rebuilt head on old bottom end - Issues? and other questions

[Pablo M]

My head is out for a rebuild-dead cylinder diagnosed to a hole in an exhaust valve. 

Mechanic that originally looked at it said it would be a bad idea to put a rebuilt head on an old long block. Said it wont hold compression and will blow oil. Never heard such a thing and always heard about people rebuilding heads. But he's also the one that wouldn't bother diagnosing it for me in the first place so there's that. 

 

Anyone heard of such a thing? I don't really have a choice but don't want to make things worse. 

For sure, the engine has lots of miles on it-could be 185k or 285k as the records I have arent complete. It burns oil for sure too. I dont see any driving around but when I rev the engine in neutral to high rpm it blows blue smoke. I don't know if that was on acceleration or on lifting. I think on lifting. Eventually it will get rebuilt but not anytime soon. 

 

Second question:

Replacing all the exhaust manifold studs in the head- blue locktite on the head side of the studs is what I read, but won't that burn off? Is that ok to use or am I supposed to use something else? 

Same question for downpipe studs. 

[Son of Marty]

Yes there's a risk putting a rebuilt head on a tired lower end but what do you have to lose trying it if it holds good if not it's time to rebuild the bottom end but hey the good news if that happens is you have a rebuilt head to go with your rebuilt lower end. Red loc tite on the upper studs for sure and red or blue for the others.

[AceAndrew]

easy to put this way… if I’ve got a slightly leaky old engine, then I take half of that engine and seal it up new and tight… then the other half of older leaky bits will see the increased pressure/blow by.  In short, the existing issues will be exacerbated… but to what degree it’s impossible to say exactly.

 

I get where he’s coming from.  But as long as you realize that your bottom engine issues wont get better and may be slightly more noticeable, then slap it on.

 

[Son of Marty]

2 minutes ago, AceAndrew said:

then slap it on.

 

It's not like you have a whole bunch of other options anyway.

[dlacey]

1 hour ago, Pablo M said:

is what I read, but won't that burn off?

The the temperature at the threads in the head casting shouldnt get much above 100C, so the acrylic threadlock should survive.... agree that threadlock will burn-off on the downpipe joint...use hefty lock washers there.

[jimk]

Based on numbers from a Pyrometer exhaust temperature gauge, the exhaust at idle is around 600F, running at load around 900-1000F, wot around 1100 to 1150F.  Your results with Loctite will vary. 

[tech71]

3 hours ago, Pablo M said:

I don't really have a choice but don't want to make things worse. 

 

3 hours ago, Pablo M said:

Eventually it will get rebuilt but not anytime soon. 

You pretty much answer your own questions here.

If a block overhaul is not in the plan right now run the new head and see how much (if any) of the smoking issues go away.

Once its all back together and sorted a leak down test will tell you how good or bad your bores are.

I use Permatex Red Loctite on all exhaust studs going into the head. Not just about locking, also about sealing.

Some of them thread into open holes where oil can make its way out, drip onto the manifold and smoke.

Sounds like you have enough of that going on.

Have also used high temp silicone with decent results.

Look at your exhaust manifold carefully! Many are cracked.

Install exhaust manifold with all new copper coated nuts, use copious amounts of high temp anti seize.

I see no point in using anything when installing downpipe studs except anti sieze, better if they come out than break off

Edited September 27, 2023 by tech71

[Pablo M]

31 minutes ago, tech71 said:

Look at your exhaust manifold carefully! Many are cracked.

Thanks for all the info. Appreciate it.  
yes I’ve looked over the manifold and no cracks visible. Also removed rust and painted it with Eastman manifold paint. 

[Mike Self]

From experience...at 167k miles, had to remove the head from my otherwise unopened '69 engine due to a water passage eroding into #1 combustion chamber.  Had it welded up and surfaced, and while apart ground the valves, sleeved the valve guides and installed new valve stem seals.  Left the bottom end alone.

 

Prior to that work, I showed a pretty impressive smoke screen on deceleration with the throttle closed--classic worn valve guides/stem seals.  Virtually no smoke on startup or acceleration.  

 

Post head work.  Not a wisp of smoke on deceleration, but now some (but not excessive) smoke on startup, and on hard acceleration.  Classic blowby from the rings.  But smoke and oil consumption have remained pretty steady (5-700 miles/qt) in the succeeding 60,000 miles.  And since I drive the car only a thousand or so miles per year, until I start fogging for mosquitoes, I'm gonna leave it alone.  Oil's a lot cheaper than engine overhauls!

 

mike

 

[Dudeland]

Thanks so much for asking this question.  I am considering going through my head and see what is what.  
 

I am not smoking, and compression/oil consumption is fine.  

The future is a turbo, but I may just stick in a 292 to run next summer.  

[Rich]

when I saw the head line for  this thread I thought you were talking about my ex wife 🙂