Blown head gasket vs. cracked block
 

Ok, folks when I got my '66 (inline 250) there was lots of white smoke coming out of the tailpipe that I chalked up to bad gas and a messy carb. However, after only 20 mi on it, I found the crankcase is down a couple quarts and the rad is dry. Is there a good way to determine if I just need to replace the head gasket or if the engine is toast (cracked block)? The compression is pretty good and reasonably uniform across the cylinders. Ideas? Thanks!

Re: Blown head gasket vs. cracked block
 

Sounds like a crack in the head somewhere . Good compression would indicate that the gasket is good. I have seen some cracks in the exhaust ports that act just as you describe. The oil use is really extreme and I am surprised that the smoke is not blue. This could be caused by lots of things. Bummer bummer, bummer. When I get back from the woods I will pm you. BC .

Re: Blown head gasket vs. cracked block
 

Howdy, Vern.

Good to see ya.

IME, the weak spot prone to freeze damage on the I-6 is external, just above the freeze plug (ironically) under the manifolds.
I've seen 4 or 5 with the same failure. At least two were 292's....but I do remember a 250/230 or two with the same pattern.

But that's not the only way to crack a block, as we all know.
It doesn't take much compression to puke out all yer coolant.
I'm thinkin if you warmed it up a little, you could pick up an internal crack (or head gasket leak) with a compression guage in the bleed down mode.
You could also pull your thermostat and housing and top it off with coolant (water) and start her up and let it warm up.....and watch for a constant stream of bubbles (or a gusher).

Maybe.

Good luck and keep us in the loop.

Re: Blown head gasket vs. cracked block
 

Rock Driller, thanks for your help! My mechanical skills aren't the best so, bear with me here. I did run a block test and it was negative. The bumper next to the tail pipe is black, so it seems to be burning lots of oil. Given that the engine is really messy and leaking oil all over the place, I was thinking about buying a gasket set and replacing the head gasket. Would that be a potential fix or should I run other tests first? Much appreciated!

Re: Blown head gasket vs. cracked block
 

In either circumstance you have to pull the head off for repairs. If you are going to do a head gasket and there is no obvious deterioration of the old head gasket when you take it apart then you will automatically get a mag test and or pressure test done on the head to look for cracks. I think the white smoke does point more to the head than the block.

There is always a risk that a bad gasket could fill up a cylinder with coolant after you shut off the engine and possibly cause severe breakage the next time you turn the engine over and it can't compress the fluid. If the engine still runs and starts okay you can guess that the leak could be going into the exhaust port as suggested already.

A head gasket leak on the compression side could also put a puddle on the ground and pressurize your radiator blowing coolant out the cap, possibly blowing a weak hose and or cause the water pump shaft to start leaking.

Depending on what you know about the engine history you could just have the head gasket/head replacement done but in my experience it makes sense to at least do rings and bearings along with that if not an even more complete rebuild.

Or maybe you have access to another good dropin engine.

Re: Blown head gasket vs. cracked block
 

It's always a crap-shoot at this point, Vern.
Pulling an I-6 and doing it on the stand is usually as attractive as leaning over (or jumping in) and doing the job that way.
That being said,....if you do pull it to change the head gskt.... and find out that the head gskt was the problem.....then that gives you something constructive to do with the rest of your gasket set. (and you might find other things that need attention).
But then you have to make a pile of other hard decisions.....like (but not limited to)....do I pressure wash the engine bay....? and while it's so clean and accessible ....do I paint it...? Should I order some grommets...and so on, and on and on...blah blah.
Let me know what you decide...
At least it's not yer D-Driver.

Re: Blown head gasket vs. cracked block
 

Based on your earlier description of all the white smoke, leaks, no oil, no coolant(did you see any blue smoke in there or oil burning?) I wouldn't replace the head gasket without getting the head examined at the machine shop. see if your valves and valve guides are still serviceable and get the head magnafluxed for cracks first. It's not worth wasting a gasket set to seal up engine leaks if it needs a rebuild or replacement anyway, if it's worn out... it's worn out! It does kinda sound like it is at the of it's service life.

Sometimes you can get away with a budget rebuild such as saving your crank, cam, lifters, pistons, valve train, even the oil pump and water pump. If these parts are not excessively worn. you could possibly getaway with tank cleaning everything and put it back together with rings, bearings, gaskets and maybe valve guides. If you have not done this before and you like mechanical work just do a little research, ask for a little help here and you will do fine, it's easier than you might think. It will be fun to do!:goodluck:Hope it goes well.

Re: Blown head gasket vs. cracked block
 

YeeeeHaww

Re: Blown head gasket vs. cracked block
 

OH Yeah, I have been in the "one thing leads to another" position before. Started off by one time to R&R a 350 with a friends rusty 79 Chev 4x4, honestly all we wanted to do was get rid of a worn engine with bad head gaskets and drop a good used 350 in it.....BUT about 100 decisions later and $25,000 + of his cash he had almost completely new 79 Chev 4x4 right down to the carpets and stereo. And it was definitely a "Well we did this so we may as well do that" project as the weeks and months went by!
:ahhhh:

Re: Blown head gasket vs. cracked block
 

Ah, a mechanic family member says I'm crazy and need to drop in a crate 350 with fuel injection. I kinda like the put-put 250 with the manual pull choke... hopefully I can salvage it. Unfortunately, I don't know much about the engine other than it's not the original. The guy I bought it from didn't seem to know too much about it. I think the casting number puts it between '67 and '71.

Is it possible to replace the rings without pulling the engine? It seems like replacing the rings wouldn't be too bad, but could be a nightmare if it's still in the engine bay? How about those rebuilt kits that actually include new pistons and rings?

Re: Blown head gasket vs. cracked block
 

I sit behind a desk all day, so I'm looking forward to digging in. It seems like the next step will be to locate a shop that can service the head.

Re: Blown head gasket vs. cracked block
 

Well not really because you should have the block and head tank cleaned and put new cam/main/rod bearings in with the rings. Doing rings also requires using a cylinder hone and probably a ridge reemer which would contaminate the inside of the engine too much.
Because of the transmission input shaft and flywheel, the crank cannot be pulled without removing the engine first. Lifting the engine out is very simple and makes it very very easy to do the engine work. You just have a few wires and hoses, engine mount bolts, trans bolts, exhaust pipe and lift it out with a rented or borrowed hoist.

You could get a full engine kit but if this is a real budget build I would inspect & measure your pistons/cam/crank first to see if they are too far gone. If you are getting an engine kit with pistons go to 10 - 30 thou oversize and bore the cylinders. The machine shop will tell you how big you need to go.
Now you are talking going full tilt rebuild for more $$$ and if this is not the original engine it just makes sense at this point now to look into the cost of a good quality used 6cyl of any year or buy yourself a an already built long block, see if you can save any $$$ and time.

Re: Blown head gasket vs. cracked block
 

before you do all that just change the 20.00 head gasket and see if it fixes it. if it dont fix it buy a new motor v6 for 200.00.

Re: Blown head gasket vs. cracked block
 

Vern,

As far as originality, it's a moot point....right..?

If you really feel like you want a project, then I would pull it and put it on a stand, take it down to the block.....find a good machine shop that understands what your intentions are and have a good time doing something new.
It's a hoot if you're not under any time constraints or other "pressures".
BUT.....if you were to call around and do some price and availability checking, you might surprise yourself.
I don't know if you can still buy a Mr. Goodwrench Crate motor....(long or short block)....but I'm sure someone on here will pipe up and let us know.
Both options are enjoyable, and even if it's the first time on an engine swap for you, you couldn't hope to find a more simple project than a GM I-6 in a mid sixties pick-up to cut yer teeth on.

Re: Blown head gasket vs. cracked block
 

Best Way I know is to tear it down. I did one today, a small block V8 and it had; a blown head gasket, a cracked block, bad piston, and spun bearing. This was because they overheated it and ran it out of oil.

Re: Blown head gasket vs. cracked block
 

One of the comments I heard when asking around is that it's not worth getting the head worked on without replacing the rings, bearings, and getting the driveshaft machined? Sounds like I either need to just replace the gasket only and cross my fingers or go all out on a rebuild?

Re: Blown head gasket vs. cracked block
 

Now that is what you call having a bad day!

Re: Blown head gasket vs. cracked block
 

Hi Vern, a lot of mechanics claim that if a fresh head or heads are installed on a worn short block that it can cause the rings and possibly bearings to fail due to the increase in compression because of better sealing valves. I don't buy that, done it many times on race and street vehicles.

Just replacing a head gasket wouldn't change the compression and MIGHT solve your problem. Done that a lot of times too but it was usually obvious coolant was getting in a cylinder or leaking on the outside. It is definitely possible that the head gasket won't help. Just depends more about how much time you have to mess with it, not super expensive to try it.

Oh yeah, had to hit "edit"! I have no idea why you were told that the drive shaft needs machining while doing this work!!???

DAC

Re: Blown head gasket vs. cracked block
 

What you say pretty much covers what I heard. The idea was that you shouldn't fix "the top (head)" without fixing "the bottom (piston rings, bearings, crankshaft)". The guy I talked to was a racer. I just have to think about the trade off of putting money into an I6 vs the cost of buying and possibly rebuilding a V6. Might be worth the time to try the gasket fix and see what happens.

"driveshaft" was a typo for "crank shaft". The thought being that you should replace the bearings on the pistons, but not on an old crankshaft.

Re: Blown head gasket vs. cracked block
 

Yeah it is tough to make decisions on guesses, but that's all trouble shooting is anyway with experience mixed in. There is a cylinder leak down test that can be done also but that will still not tell the difference between cylinder wall or head cracks or a head gasket problem.

A used crank doesn't always mean it has to be turned either. In 1986 I built a 350 with a used, un-machined crank, new standard size bearings on mains and rods. I did check clearances and they were on the loose side of acceptable. Long story short, that engine is still running in my '72 GMC. It is getting tired again but it's only been 28 years!

DAC

Re: Blown head gasket vs. cracked block
 

So, I think I'm going to send the cylinder head to a shop in town to get rebuilt, hoping that I don't have to replace the piston rings also. I have a gasket set and the specs for correctly torqueing the head gasket. Is there anything else I need to be careful of when replacing the head?

Re: Blown head gasket vs. cracked block
 

Did you discover something that makes you think the rebuild is needed? If possible maybe ask a knowledgeable friend or the shop to let you know if the head is usable, as is, first. If the answer is no, then chances are the bottom end needs rings and bearings and maybe cam and lifters.
The reason you rebuild your head is because the valve train is overly worn. But in your case you are also trying to eliminate the possibility of a cracked head so DO NOT let the shop rebuild your head without doing magnaflux testing first. If you had any reason to think there could be a crack in any part of the head or block then the mag test is the first thing you do.
Its been said that you should do the head rebuild and not the bottom end, but I think that this is only valid if you are really on a limited budget. We have all done that at some point before however if you have the money you may as well refresh the engine top to bottom. If budget is a concern you can always do the head this year and the bottom end next year, you will just need and other head gasket.
Do you have the engine apart now? What have you found? How many miles on it?

Re: Blown head gasket vs. cracked block
 

Budget is definitely an issue, particularly considering how much needs to be fixed on the truck! Everything from a blown dome light to a temperamental fuel gauge to the "Chevrolet" emblem on the grill of a "GMC". :bbeer:

The other consideration is, given that the engine isn't original, I wonder if it wouldn't be a good idea to get another one. I have no clue how many miles are on it; the guy I bought from didn't seem to know very much. From the insurance slips in the glove box, it was only driven about 1000 miles over a 10 yr period (the tags expired in 2001). Even if I took a year or more to rebuild it as good as new. I saw an ad for a 305 with a 5-speed tranny 45 min away. It might be kinda fun to get a small block V8? So, I'm hoping that fixing the top will help minimize the oil loss so at least I can drive it a while.

Much appreciated for all the help folks. I'll definitely make sure the head is looked over closely. I don't have the engine apart yet, but hope to start on it this weekend. Patience with such a rookie!:tiphat:

Re: Blown head gasket vs. cracked block
 

Hey Vern, I hear you on the budget part! My GMC project the main money goes into doesn't fit in this forum but I have a '55 GMC that I drive almost daily that has a very similar engine to yours. Was fortunate enough to get it running real well pretty cheap but lots of labor!

It had not been driven at all since 1997 and with damage to the exhaust manifold and system, radiator and a cross member no way it could have been driven either.

We were lucky that all the stars lined up and it runs great now, but I'm still not super confident with it yet in the 3 years it has been back on the road, not knowing anything about it. We do 150 mile trips now and then but I would still feel better if I could rebuild that 250 I posted pictures of with the block casting number earlier in your thread.

Anyway, I hope it works out, and you can start doing more driving than working on it!

Yeah the Chevy emblem needs to be replaced with the GMC logo! ha!

DAC

Re: Blown head gasket vs. cracked block
 

Oil Leaking or oil burning? Which problem do you have or do you have both? Am I mistaken, I thought you were dealing with losing coolant?

If it's leaking oil for the most part then all gaskets and probably front and rear crank seals need to be done to stop leaks.

If it's burning oil for the most part then you likely need valve guides and rings(complete engine rebuild).

For budget reasons I would do some searching for a good used 6 cyl drop in engine even from a much newer truck, it keeps sounding more and more like this will be your best budget option. A 6 cyl swap will also be the simplest fix.

Doing a head rebuild to eliminate problems that you are not absolutely positive about could just be throwing away good money. You might just find a good deal somewhere on a solid 6 cyl for the price of that head rebuild and gaskets.

Re: Blown head gasket vs. cracked block
 

The more I drive it, I'm not as convinced that it's burning much coolant afterall. But I have to top off the oil 2-3 times between fill ups. The white bumper next the tailpipe is now black. There does appear to be some oil leaking from the valve cover, but not enough to explain the extent of the oil loss. I don't see oil underneath, but it is parked on gravel. The compression test put the cylinders in the 120 +/- 10 PSI range for all 6 cylinders. So, my hope is that the problem is in the head. There is a real chance that dropping a couple hundred bucks to get the head rebuilt is a gamble.
I've seen a number of 305's around, but they all look like they might need to have lots of work done (new rings, head) to them like this one does. I hope to get after it this weekend... fingers crossed!

Re: Blown head gasket vs. cracked block
 

Wow, If you are burning through 2-3 quarts of oil between fill ups you would have so much smoke behind you as you drive the you would probably get pulled over. That is a lot of oil to burn so it has to be leaking out, that much oil will make a huge cloud. I don't think this is a head rebuild issue.

If the head is bad as far as losing oil goes it is from bad valve guides/seals that will cause smoky stinky exhaust but even bad guides/seals are not going to dump 2-3 quarts of oil on one tank of gas.
If the rings are bad you will have a lot of blow-by(white smoke) coming out of the valve cover cap/breather when you take it off and a smoky stinky exhaust. but again not going to use 2-3 quarts.

If things were bad enough to use that much oil the engine would not run well or even start. The plugs would be getting fouled up and need cleaning after almost every tank of fuel. It would probably develop misfires regularly.

I think that your front and rear crankshaft seals are the most likely culprits here, they can cause this kind of sever oil loss/leaks DURING driving, they can dump a lot of oil out of the engine onto the road while driving and then show minimal dripping when parked. They only leak severely when they are being bathed in oil while the engine is running. The tell-tale sign for this usually is oil wetness under the truck (especially after driving some distance regularly) behind the engine, and if it is the front seal, then wetness from the bottom front of the engine under the truck.

Dynamic seals like these can get hardened and cracked over time and then they will do little to hold back the oil which is what you are describing now.

If you are otherwise happy with the way the engine runs you may get better results from just buying an engine gasket kit and pulling the motor out to put in all the gaskets especially the front and rear crank seal.

This is not and overly complicated job however it will require loosening and re-torquing the crank shaft. I'm not sure what parts prices are like where you are but I would guess that a complete gasket set would cost you about $50-75 plus your time of course.

If you are leaking this much oil due to old gaskets then you can bet that you are losing coolant from old gaskets too. So it now sounds like that might be you best and cheapest fix, and if you have the tools it can all be done in one day.

Re: Blown head gasket vs. cracked block
 

Wow, that makes a lot of sense. I have the truck in the garage and have been taking it apart a bit at a time (will be interesting to see if I remember how to put it all back together). It'll be a few weeks before I can sacrifice a couple days to do the job. Have to get my hands on a cherry picker, but I can rent one locally. I'll probably have some more panic posts in a couple weeks. Or there might be a '66 GMC for sale.

Re: Blown head gasket vs. cracked block
 

LOL... good luck and don't forget to torque everything correctly and re-torque the head after the engine is running again for 30 min or more and is cold not hot.

Re: Blown head gasket vs. cracked block
 

I should also mention that a complete gasket set will come with valve seals that are easy to install. You can usually purchase a basic valve spring clamp fairly cheap or rent one at the local tool rental shop. You don't need to remove the valves, just compress the spring to unlock it, remove it to insert the new seal over the valve stem and then re-seat the spring, then go to the next one. Have a look on YouTube for some examples of this.

Oh and as for the blackened rear bumper this can also come from needing a good tune up and possibly a new carb or carb rebuild. Just be sure your carb is in good working order as well as the complete ignition system when it is running again.

I have been trying to decide between the engine options for my 65 4x4. Right now it has 305. I also have a 292, a 327, a 6.2 diesel and i am really leaning towards the 6.2 diesel as I really love those engines.

Re: Blown head gasket vs. cracked block
 

It's been decades since I helped someone pull an engine, and they were V8's. So, is there a good way to pull a v6 with the cylinder head and intake/ exhaust manifolds in place? It would be nice to get the engine up on the stand, replace all the gaskets outside the truck, then put back in? Many sites I've seen pull the engine out with bolts screwed into the block.

Re: Blown head gasket vs. cracked block
 

Vern....
Good to talk to you,

The easiest way to do it ....(at least for me) is to pull the front clip, radiator and all.
Just drain everything, unhook the engine wiring and harness at fire-wall, hoses to the radiator....the bolts from fenders to cab, the core support to frame, maybe the bumper, and lift the whole marry-anne off and set it aside.
Then she's a piece of cake.
Easiest with a couple strong young-uns to handle the front clip for ya.

More after I think for a few.

Re: Blown head gasket vs. cracked block
 

Wondering if I missed something in your posts about your truck, is it a V6 or inline 6? I thought you had a 250 I-6, or are you talking about a different truck here?

If it were me I would just remove the hood and yank the engine out, but having the whole front clip off will certainly make pulling the engine (and possibly tranny all together) super easy! Not really that much extra work to do that I guess.

I usually just put longer bolts/washers trough a heavy chain into an available bolt hole either on the front/back of the head or intake/exhaust manifold.

Re: Blown head gasket vs. cracked block
 

[QUOTE=quest;53150]Wondering if I missed something in your posts about your truck, is it a V6 or inline 6? I thought you had a 250 I-6, or are you talking about a different truck here?

[QUOTE]
It's an inline 6...typo again!

Re: Blown head gasket vs. cracked block
 

I have most of the engine unbolted, a cherry picker and stand from craigslist, and hope to pull the engine this weekend.

One of the things I noticed all along is the size of the gap between the exhaust manifold and exhaust. There was also no gasket there. Is this gap supposed to be so large? It sure sounded like there was exhaust leaking when it ran.

Re: Blown head gasket vs. cracked block
 

If that 250 needs a lot I have a couple of good 292's. Complete carb to starter. I can even fire one up. Local forum member price 375.00. Barry

Re: Blown head gasket vs. cracked block
 

The gmc letters are still free.

Re: Blown head gasket vs. cracked block
 

Barry, I might take you up on the 292 at some point. It would be nice to have an engine that's been rebuilt from the ground up when I have the time and money to do it. But, I'd rather get this 250 up and running so I can drive it.

I'd love to get those GMC letters from you too.

Re: Blown head gasket vs. cracked block
 

Oh, another question. It looks like it's best to disconnect the bell housing from the tranny to pull...rather than unbolt the block from the bell housing? The bolts look darn near impossible to undo as is.

Re: Blown head gasket vs. cracked block
 

It may be Vern. I am going to guess that your I-6 GMC is very similar to this '64 Chevy I parted out a while back. They do have very different exhaust manifolds so no way to be sure everything else is similar. The transmission, if it is 4 speed like this one is not mounted, It hangs off the bell housing so you remove the access cover in the cab and pull it back out of the bell housing first. The rear engine mounts are on the bell housing.

pic1- pulling the engine

pic2-engine with bell housing

pic3-front and rear mounts in frame

DAC