Hi, Fred
A very interesting treatise on this very important exercise on a new
or fully rebuilt engine. It seems techniques are changing and this
makes me wonder if they have come about with modern engines and their
tighter engineering tolerances with consequentially higher operating
pressures. Whatever the reason and the undeniable developments over
the last thirty years on lubricant quality - the bedding in process
should not be rushed.
For comparative purposes, it may be of interest to listers to know the
procedures employed Standard-Triumph in breaking in all company cars,
especially the Press cars and those that were broken-in for customers
on the Personal Export Scheme.
This was normally done over the course of a weekend during which time
the car was driven for its first 1000 miles. We had several routes in
the UK that were carefully developed and were a combination of town
driving, open roads (not freeways) and fairly demanding hill country.
On Spitfires, for the first 500 miles, engine revs were kept to no
more than 3000 in any gear, with gentle
acceleration and gradually building up to 4500 providing the engine
was on over-run - like in descending a hill. For cars without rev
counters, road speeds were limited to 50mph, slowly building to no
more than 65mph for short periods.
We never allowed engines to idle while building up to operating
temperature as a lot of the critical friction reduction of high spots
on bearing surfaces was achieved while the unit was cold. From 500 to
1000 miles, the rev band was progressively increased to 3750 in direct
fourth gear with very brief forays to 4500 without load and the engine
was always allowed to rev more freely on a very light throttle. The
1000 mile service obviously involved draining off water-absorbing oil,
a full release of cylinder head and manifolds, followed by a full
re-torque and re-setting of valves clearances.
We found from regular engine stripdowns by Engineering that this
extensive mileage in a very short time period maintained optimum
engine coolant and oil temps for prolonged periods and these were the
best environments for progressive bedding in of related friction
surfaces. Allowing the engine to rev freely but not hard was
favourable and while 1000 miles was something of a threshold, engines
rarely started to really give of their best until at least 5000 miles
had been covered.
I have many memories of undertaking these trips and the abiding memory
is of engines that were supremely supple, free-spinning and
economical. They compared far more favourably to those which had been
broken-in on short journeys which still felt tight, unwilling and
rather unresponsive. I've always employed these techniques with new
cars of my own in the years that followed and the current 1400cc
Eurobox is shortly to turn 200,000 miles. The head and bottom end has
never been removed, compression pressures are still within factory
limits, though I'll be coming up for the third clutch within six
months and synchro between 1st and 2nd is now weak when cold. As a
tip, I've always used magnetic plugs in the engine and gearbox and
never cease to be amazed at the amount of ultra-fine swarf and
metallic paste they attract. It goes without saying that there is no
substitute for regular oil and filter changes and to run the engine on
clean oil as often as you can afford to change it. 3000 miles is my
limit.
I suppose the bottom line here is personal preference but I'm
convinced a good break-in and prolonged engine life comes from a
relatively constant speed in the very early days, a light load,
constant operating temps as long as possible and an absence of severe
load under hard acceleration. It will be interesting to see how others
view this important aspect of an engine's early life.
Cheers,
Jonmac
1950 Ferguson TED20 152318 - Grey/Grey
1970 Triumph 2.5PI MG4305DL(O) - Sienna/Tan
1974 Triumph 2000 ML2294DLO - Mallard/Black
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