Shorter pushrods ... or longer studs ??

[Spanish Dave]

Hi all
I have recently rebuilt the engine on my 65 f/b 289. it has 351w heads which I have used Comp cams springs and roller tip rail rockers. When I put the whole thing back together the nuts on the new screw in 3/8 studs (the old screw in studs were badly worn) were only just seating down to the *locking* part of the nuts and kept working loose ... causing misfires etc. As a quick fix I turned the nuts over and used them that way and they seem fine now, although not exactly *right*. I don't know wether I should look for some longer studs so the nuts can go right way up ... or I should try some shorter pushrods. Any suggestions to which way would be best and would provide the best geometry for these rockers? BTW the cam is a Comp cams 280H with new lifters. The new pushrods are the same length as the previous ones which I assume are stock length (for a 289) measuring just a shade over 6 and 3/4 inches.

 

[Edbert]

I've never heard of adjusting lash in the valvetrain but adjusting the lenght of the studs. They make pushrods in just about any length you can imagine though.

 

[thehueypilot]

Your best bet is to buy an adjustable pushrod to check for the correct length needed. The roller tip must be centered or just inboard from the center of the valve stem to be correct at TDC. Use a black marker and color the end of the valve stems on both the intake and exhaust valves. Make sure the cylinder you are measuring is at TDC. Place the adjustable pushrod in place of the stock pushrod and place the roller rocker onto the stud. Wiggle the rocker back and forth a couple of times so you get a wear pattern onto the end of the valve stem. This pattern must be at least in the middle of the valve stem or just inboard for proper valve geometry. Repeat the procedure by lengthing or shorting the pushrod until correct pattern is achieved. Measure the final pushrod length and find the closest match at Summit Racing. As far as the correct rocker arm stud goes I am told that at least a couple of threads sticking out is good enough, but I perfer at least 1/4 to 3/8 length of threads sticking out. Also do yourself a favor and install good quality locking nuts. Good Luck!

 

[MustangPaul]

yow!

Huey--that's amazing! You're the MAN!

How'd you know all that stuff?

(Sometimes it is plainly obvious that my mechanical knowledge will never let me run with the big boys.)

--Paul

 

[thehueypilot]

I guess at a very young age I grew up teething on cars? I also am cheap and have higher quality standards than most mechanics are willing to give so I have to do all my own work to make sure it is right. If I can help dissiminate a little mechanical knowledge just let me know. Besides I been there and done that before so if I can help someone learn from my experiences I'd be glad to put my 2 cents worth in.....

 

[Spanish Dave]

thanks for the replies ... I can see the way forward is to measure and get shorter pushrods. I shall use your tips to get the job done.