Inliners International Forums General Discussion Hi Performance Olds guide plates for 250/292

I was reading Santucci's book and decided to try the guide plates trick. The only thing is, I cannot drill the 7/16" holes. What are these things made of? The drill I got, which said was for hardened steel or stainless steel aint doin nothin' but chirpin at low rpm's and smokey at higher rpm's on the drill. I think I just toasted the brand new bit I bought...damn!

Do I have to take them to a machine shop? Imma guessin.

Ctown

You learned the hard way about hardened steel, huh? All guide plates are high-strength hardened units, and you will need either a quality cobalt drill bit or a carbide burr to enlarge the holes. Don't think that even a TiN (titanium nitride) bit will work. It might, but chances are you will burn it up too.

My personal preference is to chuck a carbide burr into a drill press and then slowly cut the holes up to the size needed. You could use a hand-held die grinder, but I like the control and slower cutting speed (LOTS less heat) of the drill press. Hand-held units also don't usually give you the most accurate results when lining up the bolts and slots when finished.

If you take them to a machine shop, most likely they would use a carbide bit of similar shape to a common burr and cut the holes with a vertical mill instead of the drill press. Only a different machine using a similar approach.

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David

I took them to a deburring company today. Want to have them done right.

Got them done.

I can't believe how much "less play" there is on the pushrods from side to side...it was worth the effort to get them done.

I'm hoping for a couple of ponies in return. Less friction/instability hopefully equals more hp's.

It looks pretty cool too.

Ctown

Just wanted to let you folks know it all worked out ok. It's been two weeks of hard bashing high reving fun and the push rods do not show any wear/scratches on the sides where they make contact with the guide plates.

I'll post the pics soon.

Ctown

What brand push rods did you use? My guides are destroying my push rods!
Roger

Crane pushrods. Are you running roller rockers or stock?

I forget the part #.

When I have a chance, I'll look them up for you.

CT

I am running rollers from Clifford. I just picked up a set of Crane rods but they are .280" longer than stock and I'm a little comcerned about the extra length. The rollers from Clifford are designed to be used with stock length rods. I found a set of hardened rods from NAPA. They should be here Monday. Leo's book recommended a longer rod (11.570") when using rollers, but the Crane rods are 11.665".
Stock rods = 11.382"
Napa rods = 11.406"
Leo's recommendation = 11.570"
Crane's rods = 11.665"
Confusing!!!
Roger

Roger, the objective is to have the rocker arms move in a range that works considering their fulcrum location and ratio, and one of the biggest reasons that longer pushrods are recommended is because of the shape and size of the cam lobes on a high-lift unit. The stock cams have a big base circle, and the cam bearings are only a given diameter. The high-lift cam uses a smaller base circle and still has to fit through the same hole in the block so can't be just ground with higher lobes.

If you consider the math for a new cam with about 0.500" valve lift, they grind the base circle a little less than 0.050" lower than a stocker. But the valve is going to open about 0.070" more than stock (remember the rocker ratio). So what do you do with the rocker position? If you use stock pushrods, then you lowered the pushrod end 0.05" and you will operate the valve to 0.02" beyond where it used to go. If you use roller rockers, they sometimes have a different fulcrum position, and/or use 1.70 ratio instead of 1.75. So it's a balancing act to find the right pushrod length so the rocker is in the right position to operate best.

Most competent hi-po engine shops have checking equipment to determine what length to use.

I will agree that Leo made a good recommendation for most high-lift cams, and will add that the NAPA pushrods will probably work fine, since I think you inferred you are primarily after the harder material. The extra length would be nice, but it isn't absolutely necessary.

If you have stock-length valves installed in your head, I would recommend that you do NOT use the Crane pushrods. They will work, but are designed for longer valves, and take the rocker geometry to the other side of where you are now.

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David
newbie #4153

Thanks for the info David. Tomorrow I will have both the Crane & NAPA rods in hand. I'm going to setup both and see which one stacks up the best.
Roger

Rog...

DO NOT use the crane push rods if you do not have the Crane roller rockers.

Do some homework on valve train geometry. I did and am glad I did. It's well worth your time for knowledge.

CT


[This message has been edited by CHEVYTOWN6 (edited 06-09-2003).]