what is a good oil for breaking in a rebuilt flathead?

[MarcDeSoto]

The manual says to use 10W non detergent motor oil to break in an engine for the first 1000 miles.  Is there a substitute for this oil as I'm having some trouble finding 10W nd oil?  

[Sam Buchanan]

I would break it in with the same oil intended for use long term. Driving habits during break in (no over-heating, etc) are more important than which oil is used.

 

The manual was written when oils were inferior to what we have today.

Edited January 29, 2023 by Sam Buchanan

[MarcDeSoto]

True, but I've read that the non detergent part is necessary to promote the seating of the rings.  Also 10w non dertergent is used to fill the transmission, unless there's a newer, equivalent product.  

[kencombs]

I second the oil recommendation.  Actually, most any oil is ok.  More important is a very short interval for the first oil change.  Anything in the engine or 'new' wear particles are flushed out then.  Critial on engines like these with bypass filtration as those particles will not be filtered for a while.

[FarmerJon]

I have a variety of conventional oils in the past, but the last few years I try to use a dedicated break in oil from a reputable brand. I like Amsoil, so I would likely use theirs, but any brand will do.

However, I am not familiar with the ins and outs of fluid drive transmissions, so if it draws from your engine oil, you may want to call your oil companies tech line, and double check it will be OK.

 

https://blog.amsoil.com/why-you-should-be-wary-about-using-break-in-oil-in-powersports-equipment/

 

 

ETA: If you plan on running synthetic long term, the accepted rule is DO NOT do break in with it, run a conventional oil for first 1k-6k miles. Breaking in with synthetic oil can cause the rings to not seat well, leaving you with a engine that excessively burns oil.

Yes, I know y'alls prius truck or whatever ships from the factory with no break in and synthetic oil. But ring/piston tech has come a long way in 80 years. 

Edited January 29, 2023 by FarmerJon

[Bryan G]

Non-detergent oil in general is getting hard to find. Often the stuff you do find is a poor grade. I had another car with a factory recommendation of 20w. Since the engine hadn't been apart I didn't want to risk running a detergent oil; mostly I used 30w but for a while I was able to find 20w from Kendall (they actually call it 20w20.) Perfectly clear. Anyway, there were 2 grades of non-detergent, SA which is just straight mineral oil, which went obsolete around 1932. SB has various additives and is what our cars were designed for. As of 5 years ago, only a handful of companies were selling something that met SB. I no longer see those type of designations at all on non-detergent oils. 

 

It seemed like not that long ago that Tractor Supply stocked 20w SA but it's no longer on their website. So I guess it's either 30w, maybe special order something, or just use a modern oil. 

[Sniper]

Well, you ought to ask your machinist this question, he's the one that finish honed your bores, but I don't think that is possible

 

You most assured do NOT need to run ND oil to break it in.  Old, out of date recommendations written 70+ years ago are interesting in a historical sense but not useful.

 

As for not using synthetic oil to break in an engine, wonder what all those factory synthetic fill engines are doing? 

 

There are two factors that determine ring seating, the hone and the ring materials.  If those are up to modern standards you can use modern procedures.  But if you built it like it was 1948 then you should follow the FSM recommendations.

[joecoozie]

I don't know what Non-California means but O'reillys has it.

 

https://www.oreillyauto.com/detail/c/non-california/chemicals---fluids/oil/motor-oil---conventional/2673028dc6c2/pure-guard-non-california-conventional-motor-oil-10w-1-quart/pgdn/nd10

[Young Ed]

The old timer at the shop we use has us use 30w non detergent for break in. Both mine got that treatment and it worked fine. Would detergent have worked the same IDK 

[Dodgeb4ya]

And more....

[MarcDeSoto]

2 hours ago, joecoozie said:

I don't know what Non-California means but O'reillys has it.

 

https://www.oreillyauto.com/detail/c/non-california/chemicals---fluids/oil/motor-oil---conventional/2673028dc6c2/pure-guard-non-california-conventional-motor-oil-10w-1-quart/pgdn/nd10

I just ordered this oil from O'Reillys.  They may not be able to get though as there are many products that can't be sold in Calif. now.  

[MarcDeSoto]

2 hours ago, Sniper said:

Well, you ought to ask your machinist this question, he's the one that finish honed your bores, but I don't think that is possible

I'm the "machinist" who bored and honed my cylinders.  Well, the auto shop teacher and I bored my cylinders 030 over, and I honed them.  

[Sniper]

Then you should know how they were finished and what rings you are running. 

[Sniper]

12 hours ago, Young Ed said:

The old timer at the shop we use has us use 30w non detergent for break in. Both mine got that treatment and it worked fine. Would detergent have worked the same IDK 

 

Yes he learned it in his youth and hasn't changed.

 

Can you use ND oil?  Yes

 

Do you need to?  No

 

There have been many millions of engines broken in with regular oil just fine.  In fact every engine rolling off of every production line for decades has been broken in with detergent oil.  This is an issue that isn't one.

[desoto1939]

1 hour ago, Sniper said:

 

Yes he learned it in his youth and hasn't changed.

 

Can you use ND oil?  Yes

 

Do you need to?  No

 

There have been many millions of engines broken in with regular oil just fine.  In fact every engine rolling off of every production line for decades has been broken in with detergent oil.  This is an issue that isn't one.

Sniper but the modern cars have full flow oil filters and are now being designed and engineered to accept and come with full synthetic multi-weightviscosity motor oils. My 2019 Honda CRV 4 cylinder uses 0/20 full synthetic motor oil and has a full flow oil filter.

 

Yes the older cars did not have the quality of oils that we have in today's market.  I saw that alot of owners have used the RedLine Breakin oil during the first start up of the engine.  But I am also assuming that prior to the first start up that the spark plugs have been removed and that you just turn over the engine to get oil into the cylinder walls and to at least coat the areas that need to have an oil film. Might also want to squirt some oil into each cylinder to do a top lube then crank the car over.

 

I do know that the Castrol Oil company has now produced an newer blend of oil Castrol GTX Classics which is a 20/50 weight oil and has one of the highest amount of ZDDP, Phosphorus and Boron.  In a prior topic I wrote about the oil being used for our older cars..  This oil cn be purchased at Walmart for around $25 for a 5 qt container.

 

Also would suggest that with a new rebuilt engine to install an oil pan plug bolt that has the magnet on the end to help catch any fine metal components from the initial breakin period.

 

These are all just suggestions so the owner of the car should talk also to the engine builder to verify what they would recommend.

 

Rich Hartung

[keithb7]

I must admit, the first low hour oil dump after my engine rebuild was interesting to say the least. Lots of crap floating in the oil. 
Oils and special lubes that were used during engine assembly were blended in with the engine oil. It struck a little fear in my confidence. Lol.  Was there coolant emulsion in there too? No. The second oil change was all good. Filters clean. 
 

[Marcel Backs]

I think Castrol has a new oil for older engines called Classic with extra zinc. How essential (if at all) is zinc content in oil for the flathead sixes? I use 30W in the Chevvy and that is what has been used for decades in it. If I rebuilt that 235 OHV 6, I would use a good modern oil and possibly even a synthetic blend. Regular non-detergent oil is getting expensive and harder to get. M

[OUTFXD]

My sister has been trying to sell me on Extra Virgin Olive Oil for years,  apparently its pretty good.

[Doug&Deb]

I wouldn’t recommend full synthetic oil for our engines. Modern engines have much tighter tolerances than we could ever hope for. Any quality break in oil should be fine.

[Marcel Backs]

Don"t bother 30W looks exactly like what you put on your salad! LOL

[BobDeSoto]

The Castrol is 20/50

[kencombs]

IMHO, the reason for the ND recommendation way back when was due to the lack of adequate filtration.  Think about the ring seating we hear so much about. That comes about through wear.  H the high spots of the cast block and rings wear down to improve fit.  All those cast particles are in the oil.   Detergent keeps them in suspension longer than ND.  Any stuff in the oil will circulate until it is finally routed through the bypass filter.    
 And those are the reasons mine is getting plumbed for a full flow filter. And will get a 100 and 500 mile oil change.   

[Sniper]

3 hours ago, desoto1939 said:

Sniper but the modern cars have full flow oil filters and are now being designed and engineered to accept and come with full synthetic multi-weightviscosity motor oils. My 2019 Honda CRV 4 cylinder uses 0/20 full synthetic motor oil and has a full flow oil filter.

 

Not sure where you are going with this, we were talking about detergent vs non-detergent oil, at least I was.  As for a full flow filter, not sure how that applies either.  The initial break in oil is drained after 15-20 minutes of use.  Modern detergent oils are designed to keep contaminates in suspension, which is what you'd want for the initial break in so you could get them out of the pan when draining.  After that, well you want to use a detergent oil regardless of filtration though I would highly recommend converting to a full flow filter setup on anything other than a 100% accurate restoration.  At least that is my thinking. 

[Bob Riding]

2 hours ago, keithb7 said:

I must admit, the first low hour oil dump after my engine rebuild was interesting to say the least. Lots of crap floating in the oil. 
Oils and special lubes that were used during engine assembly were blended in with the engine oil. It struck a little fear in my confidence. Lol.  Was there coolant emulsion in there too? No. The second oil change was all good. Filters clean. 
 

How many hours did you run your rebuilt motor (and at what rpms) before your first oil change?

[keithb7]

 I varied throttle and load conditions. Not pushing it too hard for first while. A few trips around the neighborhood at first. Varied speeds. Then I took her for a longer local drive. I varied my speed, up and down. Finally driving it up the hill home. I know I got the engine and initial oil up to full operating temps few times at at least then dumped it. Probably 100 miles then drained it. A few trips up the hill home and I figure the rings were well seated.