Rebuild time??? - Pontiac GTO Forum
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post #1 of 16 (permalink) Old 10-22-2012, 04:23 PM Thread Starter
 
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Rebuild time???

Well, just got off the phone with the mechanic. Looks like my rear main valve has started to leak even more.....probably time to pull it and replace.

He mentioned last time I was in about a rebuild on the motor. It is the original and hasn't had a major overhaul in a good 15-20 years. So he's getting me a rough price for a rebuilt and the main seal replacement.

My question is, since I'm likely doing a rebuild is there anything I should have done that is extra? I'm not looking for a huge increase just something that if I spend a few extra bucks would be worth it.

Also, IYO what do you think a normal rebuild on an original 389 would cost? Besides leaks there is nothing really wrong with the motor. Would it even be somthing I should do?

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post #2 of 16 (permalink) Old 10-22-2012, 08:57 PM
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A normal rebuild on a 389 will cost you about 3 to 4k if you stay stock or close to it. Less if you assemble it. Why does it need a rebuild? burning oil? Knocking? Here's my story, and I'll try to be short: I rebuilt the 389 in my '65 in 1981....a year before I got the car. (already had the engine). It's still in there today. 32 years later. And it runs great. Yeah, it only has about 50k on the rebuild, but it's still leak free, which I can't figure out. (Must be those good old asbestos based gaskets!). I rebuilt the 400 in my '67 in 1988, at 173,000 miles. It actually only needed a timing chain and a valve job, but I didn't know as much then as I do now. I pulled it last year to replace the leaking rear main and the other leaking gaskets....a complete reseal job. Cost less than $200. It had run about 77,000 miles since I overhauled it. I inspected the bearings and checked the clearances. Still like new. I put it back together and put it back in the car. Been fine for the last 4,000 miles since then. My point is, it doesn't really matter how much TIME goes by when it comes to rebuilding (or changing oil for that matter). It's the actual condition of the engine. How it was stored. How it was treated. If it runs well but leaks oil and is grimy, pull it and re-seal it. Don't rebuild it. You can only bore a block so many times, and less is better.
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post #3 of 16 (permalink) Old 10-22-2012, 09:37 PM
 
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I completely agree. Don't tear the engine apart without good reason.
But, if you pull it, don't forgot all the little dress ups. Paint the engine bay and whatever else you can touch. Not gaudy, just clean it up.
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post #4 of 16 (permalink) Old 10-22-2012, 09:56 PM
 
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This is good information. My '68 GTO convertible did not have an engine, so I picked up a '70 400 that presumably runs. I was wondering how far I should "rebuild" it. It is good to know that a rebuild is not necessarily required. I am thinking replacing all gaskets, plugs, wires, points, filters, etc. Maybe even new timing chain and replace/rebuild Carb. Then finally, a possible valve job. Does this sound about right?
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post #5 of 16 (permalink) Old 10-23-2012, 07:44 AM
 
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Originally Posted by mrvandermey View Post
This is good information. My '68 GTO convertible did not have an engine, so I picked up a '70 400 that presumably runs. I was wondering how far I should "rebuild" it. It is good to know that a rebuild is not necessarily required. I am thinking replacing all gaskets, plugs, wires, points, filters, etc. Maybe even new timing chain and replace/rebuild Carb. Then finally, a possible valve job. Does this sound about right?
Basically the right approach in my book, with one addition. I'd pull the heads and pan and take a look at a couple of bearings and the cylinder walls. That will tell you for sure whether or not you need to re-ring and replace bearings. If not, you've cleaned and painted everything and you'll have fresh heads.

When the only tool in your toolbox is a hammer, you tend to see every problem as a nail.
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post #6 of 16 (permalink) Old 10-23-2012, 09:50 AM
 
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Originally Posted by chuckha62 View Post
Basically the right approach in my book, with one addition. I'd pull the heads and pan and take a look at a couple of bearings and the cylinder walls. That will tell you for sure whether or not you need to re-ring and replace bearings. If not, you've cleaned and painted everything and you'll have fresh heads.
Well I assumed I was going to take the heads off, if for nothing else, I figured new head gaskets would be in order, plus the heads would need to come off for the valve job, so I figured that would be a good time to take a peak into the engine to see what I really have. On pan, I think you mean oil pan? I planned on that too for three reasons, 1) to replace gasket, 2) to see if there is sludge or metal shavings in pan, and 3) my oil pan is dented so I am thinking to replace it.
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post #7 of 16 (permalink) Old 10-23-2012, 12:57 PM Thread Starter
 
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A normal rebuild on a 389 will cost you about 3 to 4k if you stay stock or close to it. Less if you assemble it. Why does it need a rebuild? burning oil? Knocking? My point is, it doesn't really matter how much TIME goes by when it comes to rebuilding (or changing oil for that matter). It's the actual condition of the engine. How it was stored. How it was treated. If it runs well but leaks oil and is grimy, pull it and re-seal it. Don't rebuild it. You can only bore a block so many times, and less is better.
Not burning oil, except where it is leaking from, no knocking. Runs fine besides the fuel issue, which I believe was the timing being off and a loose distributer. And how hot she gets, even with the 2 row aluminum rad and electric fan(220-225 in AZ Summer)

Honestly the rear main is just leaking a little more. I was seeing maybe a 1/4 quart loss every other month....maybe less than 1/4. Its been garage kept unless I drive it obviously. Was garage kept for the last 15 or so year prior to me buying it too. Guess I'll just see about pulling to replace the rear main. I have a buddy that has an engine lift, would cost a lot less to do myself if its not too hard.
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post #8 of 16 (permalink) Old 01-21-2013, 09:45 PM Thread Starter
 
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Ok, so bumping this for an update and opinions.

We pulled the motor out this weekend to replace the rear main seal. Pulled the oil pan and the crankshaft has some blemishes on the outside counterweight lips. Like it was grinding a little. Also the journals aren't as smooth as they should be. I can feel a small nick, can't really describe it but they need to be smoothed out.

Didn't look at the pistons or much else, but probably doing a rebuild or at least a partial cause of the crank. So what should I look into? I plan on it dipping to get the old paint off. Again not sure if it needs bored out.
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post #9 of 16 (permalink) Old 01-22-2013, 09:41 AM
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In this day and age, I would take the whole thing to a reputable Pontiac oriented machine shop and have them prep the block, crank, and new rods and pistons. The block needs to be boiled out and the oil galleys need to be rodded out. You can't do it yourself. All of the galley plugs need to be replaced. Chevy machine shops don't do this, and huge problems arise. You should have the block zero-decked. You will need aftermarket upgraded con rods, and dished pistons for todays poor gas. This alone can be about $800.00. There are many, many threads on this forum about this exact question, with a ton of information. The biggest thing to remember is to NOT let a non-Pontiac machinist near the engine. Most machinists don't know the quirks of a Pontiac, and inadvertently do a substandard job. With luck, Mr. BearGFR will chime in and provide further information. He is very much "into" this topic.
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post #10 of 16 (permalink) Old 01-22-2013, 01:08 PM Thread Starter
 
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Originally Posted by geeteeohguy View Post
In this day and age, I would take the whole thing to a reputable Pontiac oriented machine shop and have them prep the block, crank, and new rods and pistons. The block needs to be boiled out and the oil galleys need to be rodded out. You can't do it yourself. All of the galley plugs need to be replaced. Chevy machine shops don't do this, and huge problems arise. You should have the block zero-decked. You will need aftermarket upgraded con rods, and dished pistons for todays poor gas. This alone can be about $800.00. There are many, many threads on this forum about this exact question, with a ton of information. The biggest thing to remember is to NOT let a non-Pontiac machinist near the engine. Most machinists don't know the quirks of a Pontiac, and inadvertently do a substandard job. With luck, Mr. BearGFR will chime in and provide further information. He is very much "into" this topic.
So will the afermarket con rods and dished pistions lower the compression? I don't want to lose HP.
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