'The Garage' Quest TV.

Well that's one of the design criteria. But generally only on startup.

That's not my understanding. Admittedly the thin 'white metal' surface of the shell bearing will be damaged or destroyed if unlubricated, but that isn't the primary reason for the use of 'white metal' as a bearing material. It's load bearing and wear properties are the main design considerations. Mike.

Well it's quite complicated, you also need to embed any small abrasive particles in the surface (there's an ongoing change in philosophy about that) & conduct away the heat. The tin flash on the surface is mainly there as a dry lube for the days when there isn't any oil.

White metal bearings as far as I know, were never designed run dry as perhaps you could view a sintered bush. As apprentices we cast shells and machined to fit. A test was to mount them onto a rotating shaft and run them against a very high radial load to establish life, deformation, temperature etc. I remember quite clearly the outcome of the sample that did not get an oil feed connected. Out of interest, are there any car engines using roller bearings as those of two stroke motorcycles and their pressed assembly crankshafts ?

Gio

Starting your engine's going to be tricky then. But almost nobody's put a cast babbit bearing in a new car engine since the 60s.

Yup, the bigger the clearance the faster it wears :-)

Why?. Enough oil is left in the bearing to lubricate it until the engine starts, and oil starts to flow through the bearing.

But almost nobody's put a

You'll find that cast, machined, Babitt bearings were discontinued long before that. Automotive manufacturers started using shell bearings in the 30's.

All very interesting, but it misses the point of my OP. Which is that presumably a skilled mechanic in 'The Garage' TV prog, is telling viewers that the 'white metal' used in shell bearings, is there to protect the journal if there is an oil failure.

No wonder I don't trust the majority of garage mechanics when they come out with crap like that. Mike. .

I watched that one too and was a bit taken aback when they simply changed the shells apparently without removing the crankshaft or even checking it at all. Or perhaps the editing just gave the wrong impression.

There's quite often metal to metal contact at that point.

Somebody round here nearly always comes up with something you wouldn't want to drive that uses an odd technology :-)

Well most of what he comes out with is crap.

Just changing bearing shells that have failed never works. The crank is always damaged too.

Seconded.

Been there, done that, wasted the money...

Chris

That's what I thought. Mind you, it worked as far as 'The Garage' was concerned as the knocking stopped and didn't come back during a quick test around the block.

The 1965 Honda S600

Slatts

You may be right, but I doubt it. They certainly didn't remove the crankshaft, and given the state of the big-end shells due to lack of oil, I can't see the mains surviving unscathed.

Indeed. But given the unusual circumstances, it's possible that very little wear took place on the journals themselves. Especially if the owner took the car to the garage as soon as he noticed the knocking. The oil itself can cater for a small amount of wear on the journals.

If the owner is lucky the 'repair' could last for tens of thousands of miles. OTOH the knocking could return after just a thousand or two.

I shall continue to watch the series if only to pick holes in the way they do things. :-)

As an aside I think their prices may be quite high. There seems to be too many staff for the amount of work being done.

Mike.

I doubt it. Oil is particularly tenacious, and would not be squeezed out altogether on a large bearing surface like that of a shell bearing. Even if there were spot contact at the side of a bearing, it would be lubricated as soon as the crankshaft started to rotate by the oil that 'pooles' at the bottom of the journal and crankshsft. Mike.

That's the main point of the tin flash.

If that's what you believe you are wrong.. I suggest you do a little research into why Babitt alloys are used as a bearing material, before making statements like that.

The fact remains that just because the 'white metal' bearing surface will melt and be destroyed if the bearing overheats through lack of oil was never an engine design requirement. A bearing that could last for many thousands of miles (200k is not uncommon) with little deterioration was. Mike.

The tin goes on top of the babbit. You can look it up yourself.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Mike G" saying something like:

It's true to a certain extent - I've seen some cranks that only needed a clean up and new shells after a low oil episode, and on some engines the shells are a service item - think bus diesels, for example. Ime, the old Essex benefitted from new shells around 100K. So yes, the presenter wasn't talking complete bollocks, as is usual for one of them.

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Willy Eckerslyke saying something like:

Crap editing, then. I cannot see them not checking it, if they had half a clue - I mean, really.