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I have a 1967 mk1 850 which is in the middle of a body restore. Engine ran very well before I removed it and was just starting to smoke a we bit. I want to do some historic rallying and hillclimbs. What can I do to the engine to make it a bit quicker but still reliable, that does not need rebuilt all the time after events. What size can I bore it to and what pistons to fit. I know people will just say fit a bigger engine but I want to keep the car as 850 ish as possible and just compete and say I have done it in a 850 and better my time when doing events again. I have seen mentions of 890cc but can't find what spec like pistons etc. I know the engine will have to be line bored to fit bearings as only one as standard engine. I know things could cost a bit but want to use my original engine.

Does anybody have the spec sheets of early 850 rally cars or any spec on any 850 rally/hillclimb cars.

SO WHAT CAN I DO with my engine?

I have the st data sheets for the 850 - ill scan them and post them

My mates ex-girlfriends dad was a BMC competitions dept chap. Very interesting bloke. Legend has it that he had a Cooper S with a worked on engine which was comprehensively blown into the weeds by a much faster 850 mini running a cabin blower (marshall) mounted in the passenger footwell. It needed a rebuild about every week and ran avgas but produced a silly amount of power. They didn't talk about horsepower but the 850 left the S standing in every situation.

We just had an 850 on the Liege - Brescia - Liege rally . That did ok over all the mountains .

you might also want to have a chat with Jim at RACE in chorley, he will definatly know what to do with them, he's just built one as well a stonking 850..

pad4 wrote:I have the st data sheets for the 850 - ill scan them and post them

Would be interested in seeing this myself - I have a couple of 848s collecting dust under the bench and have been threatening to rebuild one for ages.

Incidentially - do you have any st data sheets for the 998 Cooper unit - I have one of these as well that I was going to rebuild for my '62. A wee bit of poke would be nice under the lid.

pad4 wrote:I have the st data sheets for the 850 - ill scan them and post them

i would also be keen on a look, all i have in my shed is 848 bmc engines

251 ENG wrote:We just had an 850 on the Liege - Brescia - Liege rally . That did ok over all the mountains .

What you mean is that it managed to ascend all the mountains?

Do a search on 850 tuning on this forum, there has been a lot said about tuning 850's in the past.

There are a few important things to bear in mind. Tuning an 850 to ANY level of tune will be more expensive & make the engine less reliable than if you start with a bigger engine! This should not be forgotten!!!

Having said that you can have a lot of fun in a tuned 850 as long as you are not bothered about winning trophies. As far as I am aware there are NO hillclimb & sprint associations that still run a small capacity class, they usually start at 1400 & under. I don't know the score with historic Rallying currently.

With an 850 more is definitely less, you can't go for wild cams or big carbs, you need to be conservative, concentrating on making an engine as smooth and as tractible as possible. This way it stands a reasonable chance of holding together & running reliably. Realistically you can't be looking at more than 50bhp MAX, but I have built 48 bhp 850's that run as sweet as a standard engine & do go pretty well.

I say go for it, but please bear some of the above in mind.

thanks
Away to do search for 850 tuning then.

Also

251 ENG wrote:We just had an 850 on the Liege - Brescia - Liege rally . That did ok over all the mountains .

When you say you did the rally what have you done to the car? Would be intrested.

The first time he did it be was faster than ALL the Ferrari,s over the alps

The results will be on the internet somewhere , think it was 17th overall this time

I seem to remember a certain 850 winning the 1999 Fosse Rally

It saw off quite a few Cooper S's that night!

I think it was running an engine built by Smoke Grey and his father at the time....

graham in aus wrote:I seem to remember a certain 850 winning the 1999 Fosse Rally

It saw off quite a few Cooper S's that night!

I think it was running an engine built by Smoke Grey and his father at the time....

One of my favouritre cars that 400CAB. I was building a 61 850 to go historic road rallying in, i was co-driving in a Cortina on historic stage events at the time. Me and my dad went to the derbyshire area to buy a bench run only GOLD SEAL 4 synchro remote/magic wand box. Got there to find the guy also had the engine. Bench run only again it had been supplied to the local training college by BL. Interesting in that it had a thick flange blocl with cam bearings, EN16T crank and a 295 head! We put it together with a duplex chain and a NOS AEA630 cam. Hacksawed the inlet off the exhaust manifold opened up and fitted with a H4.

Mate of mine also had a rally 850 with 295 head , duplex and a 510 cam, super smooth engine and went really well, bags of fun on 3.5" rims knobbly tyres and drums all round, 90 MPH car.

mk1 wrote:Do a search on 850 tuning on this forum, there has been a lot said about tuning 850's in the past.

There are a few important things to bear in mind. Tuning an 850 to ANY level of tune will be more expensive & make the engine less reliable than if you start with a bigger engine! This should not be forgotten!!!

Having said that you can have a lot of fun in a tuned 850 as long as you are not bothered about winning trophies. As far as I am aware there are NO hillclimb & sprint associations that still run a small capacity class, they usually start at 1400 & under. I don't know the score with historic Rallying currently.

With an 850 more is definitely less, you can't go for wild cams or big carbs, you need to be conservative, concentrating on making an engine as smooth and as tractible as possible. This way it stands a reasonable chance of holding together & running reliably. Realistically you can't be looking at more than 50bhp MAX, but I have built 48 bhp 850's that run as sweet as a standard engine & do go pretty well.

I say go for it, but please bear some of the above in mind.

I can testify what Mark says from bitter experience.....when Mini 7s went to 1000s from 850s in 1991, not wanting to waste my freshly built 850 from the year before I simply plonked it on top of a ordinary 3.44 box and popped it into the road car. BIG MISTAKE . you end up looking a right berk, spinning wheels at every set of lights, junctions, roundabouts, Sainsbury's car park, etc, etc.. And you won't even make it out of a gravel drive - you'll have to get someone to tow you out! Dad borrowed it to go down the pub and got arrested for "reckless driving behaviour akin to someone half your age, sir!"

Just get an ordinary 1300 motor and change the final drive.....unless you're competition restricted, of course.

while i'm not building a rally car, I am currently building an 850 and trying to squeeze some more power out of it. So far, I've been gathering up period components for my engine as follows:

-C75B Shorrock blower
-12g206 cylinder head
-cooper 997 camshaft

Does anyone know what kind of power I could be looking at with all these toys put reasonably together (no huge boost on the blower, no silly valves on the head etc)? The reason I ask is because I am concerned about my pistons: I have always heard they were the weakest link and that I would do well to step away from the standard ones, but I have had a lot of trouble finding standard bore aftermarket pistons. If anyone has any recommendations.. I have heard many good things about hepolites, but AE doesn't seem to produce the ones i want anymore. I figured I'd ask you rallying people who have most likely been facing the problem in the mini 7 days..

thanks so much

Karl schmit pistons are the ones to get if you are going to rev it. Stocks ones can't really take the hammer and have a bit of a tendancy to loose the top off them!

Not even sure you get the schmit ones anymore and the only others I have seen recently are oversized stock ones on fleebay.

In rallying you can go to 60 thou over bore. CC is king here. stock 998 pistons are 62 thou overbore but even with stock rods (not ideal but it might be better to change to later rods), they will sit proud of the block. It could be a case of getting a stock set of 998 pistons with a thick crown and machininng them down if possible. This is so you can run a 295 head with decent valves. Think that works out to be around 870 cc.

Depends what you want to do with it. But unless you go silly on the spec, 48-50 hp is around your reasonble limit.

With the sort of setup you are appearing to go for, head, cam etc with the blower, a reasonable power output will be around 55 - 60. You are right when you recognise that pistons can become a problem if you go for any more output. You should not be revving it that hard (governed by the blower rev limit) but if you can find some solid skirt pistons USE THEM!

I would buy the pistons you can get, whatever the size may be & get the block bored appropriately.

mk1rally wrote:stock 998 pistons are 62 thou overbore but even with stock rods (not ideal but it might be better to change to later rods), they will sit proud of the block. It could be a case of getting a stock set of 998 pistons with a thick crown and machininng them down if possible. This is so you can run a 295 head with decent valves. Think that works out to be around 870 cc.

i think you'll find it's the other way round, they don't come close to the top of the block.
i had to take 110 thou off the top of my block the get enough compression with 998 pistons on an 850 crank (9.5:1)
this is because the 998 crank has a longer stroke.
and after that my pistons are still not at the top of the block

Ah yes, you are quite correct. Maybe I'm thinking the 1100 piston. Sorry if that has caused any confusion.

Either way, that was some serious milling!!

thanks for the answers guys.. I just emailed FW Thornton about solid skirts and Duncan came back saying they only supplied split skirts for 850... guess i'm on my own then... if anyone has names of companies that used to make them i'd appreciate that very much.. I can't seem to find much out about Karl Schmidt pistons yet, but i'll keep looking..
in the meantime, I'll just write a new post in the wanted section if anyone has got any for sale hehe