Tiny Power M Twin Build

[racerfrank]

I found a video on YouTube on the "mrpete222" channel And I am using one of his methods of machining an eccentric. this is my first step. Each piece was set in a 4 jaw and centered on the shaft hub. The hub was turned to dia and faced then the front of the eccentric was faced to proper depth.

I have a question about set screws. What type should I use when I assemble the engine, cup point, flat, round nose, serrated cup. I'm assuming you don't want to damage the shaft in case it needs to be disassembled sometime in the future.

There is a simple fixture to make next and I'll show photos of that when I get it made.
Here is what got done today.




Until next time
Frank

[DetroiTug]

I made a fixture out of a large piece of barstock with a 1" arbor off set from center to attach the eccentrics to. Then I machined three flats in it to secure the ecentrics via the setscrews or "grub screws". This allows turning the OD's with center key and all that. Didn't work too well.

The thing that I should have added, is a driver dowell in the fixture face a set distance from the arbor, then a corresponding reamed hole in the back of the eccentrics. This prevents the eccentrics from slipping on the screws under cutter load. And one of mine even has a crack from the set screw hole to the edge of the rim. And the arbor needs no flats, just threaded with a nut to hold the eccentrics up tight.

But since then working on another twin - new crank and eccentrics for the Locomobile twin, my next eccentrics work may be as follows. They used no set screws in the eccentric at all. The eccentrics are keyed to the crankshaft and the timing is fixed. As long as those are indexed properly, no adjustment is needed. I don't recall what the exact index angle is, but that engine runs perfect. And there is no danger of set screws loosening and allowing an eccentric to slip. Although I've never encountered that on the Tiny Power Twin. I used cup pointed screws, and yes they've marked the crank, but they've held.

If memory serves me correct, it was 135 degrees from high lobe on each. One backwards to the other for forward and reverse.



-Ron

[racerfrank]

The larger bar stock with an offset stud is basically what I am going to be doing too. I was hoping the nut tightened up would be enough to hold the eccentric from turning. I will consider a anti rotation pin to keep it located .

Did the set screws mark the crank bad enough to make disassembly hard? or hasn't it been apart?

Frank

[DetroiTug]

Frank,

Attached is a pic of the fixture I used. I drew in where a pin should have been. I thought three set screws would hold it, they did and they work, but the part shifted slightly. One of those cases where I was expecting too much out of too little. A hexnut alone may hold them, but if the part slips it's not going to be pretty If I was going that route, for some insurance I would sandwich some crocus cloth shaft paper in between the part and fixture.

They assuredly have marked the crank and have raised burrs which would complicate the eccentrics' removal. Thankfully, I've never had to remove them. On this size engine, set screws to secure running gear to the crank is not a very good solution. I'm going to key them in the future.



-Ron

[barts]

One can also use tapers to secure parts against movement while still making them completely adjustable. Fenner makes some nice units; while somewhat pricey new, they're often available on EBay and they'll transmit an amazing amount of torque. I have a small Kubota tractor w/ a unusual front PTO - 18 mm x 22 tooth spline - and I was able to machine a sleeve that was a tight fit over the spline and then use a Fenner Shrink-Disk ($20 on EBay) to (elastically) squeeze the sleeve onto the spline (edited).. This sleeve drives the front end loader's hydraulic pump via a Lovejoy coupling.

http://www.fennerdrives.com/keyless-locking-devices/

- Bart

[DetroiTug]

Bart,

Those look like a good solution to the problem of fixing rotation yet allowing some adjustment.

Some of these small car engines (2.2 litre Ford) don't use keyways on the crank anymore for securing the front pulleys. Rather a diamond encrusted washer behind the pulley and up against a shoulder on the crank. Apparently it works well as I haven't heard any recalls regarding that. When I first seen their idea, I gave it the eyeroll. I designed the dispensers for those washers on the Engine lines.

-Ron

[racerfrank]

Made some progress tonight. I started by chucking up on the eccentric's hub and facing off the backside to finished dimension of .625.

Fixture was turned true and then set upright on the mill and centered. It was offset .375 and the hole bored for the shaft, shaft installed then cross bolted in place. then I offset the other direction and added a 3/8 threaded hole for a anti rotation bolt. I further offset to the edge and milled a small notch witch indicates where the high side od the eccentric should be. A transfer punch was used in the 3/8 hole then a hole was drilled in the eccentric.

I bolted one up and turned the .O.d just until it cleaned up. I removed the small bolt and loosened the big nut and let it spin on the shaft the total vlve movement is to be .750. I missed ever so slightly as I only got .749, I COULD NOT BE MORE PLEASED!!

I thought I had a photo of the one I cut the o.d. but guess I don't .

One thing I will mention the od of the one I cut was extremely hard once I got through the crust it got much better.





Until next time


Frank

[racerfrank]

I machined the o.d. of the eccentrics tonight . Travel dials were set and zeroed . The large o.d was cut then the sides were cut.
I used a AL and a AR c2 grade brazed carbide tool bits. I was hoping for a little better surface finish , I tried a few speeds and feeds and they all seemed to give the same finish. Tomorrow night I will drill and tap for the set screws.




Until then--------

Frank

[DetroiTug]

Frank,

Looks good. Now comes the fun part, the straps. They aren't too bad, just a lot of work.

I looked yesterday to see if I still had the G-code for doing the outside perimeter on those in case you may want to use it, I couldn't find it.

Had the same issue trying to get a good finish, it just doesn't turn pretty. That may be nodular iron, the castings for the Locomobile were done in that - same problem, comes out grainy and smeared looking. Good stuff though.

-Ron

[racerfrank]

Frank,

Looks good. Now comes the fun part, the straps. They aren't too bad, just a lot of work.

I looked yesterday to see if I still had the G-code for doing the outside perimeter on those in case you may want to use it, I couldn't find it.

Had the same issue trying to get a good finish, it just doesn't turn pretty. That may be nodular iron, the castings for the Locomobile were done in that - same problem, comes out grainy and smeared looking. Good stuff though.

-Ron

Ron
I was nervous about the eccentrics but the nerves soon settled. I am a bit nervous about the straps but I'm sure they will settle the more I work on them. I don't think I'm going to do much on the o.d. of the straps other than the top where the rod bolts on and the sides so I have good reference points and a good flat for the 4 jaw to register on.

When I split the strap does there need to be any thing that will keep the 2 halves in alignment other than the bolt itself? It seems to me there should be. Maybe something like the photo below.



Frank