Rocker Arm Clearance

[EngineerDoug]

Got a quick question about setting up a valvetrain and measuring for pushrods. I have Harlan Sharp rockers on Trickflow 240 heads (mechanical flat tappet cam). I am using a checking pushrod with a cup at the top end.

I see the clearance between the cup outer edge and the rocker arm is on the order of 0.020" to 0.025" at closest approach. The adjuster is set for 1 thread visible at the rocker ball.

Is this anything to be concerned about? What is a minimum acceptable clearance?

Thanks.

 

[91r/t]

Did you get the specific harland sharp rockers for those heads? They make specific ones for those and Edelbrock heads. Does 2 threads showing get you any more clearance? i know mine were pretty close at full valve open position, but can't remember the exact number.

 

[gkent]

Go for two threads. Also, I have Smith Bros. pushrods and I seem to recall they are made to the nearest .010" - in other words if you request a rod that's 9.333" long its going to be 9.33 when you get it. With an adjustable rocker I'd rather have the pushrod a tad shorter than risk interference between the cup and rocker.

 

[dvw]

It's amazing how things move around. My race motor has individual T&D shafts mounted to a steel bed plate. There is over
040" clearance to the retainer. Yet there are witness mark's on the underside of the rockers. This system is far stiffer than factory. I would bet you need. 060" .
Doug

 

[PRHeads]

If you’re not pushrod oiling, then the edge of the pushrod cup has to be below the oil feed hole in the rocker.

One turn showing on the bottom of a HS rocker doesn’t usually get you there.

 

[EngineerDoug]

The rocker arms are indeed the "E" version intended for use with the TF heads. I will check to see what clearance I have with 2 threads showing. The HS rocker arm should be set up (per their instructions) with no more than 2 threads showing. I do see the oiling hole on the underside of the rocker arm, so I will also eyeball that with 2 turns showing.

At this point, I only have the checking pushrod, but the outer diameter of the cup - where it nearly contacts the relief in the rocker arm - is 0.495". My plan is to order custom pushrods from Smith Bros, so perhaps the "real" pushrods are not so bulky in this area?

Note I checked the contact pattern at the valve tip and it is near perfect. So aside from being able to use a less bulky cup on the pushrod, I don't see what else could be altered to increase this clearance.

Any further thoughts?

 

[beanhead]

The rocker arms are indeed the "E" version intended for use with the TF heads. I will check to see what clearance I have with 2 threads showing. The HS rocker arm should be set up (per their instructions) with no more than 2 threads showing. I do see the oiling hole on the underside of the rocker arm, so I will also eyeball that with 2 turns showing.

At this point, I only have the checking pushrod, but the outer diameter of the cup - where it nearly contacts the relief in the rocker arm - is 0.495". My plan is to order custom pushrods from Smith Bros, so perhaps the "real" pushrods are not so bulky in this area?

Note I checked the contact pattern at the valve tip and it is near perfect. So aside from being able to use a less bulky cup on the pushrod, I don't see what else could be altered to increase this clearance.

Any further thoughts?

Another option is to switch to cup-style adjusters and ball/ball pushrods. Mike Beachel (B3 Racing Engines) is also a good guy to consult with in these matters.

When you say " the contact pattern is near perfect" what are you seeing? It's okay to be off center somewhat but it should be very narrow. Like .030-.050 narrow.

When I get home this afternoon--I'll get a comparo measurement of the cups on a Smith Bro and the checking pushrods I have.

 

[EngineerDoug]

Yes the contact pattern is very narrow, and biased maybe 0.015" off-center.

I spoke with Smith Bros and described the situation. They indicated that a smaller diameter cup is not available, and did not express concern about the clearance.

They also suggested that, with a mild cam (solid flat tappet, 350 lbs @ full lift), I could get away with 3 turns showing on the adjuster. I will call Harlan Sharp to get their opinion on this.

 

[EngineerDoug]

OK more info on this.

I also called Manton Pushrods and spoke with them. They were not concerned about the clearance I measured using the checking pushrod, and told me that the cup end they use on their pushrods is 0.460" diameter. That would give me at least 0.025" + 0.017" = 0.042" clearance between the outer edge of the cup and the rocker arm relief.

 

[beanhead]

The cups on the Smith pushrods I have measure .430 dia x .287 tall (measured outside from the point they connect to the body, to the top edge).
I use the Harlan-Sharps made for Mancini so the adjuster ball should have the same radius(meaning the rods you get from Smith bros should have the same cup).
Ideally you want as little adjuster as possible exposed under the rocker, where you still have the oiling hole uncovered with no interference. The farther you screw the adjuster out the more you risk breaking parts.

And I'd love to see a pic or two of your valve contact swipe; just to see how well those rockers work on the TF heads with no correction..

 

[EngineerDoug]

Thanks!

 

[dvw]

I don’t know about Harlan’s but T&D have an increased diameter at the bottom of the body where it is threaded. This keeps the oil hole from being covered when the adjuster has very little thread showing.
Doug

 

[EngineerDoug]

Hey guys,

Just an update on this issue. I got my new Smith Bros pushrods today, and sure enough the outer diameter of the cup is 0.430". That is a good deal smaller than the diameter of the checking pushrod I used to determine the required length. So I now have about 0.040" clearance between the pushrod and the underside/relief cut of the rocker.

I spoke with Harlan Sharp about this issue and they suggested that 0.020" is about the minimum you would want to see in terms of this clearance. So all good now>

Thanks for your inputs!