Pushrod Problems

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bahamabecomb

bahamabecomb

FABO Gold Member
FABO Gold Member
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Bothell WA
New member here. Electrician by trade, but it has been 25 years since I have done anything other than minor engine work. My problem is that once I fixed the electrical wiring for the gauges and lights I took it out for a drive and about a mile in the tab on the rotor broke off under the distributor cap and there was some awful sounds (picture of rotor below). Since it was still a points ignition system I ordered the mopar electronic replacement ignition/ distributer from classic industries, installed it and then had a bad backfiring problem through the carb. After resetting the timing several times and doing a compression test I then pulled off the valve covers to find the #4 cylinder exhaust push road was mushroomed on the top and the #2 cylinder exhaust pushrod also had a piece ground off of it (pictures below). I was able to pull out the small cup for one pushrod and also find the broken piece of the other and remove them from the head. 71 Duster with a replacement 340 that I do not have any info on regarding the build.

It looks like Summit has the replacement pushrods but I have the following questions:
How do I know if this is the correct pushrods for the rocker arms installed?
Should the rocker arms be adjustable locking rockers?
How do I set the lash on these once the new pushrods are installed?
Any additional parts that I should purchase with the pushrods?

Thanks for any advice

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Hydraulic or solid lifters?

Those adjusters are backed off too much (push rods too long?)allowing the rocker arm to com in contact with the pushrod cup is what appears to be happening.
 
You need to have a look at your timing chain before going too much further.
Before you know how to adjust them, or what the correct length pushrod is, you need to know what type of cam is in it, hydraulic or solid. Then you measure for pushrod length with an adjustable pushrod and adjust the rockers accordingly, ie preload for a hydraulic and lash for a solid.
 
Thanks, I should be able to get the timing chain cover off this weekend, hopefully there is a # on the end of the cam shaft? Adjustable pushrod is ordered.
 
Most cam manufacturers stamp the end of the cam but it makes no difference really what cam it is. You can tell what TYPE of cam it is by looking at the lifters.
 
Man that sucks! And like CFD244/Troy said those adjusters are backed out approx 2 threads too much, but you won't know exactly how much until you verify the cam/lifter and measure with adjustable push rod. Can u post pic of lifter?
Good luck.
 
The push rods are too long they are hitting the rocker arm the adjusters should be lower down
 
Is it possible he has mixed and matched hydraulic vs solid lifters and push rods? I forget, anymore, which ones are longer.
 
bahamabecomb said:
Thanks, I should be able to get the timing chain cover off this weekend, hopefully there is a # on the end of the cam shaft? Adjustable pushrod is ordered.
Click to expand...


When you measure for pushrods you need to set the adjuster at 9/32 inch or .281 thou.

That is the Chrysler specified number and that’s where they should be.

I don’t have the book at hand, but IIRC the spec is 9/32 out plus .010 minus .000

It’s critical the adjuster is at the right depth. I know guys don’t always do it but anything other than what Chrysler says they are doing it incorrectly.
 
The adjusters on those rockers rely on thread interference to remain in place. Some may have come loose from too many adjustment cycles....& backed out causing your problem.

I believe those rockers can be tapped to use a stud/locknut arrangement.
 
Agree pushrods too long. You need to know what cam. Solid or hydraulic. Solid you set valve lash. Hydraulic you remove lash then go half turn preload.
 
Thanks again for the input. I'll get the intake off in the next couple of days and post some pictures of what the lifters look like.
 
Have you adjusted valves before? If not this is a simple method of doing it. Or you can set crank with Valve chart.
Valve Lash Adjustment

Starting at Number 1 cylinder, rotate the engine until the exhaust rocker just starts to open the exhaust valve. Set the valve lash on the intake rocker at this time. Continue rotating the assembly and stop when the intake rocker starts returning from full lift. Now the lash on the exhaust rocker can now be set. Continue this procedure for the remaining cylinders following the engine’s firing order.

If setting preload for Hydraulic lifters remove up and down play on pushrod then add ¼ to ½ turn of preload. Some people say tighten until you it gets hard to turn the pushrod then set preload I don’t agree with this method as the lifter may not be pumped up. JMO. If the motor was just running then yes this works.
This method works on almost any flat tappet engine
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Pull a complete push rod and measure the length, then order shorter closest to a couple turns of the screws. 340 hydraulic are 7.534" x.28 od. I expect you need 340 mech which are 7.250 x 0.375.
 
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I removed the intake an pulled the lifters out, they look to be hydraulic. 6 of the 8 push rods are stamped with RP3219R-100 and a 7.565 inch overall length. The other two look like they were made by a junior high kid in shop class (exhaust on #1 & #7 cylinders) and are both slightly bent. The new ones that are bent/ smashed are the #2 intake and #4 exhaust. There is also a significant amount of scoring on both the rocker arm shafts. Lifters and camshaft look to be fine, compression test was good.
Pushrod length checker is due to arrive on Monday. Once I have that and can confirm length I am planning to order new rocker arm assemblies and pushrods.
Let me know if I should be looking to change out anything else? Is it worth the money to switch to a roller rocker assembly?

Thanks for any feedback

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Those shafts need to be polished and measured and then measured to see if they are even worth using.

Then with groove the shafts or get new shafts with grooves in them.

Get your oil pressure at idle to at least 25 psi.
 
I don’t know if you rotated the shafts for the pics, but they go with the oil holes down when installed on the heads.

“If it were me”, I’d be replacing the rockers and shafts with the Mancini aluminum rocker kit, the ones made by Harland Sharp.
 
I was just looking at the Mancini site 20 minutes ago, leaning toward the

Mancini Racing Roller Rocker Arm & Pushrod Pkg​

Item #: MRE67001-15-9284
Pushrods are cut to fit

Old shafts are going to the recycle bin where they belong, thanks for the reminder on the oil holes.
 
RP-3219R-100 is supposed to be chromoly, 7.3900" O.A.L (cup depth subtracted) and fit 273 and the 340 in 70-71".
 
Thanks for the hep everyone, she is running and back on the road. Went with the Hughes roller rockers and shafts, definitely overkill for this engine but others I found online did not have very good ratings. I will say the customer service at Hughes was excellent and will use their products when I get to rebuilding the original block. Pushrods (Summit G6420) came out to be a stock measurement with the pushrod measuring tool and Comp cams hydraulic lifters.

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