1931 Franklin Advice Requested

[Lisa P]

A friend of mine dropped off his 1931 Franklin for some minor work (brakes, clutch adjustment and steering adjustment). That has since turned into an engine cleaning, complete with the removal of all cylinders. Why clean the engine? Well, when I was finally able to crank it over by hand, I found that two of the exhaust valves weren't moving. Upon further inspection, it was discovered that mice had set up residence inside the exhaust manifold. As the valves would not budge with any amount of penetrating oil and tapping on the top of the stem, we decided to remove the two cylinders with the stuck valves. After seeing the deposits, seeds, droppings, and nesting material, the owner decided that every cylinder should be removed for proper cleaning. I couldn't agree more. Ironically, the engine had been rebuilt around 1974, but the mice had been in there too long.

At some time in the past, or perhaps I did it, a chip was taken out of one of the piston skirts. We believe that this piston will need replacement along with all of the piston rings. I see in past posts, there is a source for correct rings. Would anyone know where I can locate a piston?

As for my background, I have a couple of DeSotos that I have rescued, along with a 1948 Kaiser, but nothing that comes close to such an amazing machine as the Franklin. Despite the fact that I currently live in IL, I used to live in Cortland County, the heart of Central NY. My grandfather and I used to go to Syracuse all the time to baseball games, and Cazenovia was one of the towns we'd like to go through on our Sunday drives. I've probably seen a few Franklins and never even knew it! I also am fortunate enough to have an older (>70) mechanic mentor that works on his aircraft engine when necessary. As for the Franklin, we appreciate all the advice you have to offer!

[odyssey]

Hi Lisa-

If you need to replace one piston, it must weigh the same as the rest. What kind of piston is it?

Tom Rasmussen

[Lisa P]

Tom, I believe it is an original. The previous owner had the engine rebuilt due to a rod knocking but is not aware that any of the pistons were replaced. I had read that they are balanced, which is yet another reason I'm worried about the chip in the skirt. The piston has a large number 50 stamped in the top along with a smaller 0.0025 stamped into it as well. I can also make out the letter G. Does this help? As always, thank you again for the advice!

[odyssey]

That's an original Franklin piston, 0.0025" oversized. It might be difficult to find a 0.0025" piston, but I can look.

The next question is what size is the cylinder? How much taper is there from bottom to top?

It is another step to fit a piston to a worn cylinder. Most are quite worn.

And yes, rings can be purchased to fit the shallow grooves in the factory piston. But chances are the top groove is badly worn and the 2nd groove as well. New rings are not too effective in worn grooves. A groove insert spacer can be installed to bring the grooves back to size, but you will need to find a someone to machine the grooves wider for the inserts.

If you go to the trouble to machine the rings grooves wider, might as well maching them deeper as well, for modern, off-the-shelf rings.

For one piston, this isn't so bad. But if you end up doing all 6 due to the wear, oftentimes new pistons are a better alternative.

The slippery slope....

Once you measure the cylinder for taper and size at the bottom of the bore, decisions will be easier. Let me know and I can see if I have an old piston that might be worked to fit.

Tom

ps - I have seen lots of pistons with similar chips that came out of running engines. Some might just put it back in. I wouldn't, but I also couldn't say it could not work...

[Lisa P]

Ok Tom, I've measured the cylinder bore as 3.495 top and bottom. This is with an inexpensive caliper which is not calibrated (but was zeroed out). Does that bore size sound likely? Yes, I had read about machining the ring grooves out to accept modern rings. I have measured the third ring down from the top as having a depth of .154", however I could be off by a bit. My mechanic mentor has the equipment to do make the grooves in the piston deeper, but he has recently had cataract surgery and is waiting for new glasses...If there are any other measurements you need, let me know. I really appreciate your advice! And yes, it would be nice to just ignore the chip, but I would love to see this car run well for a very, very long time.

[odyssey]

I'm not too confident in caliper measurements. It's possible the piston you have is actually -0.0025" and not +0.0025 - but even if it was, your measurement of 3.495 still does not make sense.

The only way to know is with accurate micrometer measurements of the cylinder bore. Can you get these?

Let me know what you come up with and we can start to look for a piston.

tom

[Lisa P]

Tom, the owner had the cylinder measured at a machine shop. He was told the bore was 3.5" with 0.004" of wear at the top. Now I remember that there are instruments to measure bore sizes and I've actually used one before.

Also, another one of the pistons has pins that go from the exterior of the piston (intake side) to the interior of the piston. Any idea what they are for? Would the be used to balance the piston? To add more weight? To hold it together??

And, the walking beams have bronze inserts that are not drilled where the small circular wells are on the tops of the walking beams. It seems as though someone else on here had the same problem and drilling them out was recommended so that oil could reach the pins on which they pivot. There weren't any felt pads on top of the beams either, but they are currently on order. I see that forum members recommend using synthetic oil on these. I can't wait to hear the Franklin run. The owner promises to give myself and my three little girls a ride when it is running.

Edited October 17, 2013 by Lisa P
Additional information added. (see edit history)

[odyssey]

Hi Lisa -

Interesting photo:

Those pins in the piston are part of a piston skirt expander. These were commonly installed after a cylinder had worn to quiet down a noisy (loose-fitting) piston. It was an old remedy.

But do you also notice the piston skirt has a specific section of diagonal lines? Those lines are the result of knurling the piston skirt, which was done to expand the piston skirt (size) to quiet down a noisy (loose-fitting) piston. This is a somewhat more modern remedy.

So you have on one piston two remedies for noisy, loose pistons.

What do the other pistons look like?

And yes, the rocker arms should certainly have the oil holes drilled out. My guess is that they were rebushed by a rebuilder and just never drilled. Once drilled out, the inside must have the flashing from the drilling priocess removed carefully so the rocker arm pin will not get hung up on it.

I will look for a piston and let you know.

Tom

ps - feel free to call me

Or email me to send your shipping address

Odyssey Restorations, Inc.

763-786-1518

odyrestorations@aol.com

[Lisa P]

Tom, thanks for the insight. The other pistons have the same knurling pattern on them so I guess that means they were all worn. The engine was rebuilt around 1974 and only has run about two hours since then, so that may explain the modern (knurling) vs. older (expander) repairs.

The owner has the rocker arms and will drill those out as well as remove the flashing.

I took a look at that Series 12 engine you restored/rebuilt. Wow, does that look great! thanks again for the help-I'll send an email with my shipping info.

Lisa