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Mike Eames
New User
Username: mike

Post Number: 2
Registered: 01-2005
Posted on Thursday, 06 June, 2024 - 17:21:   Edit PostDelete PostView Post/Check IP

Hi Guys, We need a crankshaft for SDB78 a '51 Dawn 4 1/4 L. I would expect to regrind the journals, but otherwise it should be undamaged. I am aware that they are available from the US & UK but thought I'd check locally (Australia) first. Thanks.
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Jeff Martin
Frequent User
Username: jeff_r_1

Post Number: 652
Registered: 07-2018
Posted on Friday, 07 June, 2024 - 02:03:   Edit PostDelete PostView Post/Check IP

Consider looking for a 4.5 litre engine, there were many improvements over the 4.25 that make it worth while to change it out.
I'm also going to ask a question that you may already know the answer to, so don't be insulted.
Does your engine have the bakelite screw on oil cap, or the quick-release type ?
The quick release type will be a 4.5 litre.

In 1951, you may have the 4.5 engine.
If it is the 4.25 and it has not been changed to a full flow oil filter, consider doing that.
Sorry I can't help you on the crank.
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NormanGeeson
Unregistered guest
Posted From: 81.98.117.162
Posted on Tuesday, 02 July, 2024 - 22:18:   Edit PostDelete PostView Post/Check IP

Jeff

The flip top oil filler is an interesting one!

Here in the city of Peterborough UK a friend of mine had a 1949 Silver Wraith, that had been fitted in service with a 4.5 Lr by R-R.

The rocker cover had a screw oil cap!

During an engine overhaul I had chance to closely inspect the rocker cover on this engine. It was obvious that the rocker cover had been produced as a 4.5Ltr there was no sign of alterations or welding to convert the cover.

I do know that 4.5 ltr cylinder blocks were produced in 1949 and bored for 4.25 ltr engines. The idea was to eventually use these for a change over to 4.5 ltr in 1950.

In the event it was decided to produce yet another block for the 4.5 ltr engines and it would not be the last.

In recent years I have spent countless hours in the archive studying the cylinder blocks and pistons and in particular the reason for the block changes and piston and ring failures.

Very enlightening.

I think my friendís engine was used in experiments, before it was inserted into the recondition engine rebuild system.

At least I know every engine did not wear the correct cap!

.

(Message approved by david_gore)
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Jason Watson
Experienced User
Username: crikeydawn

Post Number: 194
Registered: 07-2023
Posted on Thursday, 04 July, 2024 - 04:19:   Edit PostDelete PostView Post/Check IP

Norman,
I wonder if RR were just using up old parts? In my experience no matter what brand of where a car/truck was made, be it Australian, America, Japan, England, or Europe, if you own a vehicle that is a turning point or model change, anything is possible. Furthermore go on for months. A real pain sometimes as manufacturers can be vague on such things.

With your readings, have you come across the concept/testing of shorter pistons? I know Jeff has found custom shorter pistons have given good results in fair service while eliminating bore scoring.

I guess a well oiled and cooled motor has everything to do with that. It may have been difficult for RR to test outcomes of scoring produced by heat expansion derived from poorly cooled cars, form years of silt build up. I'm not fully around the sleeve length thing, but have the choice to either install the supplied long pistons for my bored 4.9, or get some short customs made. In saying that I'm 100% the thing will have cooling or par or better than new.
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Jeff Martin
Frequent User
Username: jeff_r_1

Post Number: 670
Registered: 07-2018
Posted on Thursday, 04 July, 2024 - 13:26:   Edit PostDelete PostView Post/Check IP

Norman, you said "I do know that 4.5 ltr cylinder blocks were produced in 1949 and bored for 4.25 ltr engines. The idea was to eventually use these for a change over to 4.5 ltr in 1950".

So these engines had the 4.25 litre stud pattern ?

And therefore only the 4.25 litre head would work ?

If they were cast as 4.5 litre and only bored to 3.5 inches, what head could possibly fit on that ?

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