Running in (again!)

[fool73]

I just finished a major engine rebuild. We had a major oil leak which didn't show until about 45 minutes running (turned out to be 2 missing flywheel bolts - oops) which meant the engine has already been run at idle for about 3 hours in without moving. I'm a bit worried about glazing the bores and from reading other posts and websites am confused about how to run in. I have now put millers running in oil in it. Advice I have seen varies between keeping it below 2k revs, giving it full throttle, giving it full revs in top gear, not "labouring" it etc etc.
Can someone please tell me, in basic english, how to run it in. E.g what revs, what gear(s) to use, what speed(s), how long to do it for etc.
Many thanks

[Motorsport Micky]

If this is a rebuild which includes either new pistons or piston rings then you don't need to get to anal about glazing the bores, that's a process that normally will take thousands of miles.

Have a think, you are running in a car which is a 1970s design with many components made from the materials of that time. It was quite common in the 60s and 70s to see cars poodling about with signs in them saying " Running in, please pass, that was for normally about 1000 miles. Although some of the components or oils we use may be better quality I think mimicking the same routine is sensible.

That's what you are going to do, drive the car and restrict your revs (you don't say whether you have and auto so I'm assuming manual) to under 2500 revs in any gear for the first 500 miles. The car needs to be driven normally with regard to acceleration (just don't floor it) and ensure the car isn't allowed to labour in to high a gear (if the car objects change down). That's to allow the components involved to "bed" in, the next part is to use the car for another 500 miles taking the revs up to 3500 revs, same regime as we've just said. After that away you go, no restrictions just drive it without namby pambying it.

As regards avoiding glazing the bores it's easily done. For the engine to work correctly the pistons rings have to "bed" in to the engine cylinder bores. If you inspected the rings and bores minutely through a spectrum microscope the surfaces would have huge peaks and troughs, when you bed in the rings you remove some of the high spots and allow the rings to "gouge" their own path up and down the bore with corresponding grooves matching both bore and ring making the best gas tight seal.

To do this you need to drive the engine at BMEP (Brake Mean Effective Pressure) revs, this normally corresponds to where maximum torque is, (standard cams 3500 revs). This is where the engine has most power and pressure placed upon the pistons and rings (therebye expanding them into the cylinder walls) through out the power stroke. On a race engine we often do it on a rolling road where it's easy to load the engine with maximum load whilst holding the engine steady on the revs. If doing it on the main roads I find that motorway gradients are good for this. In top gear drive about 500 revs below max torque and give the engine full throttle (down to the floor !) hold it on whilst the car accelerates about 200 revs beyond max torque and then drop the speed and find the next gradient and do it again, and again. You need to do this for about 15 minutes (on the gradients) and I'd do it every week for a month, after which you should be fine.

It's good practice to do this every 2-3 months to keep the engine from glazing anything when we "easy foot" it the rest of the time.

Micky

[GDPR]

To be honest, I have never run an engine in in my life, and I'm not about to start now. I let the engine rev freely and just not labour it - low revs high load.

Modern lubricants virtually negate the running in process...

[Motorsport Micky]

Good man Kryten , me neither.

It's just that sometimes for people like us who work on engines it's no big deal for us to drive a freshly rebuilt engine, we even have a driving style that negates a lot of the original running in necessity. However for owners or drivers (who ask) and need the comfort of knowing they are not damaging their freshly rebuilt engine sometimes it's comforting for them to outline how to drive it.
See just stating " let the engine rev freely" means lots of different things to people, and some drivers can't decide when enough is enough and exceed it, so giving some guidance is not a bad idea if they ask for it; that's how I look on it anyway.

Micky

[fool73]

Hi Micky. Thanks for your explanation. It's really helpful.
Yes, it involved a rebore and new rings, pistons, main, big end and little ends, valve guides etc. It is manual and still has standard cams.
There are just a couple of things I wanted to clarify.
When you say "As regards avoiding glazing the bores it's easily done. " do you mean glazing them is easily done, or avoiding it is easily done ? You then say that part of avoiding glazing the bores involves going just over 3500 revs, but as you say keep it under 3500 revs between 500-1000 miles, do you do the BMEP running after 1000 miles ? or is that part of the 500-1000 miles routine ?
You are right, I don't know definitively what letting it run freely means. Also not sure what not labouring it means, but hopefully right in guessing it means not using too low revs.
Finally, hopefully I guess right when I guess you mean you do this going up motorway gradients rather than down !
Sorry they such basic points but as you see I have little clue about this sort if thing !

[73stagman]

Micky will come back with more! but.... Labouring the engine is when you are in the wrong gear for the engine speed.

Mostly happens when you let the engine revs drop too far before changing down to the next gear (or change up gears at too low an engine speed) its easy to do when running around in town or in traffic which is why a good "calm" cruise along an open road will do the engine a whole world of favours when its new. Remembering as Micky said to change down gear before you get to the uphill bit and let the engine and gearbox work to get the car up the hill. The same when coming to a stop; Use the gearbox to slow the car down by dropping gears sequentially and you will feel the engine stopping the car rather than cruising to a stop with the clutch disengaged and braking to a stop

[73stagman]

To be honest, I have never run an engine in in my life, and I'm not about to start now. I let the engine rev freely and just not labour it - low revs high load.

Modern lubricants virtually negate the running in process...

I know what you mean, and I havent driven differently just because the engine is new. The way I was taught to drive means that the engine gets run in driving normally.

[Motorsport Micky]

Hi Micky. Thanks for your explanation. It's really helpful.
Yes, it involved a rebore and new rings, pistons, main, big end and little ends, valve guides etc. It is manual and still has standard cams.
There are just a couple of things I wanted to clarify.
When you say "As regards avoiding glazing the bores it's easily done. " do you mean glazing them is easily done, or avoiding it is easily done ? You then say that part of avoiding glazing the bores involves going just over 3500 revs, but as you say keep it under 3500 revs between 500-1000 miles, do you do the BMEP running after 1000 miles ? or is that part of the 500-1000 miles routine ?
You are right, I don't know definitively what letting it run freely means. Also not sure what not labouring it means, but hopefully right in guessing it means not using too low revs.
Finally, hopefully I guess right when I guess you mean you do this going up motorway gradients rather than down !
Sorry they such basic points but as you see I have little clue about this sort if thing !

" do you mean glazing them is easily done, or avoiding it is easily done ?

Both really, however it would normally take some thousands of miles to glaze the bores and so if you drive as suggested (and especially if you carry out BMEP procedure) it will avoid them glazing and bed the engine in nicely. Remember though it's ongoing ! any easyfooting for long periods will start to glaze the bores so periodically carry out the BMEP procedure ( 2 or 3 times per summer if you are using the car for thousand of miles).

You then say that part of avoiding glazing the bores involves going just over 3500 revs, but as you say keep it under 3500 revs between 500-1000 miles, do you do the BMEP running after 1000 miles ? or is that part of the 500-1000 miles routine ?

The running at up to 2500 revs for 500 miles and then up to 3500 revs for a further 500 miles helps the engine to remove engine component machining marks and to bed in the various bearings that have been replaced. After that the engine can be used to it's fullest extent, mine sees 5500revs upon occasion(cough...and over) and there's no reason if yours has been built carefully why yours shouldn't see it also !
The reference to the bedding in procedure where the engine is run in top gear at about the 3500 revs area and then has full throttle applied to it several times (as described previously) can be carried out when you want, and with race cars it is carried out immediately after the engines initial short running period. I should carry out that procedure within a month of the initial 1000 mile bedding in period, and as I say then periodically.

You are right, I don't know definitively what letting it run freely means. Also not sure what not labouring it means, but hopefully right in guessing it means not using too low revs.

As Kryten said (and I also endorse) the engine when being used for the first times after a major bearing/bore/piston/piston ring replacement needs to be driven "briskly". By that I mean the engine needs to be driven throughout it's range without taking the revs to the extremes of it's range but without namby pambying it; ie drive it through the gears changing at the appropriate revs and be sensitive to how the varying road conditions is applying the load to the engine. For example arriving at the bottom of a hill and being baulked by slower traffic travelling at 30mph up the hill would require a change down to a suitable gear to avoid the engine "lugging" and applying high loads to all the components just mentioned.

Conversely after the initial 1000 miles has been carried out the engine is going to be exposed to the BMEP procedure which then develops the highest cylinder pressures and fully beds the internal components to one another. As we've said this also helps remove any traces of cylinder glazing and gives the best power and economy (if driven with that in mind...but remember too much easyfooting and over thousands of miles glazing results).

Finally, hopefully I guess right when I guess you mean you do this going up motorway gradients rather than down !


You are correct, the BMEP procedure should be used on an up gradient ( it can be done on flat roads but the engine loading is not as great).

Most drivers develop a brisk driving style over the years which uses the car correctly and beds in the components and keeps the engine in it's best condition without even thinking about it (as Kryten states). But even on my daily driver (Ford S Max diesel) which is used mostly in urban conditions, after I use the car for towing our 1700kg caravan about 6 times a year (running at 100% of towing vehicle kerb weight) I notice a betterment in power that is available and delivery of it (honest !).
So continual exposure to BMEP throughout the engines life is beneficial and avoids internal component glazing.

There are several other forums (Porsche as I remember is one) where engine bore glazing is causing problems, normally the control of this is in the drivers hands as we have just outlined.

Micky

[Nambo]

Iam running in a 1966 BSA 441cc single at the moment.
For the first 200 miles I am ensuring I have a clear road and a nice long hill so I can give it a big handfull to ensure those gasses are pushing those rings against the bores so that the rings dont harden before they have worn to shape.
It gets quite hot so I only do a few miles then let it cool down and then do it again, shutting off the throttle now and then to suck a load of oil up the bore, keep it revving.

I did read that the whole running in gently days of old was a ploy by the manufacturers to keep warranty claims down.

[fool73]

Thanks Mickey for such detailed explanations. I feel much more confident now about running it in without knackering it up. Just a few more minor jobs to do and I can take it for an MOT and (hopefully) start using it.
Cheers.