I am in the process of rebuilding an olds 350. I have herd of people installing a shim ( washer ) under the rocker arm pedestal. Does anyone know what this actyally does and is this necessary. This is a mild rebuild with flat top pistons and a eldelbrock performer cam. Every thing else will most likey be stock for late 70's 350.

 

Shimming rocker arm pedastals is part of setting valve lash on an Oldsmobile engine. They don't have an adjustable valve train so you have to shim the rocker arm pedastals or adjust the length of the pushrod. Here is a good article on this process.

http://www.carcraft.com/techarticles...th/index1.html

 

Not someone you should be listening to.

Also, not someone you should be listening to.

By design, the rocker assembly is not adjustable, as the proper (0.0") lash is automatically maintained by the hydraulic lifter.

Increases the distance between the cam lobe, and the valve stem. There should be no reason for such an alteration.

Not if your work was done by a competent machine shop.

The article has nothing to do with this topic.

Norm

 

I would look into other cams, the numbers on the performer cam are not as good as Lunati or other. I just finished a build with Lunati voodoo and it made a amazing difference.

 

This should never be done to factory rocker arms. You would be moving the rocker arm away from the cam and then you would have to use longer push rods or taller valves to compensate for the difference. The valve train on an oldsmobile is non adjustable and does not require a feeler gauge to adjust. Tighten it down to the proper torque spec and let it ride.

 

To add to the above posts, one common problem when having work done by shoddy shops or ones not familiar with Oldsmobiles is that they will do a valve job and get the valve heights all over the place. Having to replace the push rods is common when changing cams, or if any milling was done, but if the stem heights are not uniform, it can be a nightmare getting the preload correct. On another note, proper valve train geometry is often overlooked when rebuilding an engine.

 

Being familiar with one brand, or another, has nothing to do with a shops competence.

A competent shop, can handle anything that comes in the door.

Classic definition of incompetence. Why would anyone want to use a "shop" that does not know how to do the job?

Cam and pushrod replacement, is a normal part of a rebuild. It would be unusual, not to do so.

If you mean using longer pushrods, they would be used to compensate for a smaller base circle/heel on the cam.

Another internet myth. There should be .06" to .10" travel in any available hydraulic lifter. That makes for a very forgiving valvetrain.

The factory design is more than adequate for most street applications.

Norm

 

"
Originally Posted by captjim
........ if the stem heights are not uniform, it can be a nightmare getting the preload correct ........
Another internet myth. There should be .06" to .10" travel in any available hydraulic lifter. That makes for a very forgiving valvetrain.

This guy disagrees. Nice article, IMO http://www.supercarsunlimited.com/in.../stem/stem.htm

The point I was making is that shops get so used to doing SBCs and other engines with adjustable rockers that they often times do not take the time to do it correctly.

 

I agree Jim. Norm, that is no internet myth.

Nick

 

As a matter of fact, I posted the same link elsewhere on this site, in reference to a similar topic.

Now, where, on that page, does he disagree with anything I said?

Nothing new. It has been common practice, among "production line rebuilders". since the introduction of hydraulic lifters.

To say that it would cause some kind of "nightmare" is a gross exaggeration.

Here it is, again:

By design, hydraulic lifters compensate for variances in valvetrain dimensions, including valve stem height. Using this information, some "machinists" believe it is not a critical dimension and an extra ten, or twenty (or thirty) thou is not significant.

In the context of the opening post, how significant would .030" be?

Norm

 

You need a cushion, .030 could be alot.

Nick

 

Here it is again:

If the stem was .03" too high, and the lifter travel was only .06", there would still be .03" left, for your "cushion".

Now, how much would that .03" affect the valvetrain geometry?

Norm

 

I think some of you guys should have the "qoute" option disabled!!!!

 

The "qoute" option has nothing to do with this topic.

It is, however, an invaluable communication tool, that has been with us, since before Algore invented the internet.

If you would like to discuss it further, the "PM" option serves a similar function, as it can help to keep "trolls" and "BS artists" from trashing mature discussions, such as this one.

Norm

 

It just seems like that a lot of these threads go to hell, beacause one guy is quoting and correcting another one.

Eddie
valvetrain.jpg

 

https://classicoldsmobile.com/forums...html#post43572

Norm

 

With your self proclaimed .060-.100 travel you add .030 you are way too close to the end. A person wants it to land in the middle so variances can be made up while it is running. I always set mine with the intake off and used a round wire type plug gapper. With no oil in the lifter a .035" gauge wire was just about right between the plunger and the retaining clip.

I used to run a .005-.010 preload on my HYD racing cams.

Nick

 

How close, is too close?

.005" has worked very well on any adjustable (stock or aftermarket) system, I've dealt with.

But we are not discussing, adjustables, are we?

Norm

 

OK, I used that for racing purposes only. Stem heigths can be off by more than .030. If you ran .010 lash on a hyd lifter you know how noisy they are. Most street guys don't want this. A hyd lifter should have .030-.050 lash. It has always worked for me.

 

How many shops, do you think, would stay in business if many of them went out the door, that way?

I have.

And I only "do" street engines.

If they are "noisy" they are less than preloaded.

Factory specs that I am aware of, vary between about .040" and .060", but they are for adjustables. How many "pros" do you know that use factory specs?

And .005" has been working for me.

Norm

 

Anyone else, hear all the crickets?

Norm