New liners, rings, cams - best running in procedure?

[fergus]

Totally rebuilt engine. New cams, springs, liners, pistons, rings, all bearings, etc.

Given the potentially opposing views on getting rings to seat versus minimising load on cam lobes, what is the collective PH wisdom in terms of running in a new engine (after cranking for OP, setting initial timing, etc, etc).

Let it "fast idle" (2-3k rpm) for 20 mins to let the cams bed in, or take it straight out and give it full throttle followed by a quick lift several times to help bed in the rings and get rid of any high spots, etc?

[fergus]

McVities said:

Could you not bed in the rings on the old set of cams and lifters, then swap over to the new stuff?

An option, but the lash setup for the old and new cams, and also timing, is completely different, so a bit of a pain to swap things over....

I was thinking of removing the inner valve springs to remove some of the spring seat pressures to give the lobes an easier time.

Thanks for the suggestions so far.

PS i've been recommended not to run flat tappet cams (i.e. bucket and shims) on synthetic oil by the cam designer as they need ZDDP (or equivalent) to protect against potential follower scuffing (there is no DLC or equivalent hardening on the top of the followers)

[fergus]

Max_Torque said:

How radical is the cam profile you are needing to bed in?

The issue with slow running and extreme cams is that at low speed, the valve inertia is low, and as you'll have "heavy" springs to get the valve closed quickly, at peak lift and slow speed there is time for the oil film to get squeezed out the gap between cam and lifter, leading to scuffing. (at high speed everything is slamming open at speed and so the valve spring load is busy getting used to decelerate the valve at peak lift, not pushing into the top of the cam lobe)

Unless you are running something truly radical, like say a lofting profile, i've never had an issue with a short 10 to 15m fast zero load run (say 3krpm) then get the engine under some load to start other components bedding down)

Not crazy.

Engine is a 1969 2 litre Alfa Nord engine, and will be running 12.7mm inlet @ 261 degrees duration (0.05" lift), with a "modern" profile, i.e. the flank accelerates the valve very quickly and the cam has a relatively "broad" nose. The exhaust is 11.7mm lift with 247 degrees duration.

Thanks for the advice. I think I'll give it 10 mins at 3k rpm, then take it for a drive to get the rings bedded. Red line will be hard limited at 7k, so will limit the running in to say 4k for 300 miles or so (on 40w mineral oil), then swap to something better.