Tag Archives: hand finishing

Main Bearings; scraping thru!

Major decisions on Main Bearings

The bearing housings in the base casting were already machined a 1/16th  oversize when I purchased the castings, so the Camden-provided bronze bearing castings were not going to work.

So I set about trying to source some suitable “phozzy-bronze” from my normal supplier, and discovered there was none to be had of a suitable size. So I decided to build a fabricated version of the bearings with Cast Iron outers and bronze bearing “shells” – some friends recommended going the whole hog and white-metalling the bearings (as per loco or car practice), but I decided my approach was less error-prone, and more in line with my “skills”!

Given the “oversizedness” of the slots I also decided to up the main bearings from 1 inch to 1.25 inch diameter (I think bigger is always better in the bearing stakes.)….

So I purchased some (very) oversized square-section continuously cast iron bar, and some 1.5 inch phosphor-bronze bar for less than half the price of the Camden blanks – and enabled my “smug mode” – (However, I think pride may well come before a fall!) 😐

At this point I looked at the size (oversize)  of the square cast iron bar I had, and thought about the fact I was about to machine away about 90% of it and then do the same thing by putting a 1.25 inch hole in a 7 inch length of 1.5 inch bronze, and decided this was mad… so I found some 2-inch round cast bar, and decided this could be machined with “square” section to fit in the bearing slots and this was a more “economic” solution…. 2 months later this seemed like a very, very foolish decision! (Time will tell)

So we start cutting

My plan was to silver solder the “shells” to the inside of the bar. So the plan was bore the cast bar,rough bore the bronze bar solder one inside the other….

Well that didn’t work! 3 attempts proved that I could not persuade the easyflow to penetrate and adhere to the cast, and I just wound up with messy flux-covered non-stuck thing!

Plan B – locktite the shells in to the housings (well that is what is holding them at the moment, but I am not convinced it’s a real fix, so they will get small grub screws fitted in axially at the end to prevent any “spin” (as this would cut the lubrication and be a fast route to a bad place!.

The process in pictures – this is really an outline of how NOT to tackle this!

A bit disappointing – but a great workout!

So I assemble the machined bearings into the base casting, and try the bar stock that will form the crank main journals and “bingo”, it’s all locked solid!

The traditional approach is to line-bore this kind of assembly, but it’s too bit for my workshop, and I had hoped that my strategy for building the individual bearing assemblies would mean line-boring was not required. – but it was not to be!

Deep gloom ensues….

However, the model engineering community provides an answer – Neil and Darren say “simple Mal,  just scrape them true”…

A close shave!

So after a quick review of the theory, and armed with a tube of engineer’s blue, 20-30 hours of hard graft (this is THE most effective bicept exercise ever) and very bloody knuckles, we have a shaft that sits in, turns and does not wobble! RESULT!

What I should have done….

Start with the square bar, make it accurately rectangular to provide some reference surfaces, machine to a good fit in the base casting bearing slots, then bored this (in the mill and square), then fitted the bronze bits, then cut them in half, then finally bore the assemblies using the inherent squareness of the main bar….

Well it seems like a good idea!

Now on to the crank – and hereby hangs a further take