Rev Limit A+ Cranks.
Turbo Mini Forums

I've realised that my engine can now rev until it explodes.

What point do you reckon a realistic rev limit is? I've never broken a crank on about 20 A/+ series engines BUT they never revved that much. I used the "It sounds like it's going to explode" choice. I thought I'd ask the experts.

I thought 6000 as a useable range and rev cut at 6500, am I selling my bottom end short? (Usual crank std/std wedged balanced, lightened/balanced rods).

Stu

Bugger off, I'm getting there.

I guess it all depend on the power output of the engine. I'm running a 1450cc motor with a stroked A+ crank and coopers rods all held in with ARP bolts, everything is balanced up to the nines and I haven?t had any problems revving the thing to 7000-7500 on track days and 6000-6500 on the way to work and back daily.
The motor has had the same crank for 14 years now and every year it gets a strip and inspect over winter and all looks well.
So if it's all done properly in the first place and after hugging a VERY large piece of wood for luck you might be surprised how long a crank will last.
Oh and a good oil pump and frequent oil changes help no end.

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

I would have thought a stoked crank was less stiff and vibrated more, hence more prone to snapping/fatigue. (As a result of applied force, not balance) I would really be interested in power results from a stroked vs standard turbo engine.

But that's going off on a tangent.

Bugger off, I'm getting there.

Doodmeister:

says it all, ballance is the key +

and if you have a crank with Rolled filleted radius machined correctley

all the cranks i have seen snapped are the results of lack of lubrication or none, lack of regular oil changes, no ballancing after lightend parts fitted,

and one crank where the machining on the crank web radius was done wrong.
all standard strokers

they are suprisingley strong
even in standard form untreated

my next project is going to be a stroked turbo engine say 84 or 86 mm stroke havent made my mind up yet

will keep you posted Hedgemonkey

Maybe not a technical solution but.....

I once was unfortunate enough to slide my road mini into a large kerb in snow. The shell was knackered so I stripped it and kept all the good bits, however I then had no car (back in the days of one car.....)

A friend of mine jumped to the rescue with an F reg MG Metro that had been his sisters, parked up for 8 months with brake problems, it was still taxed and tested for 2 months, bargain price of free. An investigation into the front brakes revealed 7 out of 8 of the caliper pistons were seized solid, some second hand calipers I had cured that, and the Metro provided acceptable transport for nearly two weeks. It then blew the head gasket, which it had also done approximately 18 months ago on my mates sister. So as usual sunday afternoon halfords run, replaced the head gasket and it seemed all OK. For all of 2 days, when it promptly blew the head gasket again. This time I got hold of another head, had it skimmed and did the head gasket again. By this point I was getting quite quick at it. This head gasket lasted 10 days at which point, thoroughly pissed off, I took the Metro to the Mini specialists I worked at, to remove the head, any other useful stuff, and scrap the rest.
However before I gave it the dignity of the crusher, I decided to do a little endurance test, partially out of spite to the damn thing. It would run on 4 when off load, but overheat quickly and lose water. So we parked it outside the unit, put a brick on the throttle pedal and set the stopwatch going. It was revving to an indicated 8,000 RPM on the gauge, the limiting factor being valve bounce. It sat there doing this for nearly 20 mins, before finally we got fed up with the bloody noise and turned it off.

So maybe the std cranks are tougher than they get credit for????

I know some miglia drivers who have put in a std metro crank, not balanced and raced at 9000 rpm without problems

Team Racing

just goes to show jim that leyland did produce an excellent crank

excellent?

Three bearings and the weight of a boat anchor isn't excellent in my book!

Well made maybe!

Jims right! Miglias 9000rpm and the old metro challenge engines 8800rpm with std turbo cranks.

http://www.avonbar.com

Team Racing

ive had come to the conclusion that the a+ cranks are bloody good also, my 1380 has had one in for years and is still in tiptop cond, reving to 6500rpm bags and bags of times.

i still belive a lot of people over engineer there engines for the sake of it. my local engineer shop who makes race engines ranging from fomular fords, vauxhalls and audis to rover k series said to me years ago keep the crank standard for road use with revs upto 6500rpm any thing over that then start tweeking.

he also said if you want to lighten anything then change the flywheel but leave the rest alone as it wont need balancing. as you wont see or here and difference untill after at least 6500rpm to 7 k continious use.

obviously if the crank was tweek or rods then this would need doing but he recon there wasnt any point.
but thinking about i havekept to his word for 8 years now with no probs at all and have saved heaps of cash in the process.

he also said that all balancing machines were different plus the operaters as well.

eg you could send all your stuff to place for balancing they would takes bits of here and there and you could send it some were else and they would still end up taking bits of as well.

like anything else there is always inconsistancies in the engineering trade.

but having said all that my standard grank will now being placed under 1380 turbo power now we will see how she stands up to the stresses and strains of 12psi.

always looking for them bigger bunches of bannanas

-person opinion-
if you're using all the parts it left factory with - no mix and match- then the factory balnce will suffice , if not get it balanced .
different firms balance to different limits but is there evidence to show balancing is bad ?
As the engine heats up everything will distort to some degree thats why race engines should be balanced at as near to operating temp as possible
As a dyno operator i know the a series produces max power from 5500 - to about 6800 (road to full race cams ), ok power may continue on further -but at a loss- the main reason for reving higher is so next gearchange keeps you around that peak , meaning with most gearkit ratios, and race use 8000rpm-(when did you last get your rev counter checked?)- is about all you need
increased cycles (rpm )and power decreases reliabillity , most road engines should take 7000 ok ,reducing to 6500 can only make it last longer and with most turbos producing massive torque figures from 4000 rpm it should keep it in the power band and reliable
The standard crank is a tough item but has its life expectancy, do you know the rev or abuse history of your crank ?

Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe.

Dave also told me to balance the flywheel assebly WITH a clutchplate in there. This makes perfect sense, but what happens when the clutch plate moves around? I guess it isn't heavy enough to cause any concern??

My homemade

It has been wedged and cleaned up. Takes some time, but wedging is a good idea, although not neccessary on a roady. Homemade head as well as a matter of fact.

Edited by Vegard on 15th Jul, 2005.

I have had a home wedged crank (balanced) reved regularly to 9000RPM never broke it and as far as i know it is still going strong

i think its swindon race engines do the high temp balance