Hints and Tips - Austin 7 Tuning

The following series of threads took place in July 1998.

Dr G W Owen wrote:

Pete,

.... we also flattened the followers a little (from R3/8" to R3/4" I think) and skimmed the head.

What are you planning with the car?

Geraint

Pete Bishop Replied....

Geraint,

Thanks for the reply,I am building the car up at present and planning to compete in VSCC trials. I have a lot of work to do yet, but have got to the point where I can drive the chassis and body tub if I can get the engine running which should provide some more motivation to carry on!

I have acquired a 37 type cylinder head in good condition which I believe gives a higher compression ratio anyway.

As regards flattening the followers is this just done by grinding, and do they need to be re-hardened afterwards?

You say you do not know the needle and spring to use, is it possible to find out how your girlfriends brothers car is equipped, and if the mixture seems about right - I guess I will probably need about the lightest spring and weakest needle available?

Pete

Dr G W Owen followed up....

Pete,

The 37 cylinder head is worth using, but I think that they only allow them if you machine them to take 18mm plugs. I know I did for Alex.

I ground Alex's followers on a bench grinder. I made a little jig to ensure they ended square. I know I kept them very cool, but I don't know if that was enough to not harden them.

I think there is a choice of two springs, one gives more top end, the other more bottom end. I think the needle will have been a filed at the rolling road affair

Geraint

David Cochrane added.....

> I have acquired a 37 type cylinder head in good condition which I
> believe gives a higher compression ratio anyway.
>
Pete,

This is a good head to use, but you will have to get the 14 mm plug holes tapped out to 18 mm to get the VSCC to approve of it.......

Regards,
David.

David Laver Also responded....

> I have acquired a 37 type cylinder head in good condition which I
> believe gives a higher compression ratio anyway.

This has two advantages - an increase in CR, but more importantly the spark plug is over the valves in a much more compact chamber.

> As regards flattening the followers is this just done by grinding, and > do they need to be re-hardened afterwards?

Depends how long you want it to last!! I got mine done by Tim Myall, he's on 01892-652-215. The other person to ask is Don Rawson on 01691-661-440.

> You say you do not know the needle and spring to use, is it possible to > find out how your girlfriends brothers car is equipped, and if the > mixture seems about right - I guess I will probably need about the > lightest spring and weakest needle available?

Mine is a Number 6 needle which is much too rich. It was adjusted leaner by moving it in the piston at Wiscombe and it overheated and seized so be careful. Over lean and you seize, over rich and you get bore wash and bearing failures. Best to take it to a rolling road ASAP. Also don't keep over advancing to get more revs - I did and pulled block studs. Keep in mind that these engines are producing double to treble the original design power, at double the revs, with sixty year old castings. Have you got a stronger crank? If not then a crack test would be worthwhile. The old hands hit them with a mallet and can tell by the purity of the ring.

Other mods to make are to lighten the flywheel and have it all balanced. I haven't yet but wish I had got it done when it was all apart. Tim Myall will also regrind the cam to a fast road or race profile. Many people have larger inlets, and profile the top edge of the bore to the inlet to smooth the flow. Better to have a smooth flow and sacrifice a tiny bit of compression. Have you got the Bill Williams book?

Mods that are NOT worth doing are twin carbs and supercharging. Superchargers come in two catagories. Low boost and the losses offset the gains, or high boost and the block splits, bearings pop, pistons burn, blower drive shears, chunks get blown out the head. Twin carbs are only worth doing if the ports are divided which the VSCC don't like.

The best way to improve performance is to get rid of weight. Gram by gram drill and grind and redesign.

That said - I'd love to have a blower on it !! Back to the workshop - I want to make Prescot this year and the engine is still in bits and the bonnet needs remaking to fit the new (old cut down and against my advice heavier) cowl and the mud guard stays need remaking and and and and...

GOOD LUCK!!

David

David Whetton added....

Dear David,

I have picked up your conversation with Dr Owen about A7 settings. Having just started in 750 Trophy racing I am trying to pick everyone's brains for the secrets of the trade. What Carb/spring/needle settings do you use? I am running on an 1 1/8th SU with blue spring and a number 6 needle but have also been advised to try a 1 1/4in with a number 5 needle! Suggestions please.

David Whetton
Dorset A7 Club

David Laver Responded...

David,

Take it to a rolling road. Get too rich and bore wash seizes the bottom. Get too lean and it runs hot and seizes the top end. I suffered the latter fate this weekend so will be off to get it done properly next time its all of a piece. I was going to go before but... I've been running a 1.25 with a red spring and a number six which soots everything up.

I'd also been running over advanced. Set the car up a bit advanced of tdc. Get the car warm at a quick tickover and rotate the distributer to get a feel for the curve. Start advancing and the revs will start to rise, keep going until the revs start to fall again, keep going more and the tickover become very rough and eventually it dies. I was running a little past the 'max revs' point which is where the 'screamers' set it. These engines have hot cams, twin carbs, and very very open ports to get upto 8000rpm. This setting made my engine hammer at low revs and have no power below 3000rpm. Eventually the block shook loose of the crankcase.

I need to be a little on the retarded side of the peak so I need to start at tdc, advance until the revs start to rise, and leave it. On Sunday it would rev to 6000rpm like this with a nice tickover and plenty of torque. This is with a fixed advance distributer. When I ran a Ruby type I set it up exactly the same way. Apparently it doesn't move the advance much as they were never supposed to rev past 3000 - it just vibrates to scatter the timing. Maybe there's scope to change the springs and control the advance. When people get to that stage with an A7 then tend to have fitted a modern distributer.

Its also very sensitive to breaker gap. The distributer earthing is poor. Slop in the distributer drive is bad news as is a wobbly spindle and loose rotor. I also had a loose cap and had the LT terminal on the distributer arcing and earthing against the bonnet side.

Geriant's girl friend's brother had his A7 tuned at a place near you.

I hope you learn your lessons quicker than me - and have fun !!

David

David Laver also contributed.....

> Hopefully trials will not be as

> stressful as longer periods of high rev running would be in racing so it
> may stay together.

Oh yes !! Apparently the worse (resonant) time for them is about 3000rpm constant - so just thrash the nuts off it and you should be fine :)

> with the improved breathing
> do I need to go to double/higher rating valve springs to get a few more
> revs - where does valve bounce set in with the standard (probably tired)
> springs? If so any recommendations on where to source some?

Valve springs are cheap - just don't think about it and get a set of double springs.. I think mine came from the 7 workshop. Tim Myall is worth a phone call.

> > The best way to improve performance is to get rid of weight. Gram by
> > gram
> > drill and grind and redesign.
>
> Ummmm yes that comes through as a clear message in several texts,
> trouble is as I am putting the car back together it seems to be getting
> heavier and heavier...............

A good looking fully equipped car is going to weigh more. Then again if you were into all out competition you wouldn't have an Austin 7. But also keep in mind that lightening holes also look good. If you have the chance the sorts of places to save a lot of weight are body skin thickness, bonnet thickness, wings, lights. A few holes in the damper blades are still progress but three orders of magnitude less progress.

Every time you add or replace a part think about weight. The really serious cars have drilled crown wheels and tubular half shafts.

David

David Cochrane also picked up on the engine stress point...

Pete,

> .... Hopefully trials will not be as stressful as longer periods of high
> rev running would be in racing so it may stay together.

A strong element of wishful thinking and finger-crossing seems to be apparent here !! I strongly suggest that you get your crank crack-detected - work out how much time and money is going into your engine and imagine all that going west 2000 miles down the line (as happened to my cousin in his Top Hat a few years ago). Or holes being bashed in the sides of your crankcase (as happened to me once upon a time with a bog-standard engine). If (as is probable) it does have cracks, you would be well advised to bite the bullet, pawn the kids and buy a Phoenix spit and hope crank (01753 821303). John Newman is your man - he should remember me, as I bought over 4 dozen from him a few years ago...

> ... do I need to go to double/higher rating valve springs to get
> a few more revs - where does valve bounce set in with the standard
> (probably tired) springs? If so any recommendations on where to
> source some?

Depends on your cam followers and camshaft profile, but I think about 4500. The latest idea seems to be double up on the inlet only, as with unleaded fuel you need to treat the exhaust ones gently. John Barlow (0115 922 4926) can supply them.

> ... trouble is as I am putting the car back together it seems to be
> getting heavier and heavier...............

A Chummy can weigh about 9 cwt, or about 72 stone. Driver can weigh 12 stone, ie an extra 17%. Going on a diet could help...!

Cheers,
David.


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