Engine machining

[gs.davies]

Anybody got any recommendations on a firm to fit cam bearings to an early 850 block and how much should I expect to pay for this to be done?

Also, what machining has to be done to fit a 998 crank? My car has the early thin tail crank and it's still running with the wet primary gear and the obligatory oily clutch. I have access to a number of 998 cranks and flywheels but no 850's. Was considering keeping the original rods and pistons if the pictons aren't too worn. If they are worn, I presume I'm in some kind of trouble in trying to source oversize 850 pistons?

Thanks,
Gary

[surf-blue-850]

You'll won't get a 998 crank to a 850 block. As the centre main bearings are wider on the 850. I have a 850 crank here with the narrow tail WITHOUT the oil feed, will need a regrind however.

Line boring the block for cam bearings is a specialised job, Hamlins of Bridgewater are doing mine.

Edit: the 850 tail is the same size as the 998 crank

[gs.davies]

You'll won't get a 998 crank to a 850 block. As the centre main bearings are wider on the 850. I have a 850 crank here with the narrow tail WITHOUT the oil feed, will need a regrind however.

Line boring the block for cam bearings is a specialised job, Hamlins of Bridgewater are doing mine.

Edit: the 850 tail is the same size as the 998 crank

I thought MiniWorld's 1961 rally car had a 948cc engine which was based around a 998 crank in an 850 block..?

[gs.davies]

Narrow tail without the oil feed - so that would take the coil spring clutch? I have a New Old Stock set of 970S springs with the white dot..

[surf-blue-850]

I'm building a 948ish engine, rebored the 850 block, using 998 flat top pistons and a 850 crank. Had to remove a fair amount of the block deck though because of the shorter pistons. Did think about using a set of S rods, but would be trickier to fit.

I think the flywheel taper is the same across the board, unless someone knows differently?

[gs.davies]

I think the early coil spring clutch had a narrower crankshaft tail. Following the 'new' clutch design in '64 the tail size increased.

Isn't the weak link in a tuned 850 the crank (besides the split skirt piston..)?

[251 ENG]

The original spec of the engine in the miniworld car ( 7879 NK ) when it did you Liege rally was -

Late thick flange 850 block +40 bore with full set of cam bearings
1960,s 850 racing intruder pistons
Thick tail crank lightened , wedged , balanced , polished , shot peened , reground
Ligtened , balanced and shot peened A+ 998 rods
Head was ported 998 casting
Twin HS2 carbs
4 syncro magic wand box with "special ratio " helical gears

The engine would rev to 9000 rpm , but after doing about 6000 miles of rallying got a bit smokey . The rings on the old type pistons are not the best , so was rebuilt with +60 karl schmidt pistons and a slightly less modified crank.

It did got well for an 850 and finished something like 17th overall on the liege , beating lots of big engined sports cars over the alps.

[Spider]

Wouldn't you be better off starting from a 998 block? Everything's already done.

[gs.davies]

Wouldn't you be better off starting from a 998 block? Everything's already done.

Yes. But that's not the point - this conversation always ends up at a 998 block like everyone else has done. I want to keep with the 850 block if I can but I ideally want to move away from the wet tail crank as the clutch was forever getting oiled up. The 998 crank to make a 948 was just being obtuse really and I'd imagined that the MiniWorld rally car which is often mentioned as being a 948 was probably using a 998 crank. If I can avoid going to a 998 I will.

My options are (I think..)

- Stick with the original crank (if it checks out to be OK), block off the oil feed to the primary gear and have the gear rebushed to run dry
- Obtain another 850 crank recon if necessary and convert to a post '64 clutch
- Use one of the 998 cranks that is available to me (and do whatever machining is required to the engine to make that fit)

I don't want to create a monster performing, rev to 8000 monster, I'd just like to pursue a 'pre-Cooper' period tuning route with this car using whatever period or modern equivalent bits I can get hold of really.

[graham in aus]

You're going against the grain / norm here, it isn't like building a 1293 / 1380 clone!

I do however applaud your motives and direction!

Later 850 stuff is more robust, thicker tail crank etc. S rods will fit if assembled from below (PTFE pads in pins) then put crank in! (May need to modify small ends).

S rods not essential, we just had Mini 7 racing ones lying around! 998 A or A plus better than 850 because of getting rid of pinch bold small end.

You will have fun trying to find the parts, pistons are the biggest issue. Talk to Simon (251Eng) and Southam, they can help I'm sure!

I built a few of these for historic Monte rally car a long time ago (95), Karl Schmidt's were hard to find even back then !!

If anyone has performance 850 pistons (and 997 for that matter) chip in!

[surf-blue-850]

Pic of 7879NK

[gs.davies]

I really like that car!

[surf-blue-850]

Looks a bit different to when it was on the Monte Carlo, the roll cage has gone.

I have a lot of back issues when they restored it. makes for an interesting read.

[gs.davies]

That's interesting - I had a long while away from reading the Mags, sort of lost heart after I stopped using the Cooper in the early 2000's before eventually (regretfully) selling it.