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I-6 Engines For GMCs that came with the Inline 6 Engines

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  #21  
Old April 7th, 2014, 11:29 PM
Vern Vern is offline
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Default 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?
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  #22  
Old April 8th, 2014, 07:59 AM
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Default 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?
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  #23  
Old April 10th, 2014, 03:45 AM
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Default 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".

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!
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  #24  
Old April 10th, 2014, 04:14 AM
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Default 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
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  #25  
Old April 10th, 2014, 06:26 AM
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Default Re: Blown head gasket vs. cracked block

Quote:
Originally Posted by Vern View Post
Budget is definitely an issue, 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.
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.
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  #26  
Old April 12th, 2014, 05:52 AM
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Default 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!
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  #27  
Old April 13th, 2014, 05:13 AM
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Default Re: Blown head gasket vs. cracked block

Quote:
Originally Posted by Vern View Post
I have to top off the oil 2-3 times between fill ups.
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.
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  #28  
Old April 20th, 2014, 04:05 AM
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Default 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.
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  #29  
Old April 20th, 2014, 03:55 PM
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Default Re: Blown head gasket vs. cracked block

Quote:
Originally Posted by Vern View Post
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.
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.
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  #30  
Old April 20th, 2014, 09:42 PM
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Default Re: Blown head gasket vs. cracked block

Quote:
Originally Posted by Vern View Post
The more I drive it, I'm not as convinced that it's burning much coolant after all. 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!
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.
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