Midget engine rebore

[IslipMinor]

The SW5-07 is by reputation a good 'road' cam, quite mild in timing (242°), but has higher than 'normal' lift for its timing - very similar to the Kent 246 that uses the same philosophy. With standard rockers the tappets are set to 0.016" with Swiftune, so with 1.5" rockers set the inlets to 0.018" and exhaust to 0.020" (expect a little audible whirring from the valve gear!).

Has the head been converted to unleaded? If so you might get away with 0.018" for the exhausts as well, but to be sure, I would use 0.020" for them.

What advance curve does the Accuspark dizzy have? It should have no more than 10° 'distributor' maximum mechanical advance (20° crankshaft), so that with an initial 10° BTDC static advance to give a reasonable idle and an all in advance of 30° at ~4,000rpm. Does it have a vacuum unit? Do you know what advance that gives?

If the 12G940 head (big valve or standard?) has been well ported and flowed, a good HIF44 inlet manifold and set up on a rolling road, I would expect 85-90 bhp at the flywheel (NOT the wheels) with that sort of engine spec - so should exceed your expectations!

[olderisbetter]

The dizzy is a new one, so i will have to back track on the paper work and look up to see if i can find some curve info, and it does have a vacuum on it, as for the unleaded part and porting i am in the dark ther is an invoice from Cuerden classics for machining costing £786 plus vat but not detailed, i think just to be nosey i will take the rocker cover off and determine the head type. i pressume there is no easy way to tell if it is unleaded other than off with its head... and 85-90 bhp is sounding great.

[IslipMinor]

The head will almost certainly be the good 'ole 12G940, as that was the original fitment on the Spridget 1275 engine. For anything else, flowed, valve sizes and leaded/unleaded it is head off.

[Beatroot52]

Sorry for the hijack, islip, i have had nodiz for a year now but keep putting off the rolling road session due to upgrades and a much needed sill replacement. Are you using the standard map? Thanks dan

[IslipMinor]

Hi Dan,

No it's a very long way from it. With an alternator, the effect of load on idle is very noticeable, so the idle/low speed part of the map is a crude attempt at idle speed control, and better than not doing anything.

After that it is a mixture of the Aldon 'Yellow' curve and one of the '123' 30° curves as a starter before the rolling road session. I will very likely go to Motorsport Electronics (NODIZ) to get the map finalised.

If you send me your email address, I will send you 'my' map for you to play with.

Have you fitted the NODIZ yet? What trigger wheel are you using?

If you are anywhere near the Oxford area you are very welcome to come and see the installation.

[bmcecosse]

To go back a step or two - I would NOT use high lift rockers with the 07 cam - it is already 'high lift' and you don't need any more - you are just compressing the valve springs even more - and adding to the general wear and tear on the valve train. The rocker/valve tip geometry with such high lift is decidedly dodgy. The 07 is a bit of a busted flush these days - but since you have it, may as well use it. Better bet is to check you have a 'big valve' version of the 940 - that's more important than heaving the valves even higher. Mini/Metro place has had some very 'mixed' shall I say reviews on the Mini forums..... . Once you see the block scoring - if the other bores are all good - you can just have that one bore sleeved - then bored to the same size as the others. And yes - the 7 or 8 port heads do obviously offer more air flow - but crazy expensive... I first saw a ' 7 port ' head conversion 50 years ago - fitted with 4 Amal carbs - sadly they couldn't keep it watertight.....but I admired their ingenuity!

[Chipper]

bmc
The 1275cc Midget engine seemed to have escaped the 'porous period'.
I have yet to come across one that was sleeved from new.
Here is a gold seal 1275cc Midget block that has been sleeved but it appears to be a Gold Seal unit which when re-conditioned were nearly always put back to 'as new' specification.
http://www.ebay.co.uk/itm/MG-Midget-127 ... Sw3mpXMxEJ
May be worth a punt at the current price.
Phil

The 1275cc Midget engine I bought in the early 1990s which is currently in my Traveller has liners, yet is standard bore size and the standard 12CE... engine number.

The liners have lasted the 60,000+ miles it's been in the car without any dramas though.

[bmcecosse]

I'm sure the 1275 Spridget engine I sold recently had liners -and appeared to be otherwise untouched. Liners are harder wearing then the bare cast bores - and do indeed seem to last much longer.

[olderisbetter]

How much does it cost for a liner not looking for a quote just a rough figure, and i hope over the next few days to work out a way of using my inspection camera down the bores throught the plug hole and getting it onto youtube.

[bmcecosse]

I'm sure it will be less than a full rebore and new pistons.....But the initial problem with a 'con rod' is a little worrying - how was that resolved ???

[olderisbetter]

It was solved with a replacement conrod, so in all honesty it could need more looking into as it had alot of work done before the conrod failed.

[bmcecosse]

Hmmm - the gudgeon pin on the 1275 engine has to be pressed into the conrod eye - usually after heating the conrod to 'straw colour' . The view from your camera will be interesting!

[philthehill]

Whilst most people use the 'heating the small end method' for fitting the 1275cc gudgen pin care has to be taken because the eye of the rod can be overcooked; or if you do not get the heat right the eye cools before the gudgen pin is fully inserted .
A task not for the faint hearted - better to get an engineering company who have the correct tools or is experienced in fitting 1275cc (and later 998cc) 'A' Series gudgen pins.
Phil

[bmcecosse]

A C Dodd has a YouTube of how to do the job. A local 'engine place' I used many years ago did the job by leaving the conrod eyes in a bath of liquid white metal which seemed to get them hot enough for an 'easy' press. Not a job I have ever tackled myself - although I have drawn gudgeon pins out with a puller and gas torch . The risk of course is in damaging the piston - or indeed overheating the con rod.

[les]

Jobs like this need a jig to support the piston and as much as possible positioned before heating the rod, also a stop is helpful to stop the pin travelling too far. Yes, a company is an option, the problem is finding one to trust!

[philthehill]

Les:-
That is why I now have the correct tool for drawing and fitting the gudgen pin in a 1275cc engine and which is similar to BMC special tool 18G1150 with adapters for round and cut away pistons.
Phil

[amgrave]

Philthehill.
Do you still need to heat the rod when using the correct tool.

[les]

A picture would be good Phil!

[philthehill]

Amgrave
No need to heat the rod the tool has enough power to pull the gudgen pin out and pull pin the back in.

Les
I do not have any pistons to fit or remove at the moment but I can look the tool out and post a picture on here.
Whilst home made it is well made and does the job with ease.

This is the Churchill version:-

Phil[frame][/frame]

[amgrave]

Thanks for the info Phil, I've got a crick in me neck now though