I posted a while back about my cylinder head problems (bent pushrod, rocker) which is now in process of being fixed. I'm getting conflicting opinions on whether I should add hardened push rods and guideplates. One mechanic recommends this, the other doesn't think it is necessary and indicates that some work has to be done to the heads to accept the use of hardened rods? My heads are "461" casting, screw in studs, comp cams springs, stock rockers.

Can anyone give me some advice??

Thanks!! :cheers:

 

The only thing that could be done that would indicate the need for pushrod guideplates are the machining necessary to the stud boss to accomodate the additional pad space necessary for the thickness of the guidplates. While it is possible to mill the boss only for the stud, this is not what is commonly done.

I've seen the bent pushrod syndrome on non-guideplate heads where binding wasn't an issue. In this case, the pushrod wore on the pushrod slot in the head, got cocked and bent when the rocker arm went off the valve tip. Closely examine your pushrod guides in the head and if you see any wear in the slots, you're going to be in the position to use guideplates or you'll have to replace the heads.

 

Gerry72....thanks for your advice. It makes sense to me and I'm going to take it. Your scenario sounds like exactly what happened to my heads in the first place so I want to fix it once and for all. :cheers:

 

I've had this problem several times in my Vette. It got to be so common with my old set of heads that I would carry spare rockers and pushrods in the car so I could fix it on the side of the road if needed. I later replaced my heads and figured that my troubles would be over..............wrong! I'm convinced that it is caused by deflection in the soft pushrods when using higher than stock lift cams and heavier valve springs. If the slots have not gone too far, you can just run the hardened pushrods without adding guide plates. Trust me, it will work fine. This is what I do with my 461's on my streetrod (no guideplates)and have never had a problem on this motor with dual valve springs, over .550 lift and regular runs past 7500rpm.

Tom

 

Thanks for sharing your experience Tom!! Doing both (guideplates with hardened pushrods) sounds like good insurance for me!! :cheers:

 

Good choice. Better safe then stranded. Thought about upgrading your rockers?

 

I hadn't actually. Do you mean to roller rockers or an upgraded standard style?? I don't know much about rockers....which probably shows!! :cheers:

 

I don't think the full roller will fit under your valves covers but roller tip will. The roller tip want give you the friction reduction that full rollers will but can give you added lift if you get 1.6 ratio and they will give some friction reduction. But make sure that added lift won't make the valves hit the piston. I know very little about the camel hump heads but I bet their are others running full roller or roller tip rockers with heads like yours. Can your mechanic give a recomendation?


[Modified by Fevre, 1:06 PM 6/24/2002]


[Modified by Fevre, 1:07 PM 6/24/2002]


[Modified by Fevre, 1:07 PM 6/24/2002]

 

if your heads have the pushrod double D holes to guide the push rods you will have to open the double D holes for clearance to prevent push rod binding with the use of guide plates under the studs. :chevy

 

You better find out why you are breaking the push-rods that should never happen. All push rods are made out of Hardened steel. They should also last the life of an engine.

 

Under normal circumstances the stock pushrods will hold up, but not always. All pushrods may be hard, but not as much as you think. They are usually either case hardened mild steel or chrome moly. The case depth is not very deep and while you end up with a hard surface for wear, the steel is still very soft when compared to the true hardened chome moly pushrods.

The likely reason(s) for these problems is that the tip of the valve stem is not a flat surface anymore and the rocker will want to slide to the "path of least resistance" which is over the side. This puts a tremendous amount of lateral load on the pushrod. The load on the pushrod slowly wears on the cast iron and elongates the pushrod slot and causes the rocker to sit even further from the center of the valve stem. This keeps compounding the load on the pushrod and eventually it will bend.The chrome moly pushrod will be strong enough to take the lateral load.

The use of guideplates is a good idea and is what I eventually did, but as Clem said, you will have to pull the heads to open up the holes as well as machine the rocker stud bosses for the added thickness of the guideplate.

If you don't want to pull the heads at this time and the slots in the heads have not gone too far, you will be able to get by with the chrome moly pushrods for a long time if needed. I know this from experience.

Also, Check your rocker arm studs. It's likely that you have a few of them that the rocker arm has started to "saw" through.

Tom

 

Thank you all for your comments! I'm learning more and more from all of you and I appreciate your help!! Both heads are off and are being set up for guideplates and hardened push rods. More money, but I do have a higher than stock lift cam (XE262) and the higher pressure springs to match the cam so now I'll upgrade the rest. Thanks again!! :cheers: