in the center behind gas tank.

   

The D36  saw came with all three exhaust ports, D30 had only the two outer ones. Both had only four intake ports drilled. They were lower horsepower than the current super series models that had been introduced two years earlier. There are more details and pics specific to these saws in the next post below.

The next newer models introduced were the 1-40, 1-50 and 1-60. Even tho they had different power outputs, all three of these power heads shared the same cylinder block. But with some differences as noted.

Like the model D-30, the 1-40 had only two exhaust and four intake ports drilled. These models which include 1-50, and 1-60 had the early casting that incorporated an automatic oiling system which proved to be unreliable and was discontinued. A steel baffle was fitted on the back side of crankcase. The baffle was installed in these newer models even tho the oiling system was not in use.

   

Here is a closeup of the baffle in bottom of crankcase.

Below is the same block without baffle. Notice the ledge at bottom of baffle recess

   

Tho it shouldnt really make much of a performance difference at the rpm these motors will run, there is definitely a potential for turbulence.

   

This is what the newer casting looks like without the recess for oiling baffle. A smooth transition feeding the back intake ports.

   

All of the 1-40, 1-41, 1-42, 1-43, 1-45, and 1-46 have this port layout. Only two exhaust and four of six intake ports are drilled. No third port induction on any of them.

   

Even tho the 1-40  came with the more conventional recoil starter they used existing inventory from the previous models, D-30/36 including the shroud and side cover. The flywheel with cast gear on backside was also used until stock was depleted. This cast gear can be cut off on a lathe and used as a standard flywheel.

   
   

All of the first generation standard series saws had cylinder head reversed with spark plug exposed on the exhaust side of block. This includes D-30, D-36, 1-40, 1-50 and 1-60.

The next years introduced in the lower horsepower models included 1-41, 1-42, 1-43, 1-45, and 1-46. Not much differences in these with exception to what is noted.

The 1-41 and newer models cylinder head was flipped around and no longer had spark plug exposed. There was now a rubber boot to access the spark plug. This new shroud and side cover had the earlier pinion style casting eliminated. This saw looks just like a kart style Mc-6 engine even tho it has a shorter stroke and not all of the ports drilled.

   

This is basically what the rest of these models looked like. Minor differences that dont affect power output.

During the production of the 1-42 model year, removable heads were replaced with a fixed head block. The intake passage was also changed up.

   

You can see only two of the three intake ports are drilled and now has a fixed head that is square instead of round. Also the newer intake opening. This is a transition stage for existing intake manifolds. It also allows for early and late model interchange of parts. With exception to a parts cleanup seen in some of the 1-45 models with removable heads, there was no more major changes.  

The next higher horsepower output saws included the 1-50 and 1-60. They shared the same cylinder block as the  1-40 model. Also with the same oil baffle as described earlier. Starting with these higher powered  saws all three exhaust ports were drilled. But only the four of six intakes were still utilized. Again no third port induction on these models.

   

The 1-50 and 1-60 were identical in power output, and had the spark plug exposed like the others. The differences between these two models includes crankshaft, shroud, side cover and drive type. The 1-50 used a step crankshaft and was a direct drive model.

   

The 1-51 had the now standard style shroud, side cover and spark plug location as with the newer models. These came with three exhaust ports and now all six intake ports drilled. But the third transfer was not utilized.

The 1-52 and 1-53 production blocks had changed to fixed head and newer style intake opening. The 1-53 was end of this model number series. Another change for these last two models, they now have ball bearings on the pto side crank like a Mc10. The block is also drilled for the third port induction. Also another difference is the stroke increased to 1.5", increasing displacement now to 5.3 cubic inches. Same as a Mc6 and Mc10.

   

The 1-60 did away with that earlier shroud and side cover, but still had the spark plug exposed on exhaust side of motor. It came with the ring gear flywheel as stock depleted. It has a tapered pto crankshaft with gear reduction unit and larger chain.

   


On these gear reduction models the recoil starter was on the pto side bolted to gearbox. It engaged directly with the clutch. This model still had only four of six intake ports drilled out.

The 1-61, 1-62, and 1-63 were basically the same with some improvements. All of the exhaust and now all six intake ports were drilled out, but still no third port induction on them. The same transition to fixed heads and newer intake opening as previously covered in the other models. The 1-63 was last in lineup.

   

Here is the 1-63 showing fixed head and newer intake opening. There was a transition to the fixed head during late production of the 1-62 model, even tho the IPL does not recognize this. The 1-62 block would have an early intake opening with removable head or newer style as pictured above with fixed head.

All of these saw power heads can easily be used for a clone Mc-5. With a crankshaft stroke increased from 1.375" to 1.500", you basically have a Mc-6. The missing ports will need to be drilled out to match kart engines. With the shroud and side cover from the 1-60 model saw, you can clone a nearly identical Mc-5 by using any of the cylinder blocks after ports are added. The 1-41, 1-42(with removable head)1-51, and 1-61 are exact same casting as Mc-5/6 with exception to missing ports. All of the parts are directly interchangeable between these series saw power heads.  Either with a stepped or taped crankshaft, you have plenty of options for a kart engine that will yield the same power output with a little work.

These particular model saws use either a Tillotson HL-63 or HL-87 carburetor. Some of the later models could have been equipped with the flat back Walbro too. An obvious difference between the two Tillotsons is the HL-87 isnt drilled for a choke assembly. It uses a plunger that covers opening of air horn, instead of shutter valve rotating on a shaft. The early D-30 used a magnesium Walbro, like on the Mc-10 kart engine. It is similar to the newer flatback models used on most of the early kart engines.

There are still plenty of these saw motors showing up all the time. Eventually the supply will dry up and no more to be had. Just something to think about in your quest for the ultimate Mac powered vintage kart.

More to come.

[Terry Bentley]

D45

There is another saw worthy of mention during the early years in this standard series of Mac saws. The D45 model. It falls in with the 1-50 series of power output. Introduced in 1960 and only sold in Canada. It is identical in all respects to the 1-51 sold in the US. As much that I can determine it is actually a 1-51 stamped block but badged as the D-45. Also it is a slightly darker yellow than American built saws. It utilizes all six intake and three exhaust ports. With exception to a thicker 0.050 head gasket, it is near a perfect candidate if you find one out there. These saws are way up there on the collectable list. A much higher collector value than all of the other models during this time. If you find one incomplete or poor condition, then go for it. I had a hard time coming to grips with this one. It was in such good condition, I had to leave it as a working saw.

       

D30/D36

OK some more specifics on the first of these standard series saws. These include the D-30 and D36 models.
All of the models covered above and in previous post have the same bearing type on crankshaft. The flywheel side uses a common 203-C3 style ball bearing press fit to a 17mm journal. With exception to the 1-52/1-53 models, all of the others listed here use a a Torrington B-1210 housed needle bearing on 3/4" pto bearing journal. The 1-52/1-53 now use the same 203-C3 ball bearing on 17mm journal on pto.

   

This is what the D-30/36 model look like if you happen to find one. A pinion style starter mounted on top of chainsaw.

These first generation saws actually came with the 3/4" journal on both sides and using a housed needle bearing like on the pto side of crank. They also had a thrust bearing on flywheel side like used on the pto.

   

Here you can see needle bearing and thrust washer on the side cover.

   

The bottom end looks fairly common to newer models. But notice the larger diameter of crank on flywheel side. You can also see the recessed area where that automatic oilier baffle fits on back side of crankcase.

   

You notice the flywheel does not have the provisions for starter pawls to use a recoil starter yet. Also unlike the super series models at the time, there are no reinforcing ribs either.

       

Here is the pinion style starter drive gear used on these first models. The driver engages a ring gear cast on back side of flywheel.  They were soon discontinued and replaced with the standard recoil starter for the remainder of production for this style saw and kart engine.

       

Here are closeups of the Mac flat back and Tillotson carbs. This choke setup is same for the D30/36 and all of the 1-40 series models, that are equipped with a Tillotson HL-87 carburetor. A spring loaded plunger that covers air horn of carb. The spring slides inside of air horn and rests against small tab used for a butterfly stop on choke assembly if so equipped. Not the best idea IMHO. Seems it may be a little restrictive and possibly makes venturi not as functional. On one saw I have with this setup the high and low speed needles are only open about 1/2 turn each to run well.

One more thing to note, on the intake side of crankcase there were no cast in ribs as you have seen in the models starting with 1-40 in standard and 1-70 super series. The intake is similar to the first generation super series D44/55 model with a nearly flat surface that feed the intake ports. Still only two intakes on either side were drilled.

   

This is a D36 block. It has same configuration for the intake tract as the first super series saw motors, including D44/55 and S44/55. Please note the super series has all of the intake ports drilled, unlike the D30/36 model which on has two here as shown.

Even tho McCulloch rarely advertised the rated horsepower on these saws, occasionally it would show up in print. Originally the first of these saws, the super series model D44, followed with the gear reduction version model 55 were rated at 5 HP at 4.4 cubic inches displacement.. That is a reasonable claim since McCulloch usually produced more power than any of its competition.

The standard series starting with the D30 was rated at 3.8 HP, and model D36 at 5.2 HP both with 4.9 cubic inches displacement. The D30 rating seems very reasonable comparing to the D44. Since the D30 has only 66% of the exhaust and intake opening, the HP rating is likely very close to correct. Even with only 66% of the intake ports the D36 may make up the difference with all of the exhaust ports drilled and added displacement.

I will update some of the pics as I get them taken for better clarification of differences between models. Again more to come.

[Sterling Brundick]

$219.00 was a LOT of money back then.  That would be somewhere close to $1,000.00 or more today.  Good info though.

[ted johnson]

These saws were for professionals who wanted solid reliability and top performance. In East Central FL in those days, hundreds of subdivisions were being carved out of the pine forests and palmetto stands. These "land clearers" didn't mind paying for a unit that would run for a whole season without overhaul. Most of these guys carried points, plugs and diaphragm kits in their toolboxes so they could refresh carb and ignition in the field. Pop and I sold many, many Mac and Homelite units in the late fifties thru the sixties. Most of these guys would carry several air filter elements so  they could just change 'em out and keep going. They'd clean them after the day's work was done. The cabinet shop across the street from the lawn mower/kart shop had an electric chain sharpener. He could've just done that all day instead of making cabinets. Pop was a whiz at hand sharpening chain. I had a friend who was knocking out blanks for flywheel pullers by the dozen. I'd drill and thread them by hand and sell them for a couple bux. I always gave one out with each new saw I sold. I learned a lot about two cycle engines in those days that served me well in my kart racing and in the kart shop. Ted

[Terry Bentley]

Adding ports to saw blocks

What do you do with those saw blocks that are missing intake and exhaust ports?????

Ask Ron Popeil? Does he have a Ronco Portable Porting Protractor? It calculates, it locates, it drills, it sizes, it recesses, it does it all. But for only three payments of.......

Maybe not, but would be nice. Now the next best thing. After several years of use it still puts those ports exactly where they should be. By locating on the existing ports, lays the exact position for either missing intake port. It also recesses the back side of block for the welch plug to be placed after drilling new port.

Sounds too good to be true. Just like the Ronco Pocket Fisherman.

   

Nice idea, but I was never able to pull in the big ones. Or on a regular fishing pole for that matter.

   

This is the fixture. It will fit all standard and super series blocks with fixed or removable heads. Since all of the ports are measured from bottom of block it is easy to build a fixture to add ports. The side plates are both  drilled for all three intake ports. The two existing ports are used for locating points. Pins are driven in on both sides and then all the bolted together plates are snugged up. This will align the cylinder block for missing ports perfectly. The location of missing ports have drill bushings that are precisely sized for tooling to add missing ports.

   

On the back side you can see the two solid pins that slide in tightly and locate exactly where missing port will be drilled.  

   

From the top you can see the pins where pressed in and also inside you can just see where they almost protrude in to bore.

   

With a few choice pieces of tooling, the ports can easily be drilled and made perfect for the ideal kart engine. Taking most any of the early chainsaw cylinder blocks and precisely add the ports, you have a correct vintage and exact replica of an existing kart engine.

The block installed in this fixture is one that was pictured in the D30/36 details previously covered above. This block has all three exhaust ports, but missing two of the intakes. This will get these intake ports added, and later I will walk thru the process of adding two large booster ports as seen in the Mc 91B/92/93. Since most of these saw blocks do not have the third port induction, these two larger boost ports can be easily added without issue.

More to come.

[Terry Bentley]

Time to add some more holes

I got impatient so went ahead and started adding the missing intake ports. This is a D36 saw block that already has all three exhaust ports, but needs the other two missing intake ports added.

   

On the intake manifold side of block you can see the two steel alignment pins already inserted in to the existing intake ports. On left side you see the drill bushing for the missing port. It is precisely sized for a correct location of port using some standard machine drills.

   

Here are some choices that will yield professional results. On the left you can see a stepped drill bit. Very basic.  This would work for drilling cylinder just enough to break thru with the pilot and then continue to drill in just the aluminum. This drill bit is used only for making a pilot hole.

The next tool is an extended center drill. It will work exactly the same as step drill bit for this particular application. Use to break thru the iron liner and countersink the aluminum until it just makes contact with iron.

Next follow thru with either one of the next tool bits. A reamer with a slightly undersized drill bit tip. Or the three fluted drill reamer combination. It drills and finish sizes in one application.

   

Can it really be this simple???? Of course. This Ryobi cordless drill turns slow enough and will yield a professional job, just like if setup on a production machine. It is that fool proof. With the precision drill bushing to guide tooling, nothing is left to chance.

   

It is hard to see, but the tip of that long center drill is just breaking thru cylinder liner. The tapered part of center drill will make easy work for the next step. It keeps everything in perfect alignment.

   

Using either this drill bit tipped reamer or the three fluted drilling reamer the hole is now drilled completely thru the liner. It is finished and in perfect location.

       

Sorry about this pic being fuzzy. I tried for a good closeup. Sometimes my camera gets it right and the rest of the time I get this. With a 7/16" drill blank you can now see the correct angle of port that was just added. With drill blank removed, the new port looks just like is should.

The other side will be done same way. After port has been added, one more step is needed. Using a 1/2" counterbore, a small stepped recess will be added so the welch plug can be installed and cover the newly added intake port. I will add the pics soon as the block has been drilled out on this side.

Stay tuned.


I could not leave it alone and went ahead and drilled out the other side. The same as front side. I used the alternate tooling and came out with exact same results.

   

FIrst I drill a pilot hole hole using a 1/4" drill bit. Notice it is not centered between the intake and exhaust ports. This is due to the intake port will angle up and to back of cylinder, away from exhaust port.

   

Here you see how close to centered the intake port is now.

   

With this side of fixture removed you can see the block where port was drilled on back side. It is a 7/16" diameter thru the outer casting and also drilled thru inner liner.

   

This is a very basic counterbore. A tool that has all kinds of uses. This particular one measures 1/2" diameter and also has a 7/16" pilot on the end to guide it in the outer port opening. The pilot will keep it centered while the counterbore will make a larger recessed hole deep enough for a welch plug to be installed.

   

May not be easy to see, but the stepped recess has been added and ready for the welch plug.

   

All of the intakes successfully added to this block. They all measure just under .438" diameter. Notice all three ports on each side have different angles both up and back.


That is about it to adding the missing intake ports. The next post will show one way booster ports can be added to make a total of eight intake ports. Since many of these saw blocks do not utilize third port induction, two larger ports can be added instead of three smaller ones.

   

Jumping the gun here. This shows the two booster ports that were added to  back of  block. Since there were no previous openings for the third port induction, this is a perfect way to add more intakes. It just needs some blending in the back passage and bridge removed just like doing a conventional nine port conversion.

     

Tilting the head of mill and rotating swivel base of vice around 18 degrees on either side of centerline and the ports go right in.


I will try to get some closeups on the vertical milling machine when I add more of these ports. Very simple to  setup with minimum of tooling needed. Nothing but a mill vice with a swivel base needed. Then what ever size end mill you care to use. I chose one close to the size of booster ports in the Mc91B and newer engines.

[steve cox]

this is great information thank you for posting