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[Wheaters]

If the first event was caused by over revving it might have caused damage elsewhere in the valve train. Is it possible that the rocker arm has distorted, or the top of a tappet is chipped, meaning that the new pushrod wasn’t properly supported?

[stinkwheel]

The rockers look in good order, although I couldn't swear they are not distorted a little, wouldn't even know how you'd tell. It's bent both pushrods in its time though so unless both of them have let go...

You don't think a kickback could do it? Firing against an opening inlet valve?

[Bullet Whisperer]

Kicking back could only bend the pushrods if the valves are making contact with the piston crown. This contact could be very slight indeed - look for shiny marks on the piston crown in the valve pockets. If there is none, then the valves are not making contact. If the valves are not touching the piston, any kicking back will not bend the pushrods, just as it will not damage an oil pump spindle, for those who seem to think it will. Pre war Model J Bullets had steel pushrod tubes, if they might be long enough, should you wish to up your game, but remember, something is causing those alloy pushrods to bend and fitting stronger ones which won't bend may cause more serious damage elsewhere.

[Wheaters]

If a valve sticks open in its guide, even briefly, it can result in the pushrod jumping out of engagement at the rocker arm. If this happens, the pushrod is very likely to drop sideways and jam at the top. Next time the cam tries to lift it, it would bend. There's a witness mark on yours halfway up, which surely means it's made contact with its tunnel.

It would be worth checking the valve guides and reaming them out. If the guides have ever been changed, they should have been reamed anyway, in case the process of fitting them has burred the ends.

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!

[Wheaters]

I'm pretty sure it's kickbacks on startup that are causing it. Although the first one could have been a huge over-rev on a fluffed gearchange causing it to jump off the follower.

It's just had the top-end rebuilt after a piston failure and seizure, about 100 miles ago. That rod was straight when I did it and everything else loked tickety-boo. No violent incidents, over-revs etc since but quite a few backfires on startup.

I've ordered some 7075 alloy solid bar to make up a set of rods but they'll be (comparatively) heavy. Maybe not as heavy as steel tube ones would be though. I'll need to do some maths.

By putting extra weight in the valve train you're actually increasing the likelihood of valve train bounce.....

[stinkwheel]

The rod is bent enough that it can touch the side of the pushrod tunnel with it in-situ depending on which way round it is rotated, hence the witness mark. I'm assuming that's what the clattering sound was under load which I'd assumed with pinking. I'd also assume that once it's bent that much, it'll be flexing like crazy during use.

The head is a hitchcocks tuned head with upgraded springs, guides and valves. It was supplied assembled and I haven't touched it. Valve to piston clearance is a whopping 5.5mm as measured with the classic lump of blu-tak on the piston crown and turn the engine over technique. There is daylight visible through all four valve springs when fully compressed.

I was looking at pushrod strength because the BSA guys use steel pushrods in their tuned A65s. It might be because I'm just thrashing it too much. There again, I want to be able the thrash it, kind of the point of the thing. If it bends another, I'll pull the head and check the valves are straight. I'll also keep trying to source an appropriate size and grade alloy or steel tube to make up some custom rods. Unless anyone has a source for chromoloy steel or 7075-T6 alloy tube, 10mm OD with a 2mm wall thickness?

[Vince2]

Hi, the guides were too tight on my 350 to the point where when hot the pushrods would jump out , worth a check? Vince.

[Adrian]

A reamer down the valve guides wouldn't hurt.

As for custom pushrods, I bought some 10mm O/D, 4mm I/D (6mm I/D is available too) alloy tube from eBay here: This was for a hybrid AVL/classic engine.

https://www.ebay.co.uk/itm/391880192028

You might like to contact them and see what grade of alloy it is.

A.

[stinkwheel]

It's 6060. I messaged one seller who said theirs was 6082 in the description but they came back saying it was actually 6060.

Strong enough for rods? My google research shows manufacturers usually use 2024 T3 or 7075 T6 which are roughly twice and three times as strong respectively.

I have no idea what standard enfield rods are made of. Melted rupees like most of the other bits?

[Adrian]

A reamer down the valve guides wouldn't hurt.

As for custom pushrods, I bought some 10mm O/D, 4mm I/D (6mm I/D is available too) alloy tube from eBay here: This was for a hybrid AVL/classic engine.

https://www.ebay.co.uk/itm/391880192028

You might like to contact them and see what grade of alloy it is.

A.