Pushrod length ???

[MoparMitch]

Assembling my almost stock 383 motor . Only change really is Comp Cam XE274 cam.A few years ago a friend gave me a set of ductile iron adjustable rockers Crane # 69770-16. I dont think they even have that set available any more. I knew I needed different push rods , so a few weeks ago i ordered a set of Comp 7422-16's . They are 8.710 in length. When I assembled the shafts on to the heads today, I realized they are too long. I removed the pushrods and installed the shafts with adj rocker so I could measure for length. It looks like I need somewhere between 7.87 and 8.10 in if the adjuster screws are about half/ centered. I looked around and the shortest I could find with cup and ball were 8.25. I might be able to use them but the adjustment screws would be all the way up in that case. I need to use the stock valve covers as this is a numbers car , and I'm worried the rockers would hit the covers. Anyone with experience here on these adjustable ductile iron shafts would be helpfull. Or perhaps if someone knows where I can buy some pushrods shorter that 8.25 , that would be good. Thanks in advance for the help. Mitch

 

[HEMI-ITIS]

Mitch,give Manton a call.They will make any length you need and can answer all your questions.:sunny:

http://www.mantonpushrods.com/

 

[67 B-body]

A good idea would be to get an adjustable pushrod to obtain an exact dimension, the just order the correct length based on your findings.

 

[Meep-Meep]

It looks like I need somewhere between 7.87 and 8.10 in if the adjuster screws are about half/ centered.

The above statement is a red flag! I understand how you arrived at your answer but the real solution is counter intuitive. Or not if you understand what needs to happen.

With the adjustable rockers you only want a thread or two showing on the ball side. The closer the push rod cup is to the rocker the better. Sounds to me you have the correct push rods if you think my description is accurate to your findings.

If the push rod is too short, thus causing the ball end to stick out too far, the rocker end of the push rod will travel side to side as it moves up and down and the result can be push rods and lifters flying out at high RPM. Someone on here made a nice CAD drawing showing the effects of this geometry.

Put your engine together with the push rods you thought were too long and post a pic of the adjuster side. Note: You will need to check the push rod cup clearance to the underside of the rocker.

 

[MoparMitch]

I went ahead and bought the 8.25 length pushrods. I fit them yesterday and like Meep says, I now have maybe three threads showing under the rocker. Also I dont think I'll have an interfearence issue with the stock valve covers. Thanks for the help.

 

[RustyRatRod]

I have some bad news for you. If that part number on the rockers is correct, those are small block rockers.

 

[Meep-Meep]

Uh oh, hold the elevator! Good catch Sherlock Rusty! http://www.summitracing.com/parts/CRN-69770-16/

You need 8 ea of this one http://www.summitracing.com/parts/CRN-64770L-1/
And 8 ea of this http://www.summitracing.com/parts/CRN-64770R-1/
Right and left for the big block.

Something tells me that if you use SB rockers on a BB the tip won't be fully over the valve stem. It should leave a centered pattern on the tip of the valve stem all the way through the travel.

 

[MoparMitch]

Yeah , I guess you cant take the word of old machinist friend who told me they were for big block and gave them to me. Should have checked the numbers myself. Headed out to the shop now to check the geometry . Let you all know whats up.

 

[RustyRatRod]

If you have small block rockers, you can always sell them and get some for a big block. I need some adjustable rockers for a big block myself, just ain't ready to afford um quite yet.

 

[MoparMitch]

Well, I finally got my computer back after someone Hacked it and it crashed about a week and a half ago. Fortunatly all my data and pictures were retrievable. Hey Rusty and Meep , your'e not going to believe this . Its a parts guys nightmare , and I know because I was in the Parts business for 27yrs. When I looked at the box the rockers came in it said 69770-16 this was the outer box. The inner box had the correct number 64770-16 on it , with the correct instructions for B/RB motors , You know , right hand and left hand rockers. This was fairly common in the parts business, you know , parts boxed wrong. Like I said previously a machinist GAVE the to me about 12 yrs ago. So the 8.25 pushrods worked out just right. See Pics attached. Sorry for the poor quality pics. Gues I also need a better camera. LOL. Will finish assembly of engine this week and paint it for install in car next week.