MG Midget Forum

Greetings gents!

So I've been scratching my head (no pun) about how to rebuild a 948 to go back into an old Lotus Seven (originally a 948 Sprite powered car) and realize that I have a pile (3) of Mini motors here left from another project. Last night the cold got to me and I started pulling rocker covers and checking serial numbers. This is what I find I apparently have:

1 948 motor (based on "840" on the block and serial beginning with "8"

1 998 motor (based on a tag attached to the side of the block which reads '1000') I include photo of unique (to me) rockers on this motor as well as the stamped serial number BENEATH where the aluminum serial tag would normally be found.

1 1098 motor (based on a tag attached to the side of the block which reads '1100'). Oh, and hand inked on the transmission of this motor is "998 close"

Questions:

What's up with those 'billet' rockers and should I use them?
Will the head off the 1098 motor bolt up to my 948 block (already .040 over with flat head pistons).

Thanks in advance for the help!

The biggest difference between Mini and a spridget engines is the crankshaft. That looks to me to be an aftermarket rocker assembly, although there was an early cast rocker assembly. Camshaft will work, head will bolt on but someone will advise as to compatibility, I saw mentioned putting the 1100 on a 1275 I believe. The 1100 is probably from a MG 1100 not a Mini. As far as I know Mini range was 850, 998 and 1275.

Those rockers appear to be the sintered ones. Moss has them under part number 433-850. They aren't standard so they must be better right?

The 1098 head will bolt up. The question becomes whether the valves will hit the block under full lift due to the smaller bore and whether gaining a few CCs in the head will matter to you (could always skim the block).

How does the 7 do with that engine? I've always wondered why the A-Series wasn't a more popular option especially once the 1275 existed.



Edited 2 time(s). Last edit at 2015-01-28 04:26 PM by atm92484.

Yes, I understand I can fundamentally bolt the 1098 head onto the 948 block, but the valve question is exactly what I wonder. Thanks for the tip on the sintered rockers. Looks like they were standard on later motors, but don't know why they changed to them -- cheaper? more dependable? Lighter? I've heard the stamped and folded steel rockers are preferred by the racers for their durability... I'm after durability and lightness in this build.

Anyhow, I'm not sure that add'l machine work to clearance the block, if needed, is worth it.

With the Seven being such a light car, I'm not so worried about torque (plus I plan to lighten all the reciprocating mass as much as I can).

I could go into depth about the A Series motors in the Seven, suffice it to say that of the Sevens that were specifically and completely built for dealers to sell in the US market (not ordered direct) a significant number were 948 A motor powered. In fact, the records indicate they were for the most part Gold Seal 948 motors -- make of that what you will, Champman's wheeling and dealing considered!)

There were perhaps a half dozen actually built and delivered with 1098's as well. The 1275 currently in my car, as much fun as it is, is frankly much more power than I need - I'm running an otherwise original spec car, for street only. That means 3 1/2 wide wheels with suitably skinny tires, which are very easy to break loose up to 3rd gear with almost 90 ponies on tap in a car that only weighs about 900 lbs.

Anywho, I'll offer this up too: if anyone here already has a hotted up 948 that they'd be interested in talking trading for the 1275 mentioned (limited prep SCCA race motor with aluminum bits, steel straps, etc) I'm seriously interested. Close ratio gearbox is also on my list...

yep, I'll let Sports Cars Illustrated do the taking.
http://www.spridgetguru.com/SprtsCrsIllstrtd0660a.html

In short, since the lotus weighed 33% less than a bugeye sprite it accelerated a lot faster. 0-60 times improved a full 8 seconds over the sprite. Top speed was roughly the same for both cars at about 78 to 81 depending on who tested.

---

Seth Jones

1971 MG Midget

www.SpridgetGuru.com



Edited 1 time(s). Last edit at 2015-01-29 09:05 AM by AmishIndy.

If the seven has more than necessary with a 1275 I can only imagine what its like with the pre-crossflow, crossflow and the twin cam!

Kurt.

The rockers are what is known as the MKIV Mini rockers, they are sintered and heat treated, much more consistent than the originals-I put them on my MKII 948. The block that you have with '840' cast into it was probably originally an 850 Mini engine. The 1098 head (it would help if you had the casting # for us) will fit on the 948 without problem, other than the combustion chamber is around 28cc, rather than the 21 cc that the 948 needs. I've got a 12g295 head (1098) on my MKII that I had 0.080" milled off to bring the CR up to ~ 10:1 with flattop pistons. No problems with valve contact with the pistons using a NOS 2a948 hot road cam and the sintered rockers.
I was told (and didn't do it yet) that the sintered rockers need to be re-radiused at the tips to get the most lift possible.
Vizard has a great section on heads and chamber volumes and porting for the same that I used to port mine. It breathes very well.
You asked what transfers over- everything except the crank, oil filter housing, exhaust and intake manifold I think. The 998/1098 rods are the better ones since they don't have the pinch bolt on the small end. Rod journals are all the same size, mains changed on the 10CC engine to 2" from 1.75" in all prior engines (850 through 10CG).
HTH

---

'58 Bugeye
'05 Mini Cooper S

The engine choices for the 7 illustrate an interesting insight into the auto industry and available technology through that era:

- originally, on skinny, bias ply tires, the A series and Ford pre-crossflow engines were fine, actually, more than fine, they were amazing

- as fatter, stickier tires came along, the ability to put down more power allowed the greater power potential of cross flow engines to be made useful as increasingly mind-bending acceleration

Today, we take it for granted that fat, sticky tires will be used, and jump for the twin cam fire breathing options.

Kudos to John for running a 7 with early, skinny tires and enjoying the A series modest power to its fullest!



Norm

Amen, Norm, my sentiments as well!

Kurt.

Yes, sticky tires and bigger motors are what helped the Seven earn the 'delicate' moniker... It's been fun with the 1275, especially since I know the stress to the original frame is limited by the 155 tires. I've been taking it closer and closer to its original state, actually would love to have a Gold Seal 948 to put in it... the car started with the 948 Gold Seal (per factory records as delivered as one of nearly 50 Sevens to Kaback's dealership Grand Prix Imported Cars in NJ), the first photographic, physical, and verbal evidence of a motor is a Spitfire 1147cc, previous owners have described a Mazda Rotary installation attempt, a Twincam, and then back to a 948 as I took it over in 2000. With the clutch slipping as an excuse to pull the motor, I quickly (ha!) dropped in the 1275, a continual guilty pleasure for the last 3 years. Meanwhile, I've been deciding the best way to build a 948 to go back into it - I'm okay with some 'internal upgrades' but otherwise plan to built it fairly stock 'appearing' even to the extent of painting it Gold Seal color (if anyone has such a motor or the color spec, I'd appreciate that too!)

The gold seal was a factory rebuild color, maybe some Brits can help, try the Morris Minor side too.

Your 7 is exactly what a 7 should be - great looking car.