..how to ruin a brand new pair of cylinder heads in less than 2000 miles.
In my haste to reassemble my engine with my fancy new short travel Comp lifters I failed to revisit the valve train geometry.
Attached are pics of the the valve tip pattern with pushrods ranging from 7.1" to 7.3".
The "typical" 7.3" pushrod fro a retro-fit Gen 1 application ended up being about 2/10ths too long. The results were valve guides pounded to pieces in short order.
Live, learn, pay for your mistakes and move on.
From left to right the pushrod lengths are 7.1", 7.2" and 7.3". The last one is what killed the guides. Orientation is intake manifold to the top of the picture.
No head gasket installed which is .025" to .028" depending on whose catalog you read.

 

That's amazing. When I checked my pushrod length on my Vortec heads, I varied the pushrod length by more than that and I couldn't even make out a change to the wipe pattern. Usually the adjustable style rocker arm setup that the SBC uses is pretty forgiving.

Out of curiosity, what kind of heads were they? I know that some aftermarket heads seem to require much more precise geometry than others.

 

I had a similar issue with mine but only on intake side. Not sure why as i thought i had a fairly centered pattern, narrow sweep, but the experts believe that was the issue. Live and learn. I wonder how much if any does valvetrain stability has because i was on stud mounts but high offset rockers. Wonder if that geometry has some influence. Will be trying shaft rockers on my heads this year.

Its surprising because i did pushrods on 2 builds and never had a problem with my method. Will have to revisit things once i get parts back but pushrod sizes are not to be taken lightly.

 

The heads are RHS Pro Torker Vortec.
The rest of the valve train consists of Comp Pro Magnum pushrods, full roller rockers and 26918 (Beehive) springs.
The difference in the seat height between the traditional retro-fit roller 853 and the short travel version 15853 is .190".
I completely ruined the heads but I wanted to see what the differences in patterns are by using an adjustable pushrod.
The rocker adjustment shouldn't really enter into the resulting pattern provided that the amount of lifter pre-load is the same. In my case, using checking springs, the preload is zero or very nearly so.
It's easy to see how the 7.3" pushrod would mangle the guides. The pattern starts at the centre of the valve tip and moves out from there.
Here's a look at one of the guides.
This was an expensive mistake.

 

You can say that again!

 

The other valvetrain issue I'm dealing with is alignment. Prior to going to an adjustable guide plate, the rocker wouldn't sit square over the valve tip. Even with the adjustable plates, there is still some misalignment. I wonder how much of an effect that has on the guides?
I'm going to post up some pictures once my new parts arrive and re-assemble everything.
I suppose on the bright side, when I sent my heads to the shop (a shop I hadn't used before but local and very convenient) the machinist pointed out that he had done a little bowl work and even went so far as to cut the chambers a bit to unshroud the exhaust valves. Very handy actually as with the new short block (with its reduced deck height and smaller valve relief pistons) and my desire to keep the quench at .040" my SCR was in around 10.4:1. That was a little too high for the relatively short cam I run (adv 276/282) and iron heads. Now I'm back around 10.14 which should be a little more manageable.

 

Yup i remember going through all that mess of finding the right length pushrod and i got advice from everyone. The worst advice i got was that since i was running 1.6 roller rockers i would need a longer pushrod (forget by how much). At any rate i got an adjustable pushrod checker and actually checked the length and it came up that i needed a shorter pushrod because of all the other things going on in my motor (aftermarket cam, dart heads, decked block). So basically as far as im concerned there is NO rule of thumb for lengths once you are working with a modified engine. The right length pushrod for one motor is not necessarily the right one for another.