Cylinderhead work - please advise

thethee

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Okay so I really enjoy reading build threads but I always get stuck on what I can do on my own engine and I end up reading about what cam everyone is using and what not. It's a bit silly as my '75 Imperial is not that good and I'm pretty much using it as a learning project.

So to get my mind off it I did a compression test and yes it's a worn old engine, readings around 105-120 psi dry. Wet test had only minor changes so I'm thinking bottom end is okay. Don't mind the numbers that much as engine was cold so so far so good. Only issue is #2 cylinder which was at only 88 psi :(

Can I hook up my compressor to the cylinder to confirm it's a top end issue? If yes, what psi should I run that? I don't have a leakdown tester.

I'm thinking about pulling the heads for my next project. So now for the real rookie question, sending the heads out, that means cleaning, skimming, valve guides and valve seats right? Should I expect needing to replace valves or can those be cleaned up generally speaking?

I have little experience when it comes to heads so trying to gather information before going further. Any and all advise will be appreciated
 

Toolmanmike

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Leak down testers run line pressure in and they are regulated to 100#. Because you can't measure what air escapes and you are just listening for air escaping, any pressure will do and as long as it's enough. 70+ would be good. Let the machine shop clean and inspect the heads. They will let you know what they need.
 

Justin Plant

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Agreed, a good machine shop relies on its reputation. It'll tell you what needs to be done, I would expect or even insist on replacing all that can be replaced. Last time I had a set done it was about 500 each, and they were shot. The fella I sold the car to, is still driving it. That was 15 years ago. A good job will probably out last the car.
 

1970FuryConv

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Okay so I really enjoy reading build threads but I always get stuck on what I can do on my own engine and I end up reading about what cam everyone is using and what not. It's a bit silly as my '75 Imperial is not that good and I'm pretty much using it as a learning project.

So to get my mind off it I did a compression test and yes it's a worn old engine, readings around 105-120 psi dry. Wet test had only minor changes so I'm thinking bottom end is okay. Don't mind the numbers that much as engine was cold so so far so good. Only issue is #2 cylinder which was at only 88 psi :(

Can I hook up my compressor to the cylinder to confirm it's a top end issue? If yes, what psi should I run that? I don't have a leakdown tester.

I'm thinking about pulling the heads for my next project. So now for the real rookie question, sending the heads out, that means cleaning, skimming, valve guides and valve seats right? Should I expect needing to replace valves or can those be cleaned up generally speaking?

I have little experience when it comes to heads so trying to gather information before going further. Any and all advise will be appreciated
My experience is that you don't always have to replace valve guides. Also, exhaust valves take more wear than intake valves. I've had to replace all the exhaust valves, but the intake valves were reusable. I've also had hardened seats installed for the exhaust valves because of unleaded gas. For the intake valves, the machinist cut the seats.
 

CBODY67

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If you have one cyl that's that much lower than the rest, it is probably a "burnt" exhaust valve. When you get that head off, you'll probably find the exhaust valve has a flat/eroded section on its outer edge. If everything else is good, just need to clean and touch-up the valve-to-head contact area of the valve heads (i.e., "grinding the valves") . . . BUT valve stem wear also needs to be considered. Usually though, the guides will have more wear on them than the stems themselves.

So, with good valve guides and stem-to-guide clearances, touch the valve seats with the appropriate "rocks", clean-up the valve edges on the grinding machine, then re-use all that you can, reliably. With new silicone seals on the valve guides, OEM-spec. NOT the white scraper seals as they will keep the guide too dry from lubricant and cause MORE wear than the OEM-spec seals will.

From what my late machine shop operative mentioned, as long as the valve guides are good, the valve stem will not wobbly in the guide too much as it goes up and down. When the wobble gets to be too much, then the valve will not firmly seat as it should, which puts a "hot spot" on the edge of the valve where it does not seal effectively, which erodes that edge section of the valve head. Which leads to "a burnt valve" tha only gets worse with use. BEST to get it repaired soon so that it will not cause other issues with the valve seats.

Seems like that Chrysler used induction-hardened valve seats from 1974 and later. Probably 1973? But I know that for 1972, when leaded fuels were still around, albeit "low lead", usually . . . Chrysler recommended one tank of leaded fuel for every two tanks of unleaded fuel. But by 1974, that "band-aid" recommendation was not needed. With the head vatted and cleaned, you can usually see the heated areas from metal discoloration.

One part of the valve job is to check the valve springs for tension loss and possibly shim (with THIN shims) to get the open and closed pressures back in spec.

DO follow the recommendations of the machinist as to what is recommended to be done and how they will do it. With, of course, pricing involved. ALSO, read that section of the FSM for good measure. Possibly, they might have a set of heads they are doing a valve job on when you are there, so they could show you what they do?

Just some thoughts,
CBODY67
 

thethee

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Thanks for the help guys, appreciate it.

Follow up question though, I'm in no hurry so won't mind it if the machine shop takes its time BUT what should I do with the block in the meantime? It's still in the car which is sitting outside under a weatherproof carcover. Is it enough to cover it with some cardboard/rags or does it need more? Any pointers on that?
 

CBODY67

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For general principles, you might get a clean shop towel (or otherwise lintless towel), soak it in clean motor oil, and wipe down each cylinder bore above the piston to leave a thin layer of oil on them. WD-40 does NOT work nearly as well in the longer term, by observation. Then securely cover the short block with something akin to a breathable car cover, several layers folded, to keep out moisture and grit. Using anything plastic or impervious could trap moisture due to temperature swings, which is not desirable. Additionally, you might use a squirt can/bottle to put oil around the tops of the pistons so it will get down into the upper rings and such, for good measure. Then secure the cover with some sort of Bungee cord to make sure it stays put. Check every so often for critter issues, too.

Just some thoughts,
CBODY67
 

thethee

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Valuable info as always!

While we're on the subject, I've read about people milling the heads to decrease chamber volume to improve compression. Is that something to consider or would that just open up a whole other can of worms that I shouldn't be messing with? Engine is stock as far as I know.
 

1978 NYB

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I have come to a different view in recent years. Unless you want to keep it original.....
Why spend $500 apiece on head rebuild? Just buy aluminum cylinder heads. You can get a decent set for $1100 - $1500.
 

Toolmanmike

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I have come to a different view in recent years. Unless you want to keep it original.....
Why spend $500 apiece on head rebuild? Just buy aluminum cylinder heads. You can get a decent set for $1100 - $1500.
From what I have seen especially the lower dollar aluminum heads, you should still send them to the machine shop to get checked out. A lot of tight guide and less than acceptable seat grinds there.
 

thethee

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I have come to a different view in recent years. Unless you want to keep it original.....
Why spend $500 apiece on head rebuild? Just buy aluminum cylinder heads. You can get a decent set for $1100 - $1500.
Well, for starters, shipping those aluminum heads to the Netherlands will be brutal
 

Big_John

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In my experiences, the guides usually need replacing and often the exhaust valves.

With the limited miles you are going to drive the car, hardened valve seats aren't really needed. Your 1975 heads were built with no-lead gas in mind, so unless you see a lot of wear, I don't think you need to do that.

But, let's step back a bit. How many miles are on the car? How does it run? Did you follow up with a warm compression test?

The one low cylinder is troubling, but I'd run it (hard, if possible) and test at least that cylinder again (warm) before pulling the engine down.

Getting engine work done in the Netherlands has to be a bit pricey at best and finding a shop that's familiar with the older 'Merican iron might be tough, so I'd be hesitant to recommend taking that engine apart. It's always been my experience that once you start, it snowballs real fast and the next thing you know, you might as well do the entire engine and get it over.
 

MEV

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From what I have seen especially the lower dollar aluminum heads, you should still send them to the machine shop to get checked out. A lot of tight guide and less than acceptable seat grinds there.
I am not saying that is not a good idea, but i ran my 440 source stealths right out of the box with no problems.
 

1978 NYB

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Economy heads
Screenshot_20220312-132250_Chrome.jpg




Next step up

Screenshot_20220312-132211_Chrome.jpg
 

1978 NYB

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Well, for starters, shipping those aluminum heads to the Netherlands will be brutal

Didn't realize you are that far away. Are you planning to visit the USA soon? You could put them in checked baggage and take them back with you.

Or just have a machine shop rebuild your iron heads.
 

thethee

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In my experiences, the guides usually need replacing and often the exhaust valves.

With the limited miles you are going to drive the car, hardened valve seats aren't really needed. Your 1975 heads were built with no-lead gas in mind, so unless you see a lot of wear, I don't think you need to do that.

But, let's step back a bit. How many miles are on the car? How does it run? Did you follow up with a warm compression test?

The one low cylinder is troubling, but I'd run it (hard, if possible) and test at least that cylinder again (warm) before pulling the engine down.

Getting engine work done in the Netherlands has to be a bit pricey at best and finding a shop that's familiar with the older 'Merican iron might be tough, so I'd be hesitant to recommend taking that engine apart. It's always been my experience that once you start, it snowballs real fast and the next thing you know, you might as well do the entire engine and get it over.
All really good points, looks like I have some homework to do. Haven't decided to pull the heads yet as I'm also hesitant to do so. Needs further research
 

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You asked about cams, no one responded to that question. Hmm... I run a Stage 2 cam for that muscle car rumble. Camshaft choice is dependent on the intended usage, are you building a daily driver, a race car, or a weekend warrior? Is this a hot rod or a restoration?
You didn't say what size motor, big block or small block.

I agree with the above comments, ask around about machine shops, their reputation and quality of work. Best source of info about that would be auto repair shops and auto parts suppliers, they deal with that kind of stuff on a regular basis so they would know who's good and who isn't.

You said it's a '75, odds are good it already has hardened seats in it. If I had to rebuild my motor again, I would go for new valve springs, not shims. If only for high revving, right now I've a 5k limiter on my motor so the valves don't float and blow up. Which kinda limits my top end performance, I can feel it pull strong up to 5k then it hits a brick wall as it peaks, prompting a shift. I can tell it wants to go more but I don't dare with the 49yr old shimmed springs (it's a '73), or I risk it dropping a valve. Now if you're building it back to stock and showing off isn't in the cards, shimmed springs will be okay, as long as spring pressures are within specs. But if you're going to lean on it hard, go with new.
 

thethee

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Oh no no I think you misunderstood, I'm really fascinated by camshafts but it's pointless to think about changing one on a 46 year old worn engine with (1)67k miles on it. But it is fun to dream

Besides, I've read too many "what's the best cam for ... " threads to dare post such a question

Thanks for your other points though :)
 
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1970FuryConv

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Oh no no I think you misunderstood, I'm really fascinated by camshafts but it's pointless to think about changing one on a 46 year old worn engine with (1)67k miles on it. But it is fun to dream

Besides, I've read too many "what's the best cam for ... " threads to dare post such a question

Thanks for your other points though :)
1647563852495.png

Thanks, Theo
 

CBODY67

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ANYTHING which used a 440 as standard equipment in the middle 1970s is going to be HEAVY, so TORQUE is needed rather than 5Krpm horsepower to move things down the road. Unfortunately, many aftermarket "hot rod" cams will lose lower rpm torque, but by 3K+rpm, they might feel great. BUT with the lower rpm power diminished a bit, it'll take longer to get to those 3K+ rpm levels . . . time which that "top end rush" probably will not compensate for, usually. And then there are some aftermarket cams which "read" good, but have less duration/lift that the stock cam you now have. In addition to the weight factor, there's also that 2.71 rear axle and P235/75R-15 tires which can also complicate any "high performance" cam issues, unless . . . you might be looking for 140mph cruise speeds. Basically 5K rpm levels, as I recall.

Getting a valve job done outside of the USA should not really be that different than over here. What will be different is the diameter of the "rocks" to face the valve seats and related instruments to work the valve guides.

Default mode is to fix JUST what needs fixing, using quality gaskets/seals and such. Which means just that ONE cylinder with the lower compression. Which is what was done when the cars were "used cars". When you get things apart, IF a GASKET or seals is not sealing well, it will be obvious. Same with the condition of the rest of the exhaust valves, too. But the main thing is to find a competent machine shop that already has the needed size of items to do your engine.

Enjoy!
CBODY67
 
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