After all the machine work, stock pushrods for my 350 are too long, not allowing the valves to fully close. Initially I went longer 330 pushrods, but then my mind told me WRONG! The heads and deck were shaved, its only machining since new at the factory. I am getting blow back of gas through the carb now. Those who may know about this, is there a correct pushrod length shorter than stock that works, or should I look at adjustable pushrods, or shimming the rockers. There seems to be plusses and minuses to either way. The tower shims seems to offer the easiest way to use what parts I already have. Adjustable pushrods are expensive but allow infinite adjstments forever too.

 

Is your valve train stock with hydraulic lifters? If the pushrods are too long like you say shimming in my opinion would require too many shims, not the best way to go. Temporarily they will work for test purposes and if the issue is solved get some shorter pushrods.

 

Mine is all stock built to W31 specs, so bigger valves, stiffer springs, stamped rockers and AL cast pivots and stock lifters. The pushrods are streaming oil on cranking so they are pumped up. I kind of thought the same thing...there is enormous torque on the pivots so raising them up would seem to make them break to me. I have adjustable pushrod checkers so maybe it will take some time to find the shorter length . The Cam is not too, the W30 auto grind and it was new not reground.

 

Well, any time there is machining to the heads, block deck, or a non-factory camshaft is installed, you need to use an adjustable pushrod to measure the required push rod length to achieve correct valve train geometery, then get a set of push rods that are the correct length. "Factory length" is correct only for the original factory machined and assembled engine.

 

How much was removed off the deck and heads? Considering a Felpro head gasket is .042" compressed compared to .017", it must be quite a bit. Do the machine shop bills mention the amount removed off the deck and heads? An adjustable push rod is needed to figure out how much shorter of push rods you need. If you get it right, you can use your non adjustable valve train.

 

I’d use the shins to determine the length pushrod you need, then order replacements. If the valves are hanging open after all the machine work, your going to need a lot of shims to get the preload correct.

Once you figure out what you need, look thru the catalogs. Maybe there is a stock pushrod for a different engine or engine family that will work. When I put the roller cam in my engine, I found big block Chevy pushrods (I don’t recall if it was intake or exhaust, or the exact application) were almost the exact length I needed. The Chevy parts were in stock at a local speed shop, and were cheaper than having customs made.

 

Yes I get that....All of my previous builds had only the heads done so the geometry change was minimal and hydraulic lifters made it work with no further adjustments. 8.234" was too long and so now it is time to find how much and get this engine back to life. I have the receipts and I do not see how much was shaved anywhere so it will take some detective work and a micrometer!

 

Yes the shims will work as a baseline but I agree they make the valve train the weakpoint of the engine used permanently. Does anyone have a range of hydraulic lifters? How much slack can the absord and still be silent?

 

I think I would worry about having enough threads of the bolt screwed into the head. You want hardened Grade 8 washers. The washers should be as large as the bottom of the rocker arm stand.
1. Buy 16 washers and "mic" them. If they are all within .010" of each other, thats ok.
2. Put them under all 16 rocker arm stands.
3. Start the engine and check for the sound of. "valve clatter" (loose rocker arms).
4. Next, work with only one cylinder (#1 is handy).
5A. Add another washer to #1 intake and exhaust stands.
5B. Start the engine and listen for "valve clatter".
5C. When you get clatter, remove a washer and tighten.
5D. Start the engine. Loosen each bolt simultaneously on #1 til you hear "valve clatter.
5E. Tighten 1/4 turn.
5F. Slip feeler gage leaves between the rocker arm stands and washers to measure the gap.
You'll want a minimum of 3/8" of threads in the holes without bottoming the bolt. Grade 8 bolts might be good.
Lets see what you find out.
NOTE: They used to shim rocker arm stands in the "old days" and go racing. Grade 8 washers shouldn't mash out.
......Just my two cents worth.

 

Shims are for adjusting the valve stem height. I'm sure you could maths out a length, but it would be 1000x easier to get a checking pushrod and order new (Trend or Smith Brothers). You want the rocker sweep to stay centered on the valve stem

I thought this thing was done and you were waiting on seats to drive it?

 

I use Smith Bros. adjustable pushrods in my 455. You can get correct preload on every lifter. I don't remember the length.

 

Other than friction from the rocker arm motion, there is no torque on the pivots, only tension. "Enormous" torque on the pivots would bend pushrods.

 

That is a great primer on how to. Thank you!

 

It has NEVER come close to starting and a lot of researching brought me to too short pushrods as when I subbed in 330 pushrods of 8.4, the valves did not close. One "mechanic" looked at it before all this and stated the valves weren't opening. If this doesn't work I am going to start with the cam again. I bought the W-30 cam for automatics and the geometry starts there. I appreciate the Olds folks because ALL of the info on pushrod length measuring is Chevy style rockers and well it doesn't transfer. The only thing I have gained is that spring compressed the angle should be 90. Olds doesn't have shafts and center points to work from, but it is a start. BTW the seats and shifter are still inside the house and wlll be unstalled if I ever get the engine rumbling. It has been oiver a year trying first this and then that, I am trying very hard not to take the intake and heads off, but that has to be the next step if pushrod length does not cure it.

 

How do you adjust valve stem height with shims ? Do you mean valve spring height ?
Ordering new push rods would be easier, if there were no "supply chain" problems and he knew what he actually needed.

 

yeah, that