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[stinkwheel]

Ideally a proper reamer should be used for the job. I was taught another way for cast iron guides, which is to drift a ball bearing of the same size as the stem through them. Which reminds me, somewhere in my garage I must still have a pair of BSA C15 guides I made at Wilmorton College in about 1975 and never fitted to my bike!

They are bronze but this can't do any harm and requires a minimum of tools. It would effectively burnish the inside of the guide?

Presumably carbide ball bearings? I found an article stating this is a standard way of sizing bronze valve guide liners when people repair old cast iron ones.

[Wheaters]

The valve guides will be made by machining solid phosphor bronze and as far as I know it’s OK to burnish them. It’s bushes etc made from sintered bronze that shouldn’t be burnished because their surface is meant to remain porous so that they can self lubricate as designed.

In my day I don’t think carbide balls were available so it was common or garden carbon steel.

[stinkwheel]

Well, I think we all know sufficient lubrication in the valve guides isn't usually an issue on bullets

[Wheaters]

Precisely!

[Adrian]

Not quite sure how that double posting happened, sorry about that. If you look at metalsupermarkets.co.uk they list 7075 aluminium bar, but clicking on the link doesn't let you order it or even see what diameters they have in stock! I think you'd have to call them and ask what sizes they have.

I'm fairly certain that BSA unit singles used solid alloy rod for their push rods, with tapered and rounded ends sitting directly in the tappets..

A.

[stinkwheel]

I think I've managed to source some seamless chromoly steel tube off a mate who makes bicycles. That's what SRM use on their hot BSA A65s, and I've been overtaken by one of those when I was flat out on a GPZ500 doing a speed that would send you directly to jail if you were caught.

...Which just reminded me I have a junk bicycle frame in my shed and it being French, I bet the seat stays are 10mm Reynolds 531!

[Bullet Whisperer]

Going back to possible causes of bent pushrods, one I have experienced is caused by the depth of the cupped upper end of a pushrod, combined with the high lift of certain cams causing the ball end of the rocker to be lifted out of the cup around full lift and all the weight from the valve and springs being placed between the end of the rocker arm just before the ball end, and the edge of the cup on the pushrod end, thus applying a huge bending force on the pushrod. Check the depth of the pushrod cups, the operating angle of them in relation to the rockers and if necessary, grind the edges of the pushrod cups down a little, to make the cups shallower, to overcome this situation.

[stinkwheel]

Going back to possible causes of bent pushrods, one I have experienced is caused by the depth of the cupped upper end of a pushrod, combined with the high lift of certain cams causing the ball end of the rocker to be lifted out of the cup around full lift and all the weight from the valve and springs being placed between the end of the rocker arm just before the ball end, and the edge of the cup on the pushrod end, thus applying a huge bending force on the pushrod. Check the depth of the pushrod cups, the operating angle of them in relation to the rockers and if necessary, grind the edges of the pushrod cups down a little, to make the cups shallower, to overcome this situation.

Good one to check, another mate also suggested this so I'll get on it this afternoon. Shame my video camera doesn't have a high speed mode, could have been interesting to film the tappets and rockers with it running.

[stinkwheel]

Well, it's not fouling the tappets/rockers at full compression. I double checked the springs aren't coil bound and I popped the valves out and checked they are straight by rolling them on a mirror. The valves move in their guides like they're made of ice, I'm loathe to stick anything down there and dick it up, I'm fairly certain our hosts will have properly reamed them before sending the head out.

It was still making a pinking noise today going up my local "test hill" even after replacing the bent rod, although it started and idled beautifully. I've dropped the compression a bit (2 x 2mm plates and 3 base gaskets as opposed to 1 x 3mm plate and 2 base gaskets. It previously ran well with the 2 and 3mm plates in) so we'll see if that makes the difference. I've got materials ordered to make up some stronger pushrods. If nothing else, I'm getting a good collection of knackered pushrods so I may as well use the ends off them.

[Adrian]

I notice there are some suppliers of 10mm 7075-T6 alloy rod if not tube on eBay. What material did you order?

A.