By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

What is running-in oil?

All Topics | Latest Posts

Search for:  in Thread Title in  
Bob Wild09/03/2021 12:20:04
86 forum posts
63 photos

Slowly getting to the point of finishing the engine for my Merryweather Fire King. I have read that it needs running in with a special running-in oil. I cursory search reveals that such products do exist, but they seam to be aimed at cars, and come in 5 litre containers. So, what is this oil, and can I get just a cupful ?


AdrianR09/03/2021 12:48:08
583 forum posts
36 photos

Hi Bob,

I did not know what is special about it, but I just did some googling. Seems to be a mineral oil with a lot of anti-wear zinc and not much detergent, which makes sense. I see your point about only 5L containers, you could try motorcycle repair shops, they might sell smaller quantities, or if you have a garage that does engine rebuilds go see if you can blag a mug full.

I also found it is called break-in oil if that helps.

Of course, every new car will have it in, you could always "borrow" some out of next doors new car devil

Jeff Dayman09/03/2021 12:57:19
2225 forum posts
47 photos

I have never used anything other than normal steam cylinder oil in the steam engines I have built, which are many, and have had no premature wear or any other issues.

When rebuilding car engines , motorcycle engines and 4 stroke small engines I do use assembly lube on cam lobes and pushrods etc and if the engine is plain bearings, on them too. For roller bearing mains as in many 4 stroke Asian motorcycles normal engine oil generously applied is best. For any 2 stroke engine, 2 stroke oil only is best.

JasonB09/03/2021 13:02:08
22746 forum posts
2653 photos
1 articles

I'd just give it a heavy dose of light steam oil until it stops coming out black from the exhaust. I mostly run mine on air so just a generous squirt of light oil into the valve chest before the initial run and make sure what comes out the other side won't get on the paint or display base.

not done it yet09/03/2021 15:47:19
6809 forum posts
20 photos

Break-in oil is usually not too ‘slippery, to allow rings to bed in on cross-hatched cylinder bores. If a high quality synthetic were used, the engine may never wear in properly (and drink oil past the rings in consequence).

John Deere had a problem at one time, I believe. Lots of tractors returned to dealers for rectification. Rumour had it that as soon as the customer had departed the inlet fiter was disconnected and an abrasive powder fed into the air stream to deglaze the bores. Then likely run on a dyno for a while. Ajax or Vim kitchen scouring powder was thought to be one type of powder used. ‘Pussy-footing’ a diesel engine with new rings just fitted is not advised. Taking it out and working it hsrd for an hour or so is often recommended.

Howard Lewis09/03/2021 16:18:10
6104 forum posts
14 photos

"Running In" oils quite often are less sophisticated than "normal" oils. The idea is that parts, such as piston rings and bores can bed to (Wear ) to each other. It used to be that many years ago, colloidal graphite was added to the oil, this may have been good for the bearings, but did little to improve ring bedding.

I have come across a special "running in" fuel for diesel engines. It contained a very slight abrasive which was delivered into the cylinder to improve ring bedding.

Modern cylinder liner honing techniques such as plateau honing have done much to reduce running in times. Although the modern car probably takes a bout 20K miles before it really beds in properly.

Having had an engine returned for oil passing in to the exhaust, (Caused by bore glazing from running for long periods at high idle to set reel speed on a combine harvester, ) The solution was to run it at full load rated speed for hours on end. Eventually, the rings wore through the glaze and oil control began to improve.

Probably the best thing is to run the engine under gradually increasing loads and speeds, finishing up with a run at full speed, full load. The load is probably more important than the sped.

When we were on holiday in USA one tear we hired a car to drive from Atlanta to Florida and onto Oklahoma and return. Probably the car had never travelled more than 20 miles at a time.

On the morning of day 2, the car had consumed a lot of oil, but as each day passed the oil consumed reduced, until by the time that we handed it back it was no longer using oil. We had spent a fortnight running it in!


Samsaranda09/03/2021 16:44:19
1430 forum posts
5 photos

Back in the 60’s when oil technology was a lot different to today I used to run in both car and bike engines using colloidal graphite, never experienced any problems, in fact oil consumption when using it was very meagre. Not sure what if any products containing are available nowadays, I seem to remember one oil that I used was called Filtrate. Dave W

Trevor Drabble09/03/2021 17:10:02
281 forum posts
5 photos

Bob, Colloidal graphite is still available from Graphogen at around £20 per tube , but if you PM me your details l can supply you some of mine cos you dnt need a lot . It's main advantage is that it plasticisers the sufaces of the metal so that instead of the peaks being chopped off, the metal is deformed and moved down into the valleys . Trevor

Hopper09/03/2021 22:10:53
6393 forum posts
334 photos

Usually running in oil has no friction modifiers or detergent in it so metal components can bed in to each other. Seems like overkill on a model engine. I would just use normal oil.

Jon Lawes09/03/2021 22:19:35
926 forum posts

I always assumed a running in oil was just a cheap oil that you used to get any machining remnants out of oilways and such before putting the good stuff in! Whenever I built a car engine that was certainly what I used it for; just a cheap oil (mineral on stuff that would never work hard, synthetic on anything likely to get baked in its life) to get rid of any assembly grease and such. Run for 100 miles or so (less for a track engine obviously) and then new oil and filter of the type you intended to use normally.

I'm in no way saying this is right, just what I've done before and the reasons I was doing it personally.

Interesting about the bedding in of piston rings.

Oily Rag10/03/2021 22:08:20
540 forum posts
184 photos

Running in oil is generally a 'straight' mineral oil with very few additives, especially detergents. It has a very limited life as the molecular chains break down quickly without the reinforcing additives. Ferrari use a 'running in' oil which has aluminium powder added (no I don't know why either!) but it is strictly limited to 4,000 rpm limit - exceed that and the engine is damaged.

Modern manufacturers now first fill with commercial semi synthetics which will last to the first scheduled service. This is due to engines now being produced by manufacturing techniques superior to that of the late 20th century. These techniques allow more consistent production tolerances and finer surface finishes.

One interesting fact is that production engines are subjected on occasion to a 'butch test' as a quality check. This test takes an engine from the production line, mounts it on a test bench dyno and after a 5 minute idle period to check for leaks and oil pressure is then run for 30 minutes at peak power engine speed. It is not unusual to see the power steadily increase over the first 10 minutes of this test and then begin to fall off slightly - this is the crucial part of the test because if the engine loses more than 3% of power during this 'drop off' the test is a failure. If the engine survives this 'drop off' in power it will regain the loss and steadily increase again till it stabilises at around 20 minutes run time. An engine which survives a 'Butch test' generally returns very good power at the end of test. The engines were stripped and inspected for ring scuff, piston pick up, bearing damage and any other issues. They were scrapped after the test as they were considered as expendable destructive tests. We tested 1 engine in every 250 produced in this way. Occasionaly they were rebuilt for 'skunk development' units.


Bob Wild10/03/2021 22:44:22
86 forum posts
63 photos

Thanks chaps for all your helpful and interesting comments. They certainly have given me something to think about.
I understand that the purpose of lubrication is to reduce friction and reduce wear, which is why I wondered if running in oil had some extra ingredient. Perhaps I should have included a bit more info in my original post. I am most concerned about the three crankshaft bearings. After some considerable effort lining them up I got them to the state where you could rotate the crank by hand, but it would not spin freely. I left it running at about 500 rpm for 4 hours but that didn’t make any significant difference. Perhaps I am asking too much. I do have some grinding paste and was wondering about lapping in the bearings with a dummy shaft. Any thoughts?


Oily Rag10/03/2021 23:48:01
540 forum posts
184 photos

Don't do it!

Abrasive pastes will embed into the soft bearing material and cause premature wear. Run it as is - if it turns OK without binding it will bed in.

One other point to add to your list of qualities of lubrication - probably only second in order of importance as friction reduction is the cooling action of the lubricant.


John Randall11/03/2021 00:04:48
14 forum posts

Not sure which sort of lubrications is used on the Merrywheather hydrostatic or mechanical for the cylinders ? I know this not a locomotive but standard running in practice was to set the oil feeds to maximum on the lubricators check the bearing temperatures and oil levels frequently and when it’s felt the engine had run in ease off or restrict the oil feeds as required.

Jon Lawes11/03/2021 05:22:17
926 forum posts


Interesting stuff, thank you, are you at liberty to say who you were working for? I can't work out if one engine in every 250 is a large or small figure. Were they "perfornance" or "domestic" engines? Either way, fascinating.

Oily Rag11/03/2021 10:33:25
540 forum posts
184 photos


Well, I can't quite make out if your icon picture is a TVR or a Triumph GT6! If the latter then that's who I worked for. Although originally I did an apprenticeship with Alfred Herberts, Machine Tools in Coventry I went into the automotive trade due to having worked on CNC machine tool development and Triumph were looking for someone to develop the application of the 'new technology' of digital fuel injection. I had engine experience through racing a motor cycle and rebuilding and tuning my own engines.

After the closure of Canley I went into racing working on F3, F3000, Indy Car and WSC (Jaguar Silk Cut cars), eventually going into F1 with Benneton, Tyrell, Arrows and Red Bull on the engine teams. Then I worked for Ricardo doing a stint in China as consultant to a domestic manufacturer and then for Jaguar on the set-up of their engine facility out there. So, all in all, I've worked most of my life with engines, both road and race specs for 40 odd years. My abiding interest has always been my first love of actually working on machine tools. It is very difficult to get out of one's blood!

One final aside; at Triumph we used a heavy straight grade oil as an engine 'build oil', it was an SAE140 grade and was nicknamed by the engineers as 'liquid grease'. It protected the bearings, pistons and rings, and especially the tappets and cams during first cranking.

Bob: Thank you for your PM.


Edited By Oily Rag on 11/03/2021 10:38:49

Jon Lawes11/03/2021 13:32:37
926 forum posts

Martin, thanks for the update, what a career. Maybe you should think about getting the details down on paper, would make quite a read I'm sure.

It's my old GT6, sold to pay for my Milling Machine and general workshop upgrade.

I paid £400 for the chassis and tub, put a Sprint and Hillclimb spec TR6 engine in it and made a nusiance of myself on trackdays. Other people couldn't easily drive it as it was built around my need for hand controls so had no throttle pedal (without a right leg I didn't need one). I took it to europe several times and it saw time on track at Spa and the Nurburgring on a good few occassions.

It was only sold a little while back on eBay for an amount that suprised me a bit; I was completely honest about the aesthetic condition (best viewed at a distance through a welders mask) but I think the spec of the engine helped nudge the value up.

Martin Dowing11/03/2021 19:37:50
355 forum posts
8 photos
Posted by Oily Rag on 10/03/2021 23:48:01:

Don't do it!

Abrasive pastes will embed into the soft bearing material and cause premature wear. Run it as is - if it turns OK without binding it will bed in.

One other point to add to your list of qualities of lubrication - probably only second in order of importance as friction reduction is the cooling action of the lubricant.


I didn't try it yet, but I have been advised on this forum that abrasive pase which wears itself and breake down fast and can be run into mating parts *does* exist and it is called Timesaver(TM) lapping paste available in the UK.

So maybe try that as a small additive?

I would like for someone more experienced to comment on that though.


All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Support Our Partners
Eccentric July 5 2018
Rapid RC
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest