Glowgeek

What do you think the big end clearance should be?

706jim

Increase clearance to 0.002"

Jesse Open

Look first for streaks or patches that are brighter silver than the gray steel parent metal of the crankshaft. Clean up of minor patches can be done carefully with some dilute sodium hydroxide. (Lye, Draino, oven cleaner. Wear rubber gloves) Wet the pin and allow it to soak and scrub with the Scotchbrite. Wash well and oil the crank when done.

Also seen folks shave it off with an x-acto blade, I would still follow and finish with the etch.

the Wasp

My Feedback: (1)

Gary, what do you think the manufacturers do for the ID end fit on the rods ends ? maybe a reamer ?

Jim

Jesse Open

Never looked that hard. Either a dedicated reamer or, a better tool would be a broach. Reamers can be rather untrustworthy. Broaches are long life and very repeatable.

Those main bearing and rod bearing shells as well as insert cam bearings are usually sized with a broach, at least they were.

modeltronics

My Feedback: (27)

Gary

I looked at the crank pin under magnification. I thought I could see little lines around the diameter. I tried a little oven cleaner that I use to clean the window on our wood burning stove on it. Then I scrubbed it with Scotchbrite. After a good water clean, I could feel little groves with my finger nail. They are very hard to see but I think I can feel them. Next, I pulled a similar looking crank shaft from my parts box. I think it was from a 56. Rubbing my finger nail on that crank pin felt much smoother. I looked up the part number for the crank on the 50 and 56 and found out it was the same part number. I am not going to put the original crank shaft back in the engine, I’m going to use the spare one I had.

Interesting side note… The threaded section of the replacement crank shaft is about ¼ inch longer than the original one that was in the engine.

Since the replacement crank shaft came from a bag of parts I bought at a swap meet, I did check the run out with a dial indicator. I have no idea of its history. It was good to go.

I think the oven cleaner trick saved me from using a crank shaft that may have caused a problem further down the line.

I now have the lower part of the engine assembled with new bearings. All I need is the new con rod to come in the mail.
Pedro

Jesse Open

If those ridges were raised, good chance they are aluminum .

Jim,

Back in the early 197Os there was a time when replacement valve guides for certain mot*****les were hard to buy. I had an old Logan lathe with a six position tailstock that I pulled from the trash at a local shop. With a little effort I tooled that lathe to make guides from cored 660 bronze bar stock. I wanted a smooth but hard bore in the guides. I wound up pushing chrome bearing balls thru the .002 undersized bore with an arbor press using castor oil as a burnishing lubricant. The bores were beautiful, on size and a work hardened surface. Kept me in business doing valve jobs on those Britbike heads for the local bike shops. Had enough left over to sell across the USA via mail order too. Ball burnishing would not work so well on rod bearings however

Glowgeek

Pedro, I've had some crank pins that felt like that both before and after cleaning/polishing. The worst one I found in a well used 56 about 3 years ago, had a few deep scratches in the pin and in the rod. Many gallons of fuel later it's still running fine at over 10k rpm with those same parts. The pin/rod clearance on that one measured a little over .003" using a mic and gauge pin set. I run 15% synth/2.5% castor. If I took it apart today I'm sure I would find that castor varnish has filled in the scratches.

Built up crud or aluminum on the crank pin could case issues but scratches aren't anything to worry about imo. Think of them as micro oil channels.

Jesse Open

Of course,

As long as they are light grooves, not raised ridges. And no aluminum in those grooves.Still, if you have a crank with a pristine journal, makes better sense to use the best one with that fresh rod.

Glowgeek

By all means, yes, gunk and ridges must be removed before putting a crank back into service!

That particular 56 crank pin had raised ridges adjacent to the scratches which I removed using the "shoe shine" method and emery cloth. Sand or any kind of hard foreign debris can cause those scratches. Easy for bad stuff to enter in through an unfiltered carb or unplumbed case vent. I do use tubing on vent nipples but no carb filter as we have a nicely groomed grass runway. If I flew off of a dirt or sandy runway I'd be using a carb filter and would install a tee fitting and additional tube in the vent line,capped for injecting ARO.

Jesse Open

In a pinch I guess.

I do prefer to avoid unbacked abrasive cloth in situations like this; At least for the bulk of metal removal
Careful use of hard oil stones is a very effective means to level the the high spots without removing metal elsewhere. There are shaped stones available that work well on a radius but with practice an arc motion with even a flat stone can do a fine job. The mission is to remove only the raised edges of the furrow.

Still better to simply start with an undamaged crank.Especially when you already have one.

Glowgeek

Proof's in the pudding Gary, the crank pin mic'd great, the engine runs great and it took less the 20 seconds to shoe shine the burrs off, all without the risk of accidently creating a flat spot on the pin trying to use a stone. It took longer to clean and polish the pin than it did to remove the burrs and I didn't have to be very careful, no need.

Jesse Open

Anecdotal,
I did not say it would not work or would not run . I offered a different method.
Sure, "It worked" yet overall not as precise and needlessly removes metal that could have been preserved.

Lonnie, not certain of your occupation, but I also "shoe polished" journals at one time as well, 50 years ago. Since then, working in the metals trades I have learned other methods. Using an oilstone slip takes little, if any more time and the results are far closer to my liking.

The work we did was subject to standards and inspection. A flat anvil micrometer only measures across the high spots. It ignores the low spots that the shoe polishing created.
I would love to shadowgraph that shoe polished surface before and after.


Bottom line remains : The new, undamaged crankpin already on hand is the way to go.

acdii

This thread is like a box of chocolates, You never know what your going to get.

Jesse Open

Or why

Glowgeek

Can't argue with that.

Or this: "Bottom line remains : The new, undamaged crankpin already on hand is the way to go."

Also, can't argue that a very fine abrasive slip stone in the hands of a talented operator would yield better results. I don't have the appropriate stone and I'm not a talented slip stone operator.

Run what ya brung!

acdii

So many possible ways to use slip and stone and get banned.

Glowgeek

Which reminds me. Did you ever get around to bending your pipe with your balls?

FlyerInOKC

My Feedback: (6)

I was wondering when that would show up again!

Glowgeek

Good to see you still have a sense of humor Mike, you've been through a lot lately. I hope your feeling better brother.

FlyerInOKC

My Feedback: (6)

If you can't laugh at life's little challenges you either drive yourself crazy or lay down and die. I'm already crazy enough, and I still have airplanes to build and fly with Saitos of course!

Jesse Open

Just avoid real dirty stuff....


Like Motor***les

acdii

Tried a test bend, was quite painful. I'll use a vise instead of my teeth next time. Actually still waiting on some tooling and the hex stock to arrive, supposed to be in at the end of the month.

Jesse Open

What size hex stock do you need?

the Wasp

My Feedback: (1)

thank you Gary !!

Jim