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I have an "848" head from a '60-'62 261. While at the machine Shop they found it was cracked, the crack showed up during Magnafluxing. The crack is in the transition from the intake side to the exhaust, just past the radius. There was no leak there during pressure testing. The Machine Shop peened the area and pressure tested it again, again it past.

This head is going on "60 235, bored .060 over. I had the Machine shop Mill the head .040. They replaced the exhaust valve Guides as the were severely worn, the intakes guides were fine. I located a NOS set of 1.94 intake valves off EBay (I almost hated to open the box :D). I bought new stainless 1.5 SBC exhaust valves. I have everything cleaned and ready for assembly.

So, with all that information out of the way, I come to the question. Valve Guide seals? I have seen different opinions of how to go about this. Some say to use the newer style Umbrella seals on intake and exhaust. Some say to just use the Umbrella seals only on the intake, and use the "O" ring style on the exhaust. Looking for some real world knowledge on this.. Thanks.

I just rebuilt the head on John's 261. Here's what I used:

Exhaust: www.ebay.com/itm/156769335932

Intake: www.ebay.com/itm/122009255781

The exhaust seals ride up and down with the valve stem. The intake seals clamp onto the guide. Don't use the O rings- - - -that's too much sealing. Put short pieces of electrical insulating shrink tubing over the valve stem keeper grooves to avoid seal damage as they're installed. The 1.94" intake valves are OK, but they really can't benefit breathing much because of the geometry of the intake ports and manifold runners. They were only used on Powerglide equipped spray oiler 235s from 1950 to 53. A better idea, (and less expensive) is to use 1.6" stainless steel small block V8 exhaust valves and a camshaft such as the Melling CCS-1 which increases the exhaust duration. That provides better cylinder scavenging on the exhaust stroke without creating a rough idle.

Edit: Did the machine shop recess the intake valves the same distance that they milled the head? If the margin of the valve is exposed to the flame front that travels across the surface of the head as the spark plug fires, the valves will burn very quickly. I was given an 848 head recently because of intake valve burning- - - -the valves were not recessed after the head was milled, and the intakes lasted less than 10K miles before burning.

Jerry

The 235 engine that 848 head was on ran like a turpentined cat running from a scalded until the valves burnt up. I wish that I had checked the compression on that engine. I'm sure that it was significantly higher that stock. But like that say, there's no such thing as free lunch.

Carl, that one's got a promising future on a bored and stroked 261 (274 CI)- - - -but the valves are going to get relocated first. Thanks again!
Jerry

Jerry, I hope that head works out for you. I am still happy that I am not tripping over it in my shop anymore.

Side note: The head that I was talking about was part of a horse trade whereas I drove a thousand miles with a 848 head in trade for meal at the fanciest restaurant near Delrose, TN.
I stuck it to him pretty good. I talked him into letting me supersize...

I'm glad both of us think we came out well on that trade. The "261" in question is going to have H beam connecting rods for a Chevy big block V8, and pistons and sleeves for a Toyota 6 cylinder Diesel. Possibly roller rocker arms, also!
Jerry

Jerry, where is that 261 going after you get it together?

After some dyno testing, it's probably going to be looking for a home. Having a Rube Goldberg engine like that sitting around will be a good incentive for me to drag the old Go-Power dyno out of storage and get it working again. The last time I used it was on a 700+ HP MOPAR "Super Stock" pull truck engine.

A lot of the same bits and pieces used on a 261 modification can be applied to a GMC 270- - - -and there's a big bolt waiting down in Guntersville for a trip to my place that would be an excellent test bed for some of my mad scientist experiments! I've even got a 3 speed Brownie transmission that can be adapted to that rig so I can have two shifters to play with, plus the 2 speed rear end it has already!
Jerry

Back to the Cylinder Head... No the Machine Shop didn't recess the intake valves. Jim has a great history with Chevy 6's, however that is with the 230 - 292 versions.

I After some discussion and head scratching we came up with a plan. Not knowing if the head had been previously milled, we decided to recess the first valve and use that as a reference height for the others.

That brings me to my next question. With the valves now being recessed, do I need to shim the valve spring height the same amount?

The rocker arms and lifters are currently being resurfaced at Rocker Arms Unlimited.

It depends on how deep you had to go to get the valve shrouded properly. When raising the compression of the 54/55 head to the same combustion chamber volume of the 848 head, it's necessary to mill .090" off. When doing that, I add a 3/32" (.093") shim under each rocker arm stand, and use a lash cap on the exhaust valves to keep the rocker geometry correct. It's also possible to shorten the top of the intake valve stems as much as you recess them, without shimming the rocker shaft up. I'd suggest using .060" shims under the intake valve springs. The "VSI" 060" shim washers used to be copper-colored- - - -the .030" ones were silver. I don't recall the recommended assembled height on stovebolt valve springs at the moment. At the moderate engine speeds most of these old rigs run, valve spring tension isn't terribly critical.
Jerry

www.ebay.com/itm/265844320152?

Do I need to add rotators to the exhaust valve springs? If so, what type or P/N should I look for?

Are you planning to do truck stuff with the engine, or will it be a weekend cruiser, etc.? Rotators help extend the life of commercial engines that tend to be "rode hard and put away wet" on a routine basis. On a light duty engine, they may not be necessary.
Jerry

I found a set of NOS rotators on Ebay. They were $20.00, free shipping, they are headed this way. If I use them or not is still to be seen.

Sort of a "belt and suspenders" approach to holding one's pants up, but it can't hurt! On the V8s there was a slightly shorter valve spring used with the rotator to compensate for the extra thickness, but I don't believe that was done on the sixes.
Jerry

I just got the head back form the Machine Shop. The intake Valves are now recessed .040 to compensate for the head being milled.

The exhaust Valve spring rotators are supposed to be here this afternoon. I'll start assembling everything this week.

I started assembly last night. I received the exhaust valve rotators yesterday.

I cleaned the head thoroughly, used hot soapy water and compressed air to blow it dry. I have everything to put it together now. Umbrella seal for the exhaust valves and press on style for the intakes. I'm using new springs, with the stock retainers on the intakes and the NOS rotators on the exhaust.

Looking good- - - - -and that first pic does a good job of showing why it's important to shield the edge of the intake valve from the flame front that travels across the top of the piston as the spark plug fires.
Jerry

I am having a problem trying to locate .040 Valve Lash Caps for the exhaust valves. The closest I have seen are .060.

Craig - I tried a little web searching on 11/32" valve lash caps and couldn't find anything with the correct 11/32" valve stem diameter that was less than 0.080" thickness. The only valve lash caps I found that were listed as 0.060" thick were for 6mm (approx 15/64" or 0.236") which is too small for your valve stems.

Curious as to why you need such a reduced cap thickness given the rocker arms are adjustable and should allow for that thickness of a lash cap???

Isn't the purpose of valve lash caps for protecting the ends of the valve stems from excessive wear? Since lash caps weren't originally used, is the need because of the change to the new valves, or some other factor my mind isn't yet grasping?

The .080" lash caps will work. The rocker arm lift ratio is approximately 1.5:1, so there will be noticeably less length to compensate for at the pushrod and lash adjuster. Since the height of the rocker shaft doesn't change, lash caps on the exhaust valves aren't really necessary anyway. I use them when I mill .090" off a low compression 235 head and space the rocker stands up the same amount with a shim under them.
Jerry

In a previous discussion it was mentioned that I needed to shim the rocker arm stands the same amount as the head was milled. With that being so I thought it was necessary to use the valve stem caps to compensate of this as well. I have located a .060 11/32 cap.

I ordered a set of .060 Valve Lash Caps from Summit. They are a Crower part P/N 86121-16. These are sold in sets of 16, guess I'll have a few for my next project..

https://www.summitracing.com/parts/cro-86121-16#overview

The only time I feel that it's necessary to shim the rocker shaft stands up is when I'm converting a 54/55 cylinder head to the same compression ratio as an 848 head. That involves milling the early head .090" and recessing the intake valves the same distance. Moving the rocker shaft up avoids running out of adjustment on the rocker arm adjusters or installing shorter pushrods. The lash caps on the exhaust valve tips keep the geometry right when the shaft is raised. They also give the rocker arm tip a wider surface to contact as it sweeps across the valve stem. On a low RPM stovebolt engine with a fairly conservative camshaft profile, the rocker geometry is pretty forgiving. A high RPM racing V8 with a radical cam is a whole different bucket of snakes! I've spent lots of hours tweaking rocker geometry on some of the round track engines I used to build!
Jerry

Final assembly. I used the Rotators on the exhaust valves. The springs and keepers are new.

Looking good!
Jerry