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V8-250 Saloon: Crankshaft Bearings

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classiclife
Posts: 194
Joined: Wed Sep 05, 2018 9:55 am
Location: Ridgewood - East Sussex
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V8-250 Saloon: Crankshaft Bearings

Post by classiclife » Thu Jan 31, 2019 3:14 pm

Hello,

I was reading an article regarding the V8 saloon engine.

Within the text the following point was highlighted:

"After 30-50K miles, the centre three of five crankshaft bearings are likely to have narrowed, probably requiring replacement. That said, this operation can be done with the engine in situ".


I've not come across this particular point before and I'd like to know if this is the case and if so what other owners have done in these circumstances in order to assess the situation. Additionally, are there obvious signs of this starting occur prior to sump off and inspection ??

If this is the case, is it just good housekeeping to replace these 3x bearings at 50K miles regardless ??

Many thanks.

Richard.

Christopher Storey
Posts: 228
Joined: Wed Mar 16, 2016 6:40 pm
Location: Cheshire

Re: V8-250 Saloon: Crankshaft Bearings

Post by Christopher Storey » Thu Jan 31, 2019 6:27 pm

It's hard to know what is meant by narrowed, because on the face of it , it is a meaningless term. What is probably meant is that the bearing material has worn thin . These engines are definitely susceptible to main bearing wear, mainly because of the limited area of the shells and thus they do not have the sort of life to be expected of, say, a Jaguar XK engine. However, unless there are signs of wear in the shape of lowered oil pressure and/or rumbling I would not regard a precautionary change as necessary

classiclife
Posts: 194
Joined: Wed Sep 05, 2018 9:55 am
Location: Ridgewood - East Sussex
Contact:

Re: V8-250 Saloon: Crankshaft Bearings

Post by classiclife » Thu Jan 31, 2019 6:34 pm

Thanks Christopher,

I think your reply gives a better description from what I have read - which by the way was via Nigel Thorley.

As I am generally bringing the saloon up to spec, it was something I wanted to clarify, which I believe you have done.

Thanks again.

All the best.

Richard.

tjt77
Posts: 450
Joined: Wed Mar 23, 2016 7:01 pm

Re: V8-250 Saloon: Crankshaft Bearings

Post by tjt77 » Fri Feb 01, 2019 3:40 am

The tell tale sign of worn main bearings is a noticeable drop off in oil pressure when engine is up to operating temp.... depending on what it reads to begin with around 10-15 lbs on drop off average..it helps bearing life in saloons to add a shim (3/16" is about right) under the oil pressure relief valve spring to bring 'blow off' pressure up to about 50-55l,bs .. this is not such a problem for the SP250, because the car has less weight to pull and consequently has taller gearing ..( less engine revolutions per mile = more miles covered before wear sets in)
the good news is that the accessible bearings wear first.. (no's 2,3 &4) and can easily be replaced with the engine in situ..although is a dirty job due to the fact that , with sump removed, oil will drip out of the engine until there is none left to drip..
Unfortunately there are no original specification main bearings currently produced today.. the most common bearing source is 'King' often boxed under the 'county' brand.. these are bi-metal bearings and only capable of sustaining about 1/2 the loads of the original vandervell VP2 'tri-metal' (lead indium faced copper with steel backing) and have the added downside of a hard surface which wears crank surface at about the same rate as the bearings.. assuring that a re-size of crank is required every time the bearings are replaced (the vandervells. whilst more rigid, and dont 'crush' have a soft face ..which is kinder to crank journals) some suppliers such as Barry Thorne still have stocks ion OEM bearings in certain sizes.. 'Glacier' also made them 'back in the day' in tri metal format.(marked 'LC' on the box) as did Peter Hepworth... King DO now make tri metal con rod bearings.. these have been available since mid 2018.. the intermediate bearings can be adapted to higher grade, by narrowing BMC 1275cc 'A plus' main bearings which ARE available in lead copper..you need a competent and enthusiastic machinist to do this however..

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