Square Four Push Rods

[roger.fellows]

Hello again Gui, I am no engineer! I would want the valve caps to sit higher, I would also be happy to grind the guide tops provided it is possible to fit Mk11 type 'hats' to prevent over-oiling. Leaving the guide tops sharp and chamfered is supposed to help with the same effect.

Again only from Mk11 experience, I would expect the collets to be stepped internally to allow the caps to sit higher.

Peace be upon you and yours, Ariel or not!!!!!!!!!

[bill.bottrill]

Gui,
couldn't check all the measurements
all your measurements check out o.k. except one, top of valve guide to top of valve. you have 20.60 I have 22.19 mm
this was checked on the old valve guides still in situ with an old exhaust valve from the same engine
overall valve length 88.38 mm
top of valve to collet recess 6mm same
collet recess 10 mm same
height of valve guide in rocker box 10 mm (but this is to the raised collar (the spring sits in a groove about 2 mm lower)
the collet holder 11 mm top to bottom
bill

[Gui.dorey]

Well, I believe I have found the answer, which confirms the measurements from Bill just above. Among the box of old bits that came with the bike I found two old valves, springs and 3 old guides. The valves and the springs match the new ones exactly, so the collet groove is correct as well as the stem length.

The guide is however a different one and the bit on that protrudes above the rocker box is only 7.90mm or 0.310" instead of my 12mm on the new ones. That's where my missing 4mm of valve travel went. If someone could confirm this before I disassemble all the valves, abuse the wife's oven, and drift all the guides out it would be great.

TIA and also for all the help already given.
Gui

[Bob.Murphy]

The picture is of a Mk I guide - the later Mk IIs have cylindrical sides and a 'top hat' sleeve fits inside the valve spring to limit oil loss down the guide. These are what you have fitted.

I may have missed something here, but which model & year of Square Four are you restoring ??

It sounds as though you have solved your problem now, well done !

Bob.

[Gui.dorey]

It's a 1951 MkI, and according to the engine Nr. TM... it should already have the later valve guides. But I bought her as a basket case, so no guarantees as to what parts are really there. Here's some pics.

[paul.jameson]

Your colletts are correct but the valve guide in your head is from a Mk II. I am glad you have found the problem.

[Gui.dorey]

Yes, looks like Drags sent me the wrong ones....

[nevhunter]

Don't like the idea of taking the guides in and out. You will probably have to do the seats again, if you do. See if you can machine them down shorter still in place . A depth stop on a good drill will do If you don't have a mill. If you want to shape the top conical you might have to use a bit of ingenuity in making a suitable cutting implement. Nev

[john.whiting]

In the drawing you made,there seems to be a lot of excess length in the caps.........simpler to shorten the cap....,any reworking of the guide will need a special cutting tool,and require a power drive like a good drill press

[Gui.dorey]

I know, I hate to take those guides out and back in again. I will have to check with a mate who has all the machines and more experience to see if he can do something with the guides in place.

The valve caps are actually the right length according to the old valve I had lying around. So I prefer to leave them that way and correct the guides. You never know what other problems one might get if one starts changing other things to fit instead of solving the actual problem.

Many thanks to all of you for the great help!
Gui