Straight 6 Cylinder Engine

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Apr 22, 2020
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Weirsdale, Florida
We went to our metal supplier yesterday (Chris and I) to see what we could find. You never know what drops he has so I had not decided on a design except it was to be 6 cylinder. I settled on this chunk of aluminum 2.5 X 5 X 28" long. I only needed half that much but he didn't have a way of cutting it then so I took the whole piece. Weight over 30 lbs. I should have enough even if I really mess things up.

Cutting off a 12" piece.

The block for the engine will be 3.5 tall by 2 wide by 12 long so that means I have to slice this block length wise.

Harbor Freight band saw to the rescue.
It was a little tricky at the beginning even though I had the guide rollers open as far as they would go I had to open the vise and tilt the part back until the cut was deep enough to clear the guide.

The cut ended up off by 0.032 from one end to the other I am pleased.

Over to the mill to clean up and cut to size.

Right now the engine will be.
6 cylinder 1" bore
Overhead cam
Water cooled
Crankshaft will have 4 main bearing saddles with two 6700 ball bearings under each saddle with a stroke of 1.100.
This is the crankshaft unpainted and you can see the four bearings of either sides of #3 and #4 rod throws.

Thanks for looking
Will you use atmospheric intake valves again? If going SOHC you might consider placing the valves in a row along the length of the engine so that both inlet and exhaust can be worked by the camshaft.

Inline 6s have a distinctive sound, always reminds me of my grandparents' Ford Falcon from back when I was a kid.
The next step is to whittle out the three chambers for the crank shaft. They are 1.250 deep and 2.000 wide. I was going to mark some guide lines on the block but that is too easy for me to over cut. I decided to use the dro on the manual mill so I did make up this drawing to go by..
Crank Pockets.jpg

I started this job yesterday and worked on it for 4 hours today.
This shows where I am almost done.

Everything even fits like it should.

Main bearing caps tomorrow.

Thanks for looking
As you know if you have followed any of my other builds I usually take on projects and processes that I have never done before. On this engine there are 4 main bearing caps that are 12 " apart. I don't have a drill bit or boring bar that long and how do I keep everything in alignment over that distance. I studied on this problem for several days while on vacation Line boring seemed the only solution but there are a few extra problems.
The main bearings have a 10mm bore and 15mm OD. That's not much to play with.
I have a n 17/32 drill bit that will reach the first three bearing locations. I then will have to break everything down flip the block over reset the alignment and drill from the other side and hope they line up. Using a 1/2" rod 26" long I drilled and tapped for a M3 set screw that I had sharpened on the end.
This shows the setup I made on my lathe.

Another View

The 1/2" rod was anything but ridged and I could only take a couple of thousands at a time but after several hours I was within 0.005 of my final size.
It had been a long day but it looks like it will work. I will finish to final size with a hand reamer tomorrow.
Thanks for looking
Hi Ray,
Pretty hot down here in Florida to be working in the shop that long. Please stay hydrated and keep your salt and potassium levels up. I had to go inside and eat a plate of cucumbers and salt yesterday when my left hand froze up.

I had a similar long boring job to do on an Otto Langen engine and used the lathe and home made bar as you did. The first attempt I did as you did and cross-drilled for the cutter bit. Too much deflection and chatter. I was boring 1214L using a 3/16" round HSS blank. I pondered it a bit and came up with the idea of cross-drilling at a 45 degree angle. May not sound like much difference, but look at the drawing below and compare the material remaining at the center of the bar where the bending moment is greatest. There are known equations and theories to explain this such as the parallel axis theorem and such, but I think the cross sectional view illustrates the benefit better. I was also able to advance the cutter bit quite precisely by tapping the opposite end of the hole and using a set screw.

The build log is here:

I can see how that would have helped.
My biggest problem was that I could only use a 1/2" bar maximum. Your 1" bar would have been much better if I could have used that size.
Thanks for the suggestion and your build was great..

I spent several hours with a hand reamer and I was rewarded with this.


It turns smoothly by hand and runs true.

I have to remember not to stand in front of a fan when taking videos.

Thanks for looking
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Started on the other side of the cylinder block for the cylinder liners. After drilling 1/2" holes I next went with a 1" drill Bit.

Then with the boring bar out to 1.250 and a 0.100 larger lip on top for the liner to rest against.

I could see the connecting rods were going to hit the insides of the block so just cut out the sides.
That fixed that.

Thanks for looking
I have decided to make the engine block water cooled. I have one other model I had built that uses a radiator and water pump so active water cooling is not entirely new to me but will be another challenge.

Milling out a 2" deep section for the water jacket.

When I started with this aluminum block it weighed in at 8lbs and 4 oz.
After the diet it now weighs 4 lbs 11.5ozs.

I also made a good start on the cast iron cylinder liners.
These will be cut in half to make the 6 liners.

Thanks for looking
Can you elaborate on fabrication of the crankshaft. Are the webs dowel pinned to the main crankshaft rod? If so, how did you orientate them? Did you feed the rod completely through all web elements & cut away the middle where required? How are crank pins. held into position?
Working on the cast iron liners today.
I cut to the OD to size leaving a center section larger for the lip in the block. Then I cut them in half and drilled the center out to 7/8".

Bored the inside out to 1".

All six in a row.

I glued the liners into the block using high temp gasket maker and clamped them in place.

Thanks for looking
I decked the cylinder block to get everything nice and level again.

It looked so pretty I couldn't help my self but had to paint it.
Used Allis Chalmers orange.
What do you think?

Also cut out 6 rods on the RF31 clone CNC.

All in a row.

Thanks for looking
Nice work on the rods and all the rest as well. How are you holding the rods as they are cut from the stock? Bridges that I can't see in the photo?

Working on the connecting rods today.
Milled out slots for the 4-40 rod cap bolts.

Drilled the holes for the 4-40 screws.

Always trying something different I ran across these from McMaster Carr and will give them a try.
"863iron-copper bearings are also known as Super Oilite® bearings"

I cut them to length on the lathe and loc-tite them into the rod end.

I will let the loc-tite setup over night before sawing the rod caps off.

Thanks for looking