65 300hp rebuild...orig valvetrain?

[Jim V.]

As some of you know, I am disassembling what appears to be very orig. 300hp motor. We know the bottom end is orginal given the original bearings (see earlier post). Today, I started disassembly on the heads.

This pic shows from right to left:
(bottom)spring spacer, oil seal, spring w/ damper, shield, retainer
(above) exhaust valve, keepers

It is my understanding original factory production did not use positive oil seals, but rather a simple O ring in the second grove of the valve stem. Either somebody did a seal job from the top or the heads were removed at one point. This is bordering on archeology. What do ya think...?

Thanks

[Michael H.]

Re: 65 300hp rebuild...orig valvetrain?

Jim,

You are correct. The seal in the pic is definitely not the style used by GM. The small "O" ring used on the lower groove of the valve was the original style. Also, valve spring shims are typically never seen on factory assembled heads. Likely the heads have been removed at some point in the cars life.

[Clem Z.]

if the heads are machined for positive seals

the heads have been off. if you did not have stamped steel head gaskets that is also a clue they were off

[Paul L.]

Re: 65 300hp rebuild...orig valvetrain?

Having done that job on a 1979 with success, they were on the right track.

[Mark #28455]

big blocks commonly have a thin shim

I haven't seen the inside of a small block in about 20 years, but big blocks commonly had a very thin (about 0.010") shim under the spring. It appears they used the same thickness in all the spring pockets - maybe to protect the pocket from erosion by the harder steel of the spring? I don't recall seeing these shims on the later heads with rotators.
Mark

[Clem Z.]

valve springs with the flat wire wound internal

damper need a hardened shim to prevent the dampers sharp end from cutting into the cast iron head. i have seen deep grooves worn into the head because there was no hardened shim under the spring. always check you valve spring shims with a file to make sure they are hardened because the damper will cut right thru the non hardened ones

[Jim V.]

Clem...are you typing from an ATV...?

Based on this photo...do these springs look like originals? Do originals SB springs have dampers...?

What is the best technique to clean up the combustion chambers and valves (backs, fronts, stemps) other that a machine shop hot tank or spray tank?

[Michael H.]

Re: 65 300hp rebuild...orig valvetrain?

Jim,

Forgot to mention, on reassembly, there is a specific way that the valve springs are to be installed. There's actually an "up" and a "down". If you look closely at the valve springs, you will notice that the spacing between coils changes from one end to the other. It's called "progressive wound" and the spring should be installed with closly coiled end down, or on the spring seat of the cyl head.

[Jim V.]

Thanks Michael...always wondered about that..n/m *NM*

[Clem Z.]

i bet they are a 3911068 spring

and these have a damper.it has been years since i looked at a stock spring from the 60s so have have no idea if they had dampers or not. carb cleaner will soften the carbon and if you try bead blasting make sure you clean the parts in hot soapy water to break down the static electricty that come from bead blasting. nothing worst that putting a head on a fresh short block and have glass beads fall out of the heads water passages into the short block

[Duke W.]

Re: i bet they are a 3911068 spring

All Gen I SB OE springs have the flat wire damper on the inside - at least up to the point where GM added valve rotators in the seventies. The "068" went into production IIRC in '67. It has about the same seat force as the previous OE spring, but a slightly higher rate. This spring was used on all SBs of the era from grandma's 283 2-bbl. to the Z-28 and LT-1 engines.

It may have a spotch of paint color for ID, but I can't remember the color - maybe white???

3911068 specs are 76-84 lb @ 1.70", 194-206 lb. @ 1.25", so the nominal rate is about 267 lb/in.

With a OE mechanical lifter cam and proper lash it should be okay to about 7200.

The previous 3735381 spring is 78-86 lb. 1.66", 170-180 @ 1.26", nominal rate 233 lb/in.

I believe both are still available either from GM or aftermarket vendors.

I recommend the 068 springs for all SB rebuilds for any OE cam, and as long as pressed in rocker studs don't have a history of pulling, they should be okay.

Duke

[Joe L.]

Re: i bet they are a 3911068 spring

Duke-----

The valve springs for small blocks with exhaust valve rotators had the flat damper, too. These were used in the mid-70's and were shorter springs that the '068' to compensate for the thickness of the rotator. Later, I believe that the cylinder heads had the spring pockets machined to different depths which compensated for the rotator thickness. Then, the '068' spring was again used for both intake and exhaust. Rotators were generally eliminated after 1987.

Big blocks used rotators in the 73-75 period (75 for non-Corvettes only, of course). However, big blocks never used the different length valve springs.

Both the '068' and the '381' springs remain available from GM the last time I checked. It's always amazed me that they continued to supply the '381' for so long (after all, the last PRODUCTION use was 1966). The specs for the springs are so similar that it amazes me that they haven't just discontinued the '381' in favor of the '068'.