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Running in rebuilt 2500 engine with new camshaft


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Hi again all, it's been a while 🙂

I'm slowly creeping towards the end of a full rebuild of my 2500 engine. The block has been re-bored, with new pistons at +20 thou, new bearing shells at all +10 thou, new rings, lifters, timing gear etc, etc. The original camshaft has been reground to something close to stock 307621 profile. Everything else about the engine and head is standard.

When it's finally ready to go, what's the best running in procedure? The camshaft came with instructions to run in at 2000RPM for 20 minutes, but is this also acceptable to bed in the new rings etc? I always thought it wasn't good for new rings to be run for a long period at a steady RPM.



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Your first concern is for the cam followers, always under the most stress but especially as they meet the cams for the first time.  New followers? Cam lube?   Yes, around 2K but vary the engine speed, you don't want harmonics to limit oil supply.    About 20 minutes will be right.

Then drive the car, but in a way that promotes the wearing in, without glazing, of the rings.   find a roadway where you can accelerate in as high a gear as possible without 'bogging', up to 4-5K.  Then foot off throttle and coast back down to 1500-2K with the car in gear.    The first forces the rings against the walls, the second maximises the vacuum in the chambers and draws oil up onto the rings.      Repeat  and repeat this sequence, where ever traffic and road permit, until you have done 200-500 miles.  Then in the workshop, with the engine cold, loosen and retorque the head nuts, in sequence.  Change the oil.

Job done!


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