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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I was messing with my headers and noticed one tube being cleaner than the rest so I got to looking in my exhaust ports and noticed this, it's a wet spot that looks like a crack going from the valve guide all the way to the face of the gasket face of the head. It's not a crack, it's in all the ports, looking at the head that was off the car I was wondering if it ran down the port roof when I had it upside down on the bench, but the head on the car has the same exact thing on the port roof across the top of the port, it does not run down the sides of the port.
I had a really tough time getting a picture of it, the first few are of the worst one, and the others are of 2 of the better ones, most are pretty close to the worst one. #4 was the only one that didn't have it and that was the one with the hole leaking coolant on the intake that I welded shut, that one probably had it before it was steam cleaned by the coolant. The worst one, 5 ports are VERY similar to this
Same port, lighter exposure
One of the ports with less of it, but you can see it looking like a crack in the carbon deposits
The other one that isn't as bad, in this case clearly wet but not as long as the rest.
Looks almost gold colored under the carbon, like it was brazed and the carbon isn't sticking to it. I don't suppose that's what it is, but just what it looks like at first glance.
Could the exhaust have gotten hot enough to melt bronze? And run uphill? This is a mystery.
Are those bronze thin-wall guide liners?
If an incorrect alloy was used, they could melt (think brazing rod). Also, molten material might not "run uphill" to coat the guide boss, but it certainly could be "blown" uphill by exhaust gasses pouring out of the cylinder at over 200 MPH, just like spray-welding.
That syndrome of failure under heat and pressure seems to be fairly common inside the beltway, sometimes identified as "running crack head" which coincidentally seems to follow four-year cycles.
Unfortunately, those heads are likely to need a lot of work. I can only imagine what the seat areas might look like. Your other thread indicates that the threads in several areas are also suffering damage. It may be best to strip down the worst/most suspect head and perform a complete assessment. It may be that the rework at a knowledgeable and reputable shop exceeds the cost of replacement heads. It would be pretty easy to drop mulit-hundreds of Bitchcoins in machining, guides, seats, new springs, retainers, valves, hardened spring seats, studs, and thread inserts just to get back to serviceable heads.
Unfortunately, those heads are likely to need a lot of work. I can only imagine what the seat areas might look like. Your other thread indicates that the threads in several areas are also suffering damage. It may be best to strip down the worst/most suspect head and perform a complete assessment. It may be that the rework at a knowledgeable and reputable shop exceeds the cost of replacement heads. It would be pretty easy to drop mulit-hundreds of Bitchcoins in machining, guides, seats, new springs, retainers, valves, hardened spring seats, studs, and thread inserts just to get back to serviceable heads.
The head on the other side (passenger side) is the one that had the hole in the port. I pretty much have it stripped down now, I know the condition of things.
So here is the thing- These heads don't even have an oil change on them since they were COMPLETELY re-done (I know, from some of the pics it would be hard to tell but I'm pretty sure it's between 1000-1500miles, can't check, no battery in the car and it's a digital dash). New stainless valves, guides, 3 angle valve job, machined for PC seals, PAC beehive springs, retainers, ARP hardware... The only reason that I have them off/apart is that one of the intake ports on the passenger side had a thin spot that started filling the intake with coolant. I've had both heads pressure tested, after porting, converting to SBC, the refresh... it turned out that one has core shift and is prone to thin spots around the intake valve bowls. So far it's been easier to fix the thin spots than start over so far, but I'm about getting to the point where I would have been time ahead just converting/porting a new set, but I didn't know I had the problem when this started.
That said, the valve seats, valves, guides, springs.... are all dead-on almost brand new, and even with whatever this is that I'm seeing in the exhaust ports there is no slop in the valve guides and it wasn't burning any oil when it was running.
If I had infinite time and money (eh, money really isn't a thing, I guess i could spend a lot more than the just about nothing that I've spent on this thing so far) and the car was sitting comfortably in a garage I'd pull the short block and go through that, it's condition concerns me more, but with the car sitting at the end of the driveway (in a neighborhood with an HOA) and cooler weather coming this is becoming more and more a race to get it slapped back together and mobile.
If you're going to repair the heads, consider sintered iron guides and ditch what's left of the bronze. Hopefully there is sufficient guide boss material to retain whatever you install. If they are actually cracked, it might not hold ANY replacement guide.
If you're going to repair the heads, consider sintered iron guides and ditch what's left of the bronze. Hopefully, there is sufficient guide boss material to retain whatever you install. If they are actually cracked, it might not hold ANY replacement guide.
I'm coming to the conclusion that I need to learn more about valve guides. I mean I know that cast iron heads have cast iron guides, at one point I thought that aluminum usually had bronze guides but learned that they typically have cast iron from the factory, and past that I'm lost. I know that you can hammer out the cast iron and bronze guides and hammer in new ones, I'm assuming that only happens a few times till they won't stay and they're junk. I also know that there are various liners (different materials and designs, solid and split...) and you can ream the existing guides for the liners, but I have no idea how and why you would use one over the other. I'm comfortable with the fact that you have to machine the spring end for different seals (I even own a Louis tool to do it), I know that knurling them used to be a thing but no longer is, I know the how's and why there....
I know that these heads were gone through recently, they have new stainless valves in them, the guides were done but I don't know what that really means, but from what I can tell they appear to be cast iron with no liners (they are magnetic, they will occasionally spark when you're porting... and I don't see a liner in there and the one that I blew the corner off of welding the port doesn't have any liner sticking out or any evidence of it).
I'd love to be able to just replace a valve guide at home if I needed to (and if you don't know I have more tools than most, I converted the LT1 heads, all welding and machining in the garage, mostly on the Bridgeport, I even decked them on the Bridgeport) but there doesn't seem to be that much information out there about it.
I know that you can hammer out the cast iron and bronze guides and hammer in new ones.....
I'd love to be able to just replace a valve guide at home if I needed to (and if you don't know I have more tools than most, I converted the LT1 heads, all welding and machining in the garage, mostly on the Bridgeport, I even decked them on the Bridgeport) but there doesn't seem to be that much information out there about it.
I have worked at an automotive machine shop in the past - doing heads.
Yes, you can bang out the old guide and pound in a new one. And if you're really lucky (and you should be with < 1500 miles), you won't even have to re-touch the valve job. You will have to machine the spring end for the valve seal.
The machine shop down the street from me decks the heads on a Bridgeport. Use a fly cutter.
I have worked at an automotive machine shop in the past - doing heads.
Yes, you can bang out the old guide and pound in a new one. And if you're really lucky (and you should be with < 1500 miles), you won't even have to re-touch the valve job.
OK, so I need a mandrel/punch that fits the valve guide fairly accurately, preferably one that fits my air hammer, right? Then can I just go and get another cast iron guide (what do I look for)? Why would you use cast iron vs bronze?
You will have to machine the spring end for the valve seal.
Right, I've got the Comp Cams carbide tipped guide machining tools and guides I believe for standard .530" OD (I may have the .500" one also)
The machine shop down the street from me decks the heads on a Bridgeport. Use a fly cutter.
I usually use a largish (7 or 8" range) sandivic insert shell mill with an R8 arbor. I've experimented with the number of inserts installed and have found that fewer usually gives a better finish. 1 effectively makes it a fly cutter and the mass of the large steel shell mill stabilizes things. I actually have a bigger problem with fixturing (I keep meaning to build something custom but haven't done it yet, so I'm using 2 large angle plates and some screw jacks) and travel (I have a medium size, 42" rather than the large 48" table, which means I need to get the head EXACTLY in the middle of the travel and it only leaves fractions of an inch on either end).
These LT1 heads actually started as an experiment if I could deck a set of heads on the Bridgeport (I picked them up for $22, the cost of shipping), and after I fished with that I got to wondering if I could use them on something. 😉
OK, so I need a mandrel/punch that fits the valve guide fairly accurately, preferably one that fits my air hammer, right? Then can I just go and get another cast iron guide (what do I look for)? Why would you use cast iron vs bronze?
Exactly. We never did the air hammer method, but I suppose that might work nicely. We just pounded them out using the proper stepped punch.
The guide is a .002" press fit, IIRC. I would go cast iron, but you should probably match what is used for the rest, to keep things consistent.
Take a look at what Alex carries: https://www.alexsparts.com/categories/VALVE-GUIDES/ I know you can figure out the proper choice.
Originally Posted by 83 Crossfire TA
I usually use a largish (7 or 8" range) sandivic insert shell mill with an R8 arbor. I've experimented with the number of inserts installed and have found that fewer usually gives a better finish. 1 effectively makes it a fly cutter and the mass of the large steel shell mill stabilizes things. I actually have a bigger problem with fixturing (I keep meaning to build something custom but haven't done it yet, so I'm using 2 large angle plates and some screw jacks) and travel (I have a medium size, 42" rather than the large 48" table, which means I need to get the head EXACTLY in the middle of the travel and it only leaves fractions of an inch on either end).
In the past, I have done nearly the same for gasket matching intake ports. I bought 2 very heavy angle plates from MSC Industrial Supply. I never did get around to setting them up for doing as you described (bolting to the ends of the heads), and they are still in the boxes. I would actually love to give them to you if you would use them. But shipping would be crazy $$$. IIRC, they are similar to this: https://www.mscdirect.com/product/details/00144089
Yep, I checked them. 10" x 8" x 6".
Last edited by NoEmissions84TA; 09-25-2021 at 09:02 PM.
The large diameter shell mill is probably a lot faster than a flycutter, but it would be important to traverse the entire surface with the whole cutter in case there is any kind of runout. That's going to take a bit larger mill table than many manual Bridgeports have, and loosening/sweeping the mill head is always a crap shoot for repeatability.
As for the melting point of bronze, there are numerous alloys identified as "bronze" with melting points as low as 850°C. As mentioned, if an incorrect alloy was used (as in if they were sourced from China), all bets are off. All that is assuming they guides are indeed bronze. It may be something completely different that we are looking at in the photos.
As for the melting point of bronze, there are numerous alloys identified as "bronze" with melting points as low as 850°C. As mentioned, if an incorrect alloy was used (as in if they were sourced from China), all bets are off.
09-19-2021, 06:56 PM
