Now that my engine is running and I can start making my first outings, the question came up what is the best method for running-in a completely rebuild engine. I’ve seen quite differing opinions regarding the best way for running-in the XK 3.4 engine.
Jaguar refers to a “conservative” instruction with the “throttle restrictor” in place for the first 500 miles, followed by a period up to 1000 miles not to rev over 2500 rpm and finally a period up to 2000 miles not over 3000 rpm.
But other forum members recommend a somewhat more “daring” approach, using the throttle pedal in a more “vigorous” way to bed-in the piston rings.
Mine is an April 1954 SE engine, and we may assume Jaguar had by then quite some experience regarding the behaviour of their XK engine, but the Running-in instruction for the XK 140 didn’t change at all. So should I follow the original (above) instruction?
Is there consensus now regarding the best way how to run-in the 3.4 engine?
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Bob, this is sort of a parallel answer. When piston aircraft engines are new or rebuilt, the engine manufacturers and rebuilders strongly recommend running the engines at max power for two to four hours. The engines have mineral oil in them for the first 24 hours of operation. All of this is to prevent glazing of the cylinders and to seat the rings.
It will be interesting to hear suggestions for our engines. I have yet to break ours in.
Jaguar installed a wooden block under the gas pedal at the factory and tried to get folks to break the car in with limited high RPM’s after break-in. I suspect that was the first ‘modification’ these cars got.
Although I did the complete assembly of the block myself, I asked a well-experienced, professional engine shop to do the required work, which (unfortunately) included new liners and (fortunately) new (standard size .000) pistons.
They have a number of special honing machines and therefor I assume they used a rigid multiple hone (your example number 2).
Good machinists and good shops are becoming a rare thing as most folks don’t rebuild anything anymore, and cars these days seem to run forever. I have a very good friend who was a mechanical engineer, and he opened a shop which we used. He had all the best equipment and could not stay in business due to costs involved in doing it right the first time. Many Chevy racers were not used to spending that kind of money to have good work done. He is back being an engineer.
If the liners were done with a modern Sunnen hone, then all you really need to do is take it relatively easy for the first 500 miles, change oil and filter, then drive it like you stole it!
I notice the reference to a “Throttle Restrictor” fitted to the Accelerator Pedal, Here is a picture of an early one and the re-production I make. They were fitted at the factory and removed after the first Oil change / service.
Eeeeeeeeek !!! I don’t know of ANY car, engine manufacturer or rebuilder that would even think of this…(I know you said aircraft–but why…). The Jaguar factory had many engines running on test stands…don’t know if they varied speeds or just let them go a while. Most car manufacturers do a certain time test run on engines. The point of break in is that tolerances can be very tight…I suppose there may be some metallurgy heat cycle involved as well. Question, how many of you start up your car, a well used, many miles engine, and immediately on start up take it to 4,000 rpm…good idea?
anyway…the question resolved at moderate rpm and load for 500. I concur. The oil filter should do its job.
an aside…so a car, as factory delivered, to be totally original to the day it left the factory, should have the throttle restrictor in place…(for cars that are in the date range of when those were installed…TDB #66, April 1950–had wire with lead seal, 750 miles was the removal specified at first service. A reference was made that the factory later revised to 500 miles.
Nck
Nick
