50 Hour Engine Test

[Matt Wilson]

Good Sunday to all of you.  I've seen several mentions of a 50-hour test that Chrysler used to conduct on its engines.  It's been said that such testing is mentioned in a particular book written a couple decades ago (I think?).  To those who have read that book, does it say in what era this testing took place?  By that, I mean, do we know that flathead sixes of the design used in our vehicles underwent such testing?  I see discussions that make me think so (certainly the people posting the info think so), but I'm wondering if the book was that specific as to state the era when such testing was done.  Has anyone ever run across any examples of this data, or a source that provides any kind of detailed description of the test and its outcomes?  Maybe that book provides some detail.  I'm sort of a junkie for this kind of information and would find it interesting if anyone can offer up anything.

 

I found info online from a Chrysler engineer who said that the next generation (overhead valve) engines in the 60s were being tested under a graduated schedule consisting of 10 hours at 800 rpm, followed by 10 hours at 1600 rpm, then 10 hours at 2400 rpm, 10 hours at 3200, 10 hours at 3600, then 9 hours at 4000, and finally 1 hour at 4400 rpm, all at wide open throttle, which adds up to 60 hours.  I'm wondering if the 50-hour test was similarly conducted on an rpm schedule, or at 3600 rpm continuously, as is often mentioned here.  EDIT:  After a little more reading, it turns out the article discussing this test schedule was related to the development of the hemi-six engines, and testing took place circa 1966.  Not sure if they tested all development engines in that manner during that era, or if this was something specific to the hemi-six. 

 

Thanks for any insight into this that you guys can provide.

Edited March 4, 2019 by Matt Wilson
Clarification of info

[Dodgeb4ya]

That would be a good test and break- in on your 265 engine.

[dpollo]

i recall reading this too.  It applied to engines under development or some picked at random for testing.  

 

Production engines may have been run up to speed on a jig ( not under their own power) to check oil pressure and so on.

[Matt Wilson]

FYI - I added a little more info to my original post for clarification. 

[Matt Wilson]

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Edited March 5, 2019 by Matt Wilson
Accidentally replied to my own post.

[thisoldtruck]

I heard back in the 1930s, 1940s and into the 1950s they would pick an engine from the line and test it for the 50 hour test and run it at 3600 rpm.  It was sort of random quality controlled type test on an engine test stand next to the assembly line at the engine plant.  These tests were on all the flat head six engines, either 23" or 25" blocks.   

 

I've heard of a guy drag racing Mopar flat head sixes back in the 1950s that supposedly ran them as high as 5,000 rpm.  Not sure of what engines he used.  But could never confirm that story. 

 

There are many stories of M37s spinning rod bearings on the 230s back in the 1950s and 1960s as well.   

[greg g]

My understanding is that the engines were run at 3600 against a load.

That these engines were pulled at random from the engine assembly line.  Never heard what happened to the test engines when the test was completed.

[Matt Wilson]

On 3/3/2019 at 3:07 PM, Dodgeb4ya said:

That would be a good test and break- in on your 265 engine.

I'm afraid I'd crater my engine if I ran at those speeds and power levels.

Edited March 5, 2019 by Matt Wilson

[Matt Wilson]

11 hours ago, thisoldtruck said:

I heard back in the 1930s, 1940s and into the 1950s they would pick an engine from the line and test it for the 50 hour test and run it at 3600 rpm.  It was sort of random quality controlled type test on an engine test stand next to the assembly line at the engine plant.  These tests were on all the flat head six engines, either 23" or 25" blocks.   

 

I've heard of a guy drag racing Mopar flat head sixes back in the 1950s that supposedly ran them as high as 5,000 rpm.  Not sure of what engines he used.  But could never confirm that story. 

 

There are many stories of M37s spinning rod bearings on the 230s back in the 1950s and 1960s as well.   

Wow, I didn't realize spun bearings were a common issue in 230's.  It seems odd, considering that quite a few folks on this forum, and others, say they cruise at 3000 - 3400 rpm for miles on end with no issues, and the M37 was governed to 3200 rpm.  I assume the spun bearing issue with related to high rpms.

Edited March 6, 2019 by Matt Wilson

[dpollo]

it is just over 60 years ago that I spun a bearing on my 35 Plymouth.  It broke my heart as I was 10 years old and had farm roads to drive on.  Since then I have spun two more bearings and disassembled several others which had suffered the same fate.   None of these bearings failed without first giving plenty of warning.  As near as I can tell, excessive clearance and continued operation distorts the bearing seat to the point that the entire shell starts to rotate.  further running causes one shell half to overlap the other and  with a screeching noise the engine seizes up.  At speed this might blow the cap off the rod.  In any event it is a catastrophic failure which is not unique to these engines.   Given the hundreds of thousands of miles I have driven cars and trucks powered by these engines it is my feeling that , shown respect, they deliver pretty good service.

[Matt Wilson]

1 hour ago, dpollo said:

it is just over 60 years ago that I spun a bearing on my 35 Plymouth.  It broke my heart as I was 10 years old and had farm roads to drive on.  Since then I have spun two more bearings and disassembled several others which had suffered the same fate.   None of these bearings failed without first giving plenty of warning.  As near as I can tell, excessive clearance and continued operation distorts the bearing seat to the point that the entire shell starts to rotate.  further running causes one shell half to overlap the other and  with a screeching noise the engine seizes up.  At speed this might blow the cap off the rod.  In any event it is a catastrophic failure which is not unique to these engines.   Given the hundreds of thousands of miles I have driven cars and trucks powered by these engines it is my feeling that , shown respect, they deliver pretty good service.

Interesting experience on the matter.  When you say "respect," what does that mean for you with regard to max sustained/cruise rpm?  How about intermittent, short burst rpms?  Thanks.

 

Part of the reason for my original question about testing is because I see conflicting information about max rpm for these engines, with some folks saying that you have to keep the revs low (like 2200 - 2500 rpm) if you want the engine to last, while others say they take their engines to much higher rpms and even cruise there for thousands of miles with no discernable negative effects on the engine.  But then I see stories about spun bearings and it makes me wonder if these engines really are on the ragged edge when running at high speeds.  Your explanation for the spun bearings seems pretty plausible, though.  I figure details on the factory tests is one way to help piece together the puzzle.  As with anything, I'm sure it depends on the quality of the routine maintenance and how well the engine was built or rebuilt to begin with.  I don't doubt that running higher rpms will shorten the life of these or any engines somewhat, and the higher the rpm, the shorter the life, but some people talk as if running above the mid-2000s for any significant amount of time will cause an engine that would have otherwise lasted 100,000 miles to wear out in 25,000 miles, if it doesn't just explode right then and there.

[greg g]

The machinest that did my engine told me based on his 40 + years of experience including working with Don Gartlits in his flathead 8 days, that a cruising rpm of 80 to 85% of peak hours rpm was sustainable in continuous operation assuming stable operating operating temps between 170 and 190;degrees with minimum of 35 psi of oil pressure with oil in good condition.  He also said brief exposure to rpms over peak rpms wouldn't do harm, but in stock condition wouldn't produce enough more power to justify, owing to frictional losses inherent to long stroke engine design. 

 

Before my of install my overdrive my tires and 4:11 rear end setup gave me 62 mph at 3280 rpm.  We put many thousands miles at that speed or slightly higher with no apparent internal stress.  Oil pressure is still the same as it was when rebuilt 40000 miles ago.  Your results mat vary...

[Matt Wilson]

Thanks for the feedback, Greg.  Some people quote a 70% rule (the same people who say you shouldn't rev these engines more than 2500 rpm), but more commonly I hear the 80 - 85% rule.

 

I assume all those miles have been with factory stock crankshaft, rods, rod bolts, etc?

[greg g]

Yes internal are stock except .030 over pistons, however it does have a milled head and dual carbs and larger diameter exhaust plumbing.

[thisoldtruck]

22 hours ago, Matt Wilson said:

Wow, I didn't realize spun bearings were a common issue in 230's.  It seems odd, considering that quite a few folks on this forum, and others, say they cruise at 3000 - 3400 rpm for miles on end with no issues, and the M37 was governed to 3200 rpm.  I assume the spun bearing issue with related to high rpms.

 

Please don't miss understand.  Keep in mind, most of the stories I heard about the 230s and M37s were from people in the military during Vietnam, like from 1966 to 1972.  The M37s were old by then and I think that had more to do with it then anything else.  Plus during combat, who knows what happened to these trucks exactly.

 

I think diluted engine oil was a big cause of spun bearings.

 

Looking at all the engines made by different manufactures during the 1930s through the 1950s, I would say Chrysler had the best of the best!  I've heard a lot more unfortunate stories with Ford flat head eights, like cracked block stories. 

Edited March 7, 2019 by thisoldtruck

[dpollo]

A failure  at high speeds on a Chrysler six would more likely be on a piston due to the long stroke.

  Bearing failure is generally a result of dirty or diluted  oil.

On the 35 Plymouth I mentioned earlier,  it was #2 rod which failed.  Prior to that, I had (at age 10) rebuilt and replaced a faulty fuel pump.  I believe that gasoline sprayed into the crankcase had washed down #2 rod for some considerable time .   This ultimately led to bearing failure which was imminent before I came on the scene.  I wish I could replay the whole incident and avoid the bearing failure but in retrospect it was already well on its way.   Nothing a replacement crankshaft would not have fixed.

[chrysler1941]

Here is a copy of 1939 Cadillac factory written instruction for break-in. What's interesting, they spun engines electrically using the dynamo-meter (load) for a while before starting them up. 

It's not a MoPaR but haven't found anything form that era. But gives one the general idea from that time.

 Also attached break-in RPM and time

1939 Written Assembly Assembly Instructions.pdf

Break in.pdf

[Matt Wilson]

On 3/6/2019 at 9:21 PM, thisoldtruck said:

I think diluted engine oil was a big cause of spun bearings.

 

On 3/6/2019 at 10:33 PM, dpollo said:

Bearing failure is generally a result of dirty or diluted  oil.

On the 35 Plymouth I mentioned earlier,  it was #2 rod which failed.  Prior to that, I had (at age 10) rebuilt and replaced a faulty fuel pump.  I believe that gasoline sprayed into the crankcase had washed down #2 rod for some considerable time .   This ultimately led to bearing failure which was imminent before I came on the scene.  I wish I could replay the whole incident and avoid the bearing failure but in retrospect it was already well on its way.   Nothing a replacement crankshaft would not have fixed.

Thanks, this has been educational, and it's a bonus when two people see things in a similar manner.

[Matt Wilson]

On 3/8/2019 at 7:38 AM, chrysler1941 said:

Here is a copy of 1939 Cadillac factory written instruction for break-in. What's interesting, they spun engines electrically using the dynamo-meter (load) for a while before starting them up. 

It's not a MoPaR but haven't found anything form that era. But gives one the general idea from that time.

 Also attached break-in RPM and time

1939 Written Assembly Assembly Instructions.pdf

Break in.pdf

Great info!  I've downloaded these for future reference.  Thanks!