G'day guys,

I'm probably going to embark on rebuilding my 850 motor/box in the near future. I've got some dumb planning questions that have probably been answered a thousand times or a just general knowledge but here goes.

I've been looking on all the mini parts specialists websites looking at kits etc. 850 stuff isnt listed....is that because the 998 listed stuff is exactly the same? ie smallbore??

Can you just buy a re-ring kit or is it just normal to buy a gasket and VRS kit and purchase rings and bearings seperately?

Is there specific 850 engine stuff that will be needed that is available/unavailable new that I should be seeking out?

Is it safer/more economical to go with new pistons and a rebore regardless of the wear of the original pistons/bore?

I've got the original 850 motor and a spare 850 motor for parts, both "appear" servicable bore wise, ie. ridge, glazing etc.

I'm going to be building a reliable package with usual 850 period bolt ons. Not a race or fast road motor. No experience building mini engines but I've built a few go fast Holden red 6 cylinders in the past.

Thanks guys

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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.

Thanks Doc, that gives me a lot more to get cracking with.

Cheers Pete

Putting rings in an old engine is false economy. Regardless of whether you deglaze the bores, they are still oval and tapered.
These days, a set of oversize Hypatec (for example) pistons and rings isn't much more expensive than a ring set alone. And all it will cost you extra apart from pistons, is a rebore and hone job (~$150).
Then, it'll run like a new one again. As the bores are straight, round, and the pistons have the right clearance.

Same story with the crank. Bearings are cheap, but if the journals are worn oval it's a waste of good bearings to just replace them. Get the crank reground to the next undersize if worn.

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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 found it very hard to get 850 pistons and rings when it came to get the engine rebuilt. Morris minor world had alot of trouble and finally found a set of flat tops.
Lindsay Siebler was contacted as well and had no luck. I even asked on this forum for standard pistons as I contemplated sleeving.
Looking back, it would have been much easier to go with a 998 or an 1100 if you want to go small bore or go for a 1275.
The cost of engineering is about the same, the initial cost of acquisition of 850 engines is low because they seem to be unloved.
1275s are at the top of the cost of acquisition and 998 and 1098 are in between.
1275 you need to go to disc brake front end. If you are going from a stock 850 to a 998 or 1098 you will need to upgrade the front drums to the later twin leading shoe type.
Also, your choice of gearbox is important, if you are sticking with the stock 850 with pudding stirrer/magic wand change then you must know that the stock exhaust are hard to find. It will need to be custom built. If you are going with the remote gearbox (1st type non rod change) then the exhast will be different as to where it bends and are not available. Either custom build as per stock or extractors is the go.
If you stay with the floor start be wary of the distance between the exhaust pipe and the floor start solenoid contacts.
If you are using the later clubman rod change gearbox then you will probably need a custom built system if using the stock inlet and exhaust manifolds or go with extractors.
Search the posts.
Good on you for considering an 850 rebuild.

Thanks for the replies guys,

Here I was thinking I could just order parts, organize machining and piece it together with care!!......

So I really need to decide if I bother keeping the car period correct, I didnt want to cut the floor for a later g/box and would prefer keeping the magic wand shift.

It seems the simpler/economical way to a fresh reliable motor is to start with a 998 combo with a later box.

Although like the Doc mentioned some machining off the 850 block to suit 998 pistons might be the best all round solution

Ahh decisions....

what about sleeving the block, and machining some good 2nd hand pistons a few thou undersize - you're not chasing performance, and .005" only drops you down to 845cc. Standard rings will still work

I had your decisions too a while back....
Mine was made slightly easier as authough the magic wand box was still there, but the 850 had already been swapped for a 1098.
I was pretty determined to keep the magic wand box for some time, until i realised that it was in definate need of a rebuild, and i had a remote box sitting there that was far better condition. As i didn't have the funds for a full rebuild at the moment, the decision was made.

Don't get too worried about cutting a hole in your floor. If you decide to go back to stock later on it could be VERY easily filled in and fixed so no-one would ever even pick that it was even there.
Just think of it as a temporary big rust hole . no-one gets upset or thinks twice about fixing rust holes in their mini's do they?? no difference IMO

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Tim
Dusk Blue
1964 850

If you are not going to make it a high performance motor and rev the tits orf it, JP Pistons still list new ones for an 850.

http://www.jp.com.au/carsM.html

p/no is JP 0329.

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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.

Wood & Pickett in the UK look to have a stock of Rover 850 pistons (std bore only??)

http://www.ebay.co.uk/itm/CLASSIC-MINI-850cc-PISTON-SET-4-STANDARD-BORE-SIZE-/250894858558?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3a6a7fb93e

Standard size pistons are not much good during a rebuild, the bores will be worn... if you don't bore it oversize you are only doing 1/2 a job.
I'd deck the block and use some std 998 pistons, they are a stronger piston of better design (solid skirt, not split skirt).

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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.

Just another dumb question...

If I was to go down the 998 pistons in an 850 do you use the 850 rods?

Might take on a 850 rebuild for my old girl.

Also are the Aussie 850 a better engine than the Pommy ones, mine has been changed sometime during it's life.

Ian

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1961 Morris 850 (being restored)
1965 Austin 1800 (daily driver)

You can use 850 rods if you get a pinch bolt groove ground into the 998 gudgeon pins, and leave the circlips out.
Easier to use 998/1098 rods, they are same length and stronger (no clamp bolt)

Oz built 850 motor would be hardly different except it probably has the 1-1/2" dia crank tail, same as 998 & 1098. (early 850 was only 1-3/8")

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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.

Thanks Doc,

Might even have a set lying around here somewhere.

Ian

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1961 Morris 850 (being restored)
1965 Austin 1800 (daily driver)