15 replies to this topic

[mikep12]

Hi

A while ago I got a job lot of mini bits very cheap so could'nt resist. Just looked over some and I think I may have a bit of a rarity.

It is an 850 motor and with a very quick look and no measurements is as follows.

 

Pocketed block, AEG 515 crank, very well worked rods with solid skirt pistons and floating pin. Full strapping on mains with cap head screws. It came with a couple of 940 heads and a beautifully worked forged rocker set, have myriad carbs such as fish and webers so it looks like someone has spent a few bob on it. The guy I bought it from said he had a load more stuff he had just got 'good money' for and from his decsription it was a good bit of 'S' stuff along with a funny shell with two tanks. His good money was £200!!!!!

Is anyone familiar with this type of thing as I will probably build it up for an old mk1 I will rebuild next year. Any advice on specs compression ratios etc would be great. Thanks

mikep

[racingbob]

sounds like it could be an old 850 mini 7 race engine

 

they gave 63hp at the wheels

[Matt1293]

Second that

[mikep12]

sounds like it could be an old 850 mini 7 race engine

 

they gave 63hp at the wheels

 

Good grief that would be about 80 flywheel?  at what revs? Sounds like the original spec would be track only so would need a detune, I suppose the best thing is to measure bores and ID the cam and go from there.

[racingbob]

 

sounds like it could be an old 850 mini 7 race engine

 

they gave 63hp at the wheels

 

Good grief that would be about 80 flywheel?  at what revs? Sounds like the original spec would be track only so would need a detune, I suppose the best thing is to measure bores and ID the cam and go from there.

 

a 649 cam was used gave 61at the wheels at about 7500 revs at aldon automotive

I used to race them in the late 70's

[Cooperman]

With an 850 you need the special forged steel crankshaft. Those are like rocking-horse droppings these days and I've not seen one for years.

The standard 850 crank will not safely rev over about 6500 even when heat treated, lightened & balanced.

[mab01uk]

For interest, the most powerful high revving 850cc A-Series Mini engines were probably 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!!"

 

This 2 cylinder 850 BDA was designed and built by Gordon Allen from half a 1700cc BDA (so rated at 850cc). It was a real winner once a few niggles were overcome. It was used by Peter Day in a Mini and also a Fiat 500 (the "Mighty Mouse") Here it is at home in the Mini;







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

Edited by mab01uk, 23 December 2014 - 11:12 PM.

[Almond-1]

Wow, That's a lovely piece of engineering. I know that there were some exotic engines, but I've never seen this. It's a pity that you have to destroy a nice BDA. But I suppose that was back then.

[mikep12]

With an 850 you need the special forged steel crankshaft. Those are like rocking-horse droppings these days and I've not seen one for years.

The standard 850 crank will not safely rev over about 6500 even when heat treated, lightened & balanced.

 

Is'nt the AEG 515 the Special Tuning crank. I thought they made a batch of these many moons ago are these the ones?

[Cooperman]

I think it may well be, but I can't remember the part number.

The standard 850 crank (not the 'thin-tail' one, which was even worse) was not very strong. It was never advisable to rev them much over 6000 rpm, maybe 6300 at a push when fully balanced.

I know there was a forged steel crank but back then I could never afford one, and I bought a 998 Cooper when I could have (as you did then!).

There were some 'demon' 850 engines built from stroked 'S' cranks using the 970 'S' engine as a basis and they would really rev (10,000 rpm anyone?).

Presumably it would be easy to get an 850 billet steel crank made for competition and that would work well.

[Spider]

Thread revival since there's a recent discussion on tuning 850's, with a link to this thread,  http://www.theminifo...ne-formula-850/

 

 

 

With an 850 you need the special forged steel crankshaft. Those are like rocking-horse droppings these days and I've not seen one for years.

The standard 850 crank will not safely rev over about 6500 even when heat treated, lightened & balanced.

 

Is'nt the AEG 515 the Special Tuning crank. I thought they made a batch of these many moons ago are these the ones?

 

 

The AEG515 was indeed a Special Tuning Crank. It's the stock 850 crank that's been given the 'works' (cleaned up, trued, balanced and Tuftrided), but at the core of it, they are still only a stock 850 crank, so thinner webs than would be desirable and only EN16. While they did last better than the stock cranks, they will still break just like a stock crank only they take a little longer to do so.

 

Tuftriding is only a surface treatment, it doesn't make the cranks 'stronger' (term used in a loose way), it really only means they can usually be rebuilt a few more times before needing a crank grind. Mind you, if it's done wrong, it can make the cranks more susceptible to cracking too as it is a surface hardening treatment..

 

They haven't been made for eons and unless you came across a NOS one, I would express caution at using one as you don't know how much fatigue life is left in it. You can do your own AEG515 in any case from a stock 850 crank, just as ST did.

[Cooperman]

Interestingly, the 1071 'S' crank has exactly the same stroke as the 850.  So it would be possible to use a 1071 crank and rods to build a strong 850 assuming you could find flat-top solid skirt pistons with the correct pin c/l to crown dimension (or machine a set of pistons to suit) and the bore of an 850.

It would not be difficult to adapt the crank to fit a non-'S' 1275 block as the main bearings are the same diameter. Some machining would be needed to get the deck height correct, but the 1275 will take a lot of skimming, up to around 0.270", so it should be possible with accurate measurement and some creative design.

But would it be worth it? You decide.

[Spider]

Interestingly, the 1071 'S' crank has exactly the same stroke as the 850.  So it would be possible to use a 1071 crank and rods to build a strong 850 assuming you could find flat-top solid skirt pistons with the correct pin c/l to crown dimension (or machine a set of pistons to suit) and the bore of an 850.

 

Just to put a little more detail to the idea of fitting a 1071 Crank to any small bore block;- you'd have to either grind out and weld up the Main Bearing Cap Bolt holes and make new caps, then have it all line bored or grind the mains on crank down to next to nothing. Also, the Big Bore Blocks are 1/4" Longer than the small bore brothers, so there'd need to be some other serious (and expensive) machining that would need to be done.

 

Yeah, anything's possible,,,,,,,,

 

 

 

If the pockets are deep enough,,,,,,,,,,

[Cooperman]

 

Interestingly, the 1071 'S' crank has exactly the same stroke as the 850.  So it would be possible to use a 1071 crank and rods to build a strong 850 assuming you could find flat-top solid skirt pistons with the correct pin c/l to crown dimension (or machine a set of pistons to suit) and the bore of an 850.

 

Just to put a little more detail to the idea of fitting a 1071 Crank to any small bore block;- you'd have to either grind out and weld up the Main Bearing Cap Bolt holes and make new caps, then have it all line bored or grind the mains on crank down to next to nothing. Also, the Big Bore Blocks are 1/4" Longer than the small bore brothers, so there'd need to be some other serious (and expensive) machining that would need to be done.

 

Yeah, anything's possible,,,,,,,,

 

 

 

If the pockets are deep enough,,,,,,,,,,

 

Yes, building a high-power (in 850 terms!) is not ever going to be low-cost if it is to be reliable.

It would not be worth doing it for road use as the bottom end torque would be non-existent.

In fact the best way to get an 850 to go on the road is to fit a supercharger and this was done quite a lot when the 850 was in its younger days.

[Alex_B]

 

 

Interestingly, the 1071 'S' crank has exactly the same stroke as the 850.  So it would be possible to use a 1071 crank and rods to build a strong 850 assuming you could find flat-top solid skirt pistons with the correct pin c/l to crown dimension (or machine a set of pistons to suit) and the bore of an 850.

 

Just to put a little more detail to the idea of fitting a 1071 Crank to any small bore block;- you'd have to either grind out and weld up the Main Bearing Cap Bolt holes and make new caps, then have it all line bored or grind the mains on crank down to next to nothing. Also, the Big Bore Blocks are 1/4" Longer than the small bore brothers, so there'd need to be some other serious (and expensive) machining that would need to be done.

 

Yeah, anything's possible,,,,,,,,

 

 

 

If the pockets are deep enough,,,,,,,,,,

 

Yes, building a high-power (in 850 terms!) is not ever going to be low-cost if it is to be reliable.

It would not be worth doing it for road use as the bottom end torque would be non-existent.

In fact the best way to get an 850 to go on the road is to fit a supercharger and this was done quite a lot when the 850 was in its younger days.

 

I believe Specialist components are building an impressive engine with 888cc for a land speed record car, possibly project 64. They are using a big bore block with an uber short stroke I believe and a 16v head. I can't find the power aim anywhere as it would appear that conversation I was having with them on the facebooks has been deleted but I seem to remember it being around 120bhp~ 


Somewhat unrelated to the 850ccs of the 60s but not so far off building an engine for an 850 formula, +overbore sizes, which makes mega power.