63 fi engine assembly/parts question

[Robert B.]

Where and what should I buy for rocker arms and pushrods (360 stock rebuild ) Thanks Robert

[Joe L.]

Re: 63 fi engine assembly/parts question

Where and what should I buy for rocker arms and pushrods (360 stock rebuild ) Thanks Robert

Robert------


The GM rocker arms for your engine are discontinued. They were replaced by guided rocker arms which are not advisable for mechanical lifter applications.

The original style pushrods are also discontinued. They are replaced by GM #14095256. These are welded-ball style, OEM quality pushrods. They are excellent and I recommend them. However, they are expensive and, of course, not configured as-original (if that matters).

I recommend using Crane Nitro-Carb rocker arms. These are configured as-original (except for the embossment on one end). For stock-type rocker arm installations I highly recommend these. You can also obtain stock-style push-rods from Crane.

[Ed S.]

Re: 63 fi engine assembly/parts question

Joe, Do you by chance know if the Crane rocker arms are configured (functional dimensions) identically to the OEM GM rockers they are replacing? Specifically, information on the Crane website states that these rockers have a 1.5 to 1 ratio. According to Duke Williams small block OEM rockers which were advertized as 1.5 to 1 only had, if you measured them, a ratio of 1.37 to 1. There are tech papers written by Duke Williams and John Hinckley circulating that discuss valve lash for 30-30 cams. In their papers they advise to set the lash to .026 instead of factory recommended .030 to compensate for the difference between the advertized and actual rocker ratios. I am aware that Robert's '63 360 HP FI engine does not have the 30-30 cam found in '64 & '65 engines. But I am wondering if someone (me) were to replace worn rockers on an engine with the 30-30 cam if Duke & John's advice on valve lash still applies? Also, you would think that a true 1.5 ratio would open the valves a bit more and that difference would probably be enough to make a noticeable difference in performance. Ed

[Duke W.]

Re: 63 fi engine assembly/parts question

That's a long obsolete version of the paper. Please delete it and google the author names to find the latest revised edition (9/08 on the Web site lbfun), and attach that one if you want. The revisions have different lash recommendations based on actual review of the GM drawings rather than measurements of lift curves with a dial indicator. The drawings are much more accurate because they list lobe lift, in inches, to five decimal places every cam degree.

There are a lot of misconceptions about rocker arms. Many think that the ratio varies from piece to piece, but that is a myth.

The variation is over the range of lift - about 1.37:1 at low lift and about 1.44:1 at max lift with a 0.3" lobe, and most will measure the same total range within the accuracy of dial indicator measurements made at the pushrod and valve.

No rocker arm design that uses a rocker shaft or pivot ball like Chevrolet has a constant ratio. It's just a basic fact of geometry.

So there is no such thing as a "true" rocker arm - 1.5, 1.6...whatever. They all vary over the range of lift regardless of the claimed ratio because the rocker arm ends move in an arc, and on Chevrolet style ball-pivot rockers the fulcrum actually moves over the range of lift, but it's fixed with shaft mounted rockers.

It amazes me that in over 50 years of reading various car magazines I have only run across one article that alluded to this issue, but no details.

From high school geometry I knew the ratio could not be constant, but I didn't get around to actually measuring the variation until the mid seventies. I have suggested to many to do it themselves, but only a couple have taken up the challenge over the years despite how simple it is to do while disassembling or assembling an engine. All you need are two dial indicators, a pad on a clipboard, and a little patience.

I'm not sure about the Crane rockers, but I think they are geometrically identical to OE rockers, so they will exhibit the same variation of ratio from zero to full lift, but then someone should measure them to be sure.

I made the same suggestion as Joe to Robert on the phone. The heads have screw in guide plate/studs, which is a no-no unless the pushrods holes are opened up on early heads, but a visual check comparing to an unmodified head showed that they had been opened up.

On early heads the pushrod guides are essentially the oblong pushrod holes in the head, and if you try to "guide" the pushrod at two points, the usual result is bent pushrods. If guideplates are used the pushrods MUST have hardened tubes, which early pushrods may not have. I believe the Crane pushrods have hardened tubes, but Robert has to confirm.

I always wondered how Flint formed those non-round pushrod holes and suggested to Robert that they were broached. He agreed and mentioned he has many years experience in machining and broaching is the most likely way they were formed.

For all engine rebuilds I recommend using the original rockers/balls/pushrods assuming they have been bagged as matching sets off the engine and pass visual inspection for galling which most will, even a set you pull off a junkyard engine.

"Roller tip" rocker rocker arms are a marketing gimmick and a total waste of money as are "high ratio" rocker arms. The money wasted on these heavily advertised hot rod parts would be much better spent massaging the heads for better flow. That's were real and significant power gains can be had in the upper third of the rev range without screwing up the idle behavior and low end torque.

For most engine restorations all you need is a new OE equivalent cam, lifters, and OE replacement valve springs, and you can buy a set of 16 Sealed Power VS677 (3811068 equivalent) valve springs for about 20 bucks. Depending on cam price, which can be as little as 50 bucks for the Sealed Power equivalent of the '67 up "300 HP cam", you can restore the entire valve train to as new with dead-on OE reliability for less than the cost of a set hot rod rocker arms.

The only application that I recommend roller trunnion rocker arms are serious racing engines that see sustained operation above 5000 revs, where the rules permit their use.

Duke

[Ed S.]

Re: 63 fi engine assembly/parts question

Duke
I think I can safely thank you for your advice on behalf of all that have a vested interest in this (and many other Corvette related) issues. I believe I found the updated and current version of the valve adjustment paper you referred to. I am attaching it for the convenience of others. Please advise if it is NOT the most current.

Thanks again,

Ed

[Duke W.]

Re: 63 fi engine assembly/parts question

Yes, that's the most current version. Thanks for posting it.

Duke