970-engine in A+-block. Tech help wanted

[JCWorks]

thx, I meant pull it out of storage, it´s just put aside under a bench in the garage

Vegard, Sweden goes scrupulously by the book when it comes to AppK, correct (and how have you learnt:), that´s why I was reluctant to the longer rods we discussed

But you shed light on another matter regarding the pistons; are the only AppK pistons allowed the flat top ones? My pistons are almost certainly dished because the head is skimmed too much. If I have to change the pistons, I can´t use the head, which is a mega nice Slark built head

If you cheerful people are right, I´m left with nothing but a crank and a set of rods eliglible for classic racing, everything else in this engine would have to be changed! Not really sure if it´s worth it, it would mean buying new pistons, a new head and to have a block prepared to get a correctly built engine.

I´m definitively measuring the head now, to see what I´m left with. With my luck, probably just a heap of parts up for sale soon

[App K]

Nice head, not a problem to use dished pistons in Appendix K.

[lexie467]

I see you now have the correct part numbers covered. As said, you must for FIA App.K use the correct rods and crank. That means if you are following the " book " of rules you should be using genuine BMC parts but there are quite nice new productions for racing from various manufacturers. It is up to your conscious. However, when you read the last pages in App. K you will find " Period specific amendments " regarding BMC Cooper S ( all types ) stating the that 12G940 and A+ block is legal. The timing gear you mention is not OK. The pistons we always use are Omega +0.40". When you have put in the crank, rods and piston you will know the right hight of the block and machine it to a squish of 0.10mm. Good luck!
Lexie

[App K]

A+ block can not be used in Appendix K?

Appendix VII states block substitute to be casting number 12G1279 as used in Austin 1300.

[JCWorks]

.. found this, FIA AppK...

BMC

Cylinder heads bearing the casting number 12G940 are accepted as
an alternative only on the 970 cm3, 1070 cm3 and 1275 cm3 Cooper
S engines.
Cylinder block for the BMC Mini Cooper S
The following block (foundry n° 12G1279 as used in the Austin 1300
– homologation n° 5335) is authorised as a replacement for the original
block of the BMC Mini Cooper S.


I haven´t seen the A+ block being allowed by FIA to substitute the original, though that would make life a lot easier. Since the meaning of AppK is to preserve the authentic look, I suppose it´s not going to happen. Except maybe on a national level, that is.

If anyone knows A plus blocks are used somewhere in classic racing, that would be valuable information.

thx lexie for the tech tips regarding the pistons.

[sandman]

The A+ thing was just a mistake/typo on Lexie's part... We're only allowed to use S or Pre A+ blocks.

Seeing you will need to swap block's - I would guess it would be just as good to buy a new set of pistons anyway... You will def. need a new set of rings anyway. (a complete set of rings for "proper" Omegas cost about 1/3 of a the pistons)
I would go for flat top Omegas and then deck the new block to suit the head. (that way you can reuse the piston/block etc. should you ever need to change cyl.head... (that can crack you know )

If you're going racing and would like to have some hope of playing with the other 970's... you will need a competetive package that will need to withstand 9000+ rpm. thoughout the race.
What you need to ask yourself is; can you afford to loose the rest of the engine internals (and g'box!) due to "being cheap" in one area?

[JCWorks]

wise words, no use saving £50 to wreck £2000 worth of engine internals. And what´s the fun of a 970 if you don´t dare revving it? Basically, what I have is a crank, a set of rods and a good head. Not a bad start for a good build, but there´s still lots to be spent before completion. I´m gonna think twice about this. There are more cost-effective ways of racing, but part of the charm with classic racing is the possibility of going racing "the way it was" and there´s a lot of value to that as well. Great advice from all of you, much appreciated, thanks for sharing.


Would the "970" A+ block (block only) have a value to anyone? Would be a shame to scrap it, since it´s in good condition, but who would have use for a "classic" 970-block not eligible for classic racing Are there "sub-1 litre classes" in the UK where they use Mini engines and where the A+ is allowed?

[Vegard]

A+ blocks are so cheap that it isn't really worth anything these days. However, if you read what Richy wrote a couple of pages back, you'll see that things might change in the future Don't scrap anything!!

I'd use the crank, get some proper Omegas and have the rods THOROUGHLY checked by someone who knows. If not I'd get some H-profile or Pauter rods.

If going racing, these items might cost a bit of cash, but it's nothing in the big picture when building a FIA- race car.

[lexie467]

Lots of wise suggestions. I ment off course A+ block for App.K CT1 BMC Cooper 970S. YES, in Sweden A+ block are used according to regs. Also I forgot flat Omega 0.40" piston is what it takes at 17cc head. But one thing, FORGET everything about 9000 r.p.m. It does to even match in your wildest dreams due to no camshaft will deliver power after 8.200 r.p.m. In dicing moments however you can be forced to keep the gear to 9.000 r.p.m. but that will only be in situation of that kind. More important I think to understand in pure racing is, that average revs are lot more than a 1293cc engine. The bits are very identical and under the same circumstances the 1293 is round 7.200 r.p.m. Having said that I mean the 970S needs VERY fresh bits and frequent service and maintenance in comparison to 1293 if you use old worn parts. If you do it right you will get 90+ horses and invest 13K-15K Pounds Stirling for a top notch engine provided you do most of the job yourself. In my regular 970S race engine I logged 30 hours till I decided for the first rebuild. One of the most important part are if you have a USED crank you MUST X ray it. You MUST measure the roundness at the big end of the rods and you MUST hone line the block. Otherwise you will most certainly run in to bearing problems.
In all due respect to the other authors in regards of this issue.

Lexie

[sandman]

Dear Tommy, are you sure you're not mixing the block's up?

App.K only allows for *PRE* A+ blocks to be used... and seeing that RHK are so utterly strict on following App. K I have big problems seeing that would make a national exception on this. (FYI, the A+ block came into production in 1980 and is NOT the same block as used in the Austin 1300 etc.)

I for one have not seen any cars in Sweden that runs A+ blocks.

[JCWorks]

To my knowledge, A+ blocks are not allowed in Sweden, hence my thread

Very wise suggestion about checking the crank. The engine hasn´t been run for very long it seems, but the big end bearings showed relatively more wear compared to the rest of the engine. It made me a little curious, you might have the solution right there. Once I strip the engine I will have the crank thoroughly checked.

But regarding the crank; with the short stroke of the 970 (20 mm shorter or 4/5 of an inch compared to the 1275), shouldn´t there be less of a problem with crank unreliability compared to the 1275? Higher revs will result in higher wear, for obvious reasons, but the shorter stroke (I would say) would put the crank under less stress. My engine, although "professionally" built, doesn´t have a centre main strap, indicating crank flex is not really an issue on such a short stroke engine. I could be - and have been before - wrong, though

[carbon]

Although the inertia forces on a short stroke motor are less, it is the harmonic vibration which is the real crank killer. This is why they can go at seemingly low rpm.

There are also some stress points due to the original machining of the 970 crank.

When you're rebuilding would be worth checking all of the mains and big-end nuts are high tensile, not sure if you have these fitted at present.

[JCWorks]

Nuts seem to be not so high tensile, good point, the big end bearing nuts are Nylocs. I´m aware of how the crank suffers, but I don´t know if the 970 is more sensitive than the 1275, to me the 970 should be able to cope with higher revs. The critical vibrations in a 1275 are just over and below 4000 rpm, I believe, but that band is moved upwards in the rev range when the rotating assembly is lightened. Theory would have that the critical vibration band in a 970 would be higher ("lighter" assembly when rotating) than that of the 1275. When flywheel etc is lightened further in the 970, the critical vibrations can, by accident, be put at very high rpm, the rev range where you usually keep the engine when racing. So, a theory would be that cranks suffer if the power band of the engine coincides with the critical vibration band. As far as I know, one can´t really calculate where the vibration band is put when you lighten the rotating assembly. If one could use a viscous damper, it wouldn´t be a problem, but again, regulations rule that out.


Anyway, if the power band goes up to 8 200 rpm, there´s no use going higher on purpose, and if a 970 is prepared the same way as a 1275, it should cope with the same revs as a 1275, at least. Meaning 8000 would be "safe". Or is the 970, for some reason, more sensitive?

And what are the stress points of the crank of the 970? Is that something that can be balanced out or is it somehow integrated in the design? Mine has had work done to it, possibly to better its design or maybe just to balance it.

[Cooper 970S]

As mentioned we have at least 5 970's running as race cars in Sweden including mine with a pre A+ engine and a steel crank.
As far as I know there hasn't been any crank damages on our cars caused by high rev's, I suppose forces are less on short strokes.
There are no big secrets when building up an 970 engine, of course choice of camshaft and final gear is essential and a matter for discussions. The 970 cylinder head seem not to need big inlet ports and combustion work,done so don't put too much work on it unless you don't need to find the last hp!

Reg
Kari

[lexie467]

Off course I mean pre A+ i.e. 1300 block. Sorry, my mistake. I came to think of when we bored out the block to 0.40". We really tried to come to an
end where the honing ( end finish ) permitted the pistons to move as friction less as possible without doing it to an extend of white smoke. These little fine engines runs better the less friction you have. Aha, you say, does that not go for any type of engine? Yes, but the smaller the more critical for power!
Tommy

[dutchacme]

What about a windage tray, to minimize oil drag against the crankshaft at 9K.

Wim

[JCWorks]

Funny you mention it, wasn´t there a guy, I think in the UK, a few years back that started fabricating a new type of Mini baffle/windage tray? I think someone mentioned a 2-3% power increase because of the design. I haven´t seen them being offered for quite a while and I have no idea how correct the estimation of power increase was. It´s a good idea, new or old design, I´d say. Does anyone of the gurus know what AppK says about baffles? And I´m not applying to the "noone will ever know" rule

[dutchacme]

JCWorks,

just curious, what type of rockers came with your project and were the rocker posts shimmed to compensate for the lower block ?

Wim

[JCWorks]

Sry, no rockers or pushrods were supplied with the engine and I´m sure it´s going to take some headscratching to figure out the valve geometry. I´m sure someone else on the forum have the info you need on this.

[Vegard]

Quite easy. Small bore push rods are almost bang on..