I have a set of 186 heads and noticed that two of the valves had oil visible on the inside of the head. I pulled the springs and noticed that the valve guides are loose and can be rotated by hand. Is there a way to tighten them up or am I looking at having the guides replaced.
Take your meds, and re-read the original post. The original poster "HAS A SET OF HEADS" and is not buying or selling them. I was merely trying to help him get out of situation without spending any money on them. If you have any other ideas that will fix his problem, then speak up or MYOB.
-- Edited by Petebil on Thursday 14th of April 2016 03:51:28 PM
I think I'd attempt to Loctite them in as well (although I've never come across this issue before). Knurling the outside of the guide before Loctite might be a good idea as well, being that the knurling should (will) give the guide somewhat of a mechanical/press fit that (I would assume) would work fine alongside the Loctite although Loctite on it's own might be just fine.
One other thing I would do (I think) would be to reinstall the guide (whichever way you choose) then quickly (the idea being "before the Loctite sets") reinstall the valve and the springs then gently tap on the head of the valve so it positively seats (not to the point of damaging/bending the valve), hopefully pulling the loose guide into alignment with the seat. This way, hopefully the valve and guide will line up with the existing seat so machining isn't needed.
One other thing I'd also be wondering is, as Supernash mentioned, why are those two guides loose in the first place and how bad (or close to failing) are the others? If you can spin those two, are you able to easily move the others with some light finger pressure?
I just Googled "SBC 186 heads" and it seems those are early heads that won't (if the internet is correct) have hardened seats for use with unleaded fuel. Something to keep in mind if you find the heads need more work than you thought.
-- Edited by chips on Thursday 14th of April 2016 04:32:01 PM
If the guides were installed incorrectly they can spin in the bore. It just means the bore was cut oversize and when sizing the guides they didn't get enough interference fit. This is a pretty common mistake. You can loctite the guides in if they are thickwall iron or bronze, but thinwall liners you can't. If you do loctite the guide in, you will have to cut a new valve seat because the relationship between the seat and valve will have changed. If you don't, it may or may not seal, and if its off by a even a little it will bend the valve a little every time the valve closes, work hardening it until it fails. The two piece welded head stock valves are bad for this.
If the engine got hot enough to loosen the guides, the heads will be badly warped, and will be sunk between the center exhaust valves. The heads should be completely checked over for cracks, and if good, completely rebuilt before being used if this is the case. Heat usually doesn't loosen guides unless you BRUTALLY overheat - ie until the engine stops running. I have seen this with heads off of derby carbs.
What kind of guides are they? Cast iron? Thin wall bronze? Thick wall bronze?
They are bonze guides i'm not sure about thin wall or thick. It was the centre two exhaust valves. It started by noticing that the area around the guide was slightly wet from oil, drawing my attention I have all the valves out now and will look closer. I'm thinking of placing the heads on each other and looking for gaps or warping.
Thin wall will look like a thin liner with a split that runs the length top to bottom. They are literally just a piece of phosphor bronze sheet rolled into a tube. The split is why you can't loctite them in place, as you will loctite the valve to the guide also when it leaks through the split.
Thickwall and cast iron guides generally do not have the split.
No easy fix, 186's are good castings and worth the time to rebuild if you do the work yourself. I rebuilt my 186's this winter with the help of friends, I replaced the cast guides with bronze Brodix guides and new stainless steel valves, a more expensive option but I wasn't happy with the sleeve type insert on the previous rebuild. Do i right don't band aid it. Good luck.
The right way to do it would be to go through the heads and replace the guides that are loose, check the rest for wear and replace as needed, check the seats and put in hard seat inserts on the exhaust before cutting a decent 3 angle valve job with new one piece valves. But I don't think the OP wants to spend that kind of money on the heads.
The right way to do it would be to go through the heads and replace the guides that are loose, check the rest for wear and replace as needed, check the seats and put in hard seat inserts on the exhaust before cutting a decent 3 angle valve job with new one piece valves. But I don't think the OP wants to spend that kind of money on the heads.
The right way would be to scrap those dinosaur heads and buy some decent aluminum ones. They are not worth putting that much time-effort-money into them unless you were doing a period correct restoration.
The right way would be to scrap those dinosaur heads and buy some decent aluminum ones. They are not worth putting that much time-effort-money into them unless you were doing a period correct restoration.
Yep, either do it cheap or spend the money on aftermarket heads.
Some people don't want to spend the money for a decent set of aluminum heads when they can get the ones they have fixed for less than half the cost. But when you start talking about the cheaper iron heads, I agree. I would put a set of Iron Eagles, RHS, or even EngineQuest heads before I would pay someone to rebuild a beat set of double humps. For the couple hundred bucks difference, its more than worth it.
it was big thing in its day to have a set of these on your small block. you would always check other motors to see if they did. then came the 202 heads for the next need to have. there wasn't the supply of aftermarket stuff back then. if you had a 780 holley double pumper carb and a "tricked out" set of double humps on your 327ci motor back then you were "serious". its a nostalgic thing as much as anything else. a comfort zone if you like. don't forget the hurst competition plus shifter and the hooker headers with 4:11 gears with 12.5 to 1 compression to finish the package. - -"those were the days my friends and i hope they never ends" lol - today probably something like these, http://www.airflowresearch.com/index.php?cPath=24_26&osCsid=uk45l20f7pknts0ml3ig3tctc1
