The Steamboating Forum

On my "Semple" single cylinder engine I notice the bushing in the in the valve eccentric is loose. In the attached picture you can see there is only one clamp bolt on the yoke and there is an adjustment set screw on the opposite side from the split (single side split). I think maybe you can loosen the one clamp bolt and move the eccentric off the side of the crank and replace a split bushing in there. Does someone know what is in there?

I wonder if that setscrew has a turned down end that rides in a groove, and retains the strap on the eccentric.
it looks like the top bump is a oil cup.. I would not be surprised if there's no bushing, but that the aluminum strap
rides directly on the eccentric.

- Bart

That is what i am thinking also. i was just sure someone would "know" for sure. i am going "in" in the morning. i'll let you know tomorrow.
thanks for looking

wsmcycle,
I don't have my Semple drawings at hand, but I believe Bart is correct. The set screw has a modified end that rides in a groove to locate the strap on the eccentric, the upper lump is the oil cup and the slop is taken out by adjusting the slot. The aluminum strap rides directly on the iron eccentric. If there is a single shim you could remove it and carefully thin it a little at a time with a file, scraper and rubbing it on a sheet of emery on a flat surface , checking with a micrometer to keep it flat and parallel. If there is no shim, re-cut the slot and add shims to get the clearance in the eccentric that you need.
On the other hand, I could be completely wrong. I will check my drawings in the morning after I have had some sleep and I go to the shop.
Best regards, Steamboat Mike

i was unable to delve into the bushing because the grand kids came over. Are your drawing proprietary? Could i get a copy?
Thanks

I disassembled it and found there was nothing replaceable in the eccentric. Like Bart said the groove just maintains the outer follower centered on the eccentric. I spread the clamp and filed the touching halves so that it closed tighter. It seems good.
thanks

Be sure it isn't so tight that it expands and binds with the heat, when running.

Mike Rometer wrote:Be sure it isn't so tight that it expands and binds with the heat, when running.

The eccentric is iron and the strap is aluminum so the whole thing should loosen as it gets warmer...

aluminum has a temp coeff of 12.3 x 10^-6/F
while cast iron is 6.0 x 10^-6/F.

so if the temp goes from 65F (fitting temperature) to 100F (running temperature) and the unit is 2" in
diameter, then (100-65)*(12.3-6)*10^-6 = .0004" - prob. not enough to worry about gaining, but might
be enough to cause problems if it went the other way.

- Bart

I filled the groove with grease instead of oiling. I will oil during operation. This is a high surface contact bushing.

I was babbling on to an acquaintance about shrink fits and such and he said to me, "So shouldn't we be calculating the change in clearance on the circumference rather than the diameter?" He continued on about how if the circumference grows at a certain rate, then the diameter grows by one third as much (Pi being three, of course).

Now I know he's wrong but he has befuddled my brain enough (and it past midnight) so I can't instantly see the fallacy in his thinking. Hmm.

Bart? Fred? Anyone?