Mac saw engines

[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.