Larrys PM Research #4

[larryg]

So with the V block work done it on to other steps. For me it was figuring out how to hold the rod. Digging in the scrap box I found this black piece ( fixture);

It was machined nice, square, and parallel. The rod itself has an offset of .1625" from the side of the big end and the small end. So I machined the end of another piece of scrap to .1625" as a spacer for the big enc. Centered on one end and .650" up from the end of the fixture I drilled a tight clearance hole for a 1/4" shcs and counter bored the back side. I also drilled and tapped a couple of 1/4-20 holes to align with the angle fixture I have to hold it vertical.

So with the fixture bolted to the mill I aligned it to the travel,

Once aligned I located the the rod end and drilled and tapped the for the rod bolts.

lg
no neat sig line

 

[larryg]

One on the handicaps of my mill is there is no downstop for the spindle so I have to come up with a creative way to drill precision depth holes. On this set up I drilled the tap size holes through the rod cap and then went back and drilled the clearance hole for the rod bolt. To do this I set the drill to where I wanted to stop.

From there I have a split shaft collar on the spindle that I set to stop the quill when the collar contacts the upper pulley,

If I have to drill down from a surface I will lower the spindle contacting the surface with the bit, set the collar on the pulley, lift the spindle and then raise the knee the depth I need to drill to.

 

[larryg]

Next step is to separate the rod cap from the rod. I used a slitting saw for this as used previously on the pillow blocks. So with the fixture I know that the center of the small end is ~ .650" above the table and the rod length is to be 7.12" and the saw is .055" so the top of the saw should be 7.825 or so above the table top and this was set with the height gauge.

Also notice the block clamped to the spacer. I did this to keep the rod from moving sideways from the force of the sawing.

We have successful separation...yea.

lg
no neat sig line

 

[larryg]

So for boring the big end the fixture was separated from the angle and clamped in the vise,

The end of the fixture was located,

and then the end of the rod was located so as to confirm that the rod length was correct and where the center of the split was so the boring bar could be centered.

The boring was done with the same setup as in the above picture. I did add an additional clamp that grabbed the sides of the rod and the fixture to keep the rod from moving sideways. It was just dumb luck that the fixture was the same width as the rod allowing this clamping to happen with our packing.

For slotting the small end I replaced the SHCS holding the rod to the fixture with a shortened one that only engaged the rod to a depth of ~.235 so I would clear it with the slotting cutter.

It all worked out and I now have the short block assembled and the crank will turn with less that 20ft-lb of torque..

 

[larryg]

A couple of pictures of the fixture. As I said it was a piece from the scrap bin and the outside profile has nothing to do with this project.

lg
no neat sig line

 

[larryg]

Guy's I need an opinion. I've skipped some of the write up to get to a problem I've made for myself. You can see in the first picture that I'm to a point that I could try a bit of run in with the reciprocating assy. Things turned ok by hand snug but i could easily turn the crank with a drill chuck handle. So feeling cocky I set it up on the lathe to run it a bit more. After running for a couple of minutes the shaft slipped in the crank disk. Damn, the press fit I didn't like failed.

I'm thinking that instead of rebuilding the whole assy that I could drill through the raised part of the crank disk and insert a spring pin. The shaft is still a tight fit in the crank disk and all turns nicely in the bearings right now. I have plenty of room to get a 1/8" spring pin. My thought is to lock the crank from rotating and drill and pin while the crank is held in alignment by the bearing blocks.

So my question to the members, Is this an acceptable fix? Do you have any other suggestions?
Thanks in advance
lg
no neat sig line

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[Diversion900]

That's what I'd do, in fact I probably would have done that before testing with the lathe.
But that's just because I don't trust MY press fits either.

Cheers Neil.

 

[vederstein]

I was at a show and the same thing happened on my 5CI. The venue was a living museum (Dayton's Carillon Park) and I just went to the print shop and used their equipment to drill and press in a pin. In about an hour I was back in business.

On other engines I've actually welded the pins to the crank plate.

...Ved.

 

[larryg]

Gentlemen; I thank you for your input. After pondering just how to fixture the crank I decided that I would leave it in the pillow blocks attached to the base because I was concerned that if I removed the crank assy it had a chance of slipping out of position around the rod pin. I slid in a couple of parallels to hold the crank from rotating. I rotated the crank so the crankpin was against the parallel and then clamped the other end to the disc. Then it was clamped in the vise with the aid of a couple of blocks and a 5/8" rod at the bed of the vise. Used the DRO to locate center of the crank shaft and a feeler to set distance between the center drill and the crank disc. Proceeded with an 1/8" hole through followed by an 1/8' spring pin. I released the vise and turned the base 180* and did the other side. To my relief the crank spun freely after the procedure.

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lg
no neat sig line

 

[larryg]

SO, back to regularly scheduled progress. Looking back methinks that I was a bit over the top on posting about the Rod however I did leave out one bit of information on it. I changed up a bit in that I used a low head stripper bolt that threaded into the rod eliminating the nut on the original design. I hope that it doesn't have a tendency to unscrew itself.

So the next part was the cylinder cover. Pondering how to fixture it to get started I spied a round in the scrap box near the same diameter. With the raised round bos on the top of the cover I decided to cut a taper into the scrap that would just fit the raised feature and use the tailstock to hold it together and be able to turn the od. I ended up having to superglue the two together but it worked.

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With the OD turned I then proceeded to turn the features on the inside of the cover.

lg
no neat sig line

 

[larryg]

So at this point I'm ready to drill and tap the cylinder for the covers and drill the cylinder covers clearance holes. The prints say to match mark the holes to the to the piece being fixed to it. I have a poor record with match marked features. Way back on the crosshead guide I decided to use the bolt hole circle feature on the DRO.

I also realized that the center-line between the cylinder bore and the valve bore had to be parallel the crankshaft. If it wasn't then the valve linkage would be subject to some rotary forces that would not be good. So again I set the cylinder up with a 3/4" and a 5/16" through the bores, set that up on parallels on the surface plate and marked the center line;

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Transferring ti the mill I used a pointed scribe to locate the cylinder in the vise and the parallel to the Y axis.

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Located the cylinder bore center and confirmed that the bolt hole pattern was oriented correctly and on C/L. It was so I drilled and tapped.

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Did both ends of the cylinder and then setup the cylinder covers, located center by the raised portion of the cover that centers it in the cylinder and drill the clearance holes.

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[johnmcc69]

That's some nice work Larry!
Glad to see you got the crank sorted out, nice fix.

John

 

[Diversion900]

Nice work on the repair Larry.
I have done both concealed pin, and roll pin (for future maintenance ), repairs many times.
As I said, I don't always trust my "press fits".
The progress is looking great.

Neil

 

[larryg]

Thanks guys for lookin in. I think it is going to be fine as I ran it in for a bit more on the lathe and all seems good. Getting sidetracked lately with the garden harvest. Wife says that there are ~20 dozen jars of new stuff in the pantry, jam, fruit, and beans. Still corn, squash, salsa, tomato sauce and other good stuff to go.

lg
no neat sig line