The Stovebolt Site Forums The Shop Area Engine Shop Breaking in a 305 SBC

Hi all, I have decided not to put that 305 SBC or any other V8 in my '55 chevy but instead to juct restore it to factory original, so instead my Mom and Dad gave me a '73 1/2 ton chevy that has a 305 SBC in it, out of a '77 nova. I have it on the stand right now, and am rebuilding it. But, once its done, how do I go about "Breaking" the motor in. I was told to take it easy on the motor for atleast 500Miles, and change the oil often and not to "Whomp" on it, or punch it, to give the rings and rod bearings time to settle in. What you you guys recommend, or atleast suggest? Thanks for the help!

- Shane
[email protected]

when i rebuild my sbc i just get in and drive it how its going to be drivin hard right from the start why wait 500miles to find out if its going to come apart i say drive it hard but thats just me

Do the 20 minute cam break-in. Let cool, change oil and retorque head gaskets. Check for leaks. Examine oil for metal shavings. Cut filter open and look for metal. If its coming apart, metal will show up now.

Tune engine then road test. Accellerate and coast during test runs. No full-throttle starts or long steady-speed cruising. Find a straight streach of road, no traffic. Put truck in low or 1st, accellerate to 3000 RPM, drop foot off gas and let engine slow the truck way down. Repeat 5 or 10 times to seat rings. Drive 500 miles as normal, no abuse. Change oil, check for metal. Enjoy engine, resume normal maint schedule.

The cam break-in is on the initial start-up, rev your engine up to and set it on 2500 rpm for 15-20 minutes.
Let it cool, drain and change the oil and filter.
Take note of the drained oil to ensure you don't have metal shavings.

Good luck.

Ok, this is what I wrote down, a combination of things from both posts.

* Cam Break-In
- Run motor at 2500rpm for 15-20 minutes
- Let motor cool
- Retorque heads to proper Spec's (65 ft lbs)
- Check for leaks
- Drain oil, inspect oil for metal shavings, and the same inside the oil filter.

* Rings
- Put truck in 1st gear, accelerate to 3000 RPM's and let the engine slow truck down most of the way. Repeat 5-10 times.

What about the rod bearings, and main bearing? Do these two break-ins take care of that? Thanks for the help guys,

- Shane
[email protected]

I've performed only the cam break in, retorque, and check for leaks.

I've never cut the oil filter nor do the "ring" method.

IMO everything kinda "seats" itself during the cam break it.

Another method some use to "break-in" a recently rebuilt engine is to drive it at various speed...35 mph for 10 minutes, 45 mph for 10 miles, up to 55 mph for 10 miles. Then drive it normal but not exceed 55 mph for the first 200 -300 miles.

Yeah, I usually don't cut the oil filter open unless the drained oil makes me suspect that something is going on. And I've heard to vary the speed of the engine during the 20 minute cam break-in. But if its OK to let it sit and revv at 2500, then thats easier.

I'm about to fire up a cam swap in my Pontiac. So I'm double-checking my procedures too.

chip

Good advice!
Anybody ever wonder WHY the 20-minute fast idle to break in a cam? It's simple lubrication! A lot of oil slings off the crankshaft/rods during the fast idle time, and keeps the cam lobes flooded with oil. Since the cam & lifters are the only part of the engine that runs without any clearance during normal operation, it's essential that they get lots of oil while they're establishing a running fit between the parts. This is the same reason that a cam and lifters which have been run for any length of time must be kept in the correct order if they're removed. Running a lifter in a different position after it's been run-in on a lobe makes it reestablish a different wear pattern, and usually results in a flat lobe. I've got a cam in the shop right now with less than 1,000 miles on it, with one flat lobe, and noticeable wear on some others. The owner didn't have the engine tuned properly before the first startup, and idled it for some time while tinkering with ignition timing, etc. Now he needs a new cam and lifters.
Jerry

Hey Hotrod- I knew about using the oil throwoff to lube and cool lobes, but am unsure about RPM during break-in. Is it better to vary RPM or keep at 2500 RPM during break-in? And is there a safe minimum RPM to stay above? like 2000 or so?

chip

I use 2,000 as a rule of thumb. The exact RPM isn't critical, just enough to get a good oil flow to the crank and rods, and enough centrifugal force to bathe the cam in a good volume. I usually adjust the fast-idle on the carb to about 2,000/2200, and just let it run at a steady speed. While it's breaking in, I check for steady oil pressure, final-adjust ignition timing, etc. This is also a good time to monitor the fill on the radiator, as it's not uncommon to have an air bubble trapped behind a closed thermostat. Once the stat opens and water starts to flow, top it off and install the cap. Nothing like an overheat in the middle of a run-in to ruin your day! It's important to bring the speed up as soon as you've confirmed oil pressure, to minimize the time the cam has to start scuffing the lobes. A good cam/lifter prelube, such as the blister pack Sealed Power includes with an engine assembly kit is a good idea, although any durable lube such as Lubriplate lithium grease will do. I used to use STP as an assembly lube, until I had several lube-related problems with new engines assembled with the stuff! Coat the cam lobes and lifter bottoms with the lube as you assemble. Motor oil doesn't seem to work well on a cam, as it doesn't cling long enough to protect the lobes during startup. Filling the oil filter with oil and/or running the oil pump with a drill motor and a priming shaft before installing the distributor also helps the oil pressure come up quickly.

BTW, I always pre-fill the filter on an oil change, also.
Jerry

Like the parts- guy say,drive it.Make sure it's ready to start,give it moderate throttle, cycle the engine through the gears a few times, feel the smooth new power,wind pushing through the radiator,all broke in , happy motor .
Run it in the driveway with no load, rings won't seal quickly, sad motor .

Is Tony the only person here who knows how to break in an engine?

Number One, the only thing you need to break in right off the bat is rings. To do this you load the engine to put pressure on rhe rings. This will take no more than 10 minutes if done right. I do it by pulling hard for about five minutes then ease off a little bit for another few minutes.

DO NOT - Run at idle except just long enough to check for leaks - one minute.

DO NOT run at high speed at no load, this will ensure that the rings never seal!

After the initial 10 minutes or so drive it moderately for 5 - 10 miles then drive it normally.

NO(Over 65)high speed driving until at least 100 miles then just do what you want.

Cams do not need to break in and bearings require very little, the moderate driving takes care of this.

I have been breaking in engines in cars, trucks and airplanes for 50+ years and this works every time.

Tony, on the antique stovebolt engines most of the guys here are dealing with, that might be OK, but I've got a bunch of worn-out cams with very short running time that makes me tend to disagree with your method. Also, the low-tension rings that have been used for at least 20 years don't need the pressure of driving to aid seating. The last time I heard of the "drive it and load it" method of seating rings was about 25 years ago, in a Perfect Circle seminar I attended. Times and machining methods have changed, and our methods need to change with them. Once we get set in our ways, and quit learning, we're likely to dismiss any new information that's available. Check out the wear limits on some of the new engines, with piston skirt clearances of .0005", and 5W-30 oil! What was once a normal buildup clearance on a new engine is now "worn out".
Jerry

Jerry,by running the engine down the road, it running fast enough to splash around plenty of oil on the cam.And most new engines are OHC,the cam sees only pressurized oil, not splash from the sump. And those same new engines in new cars, does the factory run them in place with no load for 20 minutes? I don't know for sure, but I think not.I believe the first start up is at the end of the assembly line,then driven out to a holding area Then restarted by by a delivery person driven onto a truck or boat or whatever for shipment.Then delivered to the dealer an probably driven by a 18 year old new car prep guy.I do know modern hi line cars like Porshe,Ferrari etc engines are tested for proper operation on a dynometer, under load, then installed in the vehicle. Hi performance engine builders always run an engine under load for breakin and to make finalize jetting and timing.Jensen Marine here in NY ,builds big inch boat motors,all are broken in on a dyno under load, the engine even comes with a printout showing the torque and HP curves.
Ya know, it's another one of these things, you tend to do what works best for ya.

OK, we use different methods, and, apparently, it works for both of us. The engines I build average $15,000.00 each, and produce from 500 to 750 HP, mostly 355 Cubic inch NASCAR engines. They're run for a 20-minute cam break-in using light valve springs, then we swap to the triple springs with over 300 pounds of seat pressure before doing the dyno run. The engine has at least 2 hours of loaded run time before it ever gets bolted into the car, and it's worn out in less than 1,000 miles of operation.

The originator of this thread is asking about break-in on a 305, an engine that's notorious for wearing out cams. Before I got into race engine building, I made a lot of bucks replacing 305 camshafts, usually caused by oil coking around the EGR passages, locking up the pushrod on #6 cylinder exhaust, and wearing out the cam lobe. Running a short time at no-load at 2,000 RPM does not hurt a modern set of rings, especially with a diamond-honed cylinder wall surface.
Jerry

I think we are all pretty much in agreement, we are talking about two different worlds of engines.

An exotic racing engine built to last 1000 mi is a far different creature than an antique stock GM truck engine built to last 100,000+ miles. So are newer OHC engines in new cars, but this forum is mostly about antiques.

One thing I don't understand though is that a low tension ring would require less load than a high tension one for breakin?

It depends on cylinder wal finish. Most modern machine shops use diamond hone stones in a Sunnen CK-10 or a similar type machine to fit the pistons, and a low-tension ring requires very little compression pressure to seat it properly against the cylinder wall surface. The surface finish is almost perfectly smooth, and the ring relies on the compression/combustion pressure to seat it against the cylinder wall. A conventional crosshatch cylinder wall finish is far too rough to work with a low-tension ring. The cylinder wall roughness necessary to seat a conventional ring will damage the surface of a low-tension ring, and result in rapid wear, and/or excessive blowby and short ring life. Since the 305 will probably get the newer ring design on a rebuild, he should be sure the surface of the cylinder wall is compatible with the rings it's getting. On the few street engines I build now, I use Hypereutectic pistons, smooth cylinder wall finish, and low-tension rings. On the race engines, I use file-fit Total Seal rings, with the ring end gap matched to the fuel the engine will run. Alcohol burners get a much tighter ring gap than gas engines, because the combustion temperature is lower, and the ring grows less due to heat. The alky engines are mostly for drag racing, and don't run more than a minute or two at a time, also.
Jerry

according to the specs of my 305 V-6, the cam is bathed in oil every time it rotates. The can "dips" through a level of oil as it rotates. Are other engine like this?

Jake

No,I think that V-6 GMC is in a class by itself-it is kind of industrial-strength in every way, meant to run hard & slow.Brin

Yup, there's no oil trough for typical single-cam OHV engines. I've always heard to throw oil at the cam for 20 minutes in a typical 6 or bent-8 application.

Hotrod- I thought that low-tension rings had poorer oil control. I suppose there are factory low tension and racing/aftermarket low tension, right?? And I've only heard about different gaps for hypuer pistons vs other pistons vs NOS. I guess the alky burners wouldn't expand rings as much.... makes sense.

I've got an oil consumption problem with my 235 running total seal moly rings. Its bored .060, zero decked, cast pistons. Rings were gapped (from factory) .020" top, .013" second. Total Seal had to custom make them for me. The engine burns oil when warm. Most noticable after sitting at stoplights or idling. Any idea whats going on? Valves or rings?? Shop said they've never had oil control problem with total seals, unless it was a low-tension set they use for drag-racing. My engine has 3K miles on it, runs well, good power & response but burns oil. Help!!

thanks

chip

I assume you checked the ring gaps on assembly? Those specs sound about right for the 235 bore size. Total Seal rings have a habit of being rough on cylinder walls if they're run on a street engine for extended mileage, resulting in barrel-shaped cylinders with more wear in the middle than at the top. That's why I don't run them on the street. The low-mileage race engines never get a chance to run long enough for much cylinder wear, something usually tears up long before we wear out the cylinders.

I'd look at valve guide seals first. It's been long enough since I was into a 235 that I don't remember what the stock guide seal setup is, but on most of my street engines, I use the umbrella-type seals that ride the valve stems and deflect oil from the top of the guide. If yo use that type, don't use the o-ring and sheet metal deflector that is the usual type of assembly found on Chevy from the factory. It's possible to run the valve guide too dry, resulting in rapid wear of the guide. A tiny bit of oil should be allowed to run down the guide to keep it lubed. "Positive" valve seals, the ones that clamp on top of the guide with a spring, also have a habit of starving the guide of lubrication. I only use them if there's a clearance problem with multiple valve springs.

It's possible for oil to be lost down the exhaust guide, and be burned by the exhaust system, and never show up as fouled spark plugs. Be sure to check both intake and exhaust for correct stem-to-guide clearance, and correct guide sealing.

BTW, what weight oil are you using? Also, what about piston skirt clearance, and cylinder finish when the pistons were fitted? Cast pistons on that engine should have been fitted with about .0025" clearance, somewhat tighter if you're using hypereutectic pistons, which don't expand as much when they reach runnung temperature.
Jerry

Jeebus, I was gone for the weekend and look how much attention this topic gets! I can see wy though, as this is one of the most widest ranged opinionated problems with breaking in a motor (I hope you get what I jsut said). Anyway, I appreciate all the replies, butI think I know what I am going to do. I have heard 2 people mention doing this, and that what I feel would be easiest.

I think I will run the truck at different speeds instead of just going at an even speed. I will do that for a certain amount of miles, then change the oil, drive it easy for around 500 miles, then change the oil again, then call it good.

So, would you people approve of that idea? all I am buying are the rods bearings, main bearings, and rings (not counting all the gaskets, etc.). I am using the same Crank, Cam, Lifters, Push rods, as they are all in good shape, and have barely any where on them (almost new).

Well, let me know what you think thanks for the help guys!

- Shane
[email protected]

Are you going to re-ring it without reboring? If there's less than .005" taper wear in the cylinders, that's OK, but expect a very short-life rebuild if there's more. Use a button-type cylinder glaze breaker, followed by a thorough scrubbing with Tide and hot water to clean up the honing residue. I wore out a set of rings on one-cross-country trip from California to Tennessee, with what I thought were well-cleaned cylinders!
Jerry

AS LONG AS THE EXISTING CAMSHAFT MATCHES YOUR APPLICATION.

That hits on something I'm seeing:

Blue smoke out of pipes, but no oil fouling on plugs: They look great (at least when I checked them last, I'll recheck and repost). Have positive umbrellas on intakes, o-rings on exhaust. So you think its likely in the cyl head and not a ring problem? The engine has fentons, and its smoking the same out of both sides, 1-3 and 4-6. The pistons were fitted too-tight and an oil pump failure caused a re-build. Total seal rings were used and the cyls honed for about .003 clearance. The cyl finish was very smooth, cross hatched but smooth from shop. Cast badger pistons from patrick's of AZ were barely scuffed by the tight clearance. Compression is good, gas mileage is decent. Castrol 30 wt oil. Everything in head is within spec. Will recheck and repost.

What do I need to look at to determine source of oil consumption?

Sorry to hijack post, but my 235 is still fighting me.


chip

Look for excessive exhaust valve stem clearance, and bronze-line the guides, or replace if necessary. I like to use the umbrella seals on both intake and exhaust, and eliminate the steel cap and o-ring under the keeper. If you just add an umbrella seal, you'll probably keep all the oil off the guide, and wear it out.

I've been able to check stem clearance without removing the head in some cases. Be sure the piston is at TDC, to avoid dropping a valve into the cylinder, and remove the valve spring. If you can get any noticeable wobble of the stem in the guide at the top, it's probably too worn to prevent oil consumption. Lots less work to do it that way, than pulling the head and doing a full teardown!
Jerry

Chip, Maybe I can help you diagnose where the problem is, because I have done this a time or ten in the past.

The first thing I would check is, if you have a vacuum booster above your fuel pump. If you do this could easily be the source of your problem. It is easy to check. Just disconnect the accessory vacuum line at the manifold and plug the opening at the manifold. Road test it a few miles and if the smoking stops then replace the fuel pump. It could be something as simple as a broken or porous diaphragm in the vacuum booster on the fuel pump. (You may need to road test for four or five miles to get rid of the old oil in the cylinders.

There is always the possibility of oil leaking into a cylinder(s) past the head gasket.

To check if it is coming in thru the valve guides is a little bit tricker but it can be done. What you need to do is cut off, or restrict the flow of oil to the lifters, (Yes, your engine can run for at least an hour without the oil going to the lifters)(Just remember to hook it all back up correctly after the test), If you have the "external oil line, as it seems many Stovebolts end up with, then this is simple. but if your oiling is thru and around the head bolt you need to figure out which bolt it is and change it out for one of the others (this won't completely shut of the oil but will restrict it enough to see if the smoking slows down when you test run it.

Another thought that comes to mind is- Don't Chrome Moly rings take longer to "break in" and during this time they will burn a bit of oil? (I could be wrong on this, so I would best refer it ot someone like Jerry.)

Shane,
What you appear to be doing is not rebuilding an engine but reconditioning it. A rebuild would include checking all clearances and having the head, block,pistons, rods, etc. reconditioned or new. Nothing wrong in reconditioning an engine, as long as you know and realize the pit-falls to look for. (which there are many.) If you can see wear marks on the rings, pistons or cylinders, you could have problems. If you don't scuff up the cylinders with a good honing the rings will probably never seat in correctly. If in doubt take your engine to a reputable machinist and have him check it out completely (might be the best money you ever spent).

As to the break in of a "new or new-rebuilt" engine, Set the timing etc. as close as possible. Start the engine and let it get to operating temp., about 10-20 minutes depending on your cooling system. During this time, run the engine at about a 25 mph (around 2,000-2,500 rpm) fast idle. Look for leaks, check the radiator, etc..(The reason for this warm up period is to assure adequate initial lubrication for cam, lifters, rockers, piston rings, pistons and cylinders. In other words, to allow the entire engine to become well lubricated.) Then take it on the road to break it in right- get it up to 30 MPH and accelerate to about 50 MPH, then let off the throttle and let it get back down to 30 MPH. Do this at least ten times. Take it back home and you're set to go, just avoid any sustained high speed driving for the first 100 miles. After that, drive it like you will always drive it and it will respond accordingly.

Good points, Oly! I'd forgotten about the vacuum booster pumps! If it's a later model with a PCV valve, that's another possibility. If it's stuck open, it will draw enough oil out of the crakkcase to smoke, and use oil.
Jerry

I don't know Jerry, he may have a PVC valve, since it is a 235 I wouldn't think so, but I seem to recall it was a 62 model. One other possibility that I thought of was maybe he is getting the smoke from the oil bath breather being to full or leaking.

I didn't include the possibilities for a V-8 or Mechanical superchargers or turbochargers , because I didn't figure Chip had gotten to that stage yet-LOL. Give Chip time and he will be there!!!

Engine is a '60 235 with '54 head. New style rockers, crimped feedtube, no external or internal lines, no special headbolts. Plenty of oil to rockers. No booster fuel pump. No PCV, just a vented oil fill and road draft tube. Shop says the guides, etc are within spec. Manley valves have 15K on them, hardened seats, new springs.

Everything in engine is new. Holley 4bbl 390 carb, clifford water heat intake, fentons, M4F solid lift cam, tubular pushrods. Head shaved .040", block zero decked, new .060" flattop pistons, total seal rings, recon rods, '54 crank cut 10/10, melling oil pump, NOS '60 "solid" pickup, '57 oil pan baffled, petronix conversion, recurved stock dist, bottom end balanced & blueprinted during assembly.

Runs great. Smokes like its got 200K miles on it. :o

Luckily, as far as I can tell, there are only 8 or 9 ways that oil can get into the combustion chamber and fewer then that on your 235. From what you have related I narrow that down to "2" ways for this to happen. A broken ring(s) or valve guides/seals. (You could have the rocker shaft on upside down, but I doubt that. That would possibly give to much oil to the valves.)

You said in a previous post that "The engine burns oil when warm. Most noticable after sitting at stoplights or idling.". This to me sounds like valve guides/seals. If, when you first start it up after it has been sitting fo a long period, it smokes profusely, then it is nearly always that it is valve guides/seals. A compression check will tell if it is the rings, which I doubt, unless for some reason they are not seating in properly.

One other thought is that the ring gaps are all lined up, but I don't this is the case. You did off-set the ring gaps, right?- RIGHT!!!

Well, I am not worried about the cylinders, as the motor had been recently rebuilt. My Mom had driven it once, and the heater core hose broke under the hood, and she drove it home and over heated it. I tore down the motor and had a friend (diesel mechanic) help me, and we found that some valves were burnt, and rod bearings needed replacing. I dropped the block, heads, crank, and cam off at Clackamas Auto Parts to have them clean the block, and have the heads done. They are also going to hone the cylinders out. And if needed, polish the crank.

As far as I know, everything is in good, barely worn, condition. Thanks for all the more replies people. I re-read my earlier post, and almost didnt understand what I wrote, I wonder if its the same with this one???

- Shane
[email protected]

Hey Chevy,

Learn from me, have the shop add new valve stem seals and guides if needed. Burning oil stinks! You can blow a bunch of money on heads, but its worth it.

Yes, stagger the ring gaps