13 replies to this topic

[pusb]

Without taking any notice of my speed I was going down the motorway in my old 850 today.

I looked down and noticed my rev counter was on 5000, I have no red line so I'm just concerned I may have damaged something?

5000 seems very high to me, and when I come to a stop off the motorway the oil pressure dropped right down to 30 and the engine sounded like it was going to cut out.

[Alex_B]

I believe the 850 shouldnt be taken up to 6000 rpm for sustained periods, something about the crankshaft being a bit weak in the 850.

I wouldnt imagine you have done any damage at 5k though! I regularly take my 998 up to 5500 without issue 

[Stu.]

My 850 doesn't have a tacho, but generally speaking I don't like going over 50 in fourth and wouldn't want to push the engine past 60 even on a motorway. She's a standard classic 850 and should be driven easy in the style it was designed for in my opinion.

I've considered fitting a tacho but I find listening to the engine in conjunction with the speedo is sufficient.

Following motorway driving or driving for periods in fourth at 50 - 60 my oil gauge drops low at idle but quickly goes back to normal.

Do you know roughly what your speed was, and how's the oil pressure and engine sound now it's cooled, or have you not been out again yet ?

[pusb]

Once I'd driven the mile or so off the motorway back home oil pressure returned to around 50 and the engine sounded fairly normal.

I think my speed was around 75mph. I will have to be more careful in future!

[lsto]

It won't have done any harm. The engine was worked for a bit therefore the oil got a bit hotter and thinned out which is why your pressure dropped. Remember its your engine and gearbox oil so it will thin out.

I wouldn't worry. Its a classic but its still just an engine. Its not like you was revving it to the limit. I seem to remember reading somewhere that the 850 lump is actually a better revving engine its bigger brothers, they can take more abuse too.

[Cooperman]

When I had an 850 as my daily driver, I used to cruise it at between 60 & 65 which was between 4100 & 4500 rpm in 4th. 5000 rpm in top was 73.5 mph which was about flat out on a level road with zero headwind. A lightly modified 850 with an improved head would cruise all day at 5000 rpm in 4th with no adverse effects.

In the gears when looking for best performance 6000 rpm was normally considered a safe max and the sustained crankshaft revs were around 6400 rpm, although it was not wise to hold this for long periods. It was not unusual for crankshaft failure to happen at sustained or regularly used 6500+ rpm.

Oil pressure will drop a bit, but that won't be a big problem so long as a top quality 20w50 mineral oil is used.

Too many people are afraid to rev an A-Series, but when they were current production units in all sorts of cars, they used to be revved to fairly high numbers all the time.

The really poor 850 crank was the original 'thin-tail' one, but they have virtually disappeared now (all broken).

[Stu.]

When I had an 850 as my daily driver, I used to cruise it at between 60 & 65 which was between 4100 & 4500 rpm in 4th. 5000 rpm in top was 73.5 mph which was about flat out on a level road with zero headwind. A lightly modified 850 with an improved head would cruise all day at 5000 rpm in 4th with no adverse effects.
In the gears when looking for best performance 6000 rpm was normally considered a safe max and the sustained crankshaft revs were around 6400 rpm, although it was not wise to hold this for long periods. It was not unusual for crankshaft failure to happen at sustained or regularly used 6500+ rpm.
Oil pressure will drop a bit, but that won't be a big problem so long as a top quality 20w50 mineral oil is used.
Too many people are afraid to rev an A-Series, but when they were current production units in all sorts of cars, they used to be revved to fairly high numbers all the time.
The really poor 850 crank was the original 'thin-tail' one, but they have virtually disappeared now (all broken).

I'll give her a little more oomph on the open roads in future then Cooperman. Thanks for that.

[Cooperman]

But in those days it was not unusual to have to fit a 'Gold Seal' BMC replacement engine at 50000 to 60000 miles from new, or do a re-build ones-self.

Still they are easy engines to re-condition.

Remember also, peak power is at about 5500 rpm (34 bhp) with peak torque at about 3000 rpm.

We used to reckon max speeds in the gears were 20, 40, 60 & 75 mph on the 850 and 30, 50, 70 & 88-ish with the original 997/998 Cooper.

[villa3]

Back in the 70s when Minis were nearly always peoples first car they were driven with no mercy,the engines are amazingly strong,. they just ask for oil and water.Minis love being driven hard,under reving and labouring the engine can do a lot of damage very quickly.

[Stu.]

How so ? How can normal driving without over reving damage the engine ?

[Cooperman]

Normal driving is fine, it's labouring at very low revs which causes the damage. With a 3-main-bearing crank there is a tendency for the crank to 'whip' when laboured and this will cause high wear rate on the bearings whilst also causing piston 'slap'. Keep the revs over about 1800 to 2000 and all will be fine.

 

I once drove a 997 Cooper flat out from Wales to London at 80 to 85 mph, before there was any speed limit on motorways and that is 5500 to 5700 rpm. It didn't seem to do it any harm and when a 998 Cooper was my road car I used to cruise at 75 to 80 all the time.

 

It's not the revs which cause the damage, it's poor servicing, bad quality/incorrect oil, lack of frequent oil changes and incorrect timing settings.

 

Go on, rev it up, you know you want to  .

[benbrown]

And here I am taking it nice and easy as to be careful! Glad to have read this now

[Cooperman]

Just think, when a person fits a 276 camshaft, it has peak power at 6100 rpm, so up-changes when wanting maximum performance, which is what one fits a hotter camshaft for, will be at around 6400 rpm.

A 998 will rev safely and comfortably to well over 6000 rpm at all times.

I rev my rally 'S' to around 7000 as it gives max. power at 6400 rpm.

The ancient A-Series engines all need to rev.

[mab01uk]

The most powerful high revving 850cc A-Series Mini engines were those built with special Longman short stroke steel cranks for the Special Saloon Racing Mini's in the 850 'Free-Formula' class back in the 1970's. The 850cc class was full of destroked /overbored 970 Cooper S engines usually running exotic 8-port heads and the like. -Quote- "the stroke's so short the pistons only quiver in the block!!"

Then along came the ultimate 850cc Mini.........
Mini 850cc BDA Engine
One engine of this type came about by accident, literally! A 1300 Ford BDA engine, fitted to a Mini gearbox, blew up and destroyed two cylinders. The two good cylinders were cut from the engine and used to produce a two cylinder engine by means of special blanking plates and crankshaft. At first the engine did not put out much power but when its problems were sorted it put out 115bhp, over 35bhp more than any engine of its size.
Gordon Allen's Mini 850cc BDA Engine
Unlike the other 850cc BDA mention above, this unit was a purposely designed two cylinder engine built for racing Minis. A specially manufactured alloy block and forged steel crank formed the basis of this engine. Bores were 85mm diameter and the stroke 74mm, giving it 848cc. A halved, standard Formula Atlantic BDA head with full size valves giving an 11.8:1 compression ratio was employed, and this was fed by a single 45DCOE Weber. The engine was mounted on a Mini transmission using an adaptor plate. Early versions of the engine gave an extra 20bhp over a standard racing 850cc A Series, this difference nearly doubled in the next 5 years. This 2 cylinder 850 BDA was a real winner for Peter Day once a few niggles were overcome and I remember made a great noise down the main straight at Brands Hatch!
Here it is in the Mini:





http://www.racing70s...ns/mini_065.htm