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MG Midget and Sprite Technical - 1275 engine 1098 gearbox combo

Hi all,
putting a 1275 engine plus 3.7 diff and 1098 gearbox into a Frogeye but not sure what combination of release arm/bearing/slave cylinder to use.

I'm using a 1098 gearbox to take advantage of the 3.75 (or there abouts)first gear ration to go with the 3.7 diff.

Any advice would be welcome.

Rob
Rob aka MG Moneypit

Eehhh

Smooth case trannys from what ive read are not very solid...they like to go bang.

The ribby is a better choice for a lucas 4 speed.

Prop

Prop and the Blackhole Midget

You will need a 1275 release bearing and a 1275 slave cylinder as it has a larger bore than the 948/1098 one. You will also need a 1275 or 1098 release arm with a 1275 push rod .The slave has a different fitting for the clutch fluid connection to the frogeye one so you will also need an adaptor in order to connect the clutch line up. You are also better using the later 3/4" bore master cylinder from a MK111 sprite.

I assume the 1098 gearbox is from a spridget as the others say fitted to a minor or an A40 do not have needle roller bearings on the main shaft and are a little weaker. All the 1275 spridget boxes are fine and can be identified by the part number 88g229 on the input shaft.
Bob Beaumont

Rob, I thought all midgets from 1098cc onwards had the same ratios; I think you need a Morris Minor 1000 ribcase with the lower 1st and 2nd gear ratios to meet your criteria.
David Smith

Use the Spridget rib case box, it's a lot stronger and the taller first gear won't be bothered by the 3.7:1 diff….

I must ask, why are you using a 3.7..?

Mark.
M T Boldry

""" I must ask, why are you using a 3.7..?"""

Mark,

The new movie "need for speed" comes out next weekend....you have to have something cool, sick and wicked if your going to out run the cops...hahaha

Errrr, wait that maybe my masterbator fantasy

Prop
Prop and the Blackhole Midget

Go 3.9 and use any spridget ribcase.
The 3.7 is just loading the engine and box more.
A-series are not meant as torque monsters they want to rev a bit, ad the ribcase will not be happy with the added load.
Hell it is not happy with my 1380 and 4.2 for that mather ;)

Clutch slave etc depends on the MC used
Onno K

Hi all,
I've got the dual master cylinder for disc brakes. I've fitted almost everything new at the front, including discs if you were wondering.

Prop, the 1098 gearbox is a rib case.

3.7 diff because I had one handy which seemed ok and the engine (a David Smith sourced engine) was breathed on somewhat before I bought it. +60 overbore, higher lift cam, fully balanced, MG Metro head, centre main strap, baffled sump. I replaced the piston rings (3 per piston), honed the bores, new main and big end bearings, new rocker shaft, new cam followers, new duplex chain, full gasket set, new plugs etc. All up about £220 in parts. Oh, and green paint with new engine decals.
See pic.

I thought early 1098 gearboxes had higher ratio first even on Midgets but I'll check.

Now I know what I need (thanks) I will order them asap.

I've got a 3.9 somewhere but it has a bit of back-lash on the pinion but it's there in case!!!!

Not sure what to do about tyres. I'd like to keep the original Frogeye wheels. What's a good tyre for that size rim?

Rob

Rob aka MG Moneypit

Minor correction to Bob's post: 1275 ribcase has 22G229, or rarely 22G1117, on the input shaft.
The early 1098 ribcases had the A-type gears (same ratios but different tooth angle, they were a bit noisy apparently) and have 22G172 on the input shaft.
I have a spare box and clutch arm if you can't get what you want locally at a sensible price. And I recommend Klassik Transmissions for a rebuild if you want one.
David Smith

Looks great rob,

Make sure you do.a.good inspection of the oil canister gause, if its set for very long that thing can rust clogg up quick and become ineffective and allow lots of oil into your carbs

Prop
Prop and the Blackhole Midget

Rob, my frog is virtually set up the same as yours except I am using a slightly softer cam. I use the standard frog wheels (apart from trackdays)and just have pirelli 2000 which are fine. I have done a couple of trips to Europe and a couple of gentle road rallies and they have performed well They are slightly softer than the michelin equivalent. I did not find many options of 145x13 80 tyres to be honest
Bob Beaumont

Looks like it is a morris box as it has a 22G171 input shaft.

The gearbox has been fully rebuilt by Peter Cavanagh of the Classic Gearbox company who works out of an old mill not far from me.

I'll just be using it for pleasure and a few club outings and hopefully, it will make it to Le Mans this year.

We will be in France from 1st to 8th July at a place about an hour south of Le Mans and going to the circuit for at least one day and touring about the rest of the time.

Ordered all the clutch bits and bobs which should be here by the weekend and waiting for an exhaust manifold to be delivered maybe tomorrow


Rob
Rob aka MG Moneypit

Rob,
tyres, it depends on what wheels/rims size you have fitted

if it's the pressed steel 3.5" then originally they had 5.20 x 13" tyres which according to the source below at least works out at 130 to 135 width tyres as opposed to the later 145 width, see calculator in 'Classic / vintage radial tyre sizes' section on the page - http://www.carbibles.com/tyre_bible.html

vintage tyre size conversion table - http://www.carbibles.com/vintagetyresizes.html

I'd be looking at 135/80/13 or 145/70/13 but with the 145 check the actual make and model of tyre is recommended for 3.5" width rim, the 135 will be a closer match to the 3.5" rim width and have a lower load index suited to a lighter car - http://www.kouki.co.uk/utilities/visual-tyre-size-calculator

Guy says he finds the Toyo 330 good on his Mk4 Sprite all be it that his wheels and tyres are wider sizes

see 135/80/13 (330) here in the sizes and specs list for the Toyo 350 (don't buy the 350 in 145!) - http://www.toyo.co.uk/tire/pattern/350

Firestone F590 also come up in 135/80/13

(take the new tyre label ratings with a pinch of salt)

there is a much wider choice in 145/70/13 see my 'tyres (what to buy) again' thread in this forum for recommendations but check on size, many are also in 145/70/13 too
Nigel Atkins

Rob
In July you must be staying along the Loire Valley.
I am in that region from 28th June - 12 July touring with a Kent Masc crew and visiting the Le Mans Classic & the Bressuire Historic GP.
Alan
Contact via www.masckent.org
Alan Anstead

Staying at La Marechalerie in Monthodon. Found a nice place and so inexpensive it's hard to believe.

Rob
Rob aka MG Moneypit

Nigel,

Although 135 width is the nearest conversion to the original 5.20 width of crossply tyres factory fitted to early Sprites and Midgets I believe 145 was size originally offered for these cars when radial construction first became available.
Ray Rowsell

Rob
We are about 35 mile west of you at Parcay les Pins.
Could meet up?
Alan
Alan Anstead

Me and Janet would like to join you Alan. Neil and Shelley McLeod will be with me at the same place and with a bit of luck will have his Frog running by then. Also planning to get together with Mike and Karen Bennett and a few other North Westerners going to Le Mans.

Ray, I currently have 145's but a brand called Kormoran. Never heard the name before and I've spent so much so far a decent set of tyres must be an investment.

Rob
Rob aka MG Moneypit

Rob
Can you make contact via www.masckent.org?
Alan
Alan Anstead

Will do tomorrow. Off to the monthly meeting tonight.

Rob
Rob aka MG Moneypit

Hi Ray,
I've just had a look in Terry Horler's book - Original Sprite & Midget The Restorer’s Guide by Terry Horler –
http://www.amazon.co.uk/gp/product/1906133336

and the first mention of 145 tyres (Dunlop SP radials) that I saw was on page 83 for the Mk3 Sprite (Mk2 Midget) which are heavier cars than the Frogeye and the 135 generally a better fit to a 3.5" rim so I'd still consider them

as just an example the Toyo 330, 135/80/13 are for a 3.5" rim (and range) and have a load index of 70 which equals 335 (x4) = 1,340 kg

the kerb weight of the Frogeye is shown elsewhere as around 700 kg so even if you allow for petrol, loads of spares and two heavy occupants the tyres can carry lots more weight (up to 130 mph)

the Toyo (350) 145/80/13 are for a 4" rim (and range) have a 75 load index which equals 387 (x4) = 1,548 kg, so 208 kg more of unnecessary load carrying (in simplified terms)

I'm just putting the idea out there (for others as I doubt Rob is interested in my ideas and that's fine) each to there own
Nigel Atkins

This thread was discussed between 10/03/2014 and 12/03/2014

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