I hope someone can help with this. I bought some eccentric straps in the museum auction at Kingfield a while back and got what I thought were 4 good ones out of the bunch to use. When I fitted them to the eccentrics though, I discovered that none of them were quite the dimensions they should have been. As far as I know the bottom of the ball bearing groove in the eccentrics should be 3.125" which means the diamter in the bootom of the groove in the eccentric straps should be 3.75 inches once you add 0.625" for two 5/16" ball bearings. I've attached a chart showing my dimensions of the eight halves and the variation from the correct diameter and radius - as you can see there is a big variation and one thing I have discovered is that there is very little room for variation in clamping the two haves up. I could use a stud pushing against a couple of balls to open up the width but this would only help one dimension and not the dimension in line with the main axis. The only thing I can think of is that they were not originally machined with the joint between the two halves being exactly in the center but I suspect I haven't got matching halves. These things are really hard so remachining them is out of the question. I did wonder about using undersize ball bearings but don't know of any suppliers or how to decide on what size they should be. The only other option is to make all new eccentric straps but I am a bit wary of my ability to machine the grooves for the balls and to harden them correctly. Does anyone have any ideas on the best way to get these fitted??

Jeff

Jeff for most small shops that is a problem. My large 16-inch lathe could not swing a Stanley eccentric strap. I have a large universal mill that I sometimes set up and use as a gap lathe. See attachment. It would take some rigging to center the strap in a four jaw chuck but could be done. Or on the face plate. Then I would have to rig the tool post grinder to regrind the race and making it accurate would take some doing. Not something I would want to try. It would be a lot easier to regrind the eccentric. But from your chart you have to correct the straps. I think I would talk to REMPCO in Michigan 1-800-736-0108 [www.steamcar.net] they have built and rebuilt Stanley engines, and have made new eccentrics, not sure about the straps.

I think if I were to try it my self I would hog out a pocket in a block of aluminum and pot the large end of the strap in the pocket with a molding plastic. That way I could hold it much more accurate in the big four jaw chuck. You need room for the shaft of the tool post grinder to pass through. Just a thought.

Rolly



Edited 1 time(s). Last edit at 08/04/2011 11:06AM by Rolly.

Thanks Rolly, I'll contact Gilbert at Rempco and see what he says, or more to the point, what it will cost! What are you doing for the eccentric straps on the engines you are building?

Jeff

Jeff
I have a set of eccentrics, and straps and the crankshaft with a good gear. There still together and look to be well greased.

The problem with regrinding straps is holding it without distorting the diameter. Clamps on the side might work but much harder to center. If you pot it in a block with plastic then there’s no pressure or distorting. Another way you could do it is to mount the molded block on a rotary table on the mill. You can get a 2-1/2 inch diameter wheel in the hole with no problem. At 5000 RPM’s that’s 3272 feet per minute. That should be fast enough to do a reasonable job. Getting it centered will be tricky as you only want to center it on the large side. ??? Lot’s of patience’s. another thing is dressing the wheel once it’s mounted in the spindle. I hate grinding on the lathe or mill. I cover every thing with terry cloth towels and then spray them with oil so all the grinding dust will stick to them. Looking at the work you did on your engine I know you could do it if you set your mind to it. Good luck.

Rolly

Does anyone know if there is a HEALD grinder around in service They do a good job grinding Franklin cylenders,,,mostly too hard to bore w/usual boring bar,,,Ben

About 25 years ago I had to do the same grinding on my eccentrics that you are needing today. I did it all on my 16" swing South Bend lathe using my 4 jaw chuck and my tool post grinder. I did it for my type 6 ten hp engine. I filed down the caps and then put the basic shim package in before mounting in my chuck. I dressed my tool post grinding wheel to match the radius of the ball bearings. Due to the solid construction of the eccentric straps, I had no problems of mounting them in the chuck without distortion or using any extra precautions to prevent same. I removed all of the pits and then polished the surfaces well. The final use is for a low speed application with a light bearing load so it has worked well and has for the last 25 years (30,000 miles) and counting.

Made some progress today, I used a spreader to expand the undersize straps to the correct width - see pic. I slightly over stetched them and then heated them a little and air cooled them. I found I could get them exactly the correct width by doing a little at a time. Then by by selecting which half went with what, I got three of them fitted to the engine. Putting the ball bearings in must be one of the more frustrating jobs on building an engine - if there is an easy way, I don't know what it is. Another observation on Stanley engines is that the more you assemble, the less room there is to work and they are excellent knuckle busting machines! The fourth strap is beyond this repair and I'm going to attempt to grind it in my milling machine as I can just swing it on the rotary table. My lathe will only swing 14" so that option is out. One problem maybe the maximum revs on the mill at about 1500 rpm but hopefully if I take it slow, it may do the job. Need to get a suitable grinding wheel first so will spend some time working on springs while waiting.

Jeff

To get all of the ball bearings in place and keep them there, I glue them in place with grease and then assemble the eccentric straps.

This same technique of assembling bearings is used to assemble loose bearings in bicycle and motorcycle fork/frame,,choose heavy greese for hot day,,Ben

Seems so obvious - why diddn't I think of that! I'll try that on the last one.

Thanks

Jeff

Finally got the 4th eccentric strap mounted today after grinding it. In the end, I mounted a shaped wheel in my Dremel and mounted this on the milling machine so that I could use the xand y axis on the table and the raise and lower on the mill. It was a slow job as I only felt safe taking about 0.002" cuts and about halfway through, the switch on my Dremel gave up so I had to rebuild that and then reset everything up again. The strap is a really difficult thing to measure when it is bolted to the rotary table and I had to remount it after removal and discovered I was still about .005" undersize. Thought that was the end of my troubles butno! I made 4 new hardened pins to fasten the end of the enccentris straps to the reversing links and discovered (after hardenening) that the drill rod I used was .001"oversize - not much but enough to jam everytrhing up. Did a real good job hardening them so they were untouchable and eneded up making four more. Still have one to fit but so far so good!

Jeff

The rotary table on the mill was a good move. It worked well for you.

Nice job Jeff
I never thought of using the Dremel tool on the Mill. I made a magnet base drill press with mine to drill burner grates. Works great at 25-30,000 RPM

I’ve just spent the day replacing the speed control belt on my Bridgeport mill.
It was a job getting the second half of the motor pulley back on.

Rolly