Cracked rocker bosses

[RCE1962]

Just purchased a pair of 690's. Some of the rocker bosses were cracked on one head. The seller indicated that folks usually have rocker bosses cut down to accept screw in studs which was the plan in anyway as this was done for the engine in the Impala several years ago. Actually, one the heads in that engine had a cracked rocker boss however, the entire crack was removed. The machine shop indicated that one rocker boss, for the newly purchased heads, was "iffy" if it were to be cut..meaning it might not be completely removed. The plan is to use the heads in a new 409 build. Truck block with a Z11 type cam or slightly more aggressive. Need opinions as to whether an incompletely removed crack...since it may be too deep.. would affect this engine when installed in a car which might see RPM at 6200-6500?? or any other thoughts. One push rod hole is slightly out of round (oval). Push rod guide plates will be installed.

 

[scott hall]

Could you get it welded once they get it to almost final cut for guide plates? Then finish machining and tapping.

 

[La Hot Rods]

Is this after machining for the guide plate?
If so I would want some rockers stud girdles on it..

 

[models916]

Studs will take the stress off that area. I would drill a small hole at the bottom of the crack and let her live. Z11 cam and springs required the deeper/thicker spring pocket that GM put in the 583 head. You'll have to be careful selecting a spring or keeper for this cam.

 

[quik9r]

drill and pin the crack like models said.... any parts needed Ron let me know


Quik9r

 

[Fathead Racing]

Use Beehive springs from Comp Cams after machining, good for "easy on the valve train" but high rpm.

 

[Don Jacks]

I'd try cutting it then examining the crack.As to the head it's self,as long as you stay with a flat tappet,or a very mild roller,you won't need massive amounts of spring pressure,so the head could be fine for your intended use.A hyd. cam,either flat tappet or roller would be eaiser on parts yet.Ray's suggestion of the beehive spring and retainer is spot on.

 

[Greg Reimer]

After the rocker arm stud boss is flycut for screw in studs, how much crack is left? It might be possible at that point to weld up the crack using what ever process necessary, tap it out deeper, and use a stud with a deeper threaded portion. Often times, a 348,409 or a small block would pull a stud and the fix was to drive in a stud that was oversize. The part # of the 409 head was 3814690, the part # for the .003 OS replacement stud was 3814692. That was for small blocks and W motors. There was a reason why big blocks had screw in studs and factory guide plates.

 

[RCE1962]

I met with the machinist this afternoon and he showed me the worst crack area on one of the rocker bosses. It goes pretty much near the bottom. I didn't see the additional comments until now on this thread. The machinist indicated that there are various fixes that he could apply in this case. He said he would prefer to install 7/16 screw in studs and sized it up (micrometer) against the factory rocker pin that he pulled. Machining the rocker bosses even lower and sinking the thread end, in deeper . We didn't discuss drilling, pinning or welding at this point, but I will bring it up. He did go on to ask what I expected out of the engine that was to be built using these heads and would recommend using solid flat tappet lifters since a roller set up would have additional spring pressure/stress and in to be safe in that case, a stud girdle would be a good idea. ...and... saying that, using the right valve train parts, "springs" it would be ok to spin the engine to 6500 rpm or more, for this fix, if that's what you want. The screw in studs and the pin holes at the bottom of the bosses will have a product applied that when "set" not only seals but hardens like a weld.

Since it was mentioned and now I'm curious...are there any rocker arm girdles that can be recommended, as well as, bee hive spring manufacturers, lightweight keepers, valves, 3/8 pushrods. Looking on the web I only see one kind of guide plate being offered or are there more to choose from?

Please know that I am my no means an expert on this, and typically defer to the members on this forum for advise. This is probably the last 409 build for me and I really appreciate everyone's input here.

If there is anything else that you feel needs to be mentioned before we start please let me know.

I will keep you posted once this finally goes to the engine building part of the project.

Ron

 

[La Hot Rods]

Comp Cam should have the beehive springs.
How much you trying to get out of this build?

 

[scott hall]

If you are still a little nervous about it and don’t want to run big spring psi on the Springs and want a roller cam. I have an Isky Rev kit that allow you to run a lighter valve spring. I believe the Springs were only like 120# at the valve. Ran them for years on the street with the 505C-62 isky solid roller and stock pinned studs. Would keep you from having to run girdles. If you it helps your decision we turned the engine 6500 with no problem. Talk to your guy and see if he thinks it would work for you. You will still need the screw in studs.

Scott

 

[Ishiftem]

I would weld the boss, put in the screw in studs, and let it eat.

 

[RCE1962]

As far as HP goes, the thought was to consider a blower motor using these heads...so... I don't really know at this point. I was hoping to use the iron heads, find an older style blower etc. Just an old school street/strip hot rod. Maybe now since one of these heads are not as good as I had hoped...this is a bad idea?

Scott...Can I keep your offer on hold for the moment, and see how the machinist ends up with this?

The advise on this thread, has been shared with him, and is very much appreciated!

Thanks guys.

Ron

 

[La Hot Rods]

If you don't get crazy with the boost you could pull it off.
Is it on the intake side?

 

[scott hall]

the

Yes the offer will be here if you decide it will work for you

 

[427John]

Depending on how much boost you plan you may need to run higher intake seat pressure.If your willing to run different springs on the intake and exhaust you may be able find some that have similar open pressure while having the higher needed intake seat pressure.

 

[MRHP]

I personally would not chance a wounded head, especially in a blown application. There, I said it. I will go back in my box now.

 

[Ishiftem]

Party pooper.

 

[Don Jacks]

Yes,if it's on the intake side that the rocker stud failes,no biggie,you just lose that cylinder...But if it's on the exhaust side.......,you'd be testing the hell out of your anti-backfire valve,at the minimum.We don't want to even think about the worst case scenario!