How should you break in a rebuilt engine?

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DartSportDude

Old school A-body owner
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I just had my '73 340 rebuilt. I should pick up my car from the repair shop in a few days. Can anyone give me advice on the proper/best way to "break in" a rebuilt engine? How many miles must be driven during the break in period, and what style of driving is required? I understand that a special oil is recommended during break in. How long should it stay in the engine?

Thanks for your help.
 
I'm sure every engine builder on here has there own way, but I will tell you how I like to do it. I always like to hit the interstate first thing, cruise about 55 mph for probably 20 minutes or so, then hit 70 and just cruise maybe anothere 20 or 30 minutes. I think it really help set the rings at a constant rpm versus stop and go. really take it easy for atlest 500 miles or so and then change the oil to get the break in lube out. ask the guy that built the motor how tight the clearense is and probably take his recomendation on what weight oil to run, My personal favorite is Valvoline 1040. other than that there isn't a whole lot you should have to worry about, they should have the cam broke in for you.
 
I just rebuilt my 273. I put break-in additive and ran Valvoline VR-1 30 weight. The government pulled zinc out of oil because it was screwing up cat converters. Rotilla use to be the way to go but they pulled the zinc in that too. VR-1 still has the zinc because it's a "speciality" oil. Before you fire it the first time double check the distributer and make sure it's not 180 degrees out. It's a common mistake (happened to me) and the key is to get it to fire ASAP and get oil pressure. Once running set the RPM to 2000 for 30 minutes before shutting it off. I left the raditor cap off just in case it overheated so I could trickle water in it if necessary to make sure I could run it 30 minutes. The weak point is the flat tappets and without zinc you can wipe the new cam very quickly. If you are running roller lifters the zinc is a non-issue. I did not do the first oil change for 500 miles so as to keep the additive in that long. If you do change the oil before 500 miles be sure to add more additive.
I probably have 3000-4000 miles of it now and no problems.
Good luck and make sure you have cold beer on hand for the toast.
 
The engine builder suggested running up the RPMs a few times right away to "break in" the cam? Does that sound right?

Some of you guys seem very knowledgeable. Is there anything I should avoid doing at all costs -- something simple that might damage the engine?

Thanks!
 
moparsegura said:
I'm sure every engine builder on here has there own way, but I will tell you how I like to do it. I always like to hit the interstate first thing, cruise about 55 mph for probably 20 minutes or so, then hit 70 and just cruise maybe anothere 20 or 30 minutes. I think it really help set the rings at a constant rpm versus stop and go. really take it easy for atlest 500 miles or so and then change the oil to get the break in lube out. ask the guy that built the motor how tight the clearense is and probably take his recomendation on what weight oil to run, My personal favorite is Valvoline 1040. other than that there isn't a whole lot you should have to worry about, they should have the cam broke in for you.
Click to expand...

Actually, driving a constant speed is the exact opposite of what you want to do! You want vary the speed as much as possible, but don't accelerate too hard for the initial few hundred miles. When you accelerate, you force the rings out into the cylinder walls, helping them to break in. When you let off the gas, the high vacuum pulls a little oil past the rings, cooling them and flushing out any minute particles.

The shop should have broken the cam in for you. If they don't change the oil right after the initial fire-up, then the first thing you need to do is change the oil. It will look like metallic paint. This is ring and cylinder wall. After the oil change, take it out somewhere with little traffic where you can get up to 50 or 60 mph. When you get to that speed range, let off the gas completely until you drop down to about 30 or 40. Then accelerate somewhat hard, keeping it in high gear. I don't know if you have an auto or 4 speed. With an auto it will be a bit tricky to keep it from kicking down. Anyway, do this about 10 times. Don't let it overheat!

After that, just drive it around normally, don't beat on it until it has 500 or so miles on it. I would change the oil again at 500 miles, then again at 1000. After that, do your regular oil change interval.

Good luck!
 
find out if the shop has fired it up and broke in the cam !!


If so , ask if they changed the oil. and if they are moly rings.


If so go out and drive it at highway speeds or so for 5 or 10 minutes then do some stop and go driving. Put at least 20 miles on it . Check over everything . Then STAND on it . If they are moly rings they are seated fairly quickly

I use Rotella 15-40 and a bottle of Hughes oil additive or Comp , or even GM EOS at every oil change .
 
496dart said:
find out if the shop has fired it up and broke in the cam !!


If so , ask if they changed the oil. and if they are moly rings.


If so go out and drive it at highway speeds or so for 5 or 10 minutes then do some stop and go driving. Put at least 20 miles on it . Check over everything . Then STAND on it . If they are moly rings they are seated fairly quickly

I use Rotella 15-40 and a bottle of Hughes oil additive or Comp , or even GM EOS at every oil change .
Click to expand...

I tend to agree with this. Find out what the shop did and installed.

IMHO, 500 miles is old school for when sloppy tolerances were the norm.

Get on the highway, run it up to about 3500 and let it compression decel about 10 times, vary the RPM in between runs. Put about 30 miles on it if you want, then drive it like you stole it!

Even in the mid 80's for all my builds, it was cam break in (if necessary), change the oil/filter, reset lash and a 7K+ burnout and some hard romps. Roller motor got the treatment after initial fire and everything was checked out, no break in, just romp it.
 
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