Slant 6 Vibration

[nm9stheham]

FWIW, the /6 engine in my '62 Dart pictured had 58k original miles when I got it in '14 and the bores were worn to the point of needing a complete rebuild. Cylinder pressures were as good as your good ones (head and gasket OK), but the prior owner had not known of a carb gas leak and had been running it for years on horribly gas-diluted oil and the cylinder wear was horrendous. It took a .040" overbore to clean it up. So you just don't always know the history of why things wear.

Absolutely pull the head. I bet you are going to find something wrong in the gasket or in one of the valves. You can also inspect and measure the bores and make a judgement on their condition. Post pix and we can see.

 

[slantsixdan]

You mention boil over. I have only had the car for 2 months, and driven it sporadically. However, I've had several instances of it boiling out of the overflow tube

That could be a clue…!

it does get hot really quickly, like I'm my other post about the freeze plug failing.

Rust in the radiator...rusted-out freeze plug…it's not unreasonable to suspect a rusted-through head gasket, too. The original head gaskets are stamped steel.

(Too late now, but when you pulled the freeze plug to replace it, you ought to have taken steps to dig out the rust muck that tends to accumulate in the block, accessible without the freeze plugs in the way...)

 

[Poboyross]

That could be a clue…!



Rust in the radiator...rusted-out freeze plug…it's not unreasonable to suspect a rusted-through head gasket, too. The original head gaskets are stamped steel.

(Too late now, but when you pulled the freeze plug to replace it, you ought to have taken steps to dig out the rust muck that tends to accumulate in the block, accessible without the freeze plugs in the way...)

Ok, after much more a-do than I expected in getting the head off (SO MANY THINGS TO TAKE OFF!....and that 2" coolant tube that's hidden on the front!) I got my first look. The gasket around cylinder 2 looked wet, but since it was dark, I just figured it was a mix of some coolant in the cylinder from removing the head and the teaspoon of oil I put in for the compression test. None of the valves look damaged, but the area around the valves on cylinder 2 and the piston head are BLACK. Also of note is that the entire workings under the valve cover look like they were powder coated black (I know that's not the case, ;) ) and perhaps that means it's been run too lean or hot? The cylinder bores look slick and clean, with only carbon rings around the tops, no ridges in the metal that I could discern. Head bolt #14 (bottom back) was also dripping with oil once I pulled it out. All others were dry. Here's pics (sorry they're dark, I finished up right at dark):

 

[slantsixdan]

I'm not seeing anything alarming here, though some conditions that could cause your readings (sticking or burnt valve, cracked piston) would not be visible in pics like this. That amount of black gunk on the rocker assembly is really normal. Clean it up and assess the condition (turn-resistance) of the adjustors as per here.

Er-ruh…I'm assuming you did a proper valve adjustment before taking the head off…? If not, a too-tight exhaust valve or two could explain your rough running and your compression results.

Anyhow: at the very least, you're up for some new gaskets. It is very much worth your while to get the good gaskets for the manifolds.

 

[Poboyross]

I'm not seeing anything alarming here, though some conditions that could cause your readings (sticking or burnt valve, cracked piston) would not be visible in pics like this. That amount of black gunk on the rocker assembly is really normal. Clean it up and assess the condition (turn-resistance) of the adjustors as per here.

Er-ruh…I'm assuming you did a proper valve adjustment before taking the head off…? If not, a too-tight exhaust valve or two could explain your rough running and your compression results.

Anyhow: at the very least, you're up for some new gaskets. It is very much worth your while to get the good gaskets for the manifolds.

For some idiotic reason, I removed the rocker arm assembly prior to removing the head. I figured I'd rather do the adjustment after I got it all back together and do it while running.

Are there any tests I can run at this point to detect a cracked piston?

I'll snap up those good gaskets per your link, I've followed your recommendations per other posts as well (Remflex, electronic ignition, electric choke, etc). Here's to hoping a freshening up and valve adjustment will prove out! Thanks!

 

[pishta]

Id rather see the black than the rust and coke I saw in my slants valvetrain when I got it. It looks like #2 may have been leaking into the water passage from what I can see, but a new head gasket is inexpensive (cometic excluded) and a new valve lash will be in order after the thicker replacement gasket is installed anyway. Save the drama until you get the new head gasket on and find out all the cylinders are +- 10psi from each other. RTV for the entire intake/exhaust gasket? Wow! ...and plug that EGR hole! the CA cutoff date for smog is still 75.

 

[nm9stheham]

With the engine overheating, your head could be warped, so I would certainly take the head to a shop to be checked for flatness. That warpage could cause a head gasket leak; those 2 things, warpage and head gasket leaks, often feed each other.

It aaaaalmost looks like there is some leakage between 1 and 2, but it is hard to tell from just a pix. And it looks like the normal rust-through spots in the head gasket have occurred, which lets some of the coolant bypass some of the block and raises engine temps. So it is good to get that old metal shim gasket replaced.

And again hard to tell, but it almost looks like #2 exhaust is a bit open (...which would be odd, so it is probably just the pix). Check all of your valve springs to see if any are broken. As said, you cannot really see if you have a bad valve seat until the valves are pulled. So either buy/borrow the tool to remove the valves or take it to a shop to examine. If you get the springs off, then this is the time to put in new valve stem seals; the old ones are no doubt shot. Cheap....

The inside looks VERY good! And good on the cylinder bores. Just for education, too shiney is actually not good; that can be what is called cylinder glazing and the ring seals fail. But if the compression did not come up with oil in the #2, then that is not likely any issue for you. Since the head is off, I would borrow the tools to accurately measure the bore diameters; not essential to do, but now is the time to find out. (Measure them across the long axis of the engine.)

When you take the head to the shop, they will likely find:
- perhaps some head warpage
- very possibly a burnt valve or seat in #2
- loose valve guides
If you are going to keep the /6, then now is the time to do it all: head mill, valve guides, and valve job. That all is gonna run a few hundred bucks, BTW. If you are not going to keep the /6 long term, then skip the guides, but you'll need to get any head warpage milled out, and any burnt valves/seats re-worked.

And know that the newer head gaskets are thicker and thus will lower the compression ratio a tick, and make the eninge a bit less torquey. If the head is going to be milled to remove any warpage, just go ahead and mill it .060" and you'll end up with better compression and a bit more low RPM torque. You will indeed feel it.

While you have the head out for work, remove the lower block plug ( under the oil pump) and see if there is a lot of rust in there. I agree that some further efforts at rust removal are in order, based on what can be seen in the block, your rusted core plug, and the rust-through spots in the head gasket.

No certain test that you can run for a cracked piston at this point. That seems very unlikely to me anyway. What you can do:
- Inspect the tops and edge very closely
- Bring each piston up near the top of the bore and alternately push on the left and right sides (looking from the front of the car); the piston should rock very slightly back and forth to when you do this. They all ought to rock back and forth about an equal amount. This is looking for any severe breakage in a piston skirt (down in the bore) but it won't find any slight cracks. But cracked pistons are not common anyway, so I would not lose any sleep over it.

 

[pishta]

...
- Bring each piston up near the top of the bore and alternately push on the left and right sides (looking from the front of the car); the piston should rock very slightly back and forth to when you do this. They all ought to rock back and forth about an equal amount...

Bro, that is awesome. Ill have to try that but if I found that before reading this, I would have scrapped those in a heartbeat!

You can use a straightedge across the head to find any obvious warpage. Use a flashlight behind the straighedge and look at the light passing, its about an 8:1 magnifier (Iv had that stat in my head for years and finally used it! Don't know where I read it) you can also stick some sandpaper on a mirror (uber flat) and run it over the head in a figure 8 pattern and look for low spots. Autozone loans the 'OEM' valve spring compressor tool that allows you to pop the springs and valves. while you are there, order some $3 valve seals as yours a guaranteed toast or already in the pan. A machine shop will dress your valves (mine does it for a buck a piece if you bring them in) and can tell you if any exhausts are spongy and past facing. You can also ID any sunken seats while your in there. If you need a head ASAP, I got a pulled one down in Tustin.

 

[nm9stheham]

Bro, that is awesome. Ill have to try that but if I found that before reading this, I would have scrapped those in a heartbeat!

It is just a rough check to see if anything is really grossly bad on one bore or piston. I was just thinking of how could the OP look for a really bad piston issue, since that seemed to be a concern. I do it only for that reason: just some assurance that a 1-2 reeeeally bad problems aren't there. It does not quantify regular wear in any useful way or tell you anything about rings, grooves, etc.... A broken ring would have typically shown some compression improvement with oil (since the 2nd ring is now the compression ring), and some vertical scars in the bores. It sounds like that is not the case.

The only REAL way to examine a piston is to pull it. That is why a pressure test in cylinder 2 and listening on intake and exhaust would have been good before pulling the head; that would have told the story on the valves, and if one was bad, then would have made a piston issue even less likely.

 

[Poboyross]

It is just a rough check to see if anything is really grossly bad on one bore or piston. I was just thinking of how could the OP look for a really bad piston issue, since that seemed to be a concern. I do it only for that reason: just some assurance that a 1-2 reeeeally bad problems aren't there. It does not quantify regular wear in any useful way or tell you anything about rings, grooves, etc.... A broken ring would have typically shown some compression improvement with oil (since the 2nd ring is now the compression ring), and some vertical scars in the bores. It sounds like that is not the case.

The only REAL way to examine a piston is to pull it. That is why a pressure test in cylinder 2 and listening on intake and exhaust would have been good before pulling the head; that would have told the story on the valves, and if one was bad, then would have made a piston issue even less likely.

I'll check all that on the pistons while the head is at the shop. We've got a place here where you can trade yours in as a core on a rebuilt one, or they will do yours MTO. As long as things check out on the lower end, does increasing the compression by milling the head doom the lower end as long as there's no major known problems? I figured that since it was all apart, might as well give it some gumption. Ideally, I'd like to keep the slant and hop it up via head work (now), a different intake/carb/exhaust combo (later), and even turbo it (MUCH LATER). Slants are an enigma engine for me, and not a belly button engine. I just wasn't willing to do a full rebuild right now if the whole thing was shot, hence if that had been the case, dropping in a v8.

When I put some oil in cylinder 2 to redo the compression test, it jumped from 35 to a whopping 40-45. I didn't figure that qualified as "improvement".

 

[Poboyross]

Well fellas, this might make it toast. I wanted to check out the full depth of the cylinder walls, so I went out to turn over the engine and check it out. Attached is a pic of the scoring on the bottom 2/3 of the cylinder. It's not mega deep, but I can feel it with my finger tips. There's about 5-7 strips about 1/4" wide spread out around the cylinder wall.

And in case I had any doubts that little to no coolant was actually making it through the head:

 

[nm9stheham]

Not necessarily bad..... so not time to panic. It could be some crud or something that got in there at one time and just got scrubbed up and down the bore. Or, the engine got a bit too hot, the piston expanded and momentarily scrubbed the cylinder wall.

If it got bad enough, it might have scuffed the piston; that is indeed a bad piston. (But I normally see a lot worse on the cylinder wall in that case. And you would have felt the engine slow or knock a bit or jerk a bit when that happened.) Run the other pistons down in their bores and see if you see similar in some others. Let us know what you see.

My next step would be to measure the bore diameters. Then have the head checked for warpage and any bad valves or seats in #2. (That 'pssss' that you heard really makes me think valve.) If the head is all good, THEN it is time to suspect that ring set or piston, and pull it out, or pull the whole bottom end.

Buuuuut... maybe 1st decide if you want to keep this engine. Do you want to get it fully up to snuff, or just get it running again? Or do the V8 thing? If you really are contemplating a turbo, then you don't want to do that on an unknown block and pistons.... and bearings.... and oil pump.... etc.

BTW, that plugged hose is either one of the heater core hoses, or the short hose to the head, which is the bypass hose. Neither being blocked will 100% block flow to the head; the bypass just allows some modest amount of coolant to flow around while the engine is heating up.

does increasing the compression by milling the head doom the lower end as long as there's no major known problems?

Not sure I follow the question here.... did spell-checker change that word 'doom'?

 

[Poboyross]

Not necessarily bad..... so not time to panic. It could be some crud or something that got in there at one time and just got scrubbed up and down the bore. Or, the engine got a bit too hot, the piston expanded and momentarily scrubbed the cylinder wall.

If it got bad enough, it might have scuffed the piston; that is indeed a bad piston. (But I normally see a lot worse on the cylinder wall in that case. And you would have felt the engine slow or knock a bit or jerk a bit when that happened.) Run the other pistons down in their bores and see if you see similar in some others. Let us know what you see.

My next step would be to measure the bore diameters. Then have the head checked for warpage and any bad valves or seats in #2. (That 'pssss' that you heard really makes me think valve.) If the head is all good, THEN it is time to suspect that ring set or piston, and pull it out, or pull the whole bottom end.

Buuuuut... maybe 1st decide if you want to keep this engine. Do you want to get it fully up to snuff, or just get it running again? Or do the V8 thing? If you really are contemplating a turbo, then you don't want to do that on an unknown block and pistons.... and bearings.... and oil pump.... etc.

BTW, that plugged hose is either one of the heater core hoses, or the short hose to the head, which is the bypass hose. Neither being blocked will 100% block flow to the head; the bypass just allows some modest amount of coolant to flow around while the engine is heating up.

Not sure I follow the question here.... did spell-checker change that word 'doom'?

I checked the other cylinders and that's the only one with any scuffs.

I'm on the fence about keeping the engine. I want something with more gumption than a stock Slant, hence considering all the upgrades. However, that was when I thought the engine was in a better state than it actually ended up being.

As it sits now, if it's likely that the bottom end needs major work, I'd rather just get it running until I can do a swap (go crazy and put a 440 in it a year or two down the road). I'm reluctant to have a lot of head work done due to the overall uncertainty, as if it turned out it needed all that bottom end work, that money would have been wasted. I've already chased this ghost through buying a NOS Holley carb, along with doing the Pertronix electronic ignition. It's already feeling like a money pit, and the specter of having to do major bottom end work makes me a bit ill. I don't mind stripping the head down myself and getting it looked at by a shop, but I think barring the entire problem being with the head, I'd rather get it running as cheaply as possible and run it til it becomes a boat anchor.

 

[nm9stheham]

OK, very good. Then the next step is to strip the head and find out if it is warped and if there was a bad valve in #2. Keep the valves in order. If either is the case, then it is likely that #2 piston and rings are OK and that the issue was in the head. It is not 10000% guaranteed at that point that the #2 piston is OK but at least you would have found a definite head issue that would explain the low compression. Also, have the shop look at the head gasket to see if they think it was leaking.

Then get the report on head and guides and cost and decide from there on the head.

If NO head problems are found, then you can just risk that all is OK with some minimal head work and put it back on.... OR you CAN pull the #2 piston. (I've done it more than once...OK, twice total LOL) The oil pan has to come off (easiest out of the car but you can hoist or jack up the engine carefully and do it from underneath), then remove the 2 connecting rod cap nuts, and carefully push the rod bolts up and past the crank, and then the rod and piston on out the top of the engine. It'll take a bit of force to pop it past the carbon and ring ridge at the top of the bore. It is not easy to do in car with the crossmember under the engine. So most guys would pull the engine at that point.

But if you do find some evidence of the piston scuffed at that point, then what do you do? You can indeed put back in one new piston and ring set. You would hone the cylinder to get the rings to seat. But now you have 5 other worn pistons and worn bearing sets, etc. So your solution may be best; just do minimal work and put it back together. It was basically running and not exploding, right? It won't be worse now.

Hey, don't feel bad. We have all been there. It is an old engine and anything can be inside there. And the good thing is that the oil-in-the-cylinder test indicated that there was something in the head area wrong. Next time, slow yourself down and do an air pressure test in the cylinder as a extra step; that would have shown right where the problem is. That is why mechanics do that extra step.

FWIW, I would call those cylinder 'scratches'. Those are not at all uncommon. A scuffed piston is one where it has overheated and expanded to the point of rubbing the cylinder wall hard, and getting so hot that the aluminum in the piston softens. When it cools, it will then shrink to under normal size and will rattle in the bore. The cylinder wall usually shows some broad darkening when that happens and often some bits of embedded metal from the piston; I don't see that here. That is why I think you ought to keep on with the head investigation.

As Red Green would say, "We're all pullin' for ya!"

 

[pishta]

Head work and a new head gasket. The head work is permanent and can be sold as a rebuilt head to another slanter. The head gasket is just labor and maybe a 12 pack you never bought. Pull that piston and check the rings. Dingle ball hone the cylinder and rotate them in there if it makes you feel better, just keep them 90/180 out of alignment with each other. Bottom end is pretty much bullet proof as they dont work that hard. As they say on 'Forged in Fire'..."It will run".

 

[Poboyross]

OK, very good. Then the next step is to strip the head and find out if it is warped and if there was a bad valve in #2. Keep the valves in order. If either is the case, then it is likely that #2 piston and rings are OK and that the issue was in the head. It is not 10000% guaranteed at that point that the #2 piston is OK but at least you would have found a definite head issue that would explain the low compression. Also, have the shop look at the head gasket to see if they think it was leaking.

Then get the report on head and guides and cost and decide from there on the head.

If NO head problems are found, then you can just risk that all is OK with some minimal head work and put it back on.... OR you CAN pull the #2 piston. (I've done it more than once...OK, twice total LOL) The oil pan has to come off (easiest out of the car but you can hoist or jack up the engine carefully and do it from underneath), then remove the 2 connecting rod cap nuts, and carefully push the rod bolts up and past the crank, and then the rod and piston on out the top of the engine. It'll take a bit of force to pop it past the carbon and ring ridge at the top of the bore. It is not easy to do in car with the crossmember under the engine. So most guys would pull the engine at that point.

But if you do find some evidence of the piston scuffed at that point, then what do you do? You can indeed put back in one new piston and ring set. You would hone the cylinder to get the rings to seat. But now you have 5 other worn pistons and worn bearing sets, etc. So your solution may be best; just do minimal work and put it back together. It was basically running and not exploding, right? It won't be worse now.

Hey, don't feel bad. We have all been there. It is an old engine and anything can be inside there. And the good thing is that the oil-in-the-cylinder test indicated that there was something in the head area wrong. Next time, slow yourself down and do an air pressure test in the cylinder as a extra step; that would have shown right where the problem is. That is why mechanics do that extra step.

FWIW, I would call those cylinder 'scratches'. Those are not at all uncommon. A scuffed piston is one where it has overheated and expanded to the point of rubbing the cylinder wall hard, and getting so hot that the aluminum in the piston softens. When it cools, it will then shrink to under normal size and will rattle in the bore. The cylinder wall usually shows some broad darkening when that happens and often some bits of embedded metal from the piston; I don't see that here. That is why I think you ought to keep on with the head investigation.

As Red Green would say, "We're all pullin' for ya!"

Got some pricing info from a local joint that does head rebuilding only. Looks like it's about $300 for me to trade in my usable head for a rebuilt one (done in house) or same price to rebuild mine. It comes with new valves/springs/enchilada. What I wanted to know was if it's worth having it milled down a little extra for more compression? I talked to them about doing larger valves, but I got to thinking that's a potential rabbit hole of also wanting to do porting, polishing, etc etc. . Plus, that doubles the investment at minimum. I thought that perhaps sticking with just the milling, added to everything else being stock, might be a little extra bang for the buck...that is unless *not* doing the OS valves creates potential issues?

 

[cdnEHbody]

You could knock it down a bit anywys as the new head gasket will be a bit thicker, i should have done mine when i did the head gasket, decided i want to pull and refresh anyways so i left it alone.

It seems like a good low buck upgrade,

 

[KosmicKuda]

I agree with Pishta's post 40. Im guessing the Pssst sound from #2 when doing the compression test was a leaking exhaust valve. Personally I'd keep the same head and have it rebuilt. Maybe pull #2 piston and check it and the rings, dingle ball it and run it. Make sure you check the small 1/8" diameter oil feed holes in the rocker shaft for pluggage. Mine were all clogged but it hadn't been run for 31 yrs.

My personal experience is with my 64 225. From the outside it looks normal but when I COMPLETELY rebuilt it I couldn't just put it back together stock so...I had the head rebuilt with hardened seats and milled .080. Charlie S says that's the #1 upgrade with no negatives. I also spent about 10 hrs gasket matching and pocket porting. I had the cam reground by Oregon cams for about $100 invluding shipping, stock lift was .375 and now i have (IIRC) .420 and 252* duration. I hogged out the short turn radius in the stock intake under the carb and opened the bore to match the carb gasket. Also increased the exhaust pipe diameter. Looks stock but really runs well.

 

[slantsixdan]

If you're going to swap or regrind the cam, get Oregon Camshaft Grinding № 2106R, that is the Dutra RV-10RDP, which does a great job of waking up a stock or near-stock Slant-6 without making new problems (no idle/driveability problems, economy gets better and not worse, etc).

 

[nm9stheham]

Personally, yes I would absolutely mill the head .060" or so and forget the valves. The cam suggested above is a very good choice. Both will make a very noticeable difference and are worth the money IMHO. And I'd replace the timing chain; it will be stretched by now and the 3-5 degrees (or more) of cam retard will make the car sluggish.

 

[Poboyross]

UPDATE (and a question):

After much ado, and realizing the funds weren’t there for a rebuilt head, I decided to just clean up the mating surfaces, put it back together, and do a valve adjustment. So far I’ve just gotten the head back on and still have the adjustment to do. With funds being tight, and the car in need of moving under its own power to get it out of the driveway, I decided it best not to sink extra cash into it for now. Even if I got that new head, the ring in cylinder 2 might likely still be toast. Work for another day, I say.

In the mean time, I have removed all of the smog equipment, and was wondering what is the part number of the standard belt on these engines NOT running smog? Figured I’d ask to see if anyone knew it offhand.

 

[slantsixdan]

I have removed all of the smog equipment

Please tell us in detail (make a list) exactly what-all you removed.

 

[Poboyross]

Please tell us in detail (make a list) exactly what-all you removed.

I removed the smog pump and all associated parts going all the way back to the back of the cylinder head. I plugged the floor jet in the manifolds with a brass plug. I left the charcoal canister because I know that serves other purposes.

 

[slantsixdan]

OK, good deal. Guessing you securely plugged off the air injection port at the back of the head, too.

Belt: use any online parts lookup tool. RockAuto, O'Reilly, NAPA, etc.