Stuart 10v

[swarf]

Here's my second attempt at the piston. Worked out well.

 

[kf2qd]

Metric English, English Metric. For the purposes of building a model where you have to make and tap the holes I would think whatever is handy in the area you live, it is easy enough to figure out the major diameter of the threads called for (albiet easier for the metric than the English...) and use what is locally available. The only person that will know is you...

 

[swarf]

Hi Richard, suppose to be 1 11/16" or 1.687". I used digital calipers. Then checked with a height gage on a surface plate.
In order to center the little end I had to take off 50 thou on each half of the big end
That worked, but now there's not enuf meat for the hole on the big end. Will see if I can send a pic. My phone takes pics that make files to big to upload.

 

[swarf]

Maybe this will help explain what I'm getting at.
You'll notice the split at the big end to little end center is what it should be.
The problem is I had to remove .050 from each half of the big end to get it right.
In doing so, I now have insufficient material to drill and ream the big end bore.

 

[GreenTwin]

Normally the big engines use shims between the rod and the bearing cap, with the idea that as the bearing wears, the shims can be removed to tighten things up a bit.

So install some shimstock, and then drill/ream ?

I am not positive I am following what the problem is.

.

 

[swarf]

Normally the big engines use shims between the rod and the bearing cap, with the idea that as the bearing wears, the shims can be removed to tighten things up a bit.

So install some shimstock, and then drill/ream ?

I am not positive I am following what the problem

Normally the big engines use shims between the rod and the bearing cap, with the idea that as the bearing wears, the shims can be removed to tighten things up a bit.

So install some shimstock, and then drill/ream ?

I am not positive I am following what the problem is.

.

How obvious, never thought of that. They'll need to be .100 thick.
I went and ordered another con rod yesterday. No big deal. Live and learn.
Thanks

 

[AndrewW]

Hi Swarf
I encountered a similar problem with the conrod. I think it's probably down to the fact that these are brass extrusions.
I covered it in my YouTube vid:

One way around it is the machine the whole of the conrod from some bar stock.
Hope that helps.
Cheers
Andreww

 

[Mike Ginn]

swarf Other simple ways to reduce size is to send the photo to your computer by email, display the photo and use windows key, shift and the letter "S". you can then use the cursor to capture the whole or part image to the clipboard and then paste it into the post. From the computer you can also paste the image into Word or PowerPoint and save as a pdf to paste into the post. Alternatively do as Richard suggests.
Best of luck
Mike

 

[swarf]

Hi Swarf
I encountered a similar problem with the conrod. I think it's probably down to the fact that these are brass extrusions.
I covered it in my YouTube vid:

One way around it is the machine the whole of the conrod from some bar stock.
Hope that helps.
Cheers
Andreww

Hi Andrew,
As a matter of fact, I'm watching most of your videos to build this engine.
The vid of the con rod is what I've looked at recently.
Good for you on adapting to the twisted small end of the rod.
It worked out well and doesn't seem to affect the engines performance at all.
Thanks

 

[terryd]

Hi Richard and Swarf,

I agree about Gimp it reallis an excellent free open source app. Richard you can't do a 'save as' to convert a file to say a jpg or png format, you have to do an 'export as' from the file menu You can then change the format manually by deleting the one given and then replacing it with your chosen format (.png or.jpg).
To change size you need to go to the 'image' menu and then select 'scale image'. You can then scale the image by physical measerements (inches, cm or mm) or by percentage. You can check a suitable % change by going to the 'view' manu and selecting zoom and experiment with the %s. that will give you an idea of the size of the final psize after scaling.
Gimp is a powerful but smallish program with lots of possibilities for picture enhanceents - it's worth experimenting. Download here or from the Microsoft store - there is an Apple ios version as well

Hope that helps,

TerryD

 

[timo_gross]

Metric English, English Metric. For the purposes of building a model where you have to make and tap the holes I would think whatever is handy in the area you live, it is easy enough to figure out the major diameter of the threads called for (albiet easier for the metric than the English...) and use what is locally available. The only person that will know is you...

Some purists insist on the correct sizes that were "original" to the design.
I think I would go with the "whatever is handy" (aka metric) approach.
If the model will be sold in order to buy castings for the next project. It might be worth considering.

 

[Steamchick]

Thanks Green-Twin for post #125. The simple and obvious solution is often the least obvious! I have adjusted worn big-ends by removing the said few thou off bearing faces - just like fitting thinner shims - but your obvious solution didn't come into my duff brain... too much beer last night?
Thanks!
K2

 

[Jasonb]

Not quite so simple when the two pieces of shim will be 0.100" thick as they will form the majority of the bearing surface, hole is 0.218" dia ( no separate bearings on this conrod, the cap is the bearing) so trying to keep them in position will be difficult unless they are silver soldered into place.

One other point the conrods were never supplied as extrusions, they used to be hot brass pressings but are now supplied as CNC machined brass parts requiring some finishing ops

 

[swarf]

I opted out for two more connecting rods, as they are reasonably priced and readily available.

 

[Richard Hed]

Thanks Green-Twin for post #125. The simple and obvious solution is often the least obvious! I have adjusted worn big-ends by removing the said few thou off bearing faces - just like fitting thinner shims - but your obvious solution didn't come into my duff brain... too much beer last night?
Thanks!
K2

or not ENOUGH beer.

 

[Steamchick]

Hi Jason, maybe I mis-understood the simple solution of using shims? My understanding: Make 2 square shims, with holes for the big-end bolts, and bolt the big-end together with the shims in place where the big-end bolts join the cap to the body. Then machine/ream the hole to size for the big-end. Mark ends of the cap so it can be re-fitted correctly, dismantle, then reassemble onto the big-end journal. The shim material isn't in the bearing, just at the ends where the cap is bolted to the rod half of the bearing.
But add a drilling through the top half of the bearing so oil can be fed into the bearing for running. Even add an oil cup? Usually you can make one to hold a single drop of oil! Maybe even 2 drops? I have even seen oil cups that wipe of a bit of felt or string the gather oil that is fed down a suitably positioned pipe from a larger reservoir...
On an engine that was made by some apprentices in the 1930s, and demonstrated twice a year at shows, the big-ends had not seen enough oil (who wants dirty black oil splashing off a working engine on a public display stand?) so had about 0.010in. Play in the big-end bearings. I skimmed the flat joint surfaces of the bearing caps -carefully, after measuring the play - and when refitted the play was impossible to measure. It runs well, now, without the previous knocking.
K2

 

[Jasonb]

"The shim material isn't in the bearing,"

Yes it is as there are no separate bearing shells on the engine the crank pin runs straight in the brass pressing/CNC'd part So you would end up with the shims running against the crank pin. You would end up with something like this to get the extra 0.100" would require 0.050" shim on each sid eof the ctr split and all those surfaces trying to run on the crank pin is not ideal.

Yes Idea is fin with big engines as Pat says that have separate bearing shells

 

[Steamchick]

2 things.
1: Brass shim can happily run against the big-end journal.
2: leave the shim short of the bearing area, so it does not contact the journal, and the bearing will still work as 95% of the work of the bearing is the thrust from the piston - in 2 directions 180 degrees apart - and only a very small amount of thrust side-to-side "swinging" the con-rod mass from side-to-side. No significant power is transmitted in the side to side thrust..... so the loss of a bit of surface is OK - on my models (some with 70 plus years of service).
That's my logic, based on worn bearings and results of play after skimming the flat joint surfaces where the caps are bolted to the conrod.
Take it, or leave it.
When I was designing rod-ends "conventionally" in industry, a university Professor of Engineering design advised we change the company standard, as what we had been building since the 1920s wasn't the best optimised stress for bearing distortion (or lack of) for durability of the bearings. So I changed design to his recommendations - basically 50% extra material in the cap at the thinnest point, for bearing stiffness - but the negligible wear we had experienced with the old design seemed unchanged on the new design after simulated lifetime durability testing. Yes it was a better design, but simply not necessary for the duty cycle we were imposing on the bearings.

K2

 

[Jasonb]

So you are suggesting two 0.100" shims, one each side something like this

And then hoping to ream the 9/32" hole and turn the two bosses?

 

[swarf]

So you are suggesting two 0.100" shims, one each side something like this

View attachment 148344

And then hoping to ream the 9/32" hole and turn the two bosses?

View attachment 148345

That's what I pictured.
In any case I purchased a new rod forging and will start over. Good practice for me.