Bearings

[Theunis]

Hi im not new to this site but have never posted, however i read all new posts every morning and the information here is priceless.

My question is whether i would need bearings of any kind if i use brass conrods on a brightsteel crank with oil pressure feed on a beetle engine scale model of 200cc

Would brass on steel be fine if i use oil under pressure as lube

 

[kf2qd]

How much do you plan on running it?

 

[Theunis]

I would love to have a engine that could potentially run many hours

 

[Richard Carlstedt]

That will work, but what type of brass are you using ?
That will determine life expectancy. A bronze alloy will wear much better than brass
Also look at "superfinishing " the steel crank pin surfaces to get greater life.
I converted an old electric shaver by adding a small stone to do the finishing
Rich

 

[Theunis]

Hi Rich.

What bronze alloy would be best and would polishing crank journals with diamond paste to get mirror finish be good , also could i make insert bearing halves from bronze and use alluminium as material for conrod

Regards
Theunis

 

[Hopper]

6061 or similar aluminium rods with bronze inserts would work well too. I would not use brass. Too soft to withstand the pounding a big end cops. A leaded bronze such as SAE 660 should work OK. I would not use phosphor bronze unless the steel shaft is hardened.

 

[davidyat]

My interest is "beetle engine". A VW? If so would love to see pictures, plans or anything, if it is a VW model engine. I have a real 1967 VW that is my daily driver. Would also love to make a VW Model engine.

 

[Richard Carlstedt]

What Hopper said is on the money. 660 is a Bearing Bronze that would work very well and it's new (er) designation is 932 C . There are harder bronzes like Aluminum bronze or Phosphor bronze and they work well with Hardened steel journals, but are really tough for home shop machining. I am not sure of metal numbering systems in Kiwi land ?
Diamond paste polishing will work, but when most guys polish they use a soft support surface, like a rag and what you want is accomplished by superfinishing which eliminates all the "mountains" on the micro surface of the metal . If you do use Diamond , try using a vary hard piece of wood that is slightly narrower then the journal and shift/oscillate it back and forth. The wood should be hard,smooth and FLAT...or maybe even use a piece of brass
Rich

 

[jagwinn]

I converted an old electric shaver by adding a small stone to do the finishing
Rich

Sounds like a nifty project! Details please?

 

[Richard Carlstedt]

I wrote it up on another thread/website, but here is a repeat:

Well My photobucket account is shot so I will try to explain a few things without pictures.
The Process was invented by Chrysler Automotive back in the 1930" s to improve crankshaft bearing life, and it did dramatically by producing a surface finish far finer than turning and grinding did and reduced wear measurably.
So much so that is is used throughout the world today. It involves presenting a fine abrasive to a turning surface and oscillating that abrasive cross-wise to the rotating metal. Industrial machines are very expensive and I have given links at the bottom below to show you the commercial machines and some commentary. Basically you have a non repeating oscillating abrasive move irregularly across a rotating workpiece to remove offending surface protrusions created by earlier machining /grinding work. It is not a heavy force application like milling or grinding (!) ( OR Burnishing !). Low forces ( hand pressure) are all thats required to remove the high points and it does not remove "valley" irregularities
Now let me tell you how to make one at home .
One of the secrets to Superfinishing is variability. you do not want a oscillation that is controlled time wise ( think metronome ) and the more irregular, the better. While commercial machines use rolls of abrasive or stones , a home machine can use a small stone...like a 600 India stone or finer .
Let me tell you what I did as I am not sure whats available today. I found a old electric razor at a flea market 20 years ago. This was a Palm unit that is similar to this eBay sales item

https://www.supfina.com/products/sup...hing-machines/

 

[Richard Carlstedt]

Here is the rest of the posting

Now let me tell you how to make one at home .
One of the secrets to Superfinishing is variability. you do not want a oscillation that is controlled time wise ( think metronome ) and the more irregular, the better. While commercial machines use rolls of abrasive or stones , a home machine can use a small stone...like a 600 India stone or finer .
p important part is that it is not a rotary unit shaver, these old ones oscillate quite fast ( 500 CPS ?) and vary with load as the vibrators are not strong
Throw the head away and make a adapter to hold a stone ( 1/2 x 1/2 x 4 ?) . My adapter was a small piece of walnut (1 x 2 x 3/8" thick ) that was milled to hold the stone . make the slot about .002 smaller and the wood will hold it. the wood milled so it is retained by the 2 vibrating arms that formerly moved the shaving blades L & R by oscillating them maybe .010-.020 "---perfect for superfinishing
Now when you have a piece in the lathe , rotate the work piece about 100 RPM and set the stone that is exposed from the end of the shaver head on the surface with a bit of oil and watch the surface get really smooth. The stone moves both forward and backward and also oscillates side to side. this criss-crossing knocks all the irregularities down to give a superior surface . If you find an old electric razor , it can be pretty cheap addition to the shop for journal turning .
Keep the rotary speed (lathe) down so you don't crash and run the lathe backward, so any force throws the offender upward and not downward into the carriage/ways. Obviously CARE must be used to keep the stone moving left to right and not hitting a crank throw.
I wrote an article for Model Engine Builder magazine a few years ago about this in magazine issue number 29 which is available pretty cheap on line
https://www.modelenginebuilder.com/

Rich


commercial machines
https://www.aaabrasives.com/shop-man...superfinishers

Description of the process
https://www.supfina.com/products/tec...y/superfinish/
results
https://www.supfina.com/products/sup...hing-machines/

 

[stevehuckss396]

The Process was invented by Chrysler Automotive back in the 1930" s to improve crankshaft bearing life, and it did dramatically by producing a surface finish far finer than turning and grinding did and reduced wear measurably.

Last time I drove by the Chrysler building was still there but in very bad condition. This is the building where the process was invented according to the Chrysler historians.

 

[karlw144]

Here’s a picture of Rich’s polisher, been meaning to make one since my visit.

Rich, hope you don’t mind me posting this.

 

[Richard Carlstedt]

Perfect Karl, Thank You !
A few more words
The stone in the picture is 3/8" wide--it can be what ever you have. ( 1/4 or even 1/8 )
Obviously I am NOT touching the crank until it is in the lathe , it was a info pic.
The wood grips the stone without glue, just make it snug.
The two splayed pins on the shaver may get loose on the wood piece so I use my middle finger to hold the wood (mandrel) against the pins .
This is not a "Precision Tool" but a very simple and effective solution .
Rich

 

[jagwinn]

Thanks, Richard!