948 tuning

[Fentuz]

Good morning all,

I have a 948cc with twin HS2 on a frogeye. I am looking into “progressive” upgrade i.e. things which are consistent and can work together a progress together. I don’t want to invest immediately a large amount time and effort in 1 shot.
Ultimately, I will want an engine compliant with FIA historic reg, period 998cc but I’m giving racing a few years break. So for now, I want a fast road configuration but however is modified will have to be consistent with the final fia config (I don’t want to change/purchase things several time).

Talking with various people and reading various forum, I understand that with the 948, head upgrade is the 1st thing to do.

A good upgrade is the 12g295 head from the cooper which can be obviously be used with the 998C engine. That said, I understand that the 12g202 is now far behind a 12g295.
So is it better to go for 12g295 (expensive) and potentially do a bit of work to it??? Or get a 12g202 (cheap), swap the inlet valve for 12g295 (or a little bigger), reshape the combustion chamber to match the 12g295 design and port accordingly???

Then, the rocker, I thought 1.3:1 or 1.4:1 would be a good thing but I have been warned that the 948 with a single “let-in” camshaft bearing does not like very much increase load on the cam lobs. Great rocket ratio will increase the mechanical mechanical advantage and double springs are stiffer so all in all, it sounds like a recipe for disaster. So, before I even consider an aftermarket cam such as SW5 from swift tune, I need to understand what the real limitations are.
I know that the engine will have to come out to be to the final desired spec but for time being, I don’t want to do so, ant thing I do to is has to be doable in-situ due to lack on time.
So, if I fit a “standard” 12g295, can I fit 1.3:1 rocket with standard 948/850 single bearing camshaft? Are there aftermarket camshafts that come with the big OEM bearing and 2 smaller bearings that seat into the block bearings allowing rotational de-multiplication and therefore limited wear?
To add to my confusion, I saw that Moss list 2 kits of camshaft bearing:
BMH1210 and BHM1211.
1210 seems to be for frogeye sprite 948cc (from spec) but it is the same part number listed for all sprigdet inc the 1275c.
1211 is listed for all the minor 948/1098cc and mini cooper 998cc.
So it is the case that they all fitted but 1211 is a better bearing alloy hence the extra cost???

Vibrations, I understand than I can flush the oil, take of the sump, remove the centre block/crank bearing cap, machine it and add the strengthening strap. Fitting the damper pulley from the cooper S /minispare is supposed to be better than the 1275cc.


Block… there a 2 ways really:
Using the 948 block, bore it out to take the minicooper pistons and con rods, redo the bearing, drill/bore out the camshaft housing to take the 3 bearing camshaft. Swap the oil point to the 1275cc style.

Using a 1098 block, fit the minicooper pistons and con rods, the 948cc crank etc. Issue with that is that the engine block has a 1098cc ID and a technical file will be required to prove that it is a compliant 998cc @ scrutineering.


Clutch, I saw in and old US owner manual that a 9 spring clutch is better for motorsport compare to the std 6 spring version. I believe the triumph Herald 948/1200 and spitfire Mk1 were fitted with 9 spring clutch to the same diameter and spline design as the frogeye but I such for a supplier, the only things I can find are 6 springs version.
Where can you source 9 spring clutch?
Alternatively, if it were a nightmare, would it not be simpler to fit a lightweight 1098 flywheel and 1098 clutch kit?

Thanks
G

[Murrayminor]

If you are not going racing, why go to the expense of building a race spec 948 engine, why not just put a 1275 engine in there and run that?

[Banned User]

Swiftune do FIA compliant 1.4:1 rockers like this,

6B0102BD-043E-4A88-B646-A388FB96A10A.jpeg (239.96 KiB) Viewed 4604 times

They’ll be very good with the SW5 cam in a 1000cc engine, BUT is the SW5 FIA compliant?

[Fentuz]

I said I'm not going to race for a few years (3 to 5)... which also means I have 3 or 5 yrs to build without pressure.
As far as I know on frogeye, 998cc is the max allowed on FIA classic.

otherwise, yes is cheaper to go for a 1275ish... by not allows registerable abroad if I have to move for work...

[philthehill]

The 948cc block is best for converting to 998cc with reliability built in.

Only the 1098cc engine with a engine number prefix of 10CC is suitable for long term tuning if you want reliability. The 10CC engine has 2" main bearings.

There is a 948cc MG/Sprite block that has white metal bearings on all three camshaft bearings and that engine number is prefixed by 9CG. Must be quite a rare item as I have been looking for one for some considerable time.

Any increase in camshaft loading by the valve train does require white metal bearings on all three camshaft journals.

There is no off the shelf camshaft kit supplied with white metal bearings. The block has to be line bored and bearings fitted and again those white metal bearings have to be line bored.

No modifications should be undertaken without replacing the oil pump (Cooper S preferably) and that does mean taking out the engine.

There is nothing wrong with the standard pressed steel rockers (with a bead of weld along the top), they are better than first imagined. Even with the pressed steel rocker there are variables with the ratio. The standard Cooper S forged rocker is very good if you can find a good set.

The standard one piece crankshaft damper is more than adequate even for high revs. The Cooper S two piece damper is good for high revs but it must be balanced along with the crankshaft assy. The damper weight must be matched to the engine power band. There is a considerable difference in weight between the standard one piece and the Cooper S two piece.

The centre main should be strapped or a steel centre main cap fitted.

The crankshaft assy including rods, pistons, flywheel, crankshaft damper and clutch cover must be balanced as one.

New standard valve springs fitted to the 12G295 head are more than adequate but can be changed to the Cooper S spec without difficulty. If the valve spring loading is high it will create unneeded/unwanted extra loading on the valve train.
The old Cooper 997cc camshaft is a good all round camshaft.

The 12G295 head is very good and even in standard form will deliver a good increase in power.

The 12G185 head as fitted to the early 1275cc Cooper S has all the right bells and whistles and will fit directly onto the 948cc block without valve to block interference but finding a good one is difficult.

You must change the simplex timing chain set up to the duplex set up - preferably steel as per the Cooper S with a good quality chain.

You need to change the conrods to the 998cc/1098cc fully floating small end type (same part number). The conrods with the pinch bolts are not really suitable for performance use.

Later BMC 998cc dished alloy pistons are more than adequate even good S/H units with new rings are suitable. Powermax pistons was the way to go when building 998cc performance engines way back.

The 9 spring clutch cover was fitted to the early Triumph Spitfire and the Reliant Kitten. I managed to find a NOS item and they do come up for sale on 'e' bay occasionally.

I could go on and on about the 948cc to 998cc engine conversions but I would suggest that you obtain a copy of Mike Garton's book 'Tuning BMC Sports Cars'. It has all the information and part number to build a very pokey 998cc engine. Also obtain a copy of the BMC Special Tuning pamphlet for tuning the 948cc Midget/Sprite.

The problem with tuning any engine is that what you do always impacts on other items of the engine and it turns into a vicious circle of improvements.

You should also get a copy of the FIA regs relating to the class of racing you intend to compete in and keep up to date with the regs as they are always changing - not always to your advantage I would suggest.

Below is a picture of my original 1958 Minor 948cc engine converted to near full race 998cc with lots of BMC Special Tuning goodies fitted.

img069.jpg (326.12 KiB) Viewed 4543 times

The carbs are a pair of 1.5 HD SU carbs sourced from a Riley 4/72 and very good they were too.

Below are a couple of photos of the near ultimate BMC small bore 995cc A Series engine the XSP series. Only a handful were made and developed by BMC.

XSP Sprite engine 2.jpg (381.95 KiB) Viewed 4521 times

XSP Sprite engine.jpg (392.91 KiB) Viewed 4520 times

It is fitted with the nine spring clutch cover - six yellow springs and three blue springs. The full competition version has nine blue springs.
You can make up a nine spring cover as some six spring clutch cover assys - that is the pressure plate and cover are already pre-formed to accept nine springs - all you have to add is the extra three springs and spring cups. Previously used and discarded clutch covers can be cannibalised for parts.
Here is a clutch that can easily be converted to nine springs as it has the preformed cover and pressure plate.
https://www.ebay.co.uk/itm/CLASSIC-GCK2 ... Sw~bldtaDd

[Fentuz]

that engine number is prefixed by 9CG.

Mine is a 8G9... so nothing special

[philthehill]

The number of your engine indicates that your engine has already been factory reconditioned so dimensions i.e. bore diameter and crankshaft bearing diameters may not be standard.

It would be good to know the dimensions as of now.

[Fentuz]

The number of your engine indicates that your engine has already been factory reconditioned so dimensions i.e. bore diameter and crankshaft bearing diameters may not be standard.

It would be good to know the dimensions as of now.

Thanks Phil, you re a fountain of knowledge. If it was reconditioned, then it would have to be stripped and measured. That s more than what i want to for now
I’ll measure the piston bore when the head gets swapped but the crank will have to wait.
Obviously, i would expect the piston bore to be oem or bigger but the crank is likely to be smaller not the best for future strength requirement.

[philthehill]

No problem with the crankshaft - just get it Tuftrided which is a form of pickling and which increases the strength of the crankshaft.

Having the crankshaft Tuftrided should be a matter of course for a performance engine.

[Fentuz]

I was thinking about the clutch plate last night... so for competition use (High torque) they use 9 blue springs. For fast road, 6 yellow and 3 blue.

Where can you get the blue from or can we find about what their spec is?
Also, is there a merit to fit 9 yellow?

[philthehill]

http://mgaguru.com/mgtech/clutch/ct_110.htm

I suspect that you would have to find a cover with one or more blue springs and rob the blue spring(s) from that cover to make up an all blue cover.

Just adding three yellow springs to a six yellow spring cover is going to make a vast improvement in transmitting power.

Below is a picture of a 6 1/4" dia full competition clutch with nine blue springs

comp clutch 3.jpg (31.43 KiB) Viewed 4375 times

Whilst you can set the release finger height by hand using the tool below make the job so much easier.

clutch tool.jpg (317.1 KiB) Viewed 4374 times

Here is one for sale on 'e' bay

https://www.ebay.ie/itm/VINTAGE-PICKAVA ... 3fd51c2ef4

See also

http://www.da7c.co.uk/technical_torque_ ... smant.html

Phil.

[IslipMinor]

The clutch fitted to the 918SV, 803 and 948 are all the same basic design and were 6.25" 6-spring clutches.

From the BMC Workshop Manual, the 6 clutch springs varied and are listed as:

918 Side valve - all blue
803 OHV - all blue
948 OHV - early 3 x blue and 3 x yellow/green
948 OHV - later all yellow/green
1098 OHV - all yellow - will they fit the earlier 6 1/4" pressure plate?

Being able to upgrade the 6-spring to a 9-spring is an ideal way forward. Are all the pressure plates suitable for this? Also the springs are located on a spigot on the back of the pressure plate, did the 9-spring plate have additional spigots for the 3 extra springs?

Since the 'new' springs are evenly spaced around the pressure plate, the exact spring rate is less important that being able to increase the clamping pressure by around 50%.

We had the original AP 9-spring plate in the 1970's and never had any problem with a very well modified 948 at the time. It came out of the car in 1992 and was stored until a few years ago, when I sold the original engine. It is now fitted to a Frogeye Sprite, still with the 9-spring clutch as far as I know!

[philthehill]

Richard
Thank you for the information above.

The pressure plate has to have the ability to accommodate and hold the springs in place. The cover also has to have nine holes.

All clutches must have the spring cups into which the spring fits and which are fitted into and through the cover.

Some pressure plates have the additional three bosses for the additional three springs, some do not. The same with the cover some have the additional three holes and some do not.

Some clutches have the additional three bosses for the spring location as well as the additional three holes in the cover whilst only having six springs.

In most cases it is a case of mix and match to achieve the nine spring cover.

If different coloured springs are fitted they must be configured around the clutch cover for example:- yellow, blue, yellow, yellow, blue, yellow, yellow, blue, yellow.

Phil

[oliver90owner]

I’m of the opinion that a diaphragm clutch linkage should have been sorted out by now - we threw out the coil spring type, as not fit for purpose, and fitted diaphragm clutch covers to Fords back in the early 70s.

Heavy on the left foot but actually worked so much better on Anglias and Cortinas which were driven enthusiastically (and usually with a larger engine).

[les]

I’m sure your company wasn’t alone in fitting diaphragm covers but I wouldn’t dismiss the spring clutch as not fit for purpose. They must have done the job for vast numbers of vehicles to be fitted with them. I’ve tried both in a Minor and within a week I’d refitted the original, just my personal preference based on drivability.

[Fentuz]

Well, I'm gonna have to look at that soon as I noticed that after 5 miles, the car squeals a little when pushing the clutch pedal...

[Fentuz]

A couple of months ago, my engine went pop... hgf
After inspection, the head is cracked so junkyarded or door stop but good thing is the block is already 998cc with flat top piston...
so I m getting a small bore ported head with big valve and higher compression.
Electronic ignition will go in too.
I also found some press steel 1275 rockers (1.27:1).

As it s bits, might be worth doing the camshaft too... so for fast road/trackday/sprint what cam? I don t mwant max un usable power, i want more torque in the std range; basically shift up the area under the curve not shift to the right...
I read about 997 cooper cam and piper bp255... what are your thoughts?

Also, what thermostat would you fit and what temperature range should I aim for to keep it reliable?

Thanks

[philthehill]

The 997cc Cooper cam is very good I had one in my modified 998cc 'A' Series. With a well modified 12G295 head, twin 1 1/2" SU carbs and LCB exhaust manifold, Power Max pistons and lightened flywheel etc, etc. it went extremely well.
The 997cc Cooper camshaft gave good tractability and performance. Any camshaft with similar valve lift and timing will give good performance and tractability with your engine set up.

I would use a 82 degree thermostat. The Minor is overcooled ex factory.

[Fentuz]

Good.
What’s the spec? How does it differ from the 948 (8G712?)?
997 is 88G229 and I read that the cam profil came from mga and b. Is this true?
Is it a single bearing or triplebearing


I believe std 998 had the 8G712 cam but the 998 cooper had the AEA630 & 12G165 also shared with the 1098.
What was the difference between 88G229 and 12G165 (and arguably the 8G712)?

Thanks

[Fentuz]

Good.
What’s the spec? How does it differ from the 948 (8G712?)?
997 is 88G229 and I read that the cam profil came from mga and b. Is this true?
Is it a single bearing or triplebearing


I believe std 998 had the 8G712 cam but the 998 cooper had the AEA630 & 12G165 also shared with the 1098.
What was the difference between 88G229 and 12G165 (and arguably the 8G712)?

Thanks