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[C2] '67 is the head coming off??

 
Old 03-21-2019, 03:44 PM
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leif.anderson93
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Default '67 is the head coming off??


Just out minding my own business, enjoying a beautiful drive on this beautiful 72*, blue sky spring day. Stop at a red light and as I accelerate away, I start to hear this knocking/clanking sound from under the hood. Ease off the gas and nurse her to an adjacent parking lot. Pop the hood and rev the engine and the noise is obviously coming from under the passenger side rocker cover. Only a mile or so from the house, so gently drive her home.
Pull her into the garage and remove the rocker cover and here's what I find. Car gave zero indication that anything was wrong. The pushrod was slightly bent but I'm more concerned with the top of the valve stem. Please take a look and tell me if the valve needs to be replaced. Also, any thoughts as to what would cause this. Car is not hot rodded at all. Thanks in advance.



Last edited by leif.anderson93; 03-21-2019 at 03:47 PM. Reason: added picture
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Old 03-21-2019, 04:03 PM
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68hemi
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I doubt it did anymore damage than what you can see and that is just from the loose rocker banging against the end of the valve. Likely cause would be the nut backing off. I would put a new push rod in and locking nut for all rockers and run it to see how it sounds. Likely nothing more needed. These old Chevy engines are pretty forgiving.
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Old 03-21-2019, 04:04 PM
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I don't like that valve stem. All the little metal particles went somewhere and that would worry me. You might be looking at a complete breakdown of the engine. Dennis
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Old 03-21-2019, 04:06 PM
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That valve MIGHT still be straight, but the tip is junk. Tear it apart and repair it the right way.
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Old 03-21-2019, 04:28 PM
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I know it is not what you want to hear but I agree with Fordracer9, that head needs to come off for at least one new valve. I do not know your history with this engine so I can't offer more than that.
Push Rods bend when they are forced against something that has locked up or can't move.
Your rocker arm nut may have backed off, the stud may have pulled out of the boss.
Your Valve spring may have broke but no matter what you need one new valve for sure and that head is coming off.
As long as the manifold is off pulling one head you might want to have both heads freshened up or checked out unless you know the full history.
Was your camshaft stock or high lift?

Mark
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Old 03-21-2019, 04:47 PM
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Mark,
Stock L79 camshaft.
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Old 03-21-2019, 04:49 PM
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Valve needs to be changed for sure....and I'd suspect others in the future. Stock SBC valves are cheap..I'd fix the heads.

JIM
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Old 03-21-2019, 04:56 PM
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The tip of the valve is a separate piece hardened and added to the valve. It is breaking apart and there is no easy fix. It HAS to be replaced.
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Old 03-21-2019, 05:04 PM
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If the engine is old and could use a valve job or complete rebuild, then do it. However, you can buy hardened caps for the end of valve stems. Given you are not terrorizing your town or racing the car and seem to just enjoy driving, I would drain the oil and check the drain plug for any metal shavings. If you don’t have a magnetic drain plug and are really nervous, you could strain the oil looking for the metal particles, but I’ll bet they are either still sitting on top of the head, in the oil pan or the filter. Once you clean up the head under the valve cover and change the oil and filter, inspect all sixteen rockers, install a hardened cap on the chewed up valve end, replace the bent push rod, adjust all the valves and off you go.
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Old 03-21-2019, 05:33 PM
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The valve isn't square on the end anymore. The tit sticking up would cause the lash cap to teeter and the rocker will run off of the valve. If you were to grind it with the head still on it still wouldn't be square and would cause the rocker would walk in the direction of any taper either running off of the valve or cutting the stud into.

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Old 03-21-2019, 05:40 PM
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To answer the thread title, YES. To repair the disintegrating valve the cylinder head is coming off. If your budget is limited so that you can’t afford to remove, repair, address issues on both cylinder heads you could remove only the culprit head and service the single valve. I don’t recommend this but it can be done.

Pull the rocker arms on the remaining valves on that side and see what you have. That can help determine your repair.
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Old 03-21-2019, 07:33 PM
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Originally Posted by Robert61 View Post
The valve isn't square on the end anymore. The tit sticking up would cause the lash cap to teeter and the rocker will run off of the valve. If you were to grind it with the head still on it still wouldn't be square and would cause the rocker would walk in the direction of any taper either running off of the valve or cutting the stud into.
Robert,
This is what I thought. And, by your background, I'm inclined to agree with you. I'm a bit surprised that that much damage was done to the valve being as I only drove it about two miles once the noise started. Thanks

Last edited by leif.anderson93; 03-21-2019 at 08:53 PM.
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Old 03-21-2019, 07:37 PM
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Originally Posted by BADBIRDCAGE View Post
To answer the thread title, YES. To repair the disintegrating valve the cylinder head is coming off. If your budget is limited so that you canít afford to remove, repair, address issues on both cylinder heads you could remove only the culprit head and service the single valve. I donít recommend this but it can be done.

Pull the rocker arms on the remaining valves on that side and see what you have. That can help determine your repair.
If one head is coming off, I guess both are coming off. Seems to make sense to get both done at the same time. This is the original, all numbers matching engine for this car and I don't want to do anything that would endanger this engine. The engine was rebuilt approximately 30k miles ago, so I'm guessing this is just a fluke I'll have to fix. It's what happens when we drive these things. Thanks for your input.
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Old 03-21-2019, 08:08 PM
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Verify the pushrod slots in the head are not worn or distorted.
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Old 03-21-2019, 08:14 PM
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Get a premium set of ex valves, not the cheapest Chinese you can find. And what brand that is I'm not sure anymore. I've been out of active rebuilding for stock engines a long time. But you can already see cheap doesn't save you money. The other seven might last for years or maybe a week after you put it back together. I think I would look at oe valves. I know if I'm working on a Chevy with a hydraulic cam I only use GM lifters, never been bit by them.
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Old 03-21-2019, 08:35 PM
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The rocker arm appears to be cracked and the witness mark on the valve end is is way of center. I don't know how centered stock rockers are but that doesn't look right to me. I would check clearances on all valves, springs and push rods before pulling the heads off.

Tom
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Old 03-21-2019, 08:43 PM
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Wow, I spoke too soon. On my cell phone, the valve tip didnít look bad at all. On my iPad, it looks horrible. I agree with Robert.
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Old 03-21-2019, 09:02 PM
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Originally Posted by Factoid View Post
Wow, I spoke too soon. On my cell phone, the valve tip didnít look bad at all. On my iPad, it looks horrible. I agree with Robert.
I'm curious as to why/how a hardened end of a valve could look like that after only a couple of miles...unless it had been getting beat up for awhile and the rocker finally slipped off the deteriorated end of the valve. Either way, I'm going to replace everything in the heads...have to assume if one's weak, the rest are sure to follow. Whose valves do y'all recommend??
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Old 03-21-2019, 09:14 PM
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All Machine Shops will want to install hard valve seats in your heads. Most on this forum will tell you not to add the hardened valve seats in your original heads. Do some reading and make a decision on that before going in to your local machine shop.

Full Head Rebuilds done right will probably cost you around $5-600. I had my L79 heads done a year ago with all new valves, springs guides.

At 30,000 miles those heads and related parts should still be perfect, something was not done correctly or inferior parts were installed at that rebuild.

Find a good machine shop. You might call the local Performance shops and ask who they use for machine work.
See what springs were installed, the L79 works just fine with factory springs like the Sealed Power VS 677.

The factory L79 cam does not have enough lift to cause any odd ball problems. Rule that out.
A good shop should be able to point out what caused your failure and advise how to avoid a repeat.
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Old 03-21-2019, 09:25 PM
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There are several Valve suppliers, not so many manufacturers but many suppliers.
Sealed Power, Manley, SBI, most of the rebuilders I knew were using SBI for stock replacements.
A good machine shop can tell you first hand what parts have worked for him, they want parts to work so they don't have complaints down the road that are bad for business. The key here is a good machine shop.
You mentioned never pushing this engine so aftermarket aluminum heads that add more power are probably not what you want although this would be a good time to consider them. Added Power is always nice.
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