Breaking in a newly rebuilt M20 engine

[twenty]

Hi Everyone,

I’m rebuilding my M20B25 for my 325i auto and was wondering what’s the opinion on break in process in 2024.

What I understand is the whole use a mineral oil etc. is basically old wives take and what’s really needed is use of a high quality synthetic oil with high ZDDP content.

In the states side, everyone seems to swear by Valvoline VR1 20w50 which is a fully synthetic oil with High ZDDP content (1400). The idea is to run it for the first few hundred miles, change it and drive for a few hundred miles and then switch to a standard high quality synthetic oil.

I haven’t checked if the VR1 is available here in the UK and was wondering if there’s an equivalent that’s easily accessible here?

Also, given that this is an auto car, how best to give it the beans as recommended during break in.

Thanks.

[flybynite]

IMHO breaking in an older engine is two-fold don't put in a modern oil that does its job so well it stops the rings from bedding in, secondly driving it is about neither 'thrashing' it or 'labouring' it. Normal driving using 80% of the rev range for 500-1000 miles.

Personally I would use the cheapest supermarket oil you can get.

Run it on the starter with no plugs, until you get good oil pressure, check the pressure does not drop (oil light goes out quicker second time). One more run with plugs in to check you get oil pressure with compression. Then start it.

Run it up to temperature 3 times. Then drain the oil. Gets rid of all the lube and any build rubbish you don't want in the oil for 500 miles. Then refill with clean oil and drive normally for 500 miles. If the oil is good when you drain it then fill it with any good 10w40 synthetic. Mannol do a suitable one in 20l drums for sensible money (classic I think they call it) but any modern oil will be better than what it was designed for. Any doubts do another 500 with the supermarket oil.

That is how I did the last M20 I built and it ran fine till I parked it up 130K miles later. It is what it will get when the new engine goes in.

[twenty]

Awesome, great advice as usual.

[DanThe]

Less lubrication is needed because you want the rings to wear into the bores, mineral oil 100% works best, I usually go for 20w50 type grades, drive the car up to around 80/90mph then shut the throttle and allow the momentum of the car to slow the engine down, this creates vacuum in the cylinders pulling the rings into the bores for excellent results. Do this around 10 times and your running in process is complete.
But dont take my word for it, there is a local Ford/Vaux race engine builder near me called John Toovey, he has an engine dyno and running his freshly built engines in on mineral oil gets an extra 4 or 5hp consistently

[twenty]

Less lubrication is needed because you want the rings to wear into the bores, mineral oil 100% works best, I usually go for 20w50 type grades, drive the car up to around 80/90mph then shut the throttle and allow the momentum of the car to slow the engine down, this creates vacuum in the cylinders pulling the rings into the bores for excellent results. Do this around 10 times and your running in process is complete.
But dont take my word for it, there is a local Ford/Vaux race engine builder near me called John Toovey, he has an engine dyno and running his freshly built engines in on mineral oil gets an extra 4 or 5hp consistently

Thanks Dan!

Mineral? Gulp. Not even semi synthetic?

Jokes aside, that sounds like a great idea and practical to do. Now to figure out hitting 80 on the tranny haha.