Skid Row Joe

Nick, 10 years before All Saints:

Frankie the Fink

I was around a lot of used cars over the years, many poorly maintained, some diligently maintained - of ALL makes. I saw maybe 3 instances were a stock, undicked-with motor, truly grenaded itself beyond a simple repair in daily driving...

As stated, they'll wear out but an "extinction level" event is seldom an issue...

Before I got my 5-speed, OD Tremec, if I didn't feel like running 75 mph with "the pack" I would get in the right lane and do 60-65 and sail merrily along....nothing says you have to keep up with all the texting, tailgating fools in their jacked up trucks and econoboxes.

rayL79

In my opinion, you won't hurt your engine by running at 3500 as long as you have plenty of oil and good oil pressure, etc. But wear is all about piston travel per mile. Your engine will wear eventually until it needs a rebuild. An engine that is running all the time at 3500 will get to the point of unacceptable wear 40% faster than one that is running at 2500, all other things being equal.
Ray

MarkC

Mercruiser, OMC and Volvo have used the 350 sbc with their I/O and inboards for years. They used Fords also. The cruise rpm’s were generally around 3000 rpm’s and the boats were propped so max rpm was 4200-4400 rpm’s. There are examples where they turn more but those are more high performance. These engines are under a far greater load than cars. They typically last about 2000 hours.

I think these old cars cars were designed for 100,000 miles, now with over drive transmissions, better oil and better design we see 200-300 thousand miles. Phlash Phelps on 60’2 on Six has close to 500,000 miles on his Honda.

I bought my 66, L79 with a 3.70 rear gear 7 years ago. I bought it to drive. Three months after I bought it, I drove it to Lynchburg, VA to a car show on Smith Mountain lake. After that trip I put a 5 speed, TKO 600, in the car. It’s the best mod you can make.

MarkC

Here is another observation comparing a boat to a car. A car doing 60 mph getting 20 mpg burns 3 gallons per hour. A boat with a sbc turning 3000 rpm’s is burning 7-8 gallons per hour. That gives you an idea of the load on a boat engine.

Factoid

There are so many factors that impact ‘safe” sustained rpm. Modern engines have addressed most of the significant wear issues:

Cam/lifter wear: roller cam and lifters
Rocker/valve tip wear: roller tipped rockers
Oil lubricity/wear: synthetic oils
Cylinder wall fuel wash: EFI

There are others, but these are the big ones for a GM V8

If you have a “vintage” engine in good shape, sustained rpm of 3000 rpm or 10% below the peak torque rpm in a C2 Corvette, which ever is greater, will not significantly reduce engine life. Interestingly, the base 250hp engine has a torque peak around 2800 rpm, while the rest of the line up needs approximately 1500 more rpm to achieve the same torque! In my world, that’s a stump puller, basically a truck engine.

cv67

3k is fine, a sbc can go 200k if taken care of
If timing/tune is on, cooling system in check theres nothing to be concerned about.

Used to run my Z at 3500 on the fwy for hours at a time nothing wore out
Your cam turns at half the crank speed by the way

SWCDuke

[QUOTE=Nick Bernier;1599102041 Just don't want to start throwing rods through the oil pan. I guess I'm really asking if the motor is sound, is a constant 3,500 rpm within reason?

Nick[/QUOTE]

283 and early 327 rods are weak and known to suffer fatigue failure at the bolt seats. The second 327 design went into production for the '66 model year. They have a little hump of extra material adjacent to the bolt seat that makes them much more durable. Plain vanilla 350 rods are even better.

Rod stress increases with the square of speed, so at 6000 max stress if FOUR times the value at 3000. Most materials including steel that are subject to cyclic loading - constant stress reversal from tension to compression have a fatigue life that is usually some percentage of yield stress - say 50-75 percent. If such a part can pass a 10 million cycle test, it's generally considered to have infinite fatigue life. This is easy to determine using a simple test sample, like a piece of bar stock that will have uniform internal stress at a given load, but rod geometry is much more complicated, and we may not know the actual stress at every location inside the rod.

IIRC Chevrolet did do a 10 million cycle test of early SB rods, but I don't know the specifics. Even then it took ten years to finally produce a fairly bulletproof rod.

Surface condition is critical to fatigue life. Most fatigue failures start from a small surface imperfection that develops into a crack that then propagates through the material. This is why used rods should be Magaflux inspected. The test will reveal tiny cracks, and if found the rod should be replaced. Also, shotpeening a set of rods that pass Mag will increase fatigue life because the process work hardens the surface, making it stronger and more resistant to cracking.

Understanding the above, Chevrolet took extra steps to produce the "pink" rods used in SHP 350s. Regular production machined rods were pulled aside and Magnaflux inspected. Those that passed were then shotpeened, but only at the bolt seats. Then the completed rod was given a dab of pink paint (thus the name "pink" rods) and assigned a different part number.

When it comes time to rebuild, those 283 and early 327 rods should be replaced with higher strength aftermarket rods like the Eagle SIR5700, which are only about $250 per set. They will make for a bulletproof bottom end, and it's the cheapest engine insurance policy you can ever buy.

I consider the second design 327 rods okay to use as is other than a dimensional check for base engines, but still recommend better rods for L-79s.

Assuming an engine has known "good" rods and was properly assembled it will likely cruise at 4000 RPM forever or until plain old wear indicates a need for overhaul, but a decent engine should last at least 100-150K miles before excessive wear becomes an issue.

Valve guide wear is basically a function of engine speed... ring, cylinder wall, and bearing wear, no so much. Bearings generally are the longest lived wear part assuming they have an uninterrupted supply of relatively clean oil, and good air filtration is critical to minimizing ring and cylinder wall wear.

When I took down my SWC's 340 HP engine at 115K miles the only measureable wear was the cylinder walls - six had three thou taper and two had 5 thou, and I attributed that to the lousy foam air filter. It ran great, but the reason I took it apart was that I was worried about the rods, and sure enough, Magnaflux inspection showed a crack clear across one of #7's bolt seats. I dodged a bullet!

I maintained the SWC to high standards, but at times ran it pretty hard. With its 3.08 axle, typical 80 MPH cruise was 3100 - no big deal, but on some cross country trips I cruised at up to 100 MPH (about 4100) and once drove the 40 miles from the CA/NV border to The Strip cruising at 130 - a bit over 5000. In addition it had about 10-20 hours of race track hot lapping, and I can recall a couple of missed shifts where the tach went past 7000. This and knowing that the rods were weak is why I tore it down.

The trouble is that most guys don't know what's inside the engine. If pre-'66, does it still have the weak OE rods that are nearing the end of their fatigue life, and how hard for how long was it run over the last 50-plus years? For sure if you do a rebuild use the highest quality parts, especially rods, and the engine will likely outlive most of us.

Back in 1977 a rod in my E-Production TR3 let go at about 6000 (redline was 6500) exiting Turn 7B at Riverside. It felt like I ran over a mine! My analysis of the pieces lead to a conclusion that the failure was initiated by a bolt failure. The rod was less than 10 hours from its last Mag check and was installed with new OE bolts. BUT, I didn't Mag the new bolts. Lesson learned!

Duke

ghostrider20

Aircraft piston engines run at a constant RPM for hours at a time. Take the Continental IO-520 series for example, 4” stroke 5.25” bore. With a max rated/certified RPM of 2700. This means the engine has been tested and is allowed to run at 2700 RPM continuously. That is 1800 FPM. Aircraft engines have a TBO (Time Before Overhaul) which is a recommendation for private operators, and mandatory for commercial operators.

AlHewitt

I have one of these - IO 520D in a Cessna Skywagon. Mine is rated for 5 minutes at 2850 RPM and makes 300 HP. I find it interesting that these engines make over 550 ft. lb. of torque. As ghostrider20 points out these engines have a fairly low time in use between overhauls of maybe 1700 hours. By comparison to automotive mileage if my airplane makes 140 kts or about 160 MPH that's close to 275,000 miles before an overhaul is needed. The starting of these engines when they are cool is when the highest ware occurs. Someone once said that they will run for 5,000 hours if started and never shut down. BTW my 2011 Tahoe shows 100,000 miles and 3,000 hours of use... Al

W Guy

As stated, I agree that the rods are the critical factor. IF it were mine, I"d be OK with 3000rpm, but not 3500rpm cruising. If you want to go faster, change your rear gear.

Verne

MikeM

Personally, I have never seen nor heard of anyone breaking a connecting rod in a street driven 265, 283 or 327.

A buddy broke one on the drag strip. Missed a shift and I think he said his tell tale tach showed 9000 rpm. That was a stock short block except for the roller cam. It was also the early version rod.

I am just curious as to how many others have personal knowledge of connecting rods breaking in SBC engines prior to the 350 design. The only other problem I've heard of as far as breakage is the main bearing webs cracking. Again, isolated instances.

One friend of mine bought a new '64 fuelie Corvette. He ordered the 4.56 axle. That car ran for about 90K miles and the second owner pulled that gear out for a 3.08 and drove it another 30K miles before the engine needed to be overhauled. The same engine is still running today, with the original '64 327 rods.

For competition use, some racers used to use Buick connecting rods and they didn't use them to be whistling Dixie. The factory rods were pretty marginal for competition. Chevy upgraded the rods in '66 for a reason. Must have been a good one as that cost a little money.

W Guy

Mike,
I had a good friend who drove his '62 327 Impala across PA with a 3.70 rear. The engine was in good shape but he lost a rod cruising the PA Tpke at 3700rpm.

Verne

MikeM

As in broke?

Anybody else?

GTOguy

Now THAT stirred a memory: I had a co-worker who had a hot '62 Impala with a 327 and a 4 speed. He was racing a Chevelle (back in the late '70's) and actually blew a rod, rupturing the oil pan or block. He coasted to the side of the road, got out of the car, and lit a cigarette, posing as if he were just hanging out. The Chevelle was long gone, but the cop that was chasing both of them pulled over and asked Glen what he was doing. Glen simply stated he was having a smoke and enjoying the afternoon. The cop asked him if he weren't racing just now. No Sir, officer. I've been parked here for awhile, was Glen's reply. About then, the officer noticed the lake of engine oil, metal bits, and ticking from the cooling down, blown up motor. The jig was up. Glen blew his engine, lost the race, and got the ticket. Love this forum.....I haven't thought of THAT one in almost 40 years!!

MikeM

So, did the rod break due to a fracture or did it break because the bearing seized on the crank and broke it up in the beam of the rod?

I would think in your line of work, if there was some kind of epidemic of broken rods, you'd know more than just one or two?

63 340HP

With respect to the OP question, with the 3-inch stroke of the 283 the piston speed is under 3000 feet per minute, even at 6000 rpm. The piston speed is 2000 fpm at 4000 rpm, well below a piston speed that motivates concern. The slow piston speed at usable rpm ranges results in internal stress loads well below most other small block Chevrolet engines.

Whatever anecdotal information anyone comes up with longer stroke configurations will be less severe with respect to the 283 engine configuration (the short stroke is an aspect of the 283/302 configuration that enhanced reliability, by design).

Enjoy the car.

jim lockwood

I've got a 283 with a cracked main bearing web. Is it rare? Can I get a lot of money for it?

Expiring minds want to know.....

Westlotorn

I have seen factory rod bolts let go causing catastrophic failure. I have seen failed rod bearings do the same.
I have not seen factory rods just fracture out of the blue but in fairness most of the engines I was around were 350's which ran the newer and better rods.
Mark

mrg

My car ran 4:11’s. There always that feeling of needing an extra shift at freeway speeds (3000/60mph). It could be gotten used to but then there was that dang shifter buzz at that rpm! Annoying over the long haul.

With a WR Muncie, first gear was almost ‘too low’ for general around town driving. Second gear starts became the norm.

3:08 pumpkin sitting in the corner of the garage. Out came the 4:11’s. The M20/3:08 combo has worked out great, since. The car is a real pleasure to drive on long road cruises now. Shifter rattle moved up the scale (about 75 mph)........a good thing.
John