bent push rods in 462

[shaunb]

hi i'm going crazy trying to figure out why my engine is bending 2 inlet push rods on each bank.The car was running perfect before removing the heads,but to keep up to date with newer fuel octane levels i removed the heads to get them rebuilt .the guy decked,replaced valves and serviced both heads. When i received them back they were already to be bolted on,After assembly as per the shop manual i started the engine, it ran smoothly but noticed a rattle in the top end.I removed rocker covers and noticed two bent push rods.I replaced the bent rods and checked rocker gear and lifters,which were all ok . Started engine again and same rods bent once again.Then shimmed up the rocker shaft to 0.05 to allow clearance,engine did not bend rods though the rattle in the valves was excessive.I then replaced those shims down too 0.024 and bent the same rods.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! HELP !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[Theo]

I assume that the machine shop had serviced your heads by machining them to accept hardened valve seats. That's the only way to make old stock heads work w. modern gas. It takes a dedicated machinist to do some extra work in order to place the seats all equally distant relative to the gasket surface.
Anyway whatever reason is responsible for bending some of your push rods, it seems that valve stem height varies. Especially on those that bend.
Llifter pre load should be altered individually to compensate especially on those 4 valves in question. Best wa to that is to install adjustable rocker arms. Those came stock w. solid lifter equipped FE engines such as some police and truck vehicles.
They are compatible with the MEL rockers if you didn't already knew BTW. You could check PAW, Summit or who ever carries them. I use Harland Sharp roller rockers on m FE engine.. They are reasonably priced and of excellent quality.
If you decide to go for these, make sure that they won't bind w. the stock valve covers. On my FE engine they do w. stock valve covers. That's why I installed Shelby Cobra alum. covers which are taller.
On an original MEL engin that wouldn't do an good as far as for original aesthetics. With orig. stck. FE adjustable push rods that wouldn't be an issiue for ou. I think Comp Cams sell those orig. stle rockers too.
It's tough to diagnose from a desk.
Good luck

[shaunb]

Thanks Theo, i have ran a straight edge across all the valve stems & all the exhaust valves are the same height & all the intakes are approx 0.20 lower than the exhaust valves but all intakes are the same height.
does this still make sense? The push rods that are bending are # 4 & 2 intake.

[Theo]

This ios a tough one from remote. Even if the stems appear to be of the same length, there will still be the possibility that the head surface has not been milled correctly. But that would lead too far into explaining blueprinting techniques w. my slow fingers on the keys.

Did you think about bent valves that get sticking in the valve sleeves? To check you could do is to take off the valve train and to remove the valve spring of each valve in question. You can do that w. air pressure right into the spark plug hole. There are adapters available and it's a common way to keep the valve from falling into the cylinder bore
Now with the spring removed grab the valve stem, bleed off the pressure and try to move the valve in its' valve guide. This way a bent valve will show.

The second check would be looking for piston to valve contact. You need to install light checking springs, so you can rotate the engine through its' circle w. a breaker bar at the damper nut. Off course you need to reinstall the valve train so you can observe the motion. The critical point to check is the TDC of the intake and exhaust stroke + a few degrees before and after. Rotate the engine into TDC position and push the valves w. the ltemp. installed light springs down towards the piston. Take measurements w. a dial caliper and compare the numbers w. those listed in the manual.

It's probably more economical to check for bent valve stems on each questionable valve and then then installing light springs afterwards. Just a few thoughts from the upper side of the globe.

Let us know what you come up with.
Good luck

Whatever result you get, put back the air pressure and reinstall the spring

[shaunb]

Hi all, it turns out that the newly rebuilt heads have 2 ceased valves. the engine builder didn't replace the valve guides. such an easy problem to diagnose that i looked straight past it. thanks Theo for your help on the matter.

[Theo]

You're welcome. Maybe they replaced the old valves w. new valves that have a different valve stem diameter. Some aftermarket valves come w. larger diameter stems. This way and if things are not excessively worn, the machinist might not need to replace the old valve guides. Only thing to do is to hone the guides to the right valve to guide clearance.
IIf the machinist skipped the honing the valve might starve from oil due to tight clearance and it will finally seize.
WEell, that's just an assumption. It's probably good practice to observe the oil flow to the valve train. Check if the valve train starves from a lack of proper oil flow w. the valve cover off.
Anyway, good to hear you guys found the reason for the bent valves.