- We've just replaced the connecting rods in the FA20 engine fitted to our Toyota 86
development vehicle.
And when it comes to the initial startup, this is where we do need to apply a little
bit of care.
Now in most instances with a fresh engine build, we would need to go through the
process of bedding in or breaking in that new engine.
In our case though, you'll recall that we haven't replaced the piston rings and
we also haven't had the engine block honed.
So there's technically no break in process required here.
All we've done is we've replaced our connecting rods and our big end bearings.
We will still be starting the engine up here with a slightly cheaper mineral based
engine oil and we're going to be running the engine up to full operating temperature
before dumping that oil.
And this just allows us to flush out any of the assembly lubricant that we've used
during the assembly process.
We'll then be refilling the engine with the normal Motul full synthetic 300V oil
that we run in the car and we'll be ready to hit the dyno.
Now if you had in fact replaced the rings, then yes a break in process is necessary
and this is one of the areas where I see a huge amount of misinformation and
confusion out there in the industry.
Mainly around what we're actually trying to do during the break in process.
There's all sorts of concepts around breaking in or bedding in the bearings against the
crankshaft, heat cycling the engine and really all of this is complete nonsense.
Let's deal with the bearings for a start, now the bearings do not run against the
crankshaft, they must be protected by a film of engine oil and any time we've got
metal to metal contact between the bearing shell and the crankshaft journal, we're going
to end up with instantaneous damage and no amount of gentle driving is going to
help you in that case.
So we're not doing anything in terms of bedding in the bearings, let's move onto
the heat cycling process.
Now I think there's some confusion here between the term heat cycling and heat
treatment and again this is absolute nonsense.
The sorts of temperatures that we're likely to see in our engine when it's actually running
are nowhere near the sort of temperatures that are genuinely used for the heat treatment of our
engine components so again, not something that we need to worry about.
Really when it comes down to it, the key aspect of bedding in or breaking in a
freshly built engine is really all about the interface between the piston rings and the
cylinder wall.
What we're trying to do is get the rings to seal against the cylinder wall and we've got
that nice fresh hone pattern on the bores that helps with that process.
And this is really critical because if we get our piston rings sealing well against the bores,
we're going to end up with an engine that produces good power, good torque and
it's also going to use minimal oil.
Now this process does require a specialised step by step approach and it's important
to understand what we're trying to do here.
We don't need to baby the engine and nurse it along for thousands of miles.
In fact what we actually want to do is use a little bit of cylinder pressure to our advantage.
Now the radial tension of the rings alone don't really help them to seal against the bore
and the key to getting the rings to seal against the bore or push outwards against
the bore is the cylinder pressure above the piston.
So when we use a light to moderate amount of load on the engine using our throttle
of course here, this helps push those rings out against the bore and helps them bed.
Of course when they are running against that fresh hone pattern though, this does create a
lot of friction and in turn this creates heat.
So we don't want to apply sustained high load otherwise we could end up with too
much heat being generated.
So instead what we're going to be doing is using moderate to light load, we're going
to be cycling between periods of moderate to light load and then we're going to be
backing off the throttle.
And when we back off the throttle, this allows the rings to release a little
bit from the bore walls and reduces that friction and of course the heat being produced.
And we're just going to be constantly changing between periods of light load
and periods of no load.
At the same time we also want to vary our RPM and at least initially we're going
to be using somewhere in the region of 2000 to 3000 RPM and maybe as much as
30-40% throttle.
After the initial bedding in process we'd then start increasing both the RPM and the load.
And this process also doesn't take anywhere near as long as most people think.
With modern honing techniques and modern ring construction techniques, the bedding in
process is usually completed within about the first 100 to 200 km of use.
Beyond that, your engine is run in and from here on in, it's all running out so you may
as well get to enjoy it and start using it how it was intended.
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