Hi guys i have just been stripping down my motor and was wondering what is the maximum capacity that can be achieved with the block.

Also when i pulled the water pump off there was a fair bit of rust on the outside of the cylinders has anybody ever had this problem and how much is permissable.

any help would be great guys coz i don't wanna waste money on a crap block

Just boring the 850, keeping stock crank-
using `998cc' pistons (+.060") you can get 937cc. You will need to deck the block about 4.0mm because these pistons are shorter than 850 ones due to stroke difference.

You CAN bore it to 68mm and then stroke it with a 1098 crank, that'll give you 1220cc.
BUT.. 850 block has wider main bearing journals so they need machining back.
Also, the 850 block only has 1 cam bearing, at front. So, not good for heavy valve springs & big revs.
Easier to just use a 998 or 1098 motor to begin with.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

How does doing these mods affect the strength of the block, i have got a little bit of rust on the outside of the cylinders and do you know how much this sort of work could cost me.

I'm not after any huge power gains i'm just after a little more driveability so i'm not a slug on the road.

don't worry about the rust, they are all a bit rusty there.. people using plain water...

Personally I would throw a 998 or 1098 in there. More power and torque without doing anything else.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

i aggree with drmini with going for a 998 or a 1098. You get more power without doing anything to the motor and also last time i looked 850 stuff wasnt cheap.

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hope be back on the road soon with a blown 1275.

850's are damn rare these days tho..
fit twin 1+1/8th carbs and extractors with a straighthrough muffler
sports 850!

you can always supercharge?

I've know someone that has some moke engines in his yard and i'm just waiting on what the owner wants to do with them, he doesn't get back till later this week, not sure what size they are???
I guess i'll have to wait and see.
If this plan falls through i might have to get a 998 or 1098. What is involved in installing a 1275? Do they just bolt straight in? I would definitely have to upgrade brakes it i want to go that way $$$

yeah man 1275 bolt strsight in except the plat thats goes on the engine steady and goes under the thermo housing maybe different.

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hope be back on the road soon with a blown 1275.

If it's still an early 850 gearbox (doubtful now), a 1275 will not swing on there- the conrods will hit the 850 casing big time. If you're going 1275 get a gearbox too, preferably 4 synchro (they are stronger...)
Remote change/rod change, your call.
If you get a remote change box it's possible to keep the 850's magic wand shifter (by keeping the 850 diff housing), provided you check the size and geometry of the diff bearing bores when bolted up.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

sorry i assumed youd change the motor and box as a unit not just the motor

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hope be back on the road soon with a blown 1275.

Cool i wait till i find out if i can get hold of this new (old) motor and then i'll tell yas about it and hopefully with all our heads combined we'll work it out