Tuesday, 6 May 2008

Terrible Headaches!

Here’s a bit of an update after a rather prolonged silence. Rest assured that while we’ve been a little lax in updating the blog since Snetterton, things are progressing. As usual there’s been more thinking than actually doing!!

Oil lines should be on their way from the friendly and helpful guys at Pirtek at Kings Cross (cam feed and main tank-motor and motor-tank oil lines). They’re also fixing me up with a front brake line. However, inside the motor, I’m still fretting about the valve gear, and we are acutely aware that time is marching on. Having received the oversize shims from Rog Key, I re-checked the spring installed height; they’re all now spot-on. However, I then wanted to just make sure that the collets weren’t going to do anything comical with the valve stem seals at full lift.

The subject of much domestic strife….!

The valve guides have already been shortened for use with the Stage 4 Megacycle cam, and the motor apparently ran very well. It may have broken the bottom end, but the top was fine!

However, the pattern valve stem seals I received were not a particularly good fit. At full valve lift (measured rather inaccurately at 12.1mm for the inlets and 11.4mm exhaust) there was indeed contact. I only tried it on one inlet valve, but turning the cam by hand was enough to feel contact. I tried to get the seals to sit a bit further down the guide but to no avail. They may have been cheap, but I can hear my old man warning me “Buy cheap, Pay dear”. Paying dear would almost certainly result from a dropped valve. I resent the time and hassle more than anything: rockerbox on, rockebox off, cam in, cam out, setting/checking the tappets every time. Measure, turn, check lift, blah blah blah! So now you see why the blog’s not been updated?? This part is just too boring, and time consuming!

A second old adage of my father’s is “Buy cheap, Buy twice”. Another accurate observation from the old felly. I duly received my new Yamaha valve stem seals Fowlers on next day delivery, having placed an order at 4-30 the previous afternoon. Top service. I was pleased to find that as a result of their better fit, there was now clearance. Not as much as I’d like admittedly, but there is clearance. And the new collets are no bigger than the old ones, so I’ll probably go with it as is. Unless of course I could remove just the slightest amount of metal from the bottom of the collets…? Hmmmm, probably not.

As a little aside, measuring lift accurately is difficult as I am not, by any stretch of the imagination, an engineer. Working with a only vernier (“very-near”) caliper is difficult in the confined space of the head. And the curves of the valves and inside the combustion chamber make it hard from that side.

So having previously made a note of the lift, I then built up the collets and retainer without the springs. You can see this here, and underneath the R/D bottom cup is Rog’s shim.

So how to measure? I ended up bodging on a bit of plasticine, removing it and measuring the distance between the top of the seal and the bottom of the collets.

Obviously not the most accurate, but just about the only way I could think of doing it. And I think it will do, in the absence of any other expertise…! Or am I just showing myself to be a fool, who can’t build an engine? Well, you can all say “I told you so” when it drops a valve!

Right. Lets get this head on!