Camshaft run in procedure and cam wear

The factory recommended break-in on virtually any vehicle I can think of is essentially the same, and always has been for as long as I can remember. The break in in the owners manual for cars of the 60's, for example, was pretty much the same as the break in for a current car. We can all say, "I do it "X" way and have never had a problem." This applies to the folks who strictly break in by the manual, those who break in using the "drive it like you stole it method" and those (probably most people) who sort of follow something in between. The reality is, in most cases, for the way most people drive and for the length of time they keep a vehicle, it doesn't really matter much.

One thing to consider about a new vehicle as opposed to rebuilding an engine/installing it back in a used vehicle is that in a new vehicle, ALL the various assemblies have to "get used" to each other - that includes everything from wheels/bearings to drive shafts/chains to brakes to transmissions/differential gears, etc, etc, etc.

Engine break in is simply a function of load/coast intensity. The time it takes to "break in" is a function of the intensity. If you follow the manual, the time is lengthy because the intensity is low. That is as it should be for a street vehicle for the reason mentioned earlier - essentially you can't legally and safely do it any other way on public roads. On a dyno or at a track, you can; but who takes their new Buick to the local shop or to the track immediately after purchase?

Again, the "break in" of a motor is simply a function of the time it takes to provide the necessary 'wear" to do the job. If the wear to accomplish that is done in 20 minutes on a dyno or in 1000+ miles on the road, the result is the same. The critical part is the acceleration/deceleration loads placed on the piston rings/cylinder walls. That's why cruising down the interstate in your brand new vehicle is the worst way to break it in.

In discussing engine break-in here the conversation has generally been about how “we” will operate the vehicle, but what about the manufacturer, how have "they" already operated the vehicle prior to us receiving it?

The following is clearly off-subject as it has nothing to do with a Norton, but certainly relates to how a new engine is initially operated by the manufacturer, and therefore thought it might be of passing interest here. The year was 1991 and I was visiting Japan on a work-related visit where our group had the occasion to visit a Nissan automobile manufacturing plant. The final part of our tour was to watch the new vehicles be driven off the production line onto rollers, be run through the gears, and then be driven away to the lot for shipment to where ever.

The production line at this juncture was a two lane affair, where 2 cars progressed side-by-side to separate roller test stations. I don’t recall the model of the cars being made at that moment in time, other than to note they were some small ubiquitous low output 4 cylinder stick shift model. The rollers provided significant load as the acceleration on the test station was by no means fast (seemed to me very similar to acceleration rate on the real road), and when the operator let off the throttle there was significant inertia that required strong braking to haul the speed down again.

With that background here is the test I observed. The cars were driven on to the rollers, a probe inserted into the tail pipe and the test commenced. Once the clutch was let out in 1st gear the engine was operated like it just left the Bonneville starting line - WOT in each gear with quick gear changes up to a speed of 135 kph (84 mph) in 4th gear, where the brakes were absolutely dynamited to haul the speed down to 90 kph (56 mph), the car quickly down-shifted into 3rd gear and instantly back to WOT, up to 135 kph, then hard braked back to a stop. At idle, emission numbers were checked, the tested cars driven off the rollers to the lot as 2 new cars were driven onto the roller test bed - about 60 seconds total cycle time/test. As every pair of vehicles left the test bay a large red display at the exit door, which counted the total number of vehicles manufactured at this site, increased by 2. It was well up in the millions at that point in time.

Bottom line - I was shocked to see how aggressive the factory tested their virgin vehicles right out of the shoot, and would never have dreamed that whatever a new owner might do to their vehicle would pale in comparison to what the factory had already exposed the vehicle to on their test bed. An eye-opener for me!

Fast Eddie said:

Glen, the Norton blurb talks about limiting the throttle to 1/3 opening. I’m not able to test this right now, but I’m pretty sure this’ll be in excess of the 2,500-3,000 cam break in range won’t it?

I’m thinking we might be crossing arguments here... the Comnoz cam break in comments never sugegsted red line runs.

Still seems to me that keeping a Cdo below 1/3 throttle would most likely constitute the kind of ‘normal use’ scenario that should lead to good cam break in?

Click to expand...

I was referring to MexicoMike's description of engine break-in using dyno.
That method included wide open throttle red line runs at the end.

Glen

I do tend to limit the RPM's a bit on a fresh motor but,

There is no reason other than heat buildup to limit hard use of a fresh motor, so no stop and go traffic or long WFO pulls up the pass for a while. Fresh motors do build heat fast.

Other than heat- If everything is right then it will handle whatever you can give it.

If something is wrong, then babying it just puts off the inevitable.

I've never been quite as gentle as the Norton Handbook advises, but have mostly followed the max Rev intervals.
The only time Ive ever had a problem with break-in was about fifty years ago with a Honda 250 Dream and that did not involve a cam break in, it was just a top end rebuild.
I was 14 years old and had a bit of a weekend and evening business going doing top end rebuilds on some of the numerous realitively new Honda MCs in our area.

At about 15,000 miles these engines were already well down in compression , were often using oil and had smoke pouring out the exhaust.
I would lap the valves, light dry hone the bores and fit new rings. This worked to get the compression back, get rid of the exhaust smoke, plus get bikes another 10,000 miles down the road at which point they were truly worn out, time for a new one.People just accepted those mileages and were very happy with my cheapie rebuild that nearly doubled the life of the bike. We expect a lot more now and generally get it!

The Honda Dream owner called about a week after picking up his bike to say that it was smoking more than before the rebuild.
He was the type of rider who hardly touched the throttle and always short shifted.

We decided that he should leave the bike with me for the weekend. I didn't take anything apart, just took it next door and thrashed it in the Gravel pit and surrounding trails, all short rides with lots of cool down, lots of short bursts at full throttle in 1st gear, but no real high revs.

The smoking exhaust cleared up completely the first day.

Glen

I had the same Nissan experience when I visited the Sunderland factory in the 90's who were using the Glacier bearings, straight off the line into the test booth and pedal to the floor. When asked they explained that the accuracy of machining dimensionally and the higher surface finishes achieved meant the rough edges that needed the old running in cycles to remove had been eliminated. The big end bearings we supplied were bored to a 3 micron tolerance and had 7 bands each of 3 microns, they measured each big end journal and then selected the big end shells to give the required clearance. They explained that by controlling the clearance to microns they could produce a quieter and smoother engine.

Then we have Triumph who claim to build their engines to even closer tolerances than the big Japanese MC companies, yet they require this long and very gradual rpm limited break in.

Glen