An inline 6 cylinder OHV engine

[gbritnell]

Hi Tim,
In the photo where I'm indicating the end of the shaft you can see the flats. There's 3 of them, 120 degrees from each other. Once I get the material roughed out I will make up a pair of fixture blocks, one with a set screw that will go in the 4 jaw chuck and the other will have a center hole for the live center in the tailstock. These will be used to offset the crank by the stroke dimension. I will post more pictures and text as I go along.
gbritnell

[cfellows]

Interesting build, George.  I've thought about building a compressed air inline six from time to time.  I still remember the sound of six cylinder engines from the 1950's with a split manifold and dual glass-packs.

Chuck

[Tennessee Whiskey]

Wot Chuck said. In the 70's we pulled cattle trailers with a 300 six. The V-8's were faster, but, by the time they had to stop for fuel we all arrived at the stockyard at the same time. The first pickup I can remember my daddy having had a 261(GM) with a 235 head, 3x2s, Corvette cam, and split manifolds running into straight stacks. Ahhhh the good old days. Still had a 6 volt system and he had to try to back in on a rise when he parked so he could roll it off to start. I might have to hock something and get you to sell me this one George. I'm pre-bagging popcorn, cause I don't want to miss any of this one.

Whiskey

[cfellows]

Hey George, I looked through this thread and the one in the plans section and can't find any indication of how big this engine is going to be.   With 5/16" main journals, I'm guessing the bore will be somewhere around 3/4"?

Chuck

[gbritnell]

Hi Chuck,
With it being based on my 4 cylinder OHV engine it will have a bore and stroke of .75 x .875. As with my differential build I had to resolve the gear making issue first. If I couldn't have made the helical gears I wasn't going to go any farther with the build. I could have used the same location for the distributor as the 4 but didn't feel it would have the proper character.
gbritnell

[gbritnell]

Gentlemen,
Here's today's installment of the crankshaft machining. At this point I am continuing to mill the material from the webs and roughing the crankpin journals. The flats on the end were indicated true and the clamps tightened. Using an assortment of .187 and .250 diameter end mills all the material was removed in preparation to turning.
gbritnell

[gbritnell]

Here is my procedure for turning the throws.

1. A .093 cutoff blade was ground square on the end. Using a Dremel with a thin cutoff disc I notched the end of the blade. The blade was then stood on end on my layout plate and an indicator was moved across the edges to make sure that both cutting surfaces were square to the edge of the blade.
2 The blade was installed in a toolholder and the QC holder was turned to square up the blade to one of the chuck jaws.

[gbritnell]

3. The crankshaft blank was then mounted in the offset fixture blocks. A set screw with a brass follower plug was tightened against the end with the flats milled on it. The other fixture block was slid onto the other end and left loose until the whole setup was aligned flat on the layout plate then the other set screw was tightened. This would insure that the crank axis was true to the lathe centers.
4. The setup was mounted loosely in the 4 jaw chuck and brought into close positioning by using the concentric rings on the chuck.
5. Using a lathe tool I touched the side of the fixture block and set a reading on my crossfeed dial. The chuck was turned 180 degrees and the tool was moved in to take a reading on the opposite side of the block. Working back and forth between the chuck jaws the fixture block was centered within .001 on the dial.
gbritnell

[gbritnell]

6. The tailstock was run up until the live center just lightly entered the center drilled hole. I check it by trying to turn it with my fingers. If the center just won't quite turn that is where I lock the tailstock in place.
7. A 1.00 travel dial indicator was set in my magnetic base and mounted on the lathe carriage. By eye I aligned it parallel with the horizon and square to the job. This would help insure that I got an accurate reading over the course of the travel. The crank was rotated to the farthest away point and the indicator set to -0-. The indicator shaft was pulled out by hand and the chuck was rotated 180 degrees then another reading was taken. Working between the opposite 2 jaws I got a reading of .875 (the crank stroke).
gbritnell

[gbritnell]

I didn't know if this crank was rigid enough to prevent springing while cutting so to help with the situation I mounted hose clamps along the crank at the other throws. I really didn't want to have to cut buttons and Loctite them in place at every main journal. That would have been 3 per journal times 5.
As it turned out the hose clamps did the job. The journals on this crank are .312 diameter. Any small than that and it would have required spacer buttons.

8. The lathe was set in the higher belt speed but with the headstock in back gear. I don't know exactly what the rpm was but I suspect it was somewhere around 180 rpm.
The cutoff blade was advanced slowly into the material at .004 per pass. After all this work there's no sense getting greedy to find out how heavy of a cut it would take. Working slowly back and forth up to the cheeks the journal was turned to size. The only measuring tool I could get in to check the size was my dial calipers. There seemed to be .001 taper in the .25 width so I left the journal a touch heavy (.0005) and with a small fine file I cleaned it up this was followed by 2 strips of emery, one medium and one fine.
gbritnell

[gbritnell]

This procedure was repeated another 2 times to do the other sets of throws. The crank was removed from the 4 jaw chuck, the fixture blocks were rotated to the next flat and tightened, the crank was reinstalled in the chuck and indicated and then the cuts were made.
Attached is a short video of the crank rotating offset in the lathe. It's can be quite intimidating as I've had them turn into pretzels in the past.
<a href="https://www.youtube.com/watch?v=2W155v9WbEI" target="_blank">http://www.youtube.com/watch?v=2W155v9WbEI</a>
After 3 hours of work I had all the journals cut.

[steamer]

The hose clamp tip is awesome George!   thanks!

Dave

[Tennessee Whiskey]

Not only is the hose clamp trick "Tip of The Month" but, everything is just awesome. Great work, George!

Whiskey

[ths]

Hi George,

Did the lump on the hose clamp cause any out of balance upset, or did you arrange them to cancel each other out? Nice work to watch.

Cheers, Hugh.

[ozzie46]

   Fantastic George! 

  I've only done a 4 cyl with the mains on each end and the pucker factor was big. I can't imagine what that was like.

   I really like those hose clamp stiffeners.

  Ron