Pushrod question

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Towner

Towner

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Feb 22, 2013
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Hello,

recently I demounted the head of my Commando to fix a leak at the pushrod tube area. Checking the pushrods I realized that a ball end of one intake pushrod is not centrical or tilted (about 0,5mm - rod is straight). The other pushrods are perfect. May be it has always been so, but I decided to renew it. Now I received the new one from AN and noticed that it is about 10gr heavier than the old (all old = 30gr, new = 40gr). Could that be a problem ? Is it advisible to renew all pushrods ? Or should I still install the old ?

Thanks in advance !

Regards,
Ralf
 
The heavier pushrods seem to work fine in a stock engine application. I would not recommend them for high performance use. Jim
 
comnoz said:
The heavier pushrods seem to work fine in a stock engine application. I would not recommend them for high performance use. Jim
Click to expand...

I think the question is can he use one of the new ones with three of the old if the weight is different?
 
I just measured a hand full ( 8 of them ) and all were 30 to 32 grams. I might think that the heavier may be a little stiffer. Whether it causes some noticeable difference having one 40g and the others 30g may be a personal issue. I would not worry too much about it.

Length may be more of a concern. Be sure intake and exhaust are equal in length respectively.
 
Hi,

may be 10gr sounds a bit fussy. But when I took it in my hand the first time, I realized directly that it could be heavier. So I was not sure whether it could effect a manner of unbalance. I am not a racer, the engine gets not much stress.

Ralf
 
My concern is they're all manufactured to the same drawing, yet one is 25% heavier?

So where is all the extra metal?
 
B+Bogus said:
My concern is they're all manufactured to the same drawing, yet one is 25% heavier?

So where is all the extra metal?
Click to expand...

Additional metal or weight mustn't be a drawback. Maybe they wanted to get it stiffer.
 
Towner said:
B+Bogus said:
My concern is they're all manufactured to the same drawing, yet one is 25% heavier?

So where is all the extra metal?
Click to expand...

Additional metal or weight mustn't be a drawback. Maybe they wanted to get it stiffer.
Click to expand...

Pushrods used to be hollow and from the MK3 AN switched to solid (heavier) pushrods :idea:
 
Mixing them is not a problem on a stock engine as long as the length is the same.

Unfortunately the heavier pushrods are not stronger -just cheaper to produce.
 
unrelated to this discussion perhaps, but it is interesting that Peter Williams chose to fit the works race bikes with steel pushrods instead of alloy as he felt they would better retain the correct valve actuation under high RPMs

this, according to my book: Norton: The Racing Story
 
We discussed this > STiffness-control matters more than the mass on push rod side of valve train. Should be undetectable on street engine till highly illegal levels of operation. Ken Canaga's side line hobby is push rod customizer.
 
pete.v said:
I just measured a hand full ( 8 of them ) and all were 30 to 32 grams. I might think that the heavier may be a little stiffer. Whether it causes some noticeable difference having one 40g and the others 30g may be a personal issue. I would not worry too much about it.

Length may be more of a concern. Be sure intake and exhaust are equal in length respectively.
Click to expand...

Hi Pete,
I was Just wondering. What is the proper length for an 850 Commando Pushrod ? Both Intake and Exhaust measurements would be great. I have found in my 73 850 engine while de-carbonising the head that I had two different lengths from some previous owner who put the head back together. They were about 0.080" taller. I am suspecting that the pair of long Intake and Exhaust set is from an Atlas but I am not to sure.
It would be good to know the numbers.
Cheers,
Thomas
 
Ya know there ain't must difference in the stack height of 850 or 750 and each variation needs a fine tune of push rods to center rocker motion on stem, so now's your opportunity to dial it for you particular set up, base plate, type of gasket, head milled, cam profile. Observe the vale stems for a clue on how yours measure, just right or too long or short.
 
Thanks for all your fast responses. That gave me a good background about the topic and helps me to decide about the approach within short time.
I will install the new one together with the 3 old. The length is the same as the other intake pushrod and the difference in weight should not
cause any detectable change.

Ralf
 
As Jim says, for a street bike it shouldn't matter. The old saying was for every gram you remove from the valve train you gain 100 rpms. Why don't you pop the crooked end off and see if there is a reason it's out of alignment. If the rod is damaged you're hooped but if it is not you may be able to fix it or use the end off the new one or what ever.
 
Again the push rod and other valve train masses importance has been discussed here and referenced to the max prior, to find the push rod mass itself is of minor important compared to all the other masses in valve train so lighter p-rod is not the part that will gain rpm by lightening, only its stiffness allows higher rpm, if the other parts light enough and strong enough for it. I suppose if rod made of cast iron tube lead filled it would hinder valve control so of course I'm not completely correct to state its mass is of no importance, just can't get em that heavy to matter in ones for sale for public operated engine.
 
Whoa let's see, lighter valve $pring cap$, rocker arm adjuster$, lightened rocker arm$ and lightened cam follower$, I'd think 10 grams off a push rod would account for something too.
 
Yeah sure it counts but so little in our street engines its ridiculous to even discuss it further until you catch up on the push rod tech posts last year or so. Tell Steve Maney that his steel push rods are a mistake in too much mass. Now rocker ends and valve mass are worth nic picking over. If ya can get-afford a very light very stiff rod then go for it, other wise No need to worry a fella just needing to get back to riding sanely a long time.

commando-pushrod-tech-t12779.html
 
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