So what is bad for a motor?

vanguard

vanguard

Well-Known Member
Joined
Oct 19, 2005
Location
Apex, NC
It seems like a dumb question, everybody "knows" that if you want a motor to last forever you just hum along at 55-70 mph and maintain it. (Let's ignore maintenance for this conversation.)

However, I got to thinking that maybe high rpms aren't so bad for a motor. Maybe the engine doesn't share my thoughts that touching 5k rpm means you're just removed 15 hours from the life of the motor. Maybe doing 30 mph in 5th gear is even more harmful.

I was talking to a very experienced wheeler/drag racer and he's convinced that hitting high rpm is good for a motor. He says if you just putt putt around it won't wear correctly and the day you ask it to perform it will break. This guy seems to think the same thing: http://www.mototuneusa.com/break_in_secrets.htm

So what do you think? What kills a motor? Lugging it, revving it, something else?
 
Yes
Lugging is bad, higher rev's than designed for is too. Too much heat, too little heat are a couple more. Viscosity break down. Improper break in. Poor oil filtration and or flow. mismatched performance mods as in valves, springs, cam, lifters, pistons, wrong fuel. Many things are bad.
 
As far as RPM range (this is what I have been taught over the years)....

Touching base with higher RPM's isn't a big deal as long as they're not sustained for a long time and there isn't a lot of mileage/wear on the engine. With higher mileage/wear the tolerances between moving parts aren't as tight as they used to be. Therefore the higher it's wound up the greater the chance of a moving part being "out of time/place" (at which point something bends/breaks/ or comes in contact with something it's not supposed to come in contact with). I've always drove in a RPM range where the engine feels it has adequate power.

I have also been told it's hard on an engine when you have it wound up high and completely let of the gas. Everything is wound up in one direction ( plus the momentum of your vehicle) - and then nothing. Kind of a reverse twisting effect..... (sorry about the description, don't know how else to put it)

Break ins... I've nursed it for the first 1000 or so, then drove it hard. Not towing, but open it up a little bit on an afternoon drive. Oil change right after, then drive normally for life of vehicle.

Things that kill engines other than poor maint/piss poor design....

Sustained high RPM - Xtra heat/friction

Lugging and Towing - It's making your engine work too hard.

How many high mileage Gasoline tow rigs do you see???? If you see one, it probably hasn't done much towing.
 
One thought to add/stir pot with.

A friend of mine who is in his 60s and has made a living building motors everywhere from NASCAR garages to NHRA drag cars to Monster trucks to spped boats swears break in is overrated.

He says obey normal rules for seating valves (vary RPMs) and do 1st oil change quick 200-300 miles as some machining debris may be in passages, but the flog the hell out of it.

His logic, if it does break, it was going to anyway, and you may have just found it during a warranty/replacement period.


Not sure if there is any truth there, but I respect his opinion immensly and I have seen him abide by his own logic so....
 
i know with the mazda 12a's and 13b rotors that if you putput along all the time it hurts the car. the rotors have to be drivin to get everything working rite. ive had one blow at 130k mostly b/c it came from a older man who babied it. my dads just blew last year at 240k. mostly b/c he keep it in good condition and ran it like it should. most engines need to be pushed every once in a while.
 
I've always been told the Break in is critical. Run it hard to start with. I'm no mechanic or engineer, so I couldn't tell you if it is better or not, just what I've been told pretty often.

But here's another trane of thought just for sh!ts and giggles.

how many blow engines have you seen from running high RPMs? now how many have you seen from low RPMs? :D

that may be over-simplified though.....
 
Get an ignition system with a rev. limiting set up, mine is set a couple of hundred below factory spec for my motor. Then you can let the limiter do its job.
 
I always built 'em, Ran 'em at 2500 for 15 min. after getting oil pressure to get the cam broke in right and drove 'em like I stole it. Check valve lash after 100 miles and retorque the head(s).

The only one I've had come unglued was a old air cooled 2.2l bug motor, poked and stroked. I turned it one too many time over 6 grand and hooked a follower in the case which killed the case, cam and bent a pushrod. Otherwise I'd get 75 to 100K out of big inch bug mills with huge cams, flow work on the heads, big carbs and massive advance lead (32~34 which is huge for a aircooled) Running them like a 2 stroke dirt bike.
 
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