Engine break in after full rebuild.

The Doc

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Staff member
Due to so many people asking how do you run an engine here is an explanation of what is what below.

On a fresh engine the main areas you are looking to break in or run in are the piston rings to bore, to do this actually needs the engine put under load , this then puts extra heat in to the liner and rings and allows them to wear together (which is what you want) the idea of bedding the components in is so that a minute amount of oil remains present on the liners to reduce friction between the piston and rings but not too much that the engine smokes, the absolute worst thing you can do at this stage is pussy foot the engine for 1000miles as you will glaze the bores and scuff the pistons as they will not expand correctly !!! Engines built correctly need very minimal time to run in these days due to machining being so good and the oils being synthetic.

if your engine has new cams then you have to follow the manufacturers instruction but it normally entails running the engine at no less than 3000rpm for ten minutes or so, the reason for this is that if you run it too slowly the lobes do not polish or bed to the rockers correctly and you get premature wear!

cranks and conrod bearings do not need bedding in as the bearings should never ever contact the crank, the idea is the oil separates the two surfaces and absorbs the shock load from the engine running.....if you have any sort of contact they normally fail very quickly.




so in summery the best way to run an engine in is to get everything set up and checked correctly on first start up, use the normal oil you are intending to use and drive the car as a normal car or run it in on the dyno......doing 1000miles using mineral oil driving like a pansy on an engine not set up properly will not run your engine in!.........if an engine has an inherrant fault or has been built incorrectly you will know within a few hundred miles of the first start up, so if you are building a super fast engine for your car, when you first start it have the timing and fueling checked by your tuner if you cannot do it check for leaks,check coolent levels and get on and drive it.
 

Fast Guy

Moderators
Staff member
I thought with these quick run ins they did use mineral oil and change it after a very short period? Then change to the good stuff?
 

shroom

Active Member
From advice and what i did was as you said fast guy, the idea behind mineral oil was to help ensure the bores dont glaze by using fully synthetic and allow a level of bedding in rather than the fully synth oil almost working to well and not allowing this.

Also a good plan on changing the oil is a must, just dropping fully synthetic oil and giving it a thrash doesnt seem to good to me
 

lakeview

Active Member
i had an engine built by norris designs(also know a few people who have had evo engines built by them) and he said something similar no real need to run it in he said just drive it as would normally drive the car
 
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vpulsar

Well-Known Member
I ran my old car's new engine in on the dyno and use mineral oil for the 3 quick changes then on to the good stuff after about 35 miles lol.




Rob
 

The Doc

Moderators
Staff member
i had an engine built by norris designs(also know a few people who have had evo engines built by them) and he said something similar no real need to run it in he said just drive it as would normally drive the car

Exactley, it also shows confidence in the build.

the next thing I will post up will be about how people over lapping valves to seats causes more harm than good and reasons why....which is basically poor flow threw the ports due to regression, seats and valves should be only cut with the right tools and then they don't need lapping in.
 

campbellju

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Staff member
Is the use of mineral oil just economics for something you're going to drop after less than 30 miles? Is it that mineral oil acting as an abrassive is a complete myth as oil is a lubricant anyway. Sidestepping what you've already said for the minute, is the use of a thicker/thinner oil beneficial in anyway?Assuming not then is it just a case of getting the cheapest oil of the correct grade. Oil degradation isn't an issue in this time. In times gone by this was mineral when fully synthetic was a luxury. Now it's just a basic semi-synth. If you've got 25 gallons of posh oil then this isn't an argument but if you are buying it by the gallon then does it matter to use a cheaper oil?

P.S. Thanks for posting up Doc. Good discussion
 

PobodY

Moderators
Staff member
I'm sure I read a thing about V8 engines in Australia, and the logic was you should run-in an engine like you intend to use it; don't be brutal about it, but if you're going to want to run it to the redline you need to wear it in to the redline. - What they were saying is that the bedding-in is like a final lapping/finish, so if you're too gentle you create an engine that will get damaged as soon as you start pushing it.
 

campbellju

Moderators
Staff member
Reading around on the oil issue, it seems the reason people favour mineral oil for even the first 30 miles /10 mins of run in is because it has no friction modifiers to help with bore glazing.

If there is an effect it's nothing to do with it being mineral semi/full synthetic.

Mobil said the oil is not a factor in the wear process, it's the metal to metal contact that beds the engine in, not the oil.
 

shroom

Active Member
Bores glaze from being too gentle on run in not the oil type ,
That's good to know Doc, interestingly I had the car run in by the chap who built the engine for the first 100 miles, he did as you said and it wasn't until after speaking to someone else on here they scared the shit out of me stating what I had said before regarding the mineral oil etc and to slowly bed the car in. As it had already been done and the engine was completely fine I just thought it was one of those things but its interesting to see peoples views on this, I know when speaking to Danny he explained about when you run his in on 30 miles etc
 

red reading

Active Member
Every engine I have built, bought or new car I have had has had the same treatment, and they all did well....things that kill engines are silly on these cars,like if the alternator packs up the fuel pump doesn't supply enough fuel on boost so you melt the engine,spark plugs etc,cold starts bugger engines, same as not warming them up and cooling them down properly, good built new engines need running in quick and then looking after with quality oil and filter changes......another thing people do is sniff the engine oil on engines with forged pistons that have been moly coddled and think there car is running rich....it's normally not, it's just the pistons don't expand properly and seal till they are driven hard so you get a lot of blowby.
 
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