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'74 Engine knock...
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Jim Bear
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PostPosted: Sun Jun 01, 2014 7:34 pm    Post subject: '74 Engine knock... Reply with quote

Hey folks. I went to move the bus so the kid could shoot hoops. The bus had not been started in a week as I was away with the family. I gave it three pumps of the accelerator and turned the key and it made some clunking sounds that were unfamiliar and startling. It barely caught and then died. I turned the key, checked the oil light (on) and then committed again. This time is started smoothly and stayed running, but there was an unsettling slight knock emanating from the engine. I backed it to where it needed to be and let it run for a minute. It idled fine, but the knock was still there. I shut it off, shot hoops with the kid, and tucked the fear into the back of my mind. I will head out tomorrow to assess further and really take a look and listen. My question is how should I proceed? Suggestions and insight welcome. Thanks in advance.
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Danwvw
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PostPosted: Sun Jun 01, 2014 7:38 pm    Post subject: Reply with quote

Well if it has set for a long time perhaps a valve seat stayed stuck to a valve! Wonder if you may have the later hydraulic lifters in it?
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busdaddy
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PostPosted: Sun Jun 01, 2014 8:08 pm    Post subject: Reply with quote

Danwvw wrote:
Wonder if you may have the later hydraulic lifters in it?

Me too.
Also check your oil level to see if it's way too high and smells like gas.
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Jim Bear
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PostPosted: Sun Jun 01, 2014 8:34 pm    Post subject: not hydraulic lifters Reply with quote

It does not have not hydraulic lifters. I'll check the oil in the AM. It only sat for a week and was driven locally quite a bit prior.
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korfmach
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PostPosted: Sun Jun 01, 2014 8:40 pm    Post subject: Reply with quote

Jim Bear--no disrespect intended toward your mechanical assessment skills...but I just went through the whole valve process on my '74. Thought for sure it was solid lifters since it was bone-stock... then found out that it was hydraulics all around--someone had replaced them at some point in the dark, distant past. Check your pushrod length--I think that is the only way to tell for sure without disassembling the whole valvetrain.

Sorry if this is a dumb-ass post and you've already verified your lifters...my engine had (to all external appearances) stock solid lifters and I was very surprised to fine out they weren't.
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Jim Bear
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PostPosted: Mon Jun 02, 2014 5:51 am    Post subject: Confirmed solid.... Reply with quote

Solid lifters for sure. I will have a chance to get out and dig on things in a bit. I am first going to adjust the valves and note issues/changes from last adjustment. Then, we'll see...
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Jim Bear
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PostPosted: Thu Aug 14, 2014 8:32 am    Post subject: All is good. Reply with quote

False alarm. Checked everything out and been running strong since...no noise.
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Wildthings
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PostPosted: Thu Aug 14, 2014 9:08 am    Post subject: Re: All is good. Reply with quote

Jim Bear wrote:
False alarm. Checked everything out and been running strong since...no noise.


I would recommend still doing that valve adjustment. What you have described so far sounds like a classic loose valve seat. The engine has been running fine, but once let sit for a while the seat will come out on start up causing a nice bang as the piston collides with the valve. The seat is now jammed most of the way back into place so you get some valve train noise for the excessive lash. Slowly as you run the engine the valve pounds the seat back more fully into place, the lash tightens and every thing seems fine. Ignored though you may soon have a rod ventilating your block. Please check your valve adjustment and watch for any further changes.
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williamM
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PostPosted: Thu Aug 14, 2014 9:47 am    Post subject: Reply with quote

x2 wild has a good point- check all you valve adjustment screws for one that is extended more than the others.

Those heads were known for that


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Image may have been reduced in size. Click image to view fullscreen.
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Check both spark plugs for any debris or metal bubbles stuck to the electrode- need a magnifying glass.
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PostPosted: Thu Aug 14, 2014 10:04 am    Post subject: Reply with quote

williamM wrote:
x2 wild has a good point- check all you valve adjustment screws for one that is extended more than the others.

Those heads were known for that


.[img]
Image may have been reduced in size. Click image to view fullscreen.
[/img]

Check both spark plugs for any debris or metal bubbles stuck to the electrode- need a magnifying glass.


a loose seat, weak spring or stuck valve is the most common. Loose pieces of carbon in a cylinder can also knock. I would follow the advice more than one poster has given and check the valve stem height to see if there is anything noticeable.
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