Square Four Push Rods

[simon.holyfield]

Before we start worrying about pushrod/cam lift vs. valve lift, are we sure that the rocker shaft is central between the adjuster and the pushrod cup? put another way, are the two arms of a rocker the same length? If so, pushrod lift = valve lift; if not, the two will not be equal...

The picture I have of my rockers suggest the arms are of equal length.

[paul.jameson]

What do your valve collets look like? They should be about 1/4 or 5/16 inch long, with a circular face one side and a tapered circular face on the outside. If, by some chance, you have collets which are rather longer and have a step half way down the inside of them then these are late MKII collets which will fit the valve but possibly not an earlier head.

[Gui.dorey]

Hi Simon,
The rocker arms are equal lengths. Did think of that as well and had checked them before.

Hi Paul,
As far as I can tell, the parts are correct - collets are 1/4" in length.

Here are some pics. Maybe you chaps can spot something. Measurements are in inches.

[Gui.dorey]

And two more.

[nevhunter]

IF you have all new inserts and new valves the valve(s) may sit a bit low to start with and not have the required travel unobstructed, Whatever the actual lift is I would check you have about 1 mm more. Just set it to full open (camshaft position)and then push further to see that you have the extra lift available. The SQ4 is just another engine with more parts. It has it's peculiarities Coupling gears press fitted and hard to lower the cylinder block onto the pistons etc but you just have to persevere and check EVERYTHING as what you don't check will bite you. All the extra parts make the COST a big factor especially doing the head properly, if it's done miles. Inserts etc You don't want motors that have had lots of metal shaved off them in a past life. Nev

[roger.fellows]

Gui, I've only ever had to do with a Mk11, but having just been for a quick peek at my head I can see valve guides which protrude at least two and possibly three different lengths above the aluminium. I hasten to add that the guides were not put in by me. The guide that I can see in your head looks as though it sticks out more than the smallest of mine. The top collar on your fitted spring seems too far below the valve cap. Mine sit level with the collars when fitted. That spring looks almost coil-bound.

[Simon.Gardiner]

When I put my FH together I found a lot of differences in the collets and top collars and ended up checking various combinations until I found sets that sat in more or less the same place on the valve stems. With some of the 'wrong' combinations the springs were noticeably more compressed.
I was puzzled by this at the time as I've never had the problem before and I've put it down to using collets and collars from several different heads, they should all be the same but maybe production quality ain't always that tight with things like this.
Dunno if you might have a similar problem, Gui, as your problem looks otherwise pretty inexplicable.

SG

[pauldridge]

I encountered a similar problem with my '53 Sq 4 MK II.. after head rebuild, I discovered that a couple of the collets were noticeably larger than the others, causing the valve tip to protrude higher than it should. With guidance from my US guru, Paul Ackerman, it was determined that I needed the later year spring caps and stepped collets..Those I was able to obtain from the UK Club spares inventory, and that solved the problem, now all stem tops are pretty well flush with the top of the valve spring hat.

Another related issue: I had one slightly bent pushrod, so ordered a replacement from Dragan for my year. After assembly, I couldn't get any clearance at all with the rocker. On closer inspection, it seems they sent me a later model pushrod that has a smaller diameter tulip cup, and so the rocker ball couldn't sit all the way down in the cup.

So many little things to go awry with these beasts.

[john.whiting]

On the subject of collets,these should be carefully inspected before assembly,and then tested in the valve groove with the cap to be used .....the whole lot should form a proper assembly,and resist being displaced ......not be so loose it all falls to pieces at a slight tap,or allows the cap to rock.........if loose ,check the taper in the cap.....it may have been grooved by incorrect prior assembly..................However ,there is an exception to this rule.....some engines use loose collets so that valves can rotate....but always with a stem cap.

[Gui.dorey]

So, here's a complete measurement of the whole assembly. All 8 are the same as all parts came new from Drags, the only difference being of course inlet and exhaust valve diameter. Springs, collars, collets, guides and stems are all identical. Comparison dimensions would be lovely if somebody has them at hand.

In the end with this lot I won't get more than 7mm valve travel, so definitely too short and I should get at least 2mm more (8mm from the cams + some leeway).

Possibilities as I see it, but please advise on the best method:
1. grind down the top of the valve guide.
2. grind down the bottom of the collar
3. a combination of 1. and 2.
4. turn the groove where the collets sits up to the valve cap, so the whole collar moves up towards the valve cap. This would also reduce the compression on the springs.

I will now sit back and have a very large single malt and try to make peace with all the Ariel gods before the the new year comes, while being entertained by your insightful and helpful responses.

Cheers
Gui