998 crank in an 850...

[gs.davies]

I've often thought about this, but could never see the point. However, I came across this today on the AROnline site..

July 1967, Oselli 1200 Mini GT.

OSELLI, then based at Baynards Green near Bicester in Oxfordshire, but is still very much in the tuning business, although it now concentrates on tuning classic cars.

For £176 the Mini 850 owner could have his engine exchanged for something more potent. The 850 engine block was bored out and fitted with a 998cc crankshaft to increase capacity to 1198cc. This was common practice to enlarge the capacity of the smaller A-series engines to attain 1275S performance levels economically. The cylinder head was fully modified,being fitted with bigger valves and gas-flowed. Carburation was by twin 1.5-inch SU’s and a performance exhaust was fitted. The camshaft was “road/race”.

CCC recorded a 103mph top speed and a 0-60 time of 8.8s. Despite the Cooper S-beating performance, drum brakes were retained all round.


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Seems like a funny old conversion - anyone know anything about this?
Gary

[gs.davies]

PS. To me this would seem to be a set of standard 1300 pistons, on a 998 stroke. In an 850 block! That's about a +300 thou overbore..!

Possible or not?

[Vegard]

Wouldn't you need inverted thrust bearings then?

[gs.davies]

I know the thrusts are different, but the bit that amazes me is the size of the overbore.. I also presume further machining is carried out normalise the compression ratio should the piston's wrist height be different. Seems like a massive amount of work when an appropriately machined 998 would have been better!

[Chalkie]

sure you need like twice the thickness thrust bearings as the 850 has a smaller center strap than the 998 off memory or its wider and doesn't fit in the 998 block either way we discussed this on the Turbo mini's forum and its possible but a shit load of work for pub points.

[ivor badger 2]

You would need to machine flats in the sides of the pistons to stop them rubbing on each other when passing on the way up and down.

A road race cam in a block with only a front cam bearing?

it's a bit like the irish man when asked for directions, "if I was going there, I wouldn't start from here"

[ianh1968]

Are you sure that it's not an 1100 crank, with Hillman Imp pistons?
This gives 1216cc with standard sized Imp pistons...
(That's 68mm bore, or approximately 2.677")

My Dad did one of these years ago using an 1100 block and crank.
I subsequently bored it out to +0.030" (Imp) to make about 1242cc.
It went quite well until it died in battle against an Astra GTE...

Before the 1275cc engines became easily available, this was how
some people made larger capacity 'A' Series engines.

Chalkie's point about it being "a shit load of work" is valid, but we
need to bear in mind what parts were available to tuners back then...

The Imp had been around since '63 and someone smart found out
that the pistons have the same wrist-pin diameter as the small-bores.
The pistons are quite short from pin to deck, so they can really only
be used with the 1098cc crank. Even with this long stroke, a large
amount needs to be milled off the top of the block.

In '67, the availability of large-bore engines on the "used market"
would not have been too good. People had to make-do with what
they could get their hands on.

A lot of work, yes - But also an instant 43% capacity increase...
= BIG BALLS

I seem to remember seeing reference to a possibility that some
of the early 1100's were made from bored 850 blocks anyway.

Ian
PS I've gone back to my usual name...

[Spider]

PS. To me this would seem to be a set of standard 1300 pistons, on a 998 stroke. In an 850 block! That's about a +300 thou overbore..!

Possible or not?

We've currently got +0.100" and +0.120" Pistons for 998 and 1100 engines. I can't recall the numbers off the top of my head, but with the 1100's it takes them out to over 1200 cc. I don't get too involved with the small bore stuff myself though, a lot of work for something that the big bore blocks already have, along with a better crank.

[ianh1968]

I can't recall the numbers off the top of my head,
but with the 1100's it takes them out to over 1200 cc.

Great memory, Spider... +0.120" is indeed just over 1200cc!

Disclaimer:
All figures are approximate, they came out of my calculator...

(All using 998/1098 bore of 2.542" & stroke 83.72mm)
+0.100" = 2.642" (67.11mm) @ 1098 = 1184cc
+0.120" = 2.662" (67.61mm) @ 1098 = 1202cc

For Reference...
+0.135" = 2.677" (68.00mm) @ 1098 = 1216cc (Hillman Imp Standard)

Ian

[gs.davies]

The 850 engine block was bored out and fitted with a 998cc crankshaft to increase capacity to 1198cc.

We reckon this is a misprint then?

[Chalkie]

I have a 850 crank and a 998 block in my unit to see if it fits

[ianh1968]

The figures certainly do calculate:
998 Crank + 1275cc Pistons = 1198cc (or thereabouts)
(Many of these old values were worked out using logarithms
so we don't always get the exact numbers we expect due
to rounding and other issues).

... and yes, it would be a +0.300" overbore... (On 850cc)

There are two considerations here:
1)
The engine would need appropriate rods/pins for whatever setup it had.
This would more than likely be 'S' rods, or something more exotic.

2)
It is a known issue that the oilway drillings for the pressure relief system
often caused a problem when "big" overbores were done. The problem
was already apparent at the Hillman Imp oversize of 68mm and boring to
this level often resulted in the bore breaking into the oilway.

Going to 70.61mm would be a major challenge and I am not sure if
bore spacings and/or repositioning would allow this to happen.

Still, us "Mini People" like a challenge... I'd love to know for sure on this one!

Ian

[Lord Croker]

I agree with Spider, it's a lot of work to get that kind of capacity from a small block engine, although I am building (very slowly) a replica of the Speedwell 1152 engine, based on an A+ block. Fortunately I have found a pristine 1100 crank at a very good price. Personally, if I wanted to go bigger than that, I would be looking at a 1275. (Then I would have to lose my much loved drum brakes! )
Regards, Rich.

[Chalkie]

I agree with Spider, it's a lot of work to get that kind of capacity from a small block engine, although I am building (very slowly) a replica of the Speedwell 1152 engine, based on an A+ block. Fortunately I have found a pristine 1100 crank at a very good price. Personally, if I wanted to go bigger than that, I would be looking at a 1275. (Then I would have to lose my much loved drum brakes! )
Regards, Rich.

think you should be losing the drum brakes anyways 1152 will be pretty rapid

and

I love how Mini's end up with such random amounts of CC 848. 970, 998, 1071, 1098, 1275
plus all the random combo's that can be made like my mates 1455cc engine

[ivor badger 2]

What keeps getting missed here is that 70.64 blocks have their bore centres moved. Small bore blocks have the outer cylinders are bored siamised when made and are close together. Therefore there is not a lot of meat between the bores.

[Vegard]

I love how Mini's end up with such random amounts of CC 848. 970, 998, 1071, 1098, 1275
plus all the random combo's that can be made like my mates 1455cc engine

I've got a 1098 +60 and a SA 1071 (1098) +40. These are infact both 1132cc

[rich@minispares.com]

I've got a 1098 +60 and a SA 1071 (1098) +40. These are infact both 1132cc

the difference is that one will shake like a shitting dog and eventually run its bearings if you thrash it, the other one will be like a motorbike and will never, ever give any problems

oh, and one of them will make about 20-30 more bhp

[ivor badger 2]

The S capacities are based on the cc class limits of international rallying/ racing. Up till the end of 63, the class limit was 1100 cc, so it's the 1071. The class limits change 1st Jan 64 to 851 to 1000cc and 1001 to 1300cc. The engine bore was specifically to allow an overbore to correct production line inaccuracies. and the 999 and 1293 capacity. 1293 is not a magic number, just a 0.020" rebore.
Lotus Cortinas got the same treatment. The first twin cams fitted to Elans are 1496cc the same as the std Ford Cortina block. This is revised to 1558cc for fitting to Lotus Cortinas giving 1598cc with the 0.040" max overbore allowed. The story is that all the original 22 Elan 1500s had the engine replaced with a 1558 and the car becomes an Elan 1600.

[Spider]

What keeps getting missed here is that 70.64 blocks have their bore centres moved. Small bore blocks have the outer cylinders are bored siamised when made and are close together. Therefore there is not a lot of meat between the bores.

Not sure if the other guys 'missed it' or not, but at 0.100" (and bigger) on a small bore block, yes, we off set them, and at 0.120" success is not guaranteed. We did look at trying to go bigger, even if sleaved, but in a small bore block, that's about the limit.

[gs.davies]

So, it seems that this Oselli engine spec is a bit spurious - the only way it can be achieved with a 998 crank as specified is to use a piston of 1275 size.

What about a 1098 crank and a big 850 overbore?