Breaking in a freshly rebuilt 258 - JeepForum.com
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  • 3 Post By whollsee
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post #1 of 11 Old 05-14-2019, 10:51 PM Thread Starter
Renegade82
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Breaking in a freshly rebuilt 258

So I'll soon be to the point of firing up my newly rebuilt 258. The block and all the internals were redone. New pistons, rods, rings, bearings, cam, ground crank, etc. The engine shop said to run it at 15-1800 rpm for around 20 minutes. I'll spin the oil pump within hours prior to firing it up to get things coated and passages filled.

My concern is I don't know that it will be ready to run correctly right off the bat, since the timing will be off and the carb may not agree. Now the carb is still as it was prior to the teardown but I can't really set the timing since the revs will be up. The timing is set to 0 and I'll set the rotor to #1 cylinder when I drop in the dizzy.

Is this a case of once it starts get it to the 15-1800 range and let it run no matter how ****ty it may be? Looking for some guidance to ease my concerns about this crucial, one shot time frame. Any insight from you engine guru's would be appreciated. Thanks in advance.


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post #2 of 11 Old 05-15-2019, 12:32 AM
whollsee
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It's all about getting oil to the cam and keeping it there for an uninterrupted 20 mins. Start and get it straight to 1800 [or even 2000] and slowly vary up and down between 1800 and 2000 rpms. Don't fart around - sort timing and carb tuning after the break-in. My timing was real rough and weber 38 was way off optimal [odd backfire or two to say the least!!!] at start-up but smoothed right out at target revs . Still try and make sure you are on #1 at TDC on compression stroke. Prime the carb plenty - which carb do you have? With all the new/refurbed bits and tolerances there will be a lot of stinky smoke. Your engine may get hotter than usual too and I had a hose on standby to spritz the radiator. Could be good to have a an offsider on hand to assist.

Anyway don't take my word for it see what others have to say. Comp Cams have a decent break-in guide online that may be helpful.

Cheers!
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post #3 of 11 Old 05-15-2019, 05:05 AM
keith460
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Quote:
Originally Posted by whollsee View Post
Still try and make sure you are on #1 at TDC on compression stroke. Prime the carb plenty...

Renegade82, when I first fired up my rebuilt 258, I primed the oil pump until the drill I was using was bogging down due to the oil pressure internally. That part was good to go. However, putting the distributor back in I inadvertently got it 180 out of time because I hand cranked the engine with a wrench and had it in exhaust mode rather then TDC. Didn't even think about it until we started the engine and quickly realized the mistake when flames backfired through the carb.
We stopped immediately and fixed that issue and started the engine up based on 0 timing. No problems there and then brought the rpm up to about 1700-2000rpm and let it run that way for about 15-20min. Used a timing light to see where the timing was and maybe made small adjustment to make sure it was high in advance.

During that run-in phase of the engine, we also discovered the power steering pump had an issue with a check valve I apparently installed backwards so the pump was now leaking fluid. Didn't matter, we kept the engine running regardless because that part was more important than a leaking power steering pump. That's what rags are for.
We also had my two sons at the ready with a fire extinguisher and the other had the garden hose at the ready in case of a fire.
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post #4 of 11 Old 05-15-2019, 05:23 AM
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You can set your timing light up prior to starting it. Once the engine fires up, you've got it to your target break-in speed and everything looks ok, use the light and just twist the distributor around to at least 40* (preferably closer to 50*) for the duration of your break-in. That'll keep cylinder temps down and hopefully prevent any micro-welding between the rings, lands and cylinder walls.

Once you're done with your break-in, set the initial timing where you want, dial in the carb, etc.


Shawn
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post #5 of 11 Old 05-15-2019, 05:35 AM
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Quote:
Originally Posted by whollsee View Post
It's all about getting oil to the cam and keeping it there for an uninterrupted 20 mins. Start and get it straight to 1800 [or even 2000] and slowly vary up and down between 1800 and 2000 rpms. Don't fart around - sort timing and carb tuning after the break-in. My timing was real rough and weber 38 was way off optimal [odd backfire or two to say the least!!!] at start-up but smoothed right out at target revs . Still try and make sure you are on #1 at TDC on compression stroke. Prime the carb plenty - which carb do you have? With all the new/refurbed bits and tolerances there will be a lot of stinky smoke. Your engine may get hotter than usual too and I had a hose on standby to spritz the radiator. Could be good to have a an offsider on hand to assist.

Anyway don't take my word for it see what others have to say. Comp Cams have a decent break-in guide online that may be helpful.

Cheers!
Follow his advice. This is the best thing to do with your engine.
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post #6 of 11 Old 05-15-2019, 08:59 AM
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I have had a successful and non-successful brake in; let me share the latter and what I did to help the next one....

Long story short, the water pump was the wrong rotation and I wasn't pumping water. I ended up overheating and cracking the block during the brake-in.
  • Get an infrared thermometer, they are cheap on Amazon or harbor freight - when you are running, shoot the head temp front and back, and then the cylinders on the sides, the intake, and top and bottom of the radiator. It should all be about the same after a few minutes and the thermostat; any wild swings could indicate an issue
  • Find an old tachometer you can wire in to be in the engine bay; this way you don't have to run back and forth around to look in the cab
  • Do it outside; there's going to be fumes
  • Make sure you have plenty of fuel
  • Ask a friend to help; don't do it alone
  • Use a good break-in oil or additive
  • Don't forget to change your oil and filter after
  • Keep an extinguisher or hose handy

That's for cam break-in. For driving break-in and the rings (unless they are premium which seem to wear in during the cam break in), find a long open stretch of highway and pick a high gear like 3rd. Don't lug the engine, but get down to a low speed and accelerate up to high speed for that gear and then let off and coast back down to the initial low speed; do this 6 times. And then after that, vary your throttle inputs as you're driving (I like to pick a town with a lot of lights or traffic). Change your oil and filter again after 500 miles.
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post #7 of 11 Old 05-15-2019, 10:45 AM
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FYI-If the shop ran this engine for 20 minutes. They should have set the timing.
Ask them what the did, and didn't do........
LG
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post #8 of 11 Old 05-15-2019, 11:54 AM
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Renegade82,

Everyone has great advice and focus points about the "Break-In" procedure for 15-20 minutes 1500-2000 RPM.

But, what breaks-in? The cam needs to have the lifter seat (rough machine edges worn off) to the lobe, the rings need to wear to the microscopically out of round cylinders, everything else needs lubrication to keep from having metal to metal contact.

My belief is you need to get oil and pressure immediately eliminating any metal to metal contact after the assembly lube has been removed. The Camshaft-lifter break-in procedure is the most important issue for initial start up. IMHO

Good luck with this you will be pleased.
UTN
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post #9 of 11 Old 05-15-2019, 12:02 PM Thread Starter
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Thanks guys, all great advice. This is the kind of insight I'm looking for, keep it coming.
It is a Comp Cam so I'll check out their site. I will hook up the timing light prior to starting it so I can at least keep tabs on where it is, then tweak later. The shop only rebuilt the block and it's internals, I only gave them the block and the two manifolds to clean up (shot blast), so they weren't capable of running it. They did spin the oil pump to verify everything was flowing oil, checked pressure.
FYI, I put a list of what the shop did to it on the last page of my build thread, parts and labor.

UTN - Next on the list is the Redline dizzy but I didn't want to change that now before I got it back up and running.
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post #10 of 11 Old 05-15-2019, 09:51 PM
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Doesn't all apply to your situation...

http://www.compcams.com/Instructions/Files/145.pdf

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post #11 of 11 Old 05-15-2019, 10:42 PM Thread Starter
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I just noticed the papers I got back from the shop are from Comp Cams and they included the file you posted above. And by the way, you ask earlier about the carb. It's a genuine Weber 38.

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