5 replies to this topic

[dgear1984]

I am almost at the stage now its time to be looking to find myself an engine for my project. I have read about 1275 s engines on mk1, 2 and 3’s and







S 1275 rods are aeg 521 (late) or aeg177 (early). 5.75” between centres. When was the change over point?







11 stud blocks with tappet chest covers. Blocks are either thin or thick? how do you distinguish between the two? Which where which ie. Thin mk1, thick mk2 etc…







Crank is en40b nitrided on mk1-2 and tuftrided on mk3. has 1.625 s big end and 2” main jurnals. 81.33 stroke. Cross drilled from sept 66. aeg479 for the nitrided post 66. AEG 316 pre sep 66







Rockers are 1.3 cast rarther than presed.







Heads 12g940, 11 stud, valves 35.6mm (1 13/32") inlet and 29.53mm (1 5/32") exhaust. Double valve springs.







Cam is aeg148 with duplex chain and sprockets, pin drive for the oil pump.







The water pump is a cast large s type but im not too sure about much else.







How do my rough prices look



Block 400



Crank 200



Rods 100-150



Head 100



Cam ?



Water pump?





pistons nos ?



Rockers 50







As far as the works engines went they where overbored to .20, where decket to .10 above piston height, had aeg648 cams fitted, heads where modified by weslake had a compbusion space o 16.4cc and a cr of 12.6:1. they had downton lcb and centre exhausts. H4 carbs.

When you see descriptions of engines for sale they often say 20/40/20 etc. what do the 3 numbers actually stand for?? i know they are over or under size and in tho and assume they refer to big end, mains and bore but which order. thanks





thanks

[Rosslin Racing]

when they say thick they are talking about the flange that the gearbox mounts to
[attachment=75212:P1010027.JPG][attachment=75213:P1010028.JPG]
the rods 521 are MG midget if I remember correctly
as for price ????
the last MK3s had EN16T cranks
20/40 means the amount that has been grind off the crank journals

Edited by Rosslin Racing, 21 November 2008 - 06:54 PM.

[taffy1967]

The Mini Cooper Register forum people are experts on original Cooper S Minis.

[dklawson]

The original heads would have been AEG163. I'm not sure when the 12G940 was introduced but I didn't think it was part of the original Mk1-Mk3 production. The AEG163 heads did use dual springs. I don't know what was standard on 12G940 big-valve heads.

The EN40B cranks (at least over here) command a huge amount of money if they are in good shape, particularly if they have not been reground yet.

Strictly speaking, the rockers were forged, not cast, although the surface appearance of the parts would make one think they were castings. However, the pressed steel arms from the standard 1275s are not bad arms. Your 50 GBP estimate on their value is probably low. You may find a good-used set for that but new ones are available.

Regardless of what the original cam was, you may not want to use it if you're rebuilding the engine. The early cams were pin drive so you needed the corresponding type of oil pump. This was replaced by the equally awkward spider drive. The current slot drive cam and corresponding oil pump are readily available with many possible grinds.

The current GWP134 water pump is a good choice for 1275s. You can opt for different pulley sizes to change the water flow rate. There's nothing magic or necessarily desirable about the cast iron pump unless you're going for a very original look.

There are also a lot of piston choices. You can spend a lot or a little and need to base your decision on how you're going to use the engine. Forged high-compression pistons won't come cheap but would be desirable in a race engine, they aren't really necessary for a street machine.

So what's your goal here? Are you going to look for the bits to build a Cooper-S engine?

[Prawn]

the rods 521 are MG midget if I remember correctly

521's are S rods, midget rods are AEG 625. Same length and journal sizes, but considerably lighter, yet still easily strong enough to cope with high power.

I've got a set of fully worked 625 rods on a worked mk3 S crank

[mk1leg]

I know of a 970s engine complete with pistons rods and crank for sale £1000..............this is in Jresey IF your interested............this may include G/box will find out ................