Good Morning
I have read recommendations on there and else where that more power can be obtained from a standard cam by increasing the radius on the cam followers. I have read 3/4" radius and 2" radius.
What figure should I use and do I need to shorten the follower guide to miss the tappet nuts.
Many thanks.
Adrian.

Location: New Forest

I've always used a 2inch radius, although some folk think that too much, especially if it's a road engine.
They are available from various suppliers - that's probably a lot easier than doing your own.

And forgot to add you will need to shorten the guide.

I don’t know what background Stanley Edge had, but someone knowledgeable must have done the arithmetic on the Seven engine. Theoretical follower acceleration is proportional to the sum of the radii of the base circle and the follower, 3/8 + 3/8. A ¾ follower increases this 50%. A 2 inch follower increases it 300%.

For those that derive diy satisfaction the followers can be held in a lathe with the radius centre carefully positioned, and rocked back and forth by hand with a drill or somesuch as a toolpost grinder. Finish on an oilstone, taking care to retain square.

Location: Auckland, NZ

Trust Bob to spoil it for everyone. Adrian only asked a simple question,
now we are all confused.

Don't worry Vince. I think his maths is wrong anyway.

Location: As far east in Kent as you can get

When I finally got my first Chummy on the road in 1989, I was staggered by the performance. It had a big valve block and modified cam followers among other mods. A few years later, I removed the cam followers to use in another engine, and I'm sorry to say that I'm only building that engine up now!
Anyhow, the point is that without the magic cam followers, the engine lost all its sparkle and ran very poorly. Here is a pic of the offending items, I reckon they're flat on the bottom!

Location: North Wiltshire

Tim Reynolds

When I finally got my first Chummy on the road in 1989, I was staggered by the performance. It had a big valve block and modified cam followers among other mods. A few years later, I removed the cam followers to use in another engine, and I'm sorry to say that I'm only building that engine up now!
Anyhow, the point is that without the magic cam followers, the engine lost all its sparkle and ran very poorly. Here is a pic of the offending items, I reckon they're flat on the bottom!

Location: N W Kent

Yes, the cam was standard and the engine certainly produced the goods; the car went like stink! I'm looking forward to putting these back into an engine shortly. I seem to remember that the downside was that they were noisy, perhaps that's why, in recent years, followers with a large base circle radius have become more popular.

Location: North Wiltshire

As I recall, the followers on the Reliant sidevalve engine, derived from the Austin 7, were simply flat.

Simon

Location: On a hill in Wiltshire

Yes, Simon, they are, and I think they are designed to rotate to avoid wear. There's nothing wrong with flat tappets, just the accelerations tend to be a bit violent and likewise the wear rate. That's why 2in radius became popular. Current race sevens might even use asymmetric tappets to vary the opening and closing rates, but that's giving away trade secrets.
Like BC suggests you can grind close to a 2inch rad simply by holding the tappet block sideways in a three jaw chuck, (think about it and all will be clear) but don't tell the health and safety people.

Hi All
Many thanks for all the interesting information and emails. After a chat with Paul Bonewell it looks like I may be wasting my time. I wish to keep my low compression head and bronze carb so these will be the limiting factors. Changing the cam followers will produce very little benefit and result in higher wear to the cam. If it aint broke don't fix it!
Adrian.

Location: The New Forest

Sorry Chaps I have to disagree about the side valve Reliant followers, they are in my experience the same shape as the Austin ones. The OHV may well be flat and able to rotate, but not the SV. I do however agree will the other MOST of the other comments
The asymmetric tappets in Seven engines go way back to Circa 1960 and Keith Dixon's tuning experiments.

Location: Auckland NZ

For those who have observed flat foot followers on many other makes, these are used with convex face cams; not tangent cams. Otherwise the theoretical acceleration becomes infinite. The so called flat seven followers are more correctly “flat with rounded edges”, which modifies the action. (One virtue of the seven type followers is that can be used with concave cams for very full lift opening without wild overlap.)

I have ground the more reasonable ¾ radius by method described. Clamped to a faceplate.

There was an error in the maths. Should have been 315%

Location: Auckland, NZ

Yes, that's what I think too.

Interesting, in the engine I worked on for my Brothers special the tappets were very similar to the Austin item, they were D section as opposed to the Austin item with two flats on the flanks, and the foot had an identical radius to an Austin tappet. I know this because when we got the engine it was in boxes, and one tappet was missing, I adapted an Austin guide and follower to replace it. I did not photograph any of it so can not post here. I hasten to add this is the only Reliant SV that I have any experience with, it makes me wonder if they changed the engines to a flat follower later in production??

Location: Auckland NZ

Tim Reynolds, your tappets look something like those my father used to supply for use with standard camshafts. I got a very stern lecture about why they were wrong for use with a high-lift shaft.

Location: Richmond, Texas

Tim your tappets look to me to be assymetrical so they will have to be installed the right way round. Can someone on the Forum suggest whether the sharp radius of the tappet makes contact first with the cam lobe or whether it is the shallower radius?
Presumably if the sharp radius makes contact first it will result in the valve opening very rapidly.
Second question, when assymetric tappets such as Tim's are used, are they only used on the inlet valves?
This is the sort of thing that keeps me awake at night!

The shallow radius allows the valve to open without too violent an acceleration. The sharp radius allows it to stay open late and then close very quickly. Think of valve opening periods in the same manner as pub opening hours and you won't go far wrong.
You could use them on the exhaust too I suppose but there wouldn't be as much point.

A question for Alan and Dave, are you sure you are not talking about an OHV Reliant engine? With a round flat tappet in a Side Valve Reliant how are the valve clearances set?

Location: Auckland NZ

Ian, I'm absolutely sure. I've never taken an OHV Reliant apart. I can only think that Reliant altered the design as time went on.

I can't check either,the engine is in storage 300 miles away.
I seem to remember they were bolts with a locknut similar to 7's.Definitely SV.

Thanks, yes the one I worked on had tappet adjusters identical to the Austin ones, with a round tappet fitted these might not work because the tappet could spin when you try to adjust. I am thinking they would have to use some kind of thimble and shim arrangement. All purely academic I know, I am just curious!

Location: Auckland NZ

Hi Ian, normally round followers had two flats to enable a thin tappet spanner to fit,
Also congratulations on the rebuilding Classes you & josh a running

Location: TINOPAI NZ

Could have had 2 spanner flats on them to stop rotation,but it was about 5 or more years ago when I last looked at it.

Yes, I believe you're all right! The early Reliant engines were virtually A7, and then developed across time. The tappets I've seen were about 1/4" longer than A7 ones though I've never seen any with just one flat side. The last engines had a flat headed mushroom tappet in a circular guide, the 'stalk' had two flats to retain it when being adjusted.

Photo thanks to Terry Griffin

One obvious question to ask regarding Tim's flat followers...

What valve spring set up was used? Do you just need a nice fresh set of standard valve springs or do they need doubling?

Location: Essex