Rebuilt motor/new cam fire up Q's

[southernspeed]

I build a lot of bike engines and have done a few car ones too and always start them up, let them gently get up to working temp while doing the timing etc then let them cool off before a long running in period.
I'm just about (well...soon) to put this TBI motor in my truck. Cam manufacturers say to fire it up and run it at at least 2000rpm for half an hour to bed the cam in. I hate the idea of this.
So I want your opinions. Who has not followed this procedure and not had any problems...or has had problems.
I think I'd rather risk my cam than my crank or bores! What do y'all think?

 

[ryoken]

i generally run em a tad lower, 1500 to 1800... for about 15 min... never had a prob with a bottom end, etc.. don't forget to prime your oil....

 

[79Stomper]

I did this on mine during last engine swap. Ran it for 20 min at about 2000 rpms, Got about 10 minutes into it and caught on fire. This was due to my plug wire contacting the headers and igniting my wiring on right side of engine. So far no problems running it only the 10 minutes and have put roughly 6000 or so miles on it since engine was replaced. Cam I will be doing next week will get the full break in period though. Place some fans in front of radiator to help with air flow to keep engine cool during break in.

 

[dyeager535]

Why would the crank or bores have problems?

The crank doesn't ride metal to metal like the lifters do, thus, no issue with heat treating.

The bores don't really ride metal to metal either technically as I understand it, since the rings are coated with something. Someone can clarify that probably. Besides, the rings are "springy" and can accomodate the different bore size based on expansion/contraction. The pistons don't expand at the same rate as the cylinder bores, so thats something beyond our control.

There is very little difference between initial firing and letting a vehicle sit a week then starting it, except the heat generated by the extra friction, and the heat treatment of the cam and lifters. If it were a problem doing it the 2000RPM/15 minute way, it would have changed.

IMO if the piston rings don't seat immediately, you more than likely have a real problem, even if GM and others say that it may take many, many miles in some cases for them to seat. Never heard of anyone have a new smoking engine "clear up" with additional run time.

The break in process for roller cam motors is pretty much nothing. Fire it up and go, although they still say take it easy for the first few hundred miles.

 

[southernspeed]

With modern meterials your right..sort of. I build a lot of Harley engines. If you treat them right when new they'll last forever. Start i up on a new bore and treat it hard and the bores will b scored to hell in no time. I've rebored several after only a few hundred miles use because the customer thought that once he was out of my street he could go and race hi mates!!

With modern oils it takes a good 500 miles to bed a set of rings in.
But I don't know what is going on with a cam 'bedding in'...hence the question.

 

[pauly383]

Last time I put one together it was lots of assembly lube , did the valve covers last and poured the engine oil in over the valvetrain , did the 2000 rpm thing and had no problems . I don't know the guy anymore , but I am sure that engine is still in the Malibu I put it in somewhere in America

 

[dyeager535]

Why do you think it takes 500 miles? I'm not saying it doesn't, but I'd expect oil smoke or contaminated oil to be a byproduct of un-seated rings, and I never hear of this problem. I know mine had no problems, from initial firing.

The procedure for how to treat the new engine IS specific for a few hundred miles, low speed, low load, etc., but that isn't initial break-in, as part of the 20 minute deal. With no load on the engine (park/neutral) it really isn't working it's internals hard at all.

Cam rides on bearings just like the crank and rods, no metal to metal contact, so no "seating" or "bedding" required. It's solely for the heat treatment/break in of the cam lobes for flat tappet lifters...camshaft lobes are NOT flat (they are angled) and the lifter actually rotates as the cam turns...if the cam and/or lifter is soft, you will either destroy the lifter, or the cam lobe will go flat, or both.

 

[southernspeed]

Just from experience and stuff learnt in the trade frm other peoples experiences. Talking to oil companies and engine parts manufacturers. Up until the fairly recent introduction of 'hone only' reboring, bores were very cours (microscopically speaking) and it always seemed to take a while to get them smooth and sealed. Plus there is just the tightness of a new bore and the heat build up and related expansion of the piston. I've seen many piston skirts that have 'picked up' on th skirt due to too greater expansion(something we've had a lot of trouble with on engines that people use for racing but weren't built for it with xtra clearance on the bores). Cast rings bed in much faster and run cooler at first than moly rings too.

Or maybe I'm just old fashioned and it's a bit of a British thang!!

 

[dyeager535]

No offense, but you brits are a bit more traditional than we are.

Seriously, that is probably where some of our differing opinions and info comes from. Engine break in period has been done this way for I don't know how many years, and with the increase of technology, break in is much less important than it used to be, at least as I understand it. The bore finish is better, clearances are more precise and even, the metals/alloys themselves are better, etc.

Look at all the new vehicles coming off the lot with 10 miles on them, do you think the new owners follow engine break in procedures on them?

 

[ryoken]

Cast rings bed in much faster and run cooler at first than moly rings too.

thats always been my understanding.. tho apparently its become less of a big deal in recent years with ring technology.

here's a pretty good article i dug up awhile back...

http://www.aa1car.com/library/2003/eb90329.htm

i understand your train of thought. but i think the cams survivability is more important for initial fireup. your still bringing it up to temp, just quicker..

i think the important thing is not romping the heck out of it. i'll generally run a motor for quite sometime before i check total timing for that reason.. usually do my break-in for 15 to 20. let it cool off, check fluids, etc, fire it up, run it at idle to make any fuel adjustments, check base timing. then after another 20 mins of idle and light throttle, i'll bring it up and check total timing...

 

[southernspeed]

No offense, but you brits are a bit more traditional than we are.

Non taken! I hear what y'all are saying....that's why I asked after all!
I'll put cotten wool in my ears and do it the proper way then!!!
Thanks for the input!

 

[ntsqd]

There is very little difference between initial firing and letting a vehicle sit a week then starting it, except the heat generated by the extra friction, and the heat treatment of the cam and lifters. If it were a problem doing it the 2000RPM/15 minute way, it would have changed.

There is one significant difference addressed in the thread later than this quote. The critical lobe to lifter wear pattern has not yet been established. They burnish each other during the break-in process and actually get more tolerent of cold starts. The higher the seat pressure of the springs the more this is important. When the seat pressure gets really high there "Break-in" springs that are used first. Then after the wear pattern has been established the correct springs are installed.

At the engine shop I do fab work for they always vary the engine speed during break-in. A couple minutes at 1500 rpm, then a couple at 2200, then a couple at 1800 etc. They follow no specific pattern. Two sets of 15 mins each, with a cool down period in btwn. If a mechanical cam with hot lash specs, they'll run the valves after the first session. The idea is that the oil gets tossed different places & times at different speeds, so you want to make sure everything that is splash oiled (like lifters of most cam-in-block engines) gets oil.

 

[southernspeed]

Thanks! You've all convinced me now! Think I'll do it in a couple of sessions instead of one 1/2 hour one....think I'd be happier with that.Thanks all