Advice on refacing a bearing journal please

Hi Peeps,

The attached pic is of a crank half from a 100cc racing engine (not the actual one I need to work on but basically the same). The main bearing journal nominal size is 20mm diameter, the minimum size due to wear before it is considered scrap is 19.95mm. The one I want to repair is 19.90.

Refacing is not permitted for racing - no mods, machining or additional metal allowed.

However - for a playtime engine it will rejuvinate an otherwise scrap engine, the reason this engine would be scrap is 'cos a new crank assembly is approx £500 and this engine with a new crank fitted would be worth approx £250 - go figure!! (BTW - a brand new engine is approx £1800).

As it is otherwise scrap I'm going to have a go at refacing the journals :-))


So - the question, could someone advise what welding rods to get please, I probably only need a couple? what amperage? any pitfalls?

I don't know what grade steel the crank is, just that it is "special grade" maybe EN24 at least, quite tough, spins up to 16K. the bearing that this journal rides on is a standard type deep groove ball bearing and it is a "sliding fit", e.g. snug fit and can be separated by hand, that is why the damn thing wears down :-(


Any advice gratefully received

 

Worth investigating if any local engine refurbishers offer this service, might avoid stress build up from normal welding

RonA

 

A light knurling and use bearing-fit adhesive.

 

Speedisleeves (not sure on the spelling?)

 

That beats the old way of building up the shaft pad-welding style. How long would that technique last compared to building up and turning back to size?

 

oversize bearing?

 

rather than spend money on this crank save yourself some time and buy an engine that someone else has fitted a new crank to

 

You need spray welding you’ll warp the whole lot it you build up with TIG/Stick

 

I wouldn't knurl it - your pressure absorbing contact area is reduced. Years ago I used to have pump shafts built up with spray transfer - they would work but quickly fail - the metal was too soft. This may have improved by now (30 years...)
If you weld it you will get shrinkage/stress etc, but maybe that doesn't matter too much?
Why is there an oilway in there? If you weld I would plug this first and redrill after from behind.
When you've done it do you want a go at my vmax crank?

 

Someone using the wrong powder. The powders havent changed in 40-50 years.

there’s a bonding/buttering later and then a journal surface, usually high in nickel so pretty tough.

 

Nosy, is that from a BT82?

If it is, then that half is available for a fair bit less than the price of a complete crank

if it isn't then take a look at BTCHHMCD on https://www.tal-ko.com/online-shop/tkm-bt82-parts/crankshaft-assy.html as it looks very similar for £160+vat

 

Yeah, unfortunately there are none for sale otherwise that would be the best option.
It's not my engine, just trying to get something working for a mate :-)

 

Yes - it is, but this needs both sides replacing and maybe a Conrod (may get away with the current one, subject to measuring when it is disassembled)

 

There is no oilway, just a trick of the light/photo

 

The one in the pic is very dead, big end journal is cracked, so I may have a practice on this one as a proof of concept, thanks everybody for your input!!

 

Less than £25 for a speedi sleeve

https://simplybearings.co.uk/shop/E...aft-Repair-Sleeves/c4713_4847_4849/index.html

 

Send it to Alpha bearings in Dudley.

 

seen them hard chrome and regrind back to standard......
look in Motor cycle mags...think the place is in Luton, Beds.....
not cheap but no heat needed and the uncertainty it causes.......

 

I'd go around that with a sharp centre punch making a grid-pattern of dots then press the bearing onto it.

 

I think he died, forgotten his name!