9 replies to this topic

[Henry8601]

I know that the best way to tune an 850 is to put it in a skip and buy a 1275, but that's not the point here!

 

I have a 1964 mk1 Austin Super De-luxe, and I want to build up a second engine (I'm not messing with the original matching number engine!!!) The idea is that this is to be a fun 850 screamer that feels fast, so massive low down torque and drive-ability is actually not what I am looking for.

 

The spec that I am aiming for is:

 

12G295 Head - skimmed to bring up C/R ~10:1 - (Vizard says aim for 11:1 if the camshaft is between 250' and 270') + rimflow 3 angle valves

Pressed steel rockers

Twin HS2 carbs (I know a hif38/44 or hs4 might be better, but I want to keep the engine looking vaguely period)

Standard Crank - (wedged/balanced/nitrided/bladed?) delete as appropriate

Lightest flywheel I can get

Block machined for full camshaft bearings + center main strap

I have two camshafts kicking around, is either suitable?

I have a choice of a minisport CA2 camshaft: http://www.minisport..._CAMCA2MK3.html

Or the minispares Evolution001 http://www.minispare...OLUTION001.aspx (my preference)

Duplex timing gear (or maybe even one of these:http://www.minispare...JJ3328RACE.aspx)

Maniflow freeflow exhaust manifold

Rebuilt gearbox with cross-pin diff and S/C drop gears, and will keep the magic wand (I have a remote housing, but I can't really bring myself to cut the shell)

 

Apart from any comments on the spec, I have three questions:

1. Where is best to get the block machined for camshaft bearings and the head machining done (I am in North Wilts)
2. Are those the best camshafts? I have seen builds using a 649 in an 850
3. What piston / rod / crank combo should I use? Options:

• Standard crank / standard split skirt pistons / standard rods
• Standard crank / solid skirt 850 pistons / standard rods
• Standard crank / solid skirt 948 sprite forged pistons (where to buy?) / 998 rods or 970 Cooper S rods (so I can take less off the top of the block)
• Standard crank - offset ground big ends / 998 pistons (effectively +65) / 998 rods or 970 Cooper S rods (so I can take less off the top of the block)
   (although vizard says that +60 pistons in an 850 produces less power than +40)

This looks like it should be fun 

[MiniElliott]

Instead of boring the block to take 998 pistons and machined for cam bearings, why don't you just get a period 998 and have that worked ?

[Vipernoir]

Hamlins in Bridgwater (01278 442452) can do all of the machine work, including offset grinding the crank.

[Henry8601]

3 reasons:

 

1. Using 998 pistons / rods is only one option for piston/rod combo
2. I don't have a non-A+ 998 block
3. The center journal on the 850 crank is wider, so I need custom made thicker thrust bearings to put the 850 crank into a 998, and I have no idea where to get them.

It's actually a really good point, but I would have thought that if the block needs boring anyway, I might as well use the 850 block that I already have?

[MiniElliott]

All fair points. The way I see it, you can pick up a pre A+ 998 engine for under £100 normally, this would include all the parts you require, already have the cam bearings and would be more suitable for later re bores. I do understand the want to make a small 'under-powered' engine powerful though.

 

good luck with whatever you choose

[Cooperman]

The 850 engine is good fun and harks back to the origins of 'tuned' Minis.

However, the standard 850 crank is notoriously weak and will easily break if taken over about 6200 rpm. This seriously limits the choice of camshaft as it means it is necessary to choose one which gives peak power at no more than 5800 rpm.

Back 'in-the-day' there used to be a special competition crankshaft for the 850, but with the capacity class up to 1 litre they sort-of disappeared. I've not seen one for very many years.

So with an 850 you need to create the specification using 6200 rpm as a max and work from there. A Kent 266 might work quite well in your car.

You don't need SC drop gears, but a close ratio SC gear set would work well with, say, a 3.9:1 FDR.

There is so little torque that a cross-pin diff is not needed, just a competition diff pin.

[Henry8601]

Cooperman, I would love to find one of those Special Tuning C.AEG515 crankshafts, but sadly I don't think that will ever happen. (unless someone has one kicking around that they would part with?)

Do you know the details of what they did to the cranks other than simply tuftriding them?

This might sound utterly stupid, but could you get a 1071 crank and machine the main journals down from 2" to 1.75"?

 

Assuming no to either of the above, it does rather limit the 'screamer' potential...

 

Thanks for the other bits of advice re. gearbox.

[Cooperman]

I thought the comp. cranks were made from a different material, but it's so long ago it's hard to remember. I did rally in a works prepared 850 and that certainly did rev and it obviously had the right crank.

An 'S' crank won't fit in a non-S small-bore block even with modifications.

If you want a 'screamer' with very little torque but mega-revs the 970 'S' is the one to go for.  My son had one in a historic rally car which I drove on a couple of events. I never liked it as it was "all revs and no go" when compared to my 1293 'S', but in its class - up to 1000 cc - it was competitive until a well-prepared 998 Imp came along!

[Henry8601]

Thanks for all the information again!

 

I will have to have a think about what to do - suddenly going for a full on 970 engine might be a bit much! I suppose I will keep an eye out for one of the competition cranks, but it might be a long wait!

[ikissminis]

Another helpful resource may be bromsgrove engine services in the Midlands, they are a small company local to me but have been in the mini scene for 40 odd years, they used to race a Miglia as well. They do all my engine work, top blokes. http://www.bromsgrov...ineservices.com