Sq4. Mk 1 Alloy engine valve clearance.

[Ian.McCandlish]

All,

this afternoon I decided to get ready for spring so thought I'd tighten the head nuts which in turn led me to address the gap between the rockers and the valve stems. Ok, the manual says 0.001in clearance but accumulated wisdom advises that with an alloy engine fitted with a reground casmshaft with quieting ramps (bought from Draganfly) clearance should be 0.006 for inlet and 0.006 for exhaust. No issues there good advice.

Right, my issue is that with piston at TDC on No1 cyl. with both valves closed on the firing stroke the only way I can get any gap is to hold the pushrod end of the rocker down overcoming the slight pressure of the sprung pushrod to raise the valve end of the rocker arm away from the the top of the valve stem. If I dont do this there is no gap between the rocker arm and the valve stem head.

I could set the gap using this method but as soon as I release the pressure the push rod will rise and the rocker will come into contact with the valve stem again.That does'nt seem right to me and is not what I've experienced on other classics I've worked on. Normally the rocker is clear of the valve stem head when in the firing position making setting the gap a simple(!) proceedure.

The bike has been running great albeit a little rich and with no more noise that I'd expect from an alloy engine.

Should I depress the end of the rocker arm and set the gap or is there a problem somewhere I'm not picking up on.

thanks

Ian

[simon.holyfield]

Sprung pushrod?

[roger.fellows]

Air bubble in the push-rod cap is the only thing I can think of. I'm not sure of the arrangement on the Mk1, but the Mk11 has caps, some of which fit tighter than others. The rocker arm may be balanced such that it falls onto the valve stem rather than the push-rod.

[Brian.Fosh]

Hi,
Waller advises to rotate the engine to full compression, just as you are doing, but then he adds.... "A safe measure to adopt is to turn the engine slightly over the full stroke in order to clear fully any cam pressure on the push-rods and rockers."

Regards

Brian

[Ian.McCandlish]

Simes, apologies. I should be more specific. If my memory serves the push rods are seated on a spring inside the cam follower guide block which has the dual purpose of keeping the cam follower in touch with the cam and the pushrod in contact with the rocker arm. They are definitely spring loaded as when pushed downwards the push rods return to their original position.

Prior to reassembly I had the head skimmed and the valve seats re-cut and I'm now wondering if the push rods are just a little too long as a result!?

Regards

Ian

[roger.fellows]

Hi Ian, that spring should not have any effect on the follower once it has been installed, it's only a circlip to keep the follower in place during assembly.

[Ian.McCandlish]

Roger,

I recall the circlip you describe, I agree its so thin and tiny it could'nt act as a return spring. Its been a couple of years now but I'm sure I dropped springs and a cup inside each of the cam follower guides before I placed the push rods in. I could be mistaken about this, failing memory and all that! The rods definitely bounce like they are seated on a spring. Admittedly there's no sign of any internal springs on the engine illustrations. I guess I'll remove one of the push rods and use my wee telescopic magnet doofir to see what, if anything comes out of the pushrod hole.

Regards

[paul.jameson]

I think you will find that your cam followers are in two parts and have a spring between these two parts. So what you are experiencing is entirely correct and you should set the valve clearances whilst holding the rocker down at the pushrod end.

[Ian.McCandlish]

Paul,

brilliant....thanks. Phew thats saved me a lot of headscratching and messing about with the top end.

Thanks to all who responded. A great illustration of the value of the forum.

Onwards and upwards......roll on spring!

[Eero.Korhonen]

Paul,

brilliant....thanks. Phew thats saved me a lot of headscratching and messing about with the top end.

Thanks to all who responded. A great illustration of the value of the forum.

Onwards and upwards......roll on spring!

Yes, that's spirit! We still have -5 and a LOT of snow.

Br, Eero