Push rods

Ricky · 04-19-07, 08:00 AM

Hi all,
I have recently started to have issues with my 347 hydraulic roller cam motor giving a constant miss fire at idle and which continually worsens as revs rise.

Nothing has changed in terms of ECU mapping and after checking all the basics (fuel, spark and compression check) have put it down to a valve not operating properly. I have noted recently - but before the current events - that the upper rev range the motor has been a bit "Fluffy"

I have arranged for the engine builder to go through and check all the valve springs, seals, etc, some time next week with luck.

In the mean time I pulled the rocker covers today and found a nice groove ground around the push rods.

Now I am not the brightest or smartest when it comes to engines but thought this just cant be right so, I pulled a couple of push rods to have a look and guess what...... a lovely reduction in pushrod diameter by about 1.5mm on all push rods! Obviously they have been wearing on the guide plates.

Is this normal wear for hardened pushrods given the motor is only 3000km old, albeit pretty hard km's over the last 4 years.

What causes this kind of drastic wear? Look forward to some interesting comments.

Jac Mac · 04-19-07, 08:24 AM

You need some hardened pushrods to run with the guide plates, those ones are not hardened, grab a small file and see if it will 'bite' as you rub it on the pushrod, it should skate across the metal, not dig into it.. You can obtain Yella Terra shaft type rockers which do away with the guide plate/hardened pushrod requirement. Just depends on which way you wish to proceed. One final thought which wont cheer you much, all that metal that is missing from those pushrods is now in your oil pan ,pump & filter. Time for at least an oil/filter change along with a magnetic sump plug along with one taped to the next new filter.

Jac Mac

Mick · 04-19-07, 09:46 AM

Hey Rick, I hate push rod guides. I used Yella Terra Platinum twin shaft roller race rockers. They recomended not to use guides. Geometry is critical but no bent or worn rods yet. Catologue No. is YT 5021
1.65 ratio, suits Edelbrock RPM performer, Victor JR.
Catologue No. for Trickflow YT 5028 1.7 ratio. Catologue No. may not be current. Give me a call if you need any more info

Mick

Ricky · 04-19-07, 11:53 PM

Thanks for the replies.

These were supposed to be hardened push rods, but obviously not. The engine builder is replacing them with CroMo items next week. (As well as valve springs, and retainers, etc) Quite frankly he was very shocked when I rang him with the news so I think he will be doing a bit of soul searching himself.

I will be doing an oil change as sugested although it is something I do every 300 - 400 kms in any case. I figure if the engine is being pushed relatively hard then frequent oil changes are cheap insurance.

Rick · 04-20-07, 12:05 AM

CroMo does not specifically indicate they are hardened, just a different material, they must be hardened and heat treated to prevent a repeat incident.

Big-Foot · 04-20-07, 12:26 AM

If the type of rocker arm you used was a self-aligning or Rail-Type roller rocker like the one pictured below - you can't use them with guide plates.

Another thing that can cause this problem is using a stock length push-rod with an aftermarket cylinder head. Many aluminum heads require a longer push-rod. a short push-rod will run very close to (if not rub on) the very bottom of the slot in the guide plate. A similar condition can also be created by running a very high lift cam or an extended length valve stem without checking for proper push-rod length / geometry..