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I have a nice set of 842 heads that I would like gone through but I don't want to just drop them off anywhere and say have fun.... They look pretty much unmolested. I want to do the least to them as possible but I want them to be safe and reliable.
What should or should not be done to them. I remember there being issues with the old original valve springs breaking, but I have no idea if the original springs are still on them. I planned on just updating the springs and valves.
If the rocker studs are nice, just reuse them and check the torque on them to make sure they are tight? Did these come with helicoils in the threads for the rocker studs?
I also heard that they would sometimes loose valve guides and it was recommended to replace the valve guides with stepped valve guides to keep them from sliding down (valve guide liners?).
Curious if it is ok to leave the valve seats alone? Pressure testing?
Opinions on good quality valves for them? Chrome? I will use a factory 435 cam. Any updated spring opinions appreciated. Just want nice reliable stuff that isn't crazy. I assume that the valve springs will determine the retainers and keepers. I live in the North West close enough to Seattle. Any places a person might recommend to go through them appreciated. Thanks!
Last edited by tfringo; 02-15-2019 at 01:56 PM.
Reason: update
GM didn't heli-coil anything from the factory. I'd have them gone thru and unless you're stuck on staying factory, put ARP rocker studs. I have not broken a factory stud, even with the LS7 cam that was .590 lift. ARP would be just a bit of insurance. Figure out what cam you're going to run, and match the springs to that. Wouldn't hurt to look at some 10* locks and retainers too. At the least, pull all the rocker studs and look at them close for wear marks. When you out them back in, a little thread sealer is a good idea- some of them (at least on the heads I have) are drilled and tapped into the intake ports.
I called a place near Seattle. The person I talked to expressed a lot of knowledge on them and had worked on several in the past. Was confident about being able to work on them and had no problem staying on the phone with me to listen to me. That is important to me. Didn't try to rush me. I expressed my concern about guide failure and using the the original guides, etc. He mentioned that they have a special process to find the center of the valve, etc. Also said he would probably heat them up to around 220 degrees and tap on the guides to see if they were loose. Said you need to make sure they are pressure tested, need to make sure the rocker studs have been updated with thread inserts. Probably a lot more to it. But, as long as they are in good shape to start with, they can be made reliable. So, I was happy to hear that.
Hmmmm, I know what you mean about sealing the threads, good point. May not suck much that direction but I prefer no oil get sucked down that direction. Thanks for the reminder.
I don't know about how Chevy did 'reworks', but they were acceptable with some [if not all] of the divisions. Threads got damaged all the time...handling, machining, attaching to them. If the cost of reworking with Heli-coils (et al) was less than the scrap loss of the part, it was reworked. ALL rework methods had to be pre-approved by Engineering and Quality before it could be applied to product being used for 'new' sales.
I called a place near Seattle. ....Said he would probably heat them up to around 220 degrees and tap on the guides to see if they were loose.
Does this guy know what he's talking about...? Stock Chevy heads don't have pressed-in guides that are separate from the head casting - the valve "guides" are part of the cast iron head. There is no "guide" to tap on to see if it's "loose"... If the machined hole for the valve stem in the cast iron head is out of spec, the hole is then machined, and a guide insert is installed. For stock-type rebuilds, these guides are usually what are called "K-Liners," and you can't "tap" on them to see if they are loose. Red flag for me - be careful.
I would assume aluminum heads used a pressed in guide. I believe early cast iron Bb heads had. Cast iron guides that were cast in place. Uncertain about that.
But, he did describe a special process for installing them in 842 heads if they leak. I guess I’ll find out. Maybe more people will chime in. I’ll look inside the the intake and exhaust ports. See what I can see.
842 are aluminum. but all big block heads have guides pressed in. small block are machined into the casting. BUT, big block guides are installed before valve and seat location are machined, so the valve is NOT centered in the guide. if one were to replace these guides, the valve would be in the wrong place relative to the seat. and they come out hard. usually break the head, so machining the existing guide and installing a liner is the best way to go. my 815's I am gonna have 11/32 liners installed in them.
I called a place near Seattle.The person I talked to expressed a lot of knowledge on them and had worked on several in the past. Was confident about being able to work on them and had no problem staying on the phone with me to listen to me. That is important to me. Didn't try to rush me. I expressed my concern about guide failure and using the the original guides, etc. He mentioned that they have a special process to find the center of the valve, etc. Also said he would probably heat them up to around 220 degrees and tap on the guides to see if they were loose. Said you need to make sure they are pressure tested, need to make sure the rocker studs have been updated with thread inserts. Probably a lot more to it. But, as long as they are in good shape to start with, they can be made reliable. So, I was happy to hear that.
If you're in or around the Seattle (Renton) area stop by and see Phill. Bring your heads and explain what you're looking to do with them. He is a great guy to talk to and does great work. https://www.facebook.com/HEAMshop/
Yes and no.... I thought the OP was referring to a small block head, casting number 3836842, which is an iron 1962-67 283/327 head. The OP is talking about the Big Block 3919842 aluminum heads, which is not obvious from the initial post. The aluminum heads use pressed-in guides, so my comment was not technically correct with regards to the BB head. My comment applies only to cast iron heads, so it's irrelevant to this post. Sorry about that!
Yup, that is what I have seen on these heads. How the original guides get in there is a special process (magic). I read somewhere that they were cast in place?? For what ever reason, the earlier big block aluminum heads had some inherent problems. I sort of assume they had to have something like a guide or liner because they were aluminum heads. The other issue is that I believe they go through the water jackets. Talking to people that have rebuilt them through the years, one of the problems mentioned was that if the engine over heated or in race applications, the guide came loose started leaking and/or dropped down. Engine failure resulted. Two other issues were rocker studs pulling out and spring breakage. But, I have no first hand knowledge of this, only information from talking to others that are more familiar with them. Yes, I have heard that the guides on the early heads were not very centered to the valve opening, so liners were used to line the original guides. Some head shops have a machine that carefully locates the guide opening to the center of the valve opening. As another solution, people just buy valves with slightly larger stem diameters and machine the guide larger to accommodate the larger stem. This is only what I am gathering for information from other sources. I think that sometimes the guides are confused with LINERS. Still learning and probably unlearned stuff as I go. Interesting though. Thanks!
Valve wear determines the need for new valves. If the guides are worn enough that even new valves are loose, you will need to fix the guides one way or another. Once you finish that, you will need to re-machine the seats as part of the overhaul anyway. Not a big deal but not really an option either. Springs are matched to the cam and everything else follows that decision.
You do not need to change everything unless you need to change everything.
I heard there are cast iron and bronze alloy guides. I was planning on using a nice valve. Would like to use good technology and reliability. If I can find a lighter valve than factory, I think that might be nice. I heard chrome stem is good. Type of valve and guide, I heard also dictates the clearances.
It seems that there are a variety of valve seals. Some require the top of the guide to be machined to hold the seal.
Does anyone know if you can do too good a job of oil control in regards to the valve stem.
3/8 is orig valve dia. 11/32 is a lighter valve with thinner stem more air fits past. I had a guy quote me 100 bucks to ream my worn 3/8 guides and install 11/32 liners.
Last edited by derekderek; 02-16-2019 at 07:43 PM.
02-15-2019, 01:51 PM
Need ideas on rebuilding some 842 heads
