C Rocker Assembly on an early motor?

[Steve Douglas]

Can the later aluminum rocker assembly be used on a stock early B motor? The ratio is slightly more on the C rocker than the old cast iron rockers. I am somewhat worried about the higher lift with valves hitting the stock normal pistons. I know that one head bolt will need to changed to hold the later stand, any other issues?
Thanks in advance

[Martin Benade]

If it has stock pistons and cam there is nothing to be concerned about.
When you swap the head bolt make sure you don’t end up with the wrong combination of bolt (nut) and washer. The grooved one needs a washer, none for ungrooved.

[Steve Douglas]

I decided to use the old cast iron set, found enough good parts to reuse what was in the originally. Thanks for the reply

[Dave Erickson]

If it has stock pistons and cam there is nothing to be concerned about.
When you swap the head bolt make sure you don’t end up with the wrong combination of bolt (nut) and washer. The grooved one needs a washer, none for ungrooved.

Martin, that is a good point. Thanks for making it. I just checked the 356A parts catalog, and sure enough, no washers are used under the head nuts. I was not aware of that. When did washers first get used? Every 356 engine I have worked on had washers under the head bolts, but they have all been B, C, SC or 912 with the later rockers. I don't have any A head nuts, so are the long head nuts a couple mm longer than the later head nuts?

[Martin Benade]

Yes they are longer. It’s also important not to have any washers stuck in the heads undetected.
I think the washers started with the B cars but not certain of that.

[Steve Douglas]

Yes, I did use the shorter head/grooved nuts with washers, but decided to use the old style cast iron as I found enough parts from a friend, I'll save the C rocker assembly for my next build.

[John Clarke]

Yes Martin
Those washers are sometimes stubborn ! A small magnet on a telescopic rod ( like for retrieving dropped nuts / Bolts) will tell You they are there, and a sharp scriber to prise them out.
Regards Jay

[Dick Weiss]

I have several rebuilt cast valve frames as the bores for the intake and exhaust shafts get worn
resulting w/sloppiness and a noisy valvetrain. Also, I match the shaft ends to the rocker bore IDs
w/in .002" and refinish the tips of the rocker arms.

[Steve Douglas]

Dick, thanks for the input, I have 3 sets of cast iron rockers, and a friend gave me a box full of parts, so I was able to go thru and find enough good parts to make up two very nice sets. The tips are all good as are the bores and shafts, many were worn to where they were sloppy, or the tips were "stepped". I also was lucky to have a bunch of shims of three thicknesses to take the end play up. I spent a few hours this afternoon and evening, added the new base shims and the engine is back together and ready to swap. But, that will have to wait until next week as I will be driving about 175 miles on Saturday and do not want to do it with a very fresh motor. One good thing was that all 4 exhaust valves seemed to hit the same, making very similar witness marks in all of the exhaust valve pockets.
I have been wondering how is the best way to test the valve to piston clearance? It would need to have all of the valve train assembled and properly adjusted. A lot of work to take apart again to check the clearance. Is there a rule of thumb about the amount of clearance? I will never rev the engine high enough to get valve float so that shouldn't be a consideration. Being this engine has many parts that differ from the original 59 normal, there are a few unknowns. Late B heads (not cut), higher lift "C" cam, 45 year old big bore flat top P&Cs.

[Harlan Halsey]

There is a simple way to solve your problem: Install a stock set of pistons to go with your stock heads and stock valve train and you're done.
There is a thread on here on how to measure head clearances. Some favor solder and some favor clay.

[Steve Douglas]

Harlan, I would have used stock/original P&Cs, it seems that the original Mahle flat topped normal P&Cs are hard to find and priced double the price of the new ones, plus I had the old Big Bore set that had been on a friends shelf for 30-40 years. I did do the clay method to check the head to piston clearance, and it was within what most say is minimum, using the base shims that came with the P&Cs, I got .040". The "sheet" that came with the NOS Big Bore said that with stock heads no machine work needed. Dave Erickson confirmed the heads were late B, 22 degree, uncut and were stock. The pistons are 22 degree flat top, and have a very low .002 deck height using a straight edge and feeler gauge. So now with thicker shims, stock rockers I hope it will be good, yes, reduced compression, 9.1 down to about 8 but it's not a performance motor.

[Martin Benade]

Personally I’d cut the valve reliefs a tad deeper instead of shimming the cylinders. Keep some decent squish. You wouldn’t need to cut much at all. Or if you are running a N cam and don’t drive hard , just put it together with no extra shims and no cutting.

[Harlan Halsey]

Steve,
I looked at your thread only because I was mildly curious as to whether the rocker arm ratio had changed between the A steel stand rockers and the B-and-later aluminum aluminum stand rockers. All my engines have the aluminum stand rockers. I still don't know the answer.
Apparently, you assumed that your cheap Kolbenschmidt big bore pistons would fit as the cheap NPR's do and you are paying a price for not making sure. Ass-u-m-e.

[Vic Skirmants]

Exhaust ratio remained the same on all. Intake ratio increased on the rockers with the aluminum stands.

[C J Murray]

I was mildly curious as to whether the rocker arm ratio had changed between the A steel stand rockers and the B-and-later aluminum aluminum stand rockers. All my engines have the aluminum stand rockers. I still don't know the answer.

The exhaust has the same ratio, iron or aluminum, approximately 1.1 to 1 I think. Racers who have been breaking the short exhaust rockers sometimes modify the stronger "iron stand version" to fit the aluminum stands.

The iron stand version of the intake rockers have the same ratio as the exhaust rockers. The aluminum stand version of the intake rockers have a ratio of 1.31 to 1.

Leo Droughton made some alloy roller rocker sets and he sold one version that had 1.4 to 1 intake rockers.

An engine with a street CR doesn't have the intake valve anywhere near hitting the piston so the ratio change is not dangerous.

All the types of exhaust rockers have the same ratio so a change to aluminum from iron is not a danger. The danger is exhaust lift or cam timing, more overlap, or pistons with shallower pockets.

We are not working on factory stock engines using factory stock replacement parts so every clearance must be checked.