A while ago I rate tested a bunch of standard A7 valve springs, largely because I could. What I found was a fair spread in stiffness from 57 lb/in to 77 lb/in with between 25 and 31 lbs of seat load - the softest set were brand new, and the stiffest had just come out of my engine.

I'm sure they all work just fine pottering about, but I did some slightly sketchy maths that suggested that the stiffest would bounce at about 4300rpm, which was 57mph in my special. This seems to be about right in reality.

To put this in perspective, a standard 850cc A series has a 113 lb/in spring with 51 lb seat load.

I'd read somewhere of folks using Maxi springs in the A7, so picked up a cheap set to measure. Testing one showed a rate of 113 lb/in, with an installed seat load of 67 lb.

Standard installed spring length in the 7 seems to be 1 1/4", to drop the seat load to 51lb as per the 850 I'd need to increase that to something like 1 3/8".

So, does a mini type setup sound reasonable? What have folks done in the past when installing maxi springs? Any suggestions how best to find the additional 1/8" spring space? Anyone have figures for double springs?

I've not tried calculating what these stiffer springs will do to valve bounce rpm.

As an aside, installing the maxi spring as above allows about 11mm valve lift before the spring goes coil bound compared to about 8.5mm for a standard spring. I believe it's normal to allow about 2mm of clearance, so that's more like a usable 9mm and 6.5mm (apologies for the mixture of units, it's just the way I roll :) )

Andy

Location: Oxfordshire

Have you thought about cam wear? 850 has a cast iron cam.

I must admit I thought the same as Bluto but have no experience to back it up.

A cast iron cam retains oil and helps the tappets live longer.

Our old BMWs run steel cams and we have the best luck with chilled iron tappets ...... I actually centerless grind A range ones to suit the BMWs Drill a couple more holes in them too.

Andrew
My advice,before installing extra strong springs look at how it holds together.
That is on 8 5/16" studs,on the tappet side 2 of the three pull out of almost nothing.
You can fit blocks or angle brackets to pull on the strongest part of c/c,over the cam bushes,or where the 2 studs which pull out of nothing,make extra long studs to pull it together to the strainer plate face using a plate to spread the load.
This isn't straight forward as the cam gets in the way.
In your calculations,do they include the weight of the cam followers,You can reduce these down to nearly half their weight.
Ideally you don't need any more valve lift than .290-.300" .
Again only my opinion.

I have now seen a few mentions of using Austin Maxi (E series engine) valve springs in 7's as an alternative to double valve springs. Does anyone know any more about using them? Are they a straight swop, or are any mods required? Thanks.

We used Maxi valve springs from about 1986 to 2010 without any issues. We gradually increased the pressure to cope with the higher RPM needed. At Cadwell Park the engine would run at 7300/7400 from Mountain to to the Hairpin without any sign of bounce.
Having said this, I suppose it also depends on the amount of lift you have. We never raced with more than 305 thou although we experimented unsuccessfully with more on the test bed. I can try to dig out the figures if you want, I'm sure they are gathering dust somewhere in the workshop.

I Have used Maxi/Wolseley 2200 valve springs in several A7 motors without any issues. However, I have always used them with BMC "A" series valves, collets, and valve caps; The BMC valve caps need to be machined down to accept the smaller diameter Maxi valve spring. The A series valves are available in a range of head sizes, but all (except the Metro turbo motor exhausts) have 9/32" stems, the same as the A7; the A series valves are slightly longer than A7 ones, so the seat pressure is reduced as against using them with A7 valves.

Location: N W Kent

Had my eye on some Maxi valves on ebay, but missed out on them. Will keep looking.

Hi Frank, it would be interesting data for future reference. What valves were you using with the springs?

All the best.

Tom

Location: Guildford

I now have a set of Maxi springs for my engine, and am looking at what else I might need to do to use them.

Currently the inlet valves are 1.156" Jack French valves, they do not have a tapered groove for the collets, but are currently installed with A7 tapered collets and caps. The exhaust valves are standard 1" A7 with the pin retention. The engine was rebuilt by my father several years ago, but has not been run yet (it's a very long term project!!).

I need to check the length of the Jack French inlet valves, but my suspicion is that they are are Mini 997cc inlet valves (part No AEA574). If so I will probably replace the collets with the Mini 3 groove collets (CAM6975) and turned down caps (AHU1897) - I think this is what the Pigsty parts are. The A7 valves are 82.6mm long, whilst the Mini ones are 88mm long, does the A7 engine accommodate this extra 5mm in length?

For the exhaust valves, I am not sure whether to retain the pin type or swap to the split collet type, the later feels like the more robust solution to me? However if the 88mm Mini valves will fit in, then I might as well fit the 1" version of those (AEA434) with the Mini collets and caps to match the inlet valves.

I would welcome your thoughts and opinions on these options.

Thanks.

Location: Kenilworth

If they are Mini 997 valves they will have a parallel collet groove about 5/16" long; as used on A series motors till (IIRC) the mid '70s. These valves should be used with the corresponding parallel collet rather than the later triple groove collet which goes with the matching style of valve. Re the longer valve length, I've never had a problem with this, but I have always used them with reprofiled tappets, which obviously drops them down in the tappet guide a bit; if the cam has been reprofiled too the tappet is dropped even more (because the cam's base circle will have been ground. Then I usually skim .050" or so off the the top of the tappet guide to ensure there's working clearance for the tappet locknut.



I've never used the pin type A7 valves in a performance application -just a bit nervous of one of the pins shearing. But using them with the Maxi springs would result in a higher seat pressure than you would have for the A series inlet valves because the installed spring length is shorter when using A7 valves; I would install mini 850/A30/A35/minor 948 exhausts, which are the same head size as the A7 valves as you say.

Location: N W Kent

I have just pulled one of my 1.156" inlet valves out, and it is 3.442" / 87.17 mm long with a 5/16" parallel collet groove, so certain it is a 977cc Mini inlet valve (it is marked AE3568). The cam is a fast road from Vince Leek, and has flattened tappets, so no clearance issues.

I will get some matching 1" Mini valves for the exhaust. As regards the correct collets for these valves, they no longer appear to be available. Maybe thats why the picture of the collet and cap set shown on the Pigsty website has the 3 groove collets and matching caps, although the pictures of their valves show they have the parallel collet grooves. On this basis, I assume using them with the earlier type valves should be OK?

Update - just looked more closely at their pictures. Collets and caps are matched to their race valves which do have 3 grooves.

The good news is that I have found and ordered 4 pairs of the correct collets from Bull Motif Mini Spares - the last ones they had :-).

For the exhausts I will go with the 74 on single groove 1" valves and collets, as these are readily available.

Location: Kenilworth