Is fitting differing weight pushrods a bad idea?

[stinkwheel]

This is on an enfield bullet, so it's a 2-valve overhead valve single with two seperate cams running off a pinnion on the end of the crank. The pushrods have a "bucket" on each end which engages onto a cam follower at the bottom with an adjuster and onto a pair of bolt-on rocker blocks at the top.

It's been heavily tuned and I keep bending inlet pushrods. I've dealt with the main problem which was poor clearances between the cam and follower but on inspection today, the inlet one is again a bit bent. No banannaed like previously but a slight compound bend in a couple of different directions when you hold a straight edge against it. I suspect full-bore-roar is simply too much for it. All the other parts of the valvetrain are upgraded to performance parts anyway (rockers, valves, springs, cams)

Now I made up a set of rods out of solid 7075 round bar instead of the unspecified Indian made alloy tube of the originals. There's no way this will bend. When I put some in a clamp and tried to bend it, I found the elastic phase is outwith the confines of the pushrod tunnel. As well as it being very strong alloy. Thing is it's significantly heavier.

I'm considering using the solid rod for the inlet and a standard, lighter one in the exhaust. I doubt it'll make much difference, I suppose the inlet valve will have a tendancy to float before the exhaust one. The rods are different lengths anyway and open and close independantly so they're not a balanced system.

Just wondering if there's something I'm overlooking that would make this a bad idea?
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Easy-X]

I suppose you could consider the push-rods to be a parasitic drain in the system like an alternator. You'd therefore want the lightest but strongest rods possible. I would imagine if it was a perfectly balanced system introducing rods of different weights might introduce some vibration... have you noticed any vibration on your Enfield?

Maybe for a perfect system you'd want to add weight to the exhaust cam lobe (or, more practically, remove weight from the inlet cam lobe) but a smooth, purring Bullet engine? Be a bit weird!
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Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[WD Forte]

I'd go for robust reliable over lite/speed/powah every time personally.

I expect we're talking a difference of adding a few grams not even ounces let alone pounds/kilos

Unless there are critical reasons to eke every tiny amount of energy out of the lump I'd want fit and forget.
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bikers smell of wee

[Pete.]

Heavier springs stands to reason you can use heavier pushrods without penalty. You could always waist or counter-bore them if the weight troubles you. Personally, I'd suck it and see.

Are you sue you have enough valve to piston clearance?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[stinkwheel]

[Pete.]

[stinkwheel]

Thinking about it, it also bent a rod when it had an additional 2mm of compression plate under the barrel to where it is now so I don't think valves are tangling.

I think it's just accelerating that rod beyond what it can cope with. The performance cam has roughly an additional 2mm of lift against a stronger valve spring and the engine revs 1500 rpm higher than standard. There is less lift on the exhaust side.

You can see daylight through the springs at fully open, and the spring/valve kit was designed to go with these cams.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jeffyjeff]

[A100man]

Could it be an issue with angles? The higher lift cam making a slight more acute angle on the rod?

I say this because I once spent a lot of time once phaffing about on my VW air-coooled motor with shims under rocker blocks etc.. to get the recommended angles when using a 'performance' cam. This was 16 years ago so I've forgotten the details, if not the time consumed..
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[MCN]

Stainless steel tube with the hardened ends swedged in. SS it more resistant to bend than alumininimimum. But lighter than solid steel bar.
Can be had for relatively cheap.

Equivalent OD and wall thickness.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[stinkwheel]

[stinkwheel]

[Robby]

They might float a bit earlier and you'll get more wear on the cam and rockers. I would be concerned if the rockers have a weedy connection to the head, because that join is going to get hammered a lot more.

But seeing as this bike is clearly a test bed for doing perverse things to an Enfield, heavier pushrods seem like a reasonable next experiment. If you wear out the cam, it's an excuse to buy an even sillier one.

You are removing your sacrificial weak link from the valve system, so if there is any piston to valve contact it's going to break a valve instead of a pushrod next.

Looking at it from another angle, does it really need the heavier valve springs? If they're killing pushrods, maybe they're a bit too strong.

[stinkwheel]

I think if anything was going to let go mechanically, it would probably push the rocker block studs up out of the head (4 x 1/4" BSC each rocker). Which is probably not as catastrophic as it sounds it might be. The studs themselves were homemade from EN8 (which was no walk in the park because four of them are an oversize 64th inch ground diameter). A broken rocker wouldn't be a total disaster either as long as it doesn't get fired out through something, they are bolt-on blocks that cost £30 complete.

I am going to invest in some Nord-lock washers for them though.

It probably does need those springs to keep in touch with the pointy cam. Also because revs. And on a more practical note, there are two off the shelf spring sets for this engine and the other ones would coil-bind with these cams.

There are no sillier cams. I checked. These are absolute maximum silly. The main bearing oil seal housing had to be undercut to fit them in the engine.

https://lh3.googleusercontent.com/pw/AL9nZEWbN3Rq3kzLbuEVJ2qrWzr4EkxCSiQ3mQ3573A8gdcvNUXB7h5Zr1wy-DNgjHf9cFGN4bbmuOXBHSYxCkctacgs99sMTfUZjAxjhqX5C2j_IHqAxj9u9ccAs3O03wTYs5_EbR3IBJhXk0vAj1__-cKE=w1182-h886-no
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Nobby the Bastard]

Not so much cam lobe as rotating hammer.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
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[virus]