hot_post in Push rod length headache  in Engine, Transmission & Rear End Author Topic: Push rod length headache  (Read 487 times)

Offline LinceCuda

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Push rod length headache
« on: April 15, 2018, 10:15:06 AM »
Ok y'all know I have a 71 340 engine with the 273 Commando adjustable rockers and shafts I'm building that was in my 73 Cuda when I bought the car. So I read that the Comp Cams 7821-16 ball and cup pushrod should work, but they seem to be too long. When I put #1 at TDC and go to adjust #2 in. and #8 ex. the pushrod is pressed up against the rocker so tight it won't move, even with the adjuster backed all the way out. So I'm just a simple minded guy but I'd say the pushrod is to long. My next move was to purchase a pushrod measuring tool so I did and I adjusted it to 7 1/8 length down from 7 3/8's. It seemed I was headed in the right direction but now when I start tightening down the adjuster to feel for drag on the pushrod the adjusting nuts on the tool get caught in the pushrod guide hole in the head and stops me from getting a true measurement. My next move I guess could be to grind the nuts to round them off so they'll pass through the hole. It does seem the 1/4" shorter pushrod measurement I made with the tools added with the adjusting screw will get me where I need to be if I buy 7 18/ pushrods. Now I'm taking my measurements from the ball to the top flat surface of the pushrod some say thats ok some say you need to measure ball to inside the cup. Any help would be appreciated. Thanks  :wrenching:

Linkback: https://forum.e-bodies.org/engine-transmission-and-rear-end/4/push-rod-length-headache/6396/

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Re: Push rod length headache
« Reply #1 on: April 15, 2018, 10:47:23 AM »
The nut catching in the head is a PITA but typical...  I've removed the nuts & applied adjustable thread locker (link below)..

https://www.amazon.com/Vibra-TITE-VC-3-Threadmate/dp/B008D6GHY6

I wouldn't just jump to 1/4" shorter, I'd measure it... A 1/4" could be fine but you don't want the adjuster out to far, it'll be nearly as bad as the pushrod to long...

When your talking 1-2 threads being important & 1/4" represents six threads......

Offline Chryco Psycho

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Re: Push rod length headache
« Reply #2 on: April 15, 2018, 10:48:56 AM »
That is not the best measuring tool , ones with internal threads work better , can you remove the nuts & just use a stud ?
I would order from Smith bros pushrods in Bend Or once you do get a decent measurement
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Re: Push rod length headache
« Reply #2 on: April 15, 2018, 10:48:56 AM »

Offline LinceCuda

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Re: Push rod length headache
« Reply #3 on: April 15, 2018, 10:57:09 AM »
Thanks for the replies. Lol hey just remove the nut now why the didn't I think of that geeze the simple things seem to be the hardest sometimes. Ok I'll go do that and see where I'm at. The other info is very go also thanks guys. :)

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Re: Push rod length headache
« Reply #4 on: April 15, 2018, 11:37:53 AM »
Ha: Last time I did that I cut down two pushrods to the right length and sent them to Tim Banning to make me a set. It's easy to get it wrong.
Sheldon

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Re: Push rod length headache
« Reply #5 on: April 15, 2018, 11:40:24 AM »
Ok s I removed the lock nuts and set the pushrod tool at 7 1/8 for a starting point and checked #2 in. and #8 ex. Seemed to me to work well but here are pics of the rocker adjusters showing the threads. The first is the #2 in. and second is #8 ex. What do you think of the amount of adjuster used? Think 7 1/8 rod length works? Thanks

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Re: Push rod length headache
« Reply #6 on: April 15, 2018, 12:16:52 PM »
Looks good to me..

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Re: Push rod length headache
« Reply #6 on: April 15, 2018, 12:16:52 PM »

Offline LinceCuda

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Re: Push rod length headache
« Reply #7 on: April 15, 2018, 01:14:34 PM »
Looks good to me..
Thanks for the input  8)

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Re: Push rod length headache
« Reply #8 on: April 15, 2018, 04:08:27 PM »
Since you have your valve train apart; now's a good time to add valve lash caps.

They're harder metal so the tops of your valve stems aren't taking the punishment.

Clearances aren't likely to alter as much over time either. 

Here's what they look like.

https://www.ebay.com/itm/New-Comp-Cams-426ci-Chrysler-Hemi-Mopar-5-16-Lash-Caps-190-Height-619-16/382415727208?epid=192390440&hash=item5909c0ea68:g:RJoAAMXQq8BQ6hw5&vxp=mtr


Contact Jegs or Summit perhaps which are best for your application.

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Re: Push rod length headache
« Reply #9 on: April 15, 2018, 05:15:16 PM »
Chrysler recommended two threads showing on the adjuster for correct angle and oiling. I think you are right on.

Offline lulurocks(Ken)

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Re: Push rod length headache
« Reply #10 on: April 15, 2018, 06:41:04 PM »
That is not the best measuring tool , ones with internal threads work better , can you remove the nuts & just use a stud ?
I would order from Smith bros pushrods in Bend Or once you do get a decent measurement

 :iagree:   I just ordered my 3 set of pushrods from smith brothers. There service and quality is bar none...


Comp cam sells a ball cup meausuring tool 7709-01 It has laser hash marks  , every turn out is .050 plusthe tool 6.8 and it gives you your effective length (inside bottom of ball cup to outside of ball)

   I buy two and walk them all over the motor as a pair confiriming my length will be correct .


And  google  EOIC   Its a very simple way to setup valvetrain once you have your stuff. 

Sorry alot of info lol


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Re: Push rod length headache
« Reply #10 on: April 15, 2018, 06:41:04 PM »

Offline Chryco Psycho

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Re: Push rod length headache
« Reply #11 on: April 15, 2018, 08:31:46 PM »
 I agree , Smith Bros are the best , fast service , they will match the pushrod to the spring load , 2 day service max is normal , I ordered a lot of sets from them over the years  :bravo:

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Re: Push rod length headache
« Reply #12 on: April 15, 2018, 09:19:35 PM »
Thanks all for the info I believe I'm good on the measurement. I have since my last post checked it on both heads and it seems I'm good to go. As far as Smith goes I too have used then twice before on my 451 and 499 strokers and was very pleased with their service and product so no reason to go elsewhere.

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Re: Push rod length headache
« Reply #13 on: April 18, 2018, 10:47:03 AM »
So dumb question  :clueless: I suppose but no one makes a over the counter set of pushrods that work with that combination?  A long time ago I installed Isky adj rockers on a 383 using Sig Erson (pre-made) push rods and it was a perfect fit.

 :wrenching:

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Re: Push rod length headache
« Reply #14 on: April 18, 2018, 07:29:15 PM »
Too many variables -
 if the heads are decked ,
 different head gasket thickness ,
 seat recession into the head using unleaded fuels & recutting the seats ,
 make of rocker arm used
 all will change the needed pushrod length

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Re: Push rod length headache
« Reply #14 on: April 18, 2018, 07:29:15 PM »

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