Small Block Rocker Arm Alignment

[Clem Zahrobsky (45134)]

Re: Addendum

no matter which method you choose you need to enlarge the push rod holes in the heads to prevent a binding problem. i would go with the screw in studs and machining the stud bosses down for the guide plates. i would also use the GM SBC screw in stud kit # 12495497 as the after market ones could give you a fitment problem with the stock rocker arms and use the guide plate # 3973418 and you will need 8 of these

[Scott Goings (7829)]

Re: Addendum

I really don’t want to pull these heads off unless I have to. Isn’t it possible to open up the guide holes without removing the head? I know there is risk involved with getting shavings in the oil system. However, careful use of shop rags and grease should prevent the shavings from reaching the oil pan. On some of the more worn guide holes I don't think any drilling will be required.

If the above is possible, the only question is what valve stem height is required for the SAR to work properly. Is there a specification or do I need to get a rocker and measure the depth of the SAR slot and compare that depth to the valve stem height?

[Clem Zahrobsky (45134)]

Re: Addendum

best bet is get one SAR and check the depth of the slot and compare it to what the valve stem tips on your engine measure. you can use a machine reamer to open the holes in the head BUT do not try to use a twist drill as it will grab and cause all types of problems to the heads and your body. with the intake off and some carefull work you can enlarge the holes without removing the heads as i have done this BUT it was on clean heads,no oil residue,on a new engine.call me if you have any questions 724-468-5692 after 9 PM

[Joe Lucia (12484)]

Re: Addendum

Scott----

One of your previous posts that was supposed to include a picture didn't have one that opened for me. However, I just noticed that you later posted one. So, now "I've got something to work with".

Actually, I've never seen a mis-alignment this bad. It could be due to the wear in the pushrod holes. However, I think that it's just the opposite. In other words, the wear in the pushrod holes was CAUSED BY this misalignment rather than the wear causing the misalignment. In a small block Chevrolet, the holes in the head for the pushrods do not really have a "guide" function. Normally, the periphery of the holes do not contact the pushrods in any substantive way. As a matter of fact, older small blocks didn't even use hardened pushrods. So, in those cases, if there was any "designed in" contact, there would be rapid wear of the pushrod. Later small blocks, like yours, did use hardened pushrods. In your case, due to substantive contact with the holes, they significantly wore the holes.

I think that there may be problems with the ORIGINAL head and/or block casting and/or machining that are the genesis of this problem. If so, the problem has existed ever since the engine was new. This sort of problem could exist for years as a "sub-acute" problem. If there is a problem with the original castings and/or machining, there's no way to rectify that now. However, you may be able to "work around it".

The first thing that I'd do is to remove the rocker arms, themselves, and inspect them for any obvious problems. Next, I'd carefully inspect the rocker studs for any obvious problems. Especially on the stud with the great misalignment, check to make sure that the stud is installed "straight and true" in the boss and that the boss is not cracked.

If you have any reason to expect that the cylinder heads have been excessively "decked" (i.e. multiple rebuilds over a period of years with the heads "cut" each time or an excessive "cut" to "machine away" some problem) and/or if the block has been "decked", then you might want to check that the stock-length pushrods are still what you need for correct valve train geometry. To check for this I'd use a Comp Cams adjustable pushrod and a Manley push-rod length checking tool. Both of these tools are quite inexpensive and are available from Summit Racing and others. I really doubt that push rod length would be a contributing factor to this problem, but, the situation being what it is, I'd still want to check it.

Next, I'd obtain one or more of the self-guided rocker arms. Install one (you can just use one if you want and transfer it from position-to-position for checking purposes). See where the pushrod position with respect to the hole ends up with the valve adjusted. If it's clear of the sides of the hole, you're "home free" for that position. If it's not, then you'll have to enlarge the hole THE MINIMUM AMOUNT NECESSARY to achieve clearance.

The self-guided rocker arms will absolutely ensure lateral centering of the rocker arm on the valve stem. They will do this as effectively or, even, more effectively than the use of guide plates (which also require the use of screw in studs). The only problem with them, and it would be the same with guide plates, is what other misalignement that they might "force" in the valve train. Clearance with the holes is one of these problems. That can, hopefully, be addressed by enlarging the holes. However, if the holes require much enlarging, then there exists some other problem (like the original casting/machining I spoke of earlier).

With the intake manifold off, you may be able to enlarge the holes without the need for removing the heads from the engine. If you go with the guide plates and screw in studs, then you'll need to remove the heads from the engine.

Let us all know how this turns out.

[Joe Lucia (12484)]

One More Thing

Scott-----

Something else has occurred to me as I thought about this. Are you CERTAIN that your block deck surfaces had the DOWEL PINS installed when you installed the heads on the engine? With the dowel pins installed, when you placed the heads on the block they would not "slide around" after the dowel pins engaged with the holes in the heads. The heads should fit tightly on the dowel pins.

The dowel pins are ABSOLUTELY CRITICAL to ensure exact alignment of the block and the heads. The cylinder head bolts WILL NOT, BY THEMSELVES, ensure proper alignment of the block and heads. The purpose of the cylinder head bolts is to RETAIN the cylinder heads to the block. The purpose of the dowel pins is to ensure proper ALIGNMENT of the heads and the block.

[Scott Goings (7829)]

Re: One More Thing

I am 99.9% sure the dowels are in the deck. I rebuilt the engine in the early nineties during a body off restoration with what was suppose to be the 350 HP cam but ultimately turned out to be a 250/300 HP cam. I was unhappy with the performance and change to an aftermarket Edelbrock. This proved to be unsatisfactory as the engine was over cammed. I then decided with advice from the board to go with the stock 350 HP cam. When I pulled the Edelbrock, I found the #8 exhaust (same valve which is severely rotated in the picture) pushrod bent and the lifter completely out of the bore. In addition, the #8 intake pushrod was off of the lifter and sitting against the valley floor. I assume this was a result of over revving the engine due to a missed shift. I did not notice the fact the car was running on 7 cylinders due to the rough idle characteristics of the Edelbrock.

During the initial engine build and during the change over to the Edelbrock I did not notice the #8 exhaust misalignment.

I have a friend who has a set of SARs which he pulled off of a low mileage car and replaced with 1.6 to 1 roller rockers. He is going to loan me this set to check the clearances to the valve keys and how much clearance I have to the head guide holes.

I'll post my findings later in the week.

[Joe Lucia (12484)]

Re: One More Thing

Scott-----

The thing that I find a bit curious here is that while the #8 exhaust is severely misaligned, the rest of the rockers I can see are all misaligned and, although to a lesser extent, all are misaligned in the same direction of lateral displacement. This is one of the reasons that I mention the possibility of missing dowel pins. I don't think that it's a great possibility, but it's something that might account for things being the way they are. If a single valve had the rocker displaced, that would not be a possibility. However, in this case, it looks like all of the rockers are similarly displaced.

It will be interesting to see how this "unfolds".

[Scott Goings (7829)]

Re: One More Thing

Here is a picture of the rockers for cylinders 2 and 4. They show the same rotation direction.

[Scott Goings (7829)]

Re: One More Thing

There is no way I assembled this engine without dowel pins. When installing the head gasket the dowel locates it in relation to the deck surface. I would have noticed a missing dowel at that point. Maybe the dowels in the deck or the receiving holes in the head are out of specification?

[Joe Lucia (12484)]

Re: One More Thing

Scott-----

Yes, in general, there would be a lot of things to "cue" one for the need for the dowel pins. Besides their criticality for alignment purposes, they are also a major engine assembly aid.

I suppose that it's possible that the block dowel pin holes were originally machined slightly out-of-spec. Or, perhaps, the mating holes in the head were machined out-of-spec.

Are the rockers on BOTH cylinder heads similarly misaligned?

[Scott Goings (7829)]

Re: One More Thing

Photo of cylinders 1 and 3

[Scott Goings (7829)]

Re: One More Thing

Photo of cylinders 5 and 7


There are misalignments of the right side but not as bad as the left. They are also random in the direction of rotation.

[Joe Lucia (12484)]

Re: One More Thing

Scott-----

These look more normal, to me. They're usually not exactly centered.

[Scott Goings (7829)]

Re: One More Thing

I just rotated the rockers on the RH head so that the tip was approximately centered on the valve stem. Doing so put all of the push rods against the rearward wall of the guide hole. In order to provide clearance when I install the SARs, I will have to open up all of the guide holes per Clem's instructions. I am not sure that I want to try to do all eight holes while the head is on the engine. I may pull both heads and swap them to see if the issue follows the head or remains on the right side.

[Scott Goings (7829)]

Re: One More Thing

I have found the issue with the #8 exhaust. The stud has a groove worn in it which caused the rocker to rotate. I have been told my a machinist that this is not uncommon on a small block chevy.

I will be pulling the heads in order to replace the studs. Is there a GM part number for the screw in studs? I assume ther are two types. One with a hex and one without. I want to use the non hex style so that I do not have to spot face the valve guide tower. I will also open up the guide holes and use the self aligning rockers.