# Engine question. Complete rebuild vs top half only



## uscfan1976 (Sep 4, 2018)

I have a question and would like some advise please:

I currently have a 1965 GTO with a 389 (Non-Numbers Matching) with a M20 4-Speed bolted to it. The engine cranks first time every time, zero knocks or pings. It is a tight engine but the valves are worn and I feel that pulling the heads and having them completely redone and leaving the bottom half alone with the exception on resealing it including new freeze plugs might be the way to go both from a time and cost perspective. 

I have priced a turn key rebuild vs buying a built 389/400 vs just pulling the heads and the difference is a few thousand dollars at minimum. The car runs and drives overall very well now but does need at least a head job at minimum. If I rolled the dice and just did the head job then i have the funds free to invest in the interior sooner than later. (I would rather do what is right I do not want to cut corners but my gut tells me that this is the way to go)

Does anyone have any input in to the pros and cons of this? What are any suggestions and what should I look for?


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## 11th Indian (Feb 15, 2018)

I was pondering the same issue.
Was repeatedly told that updating the top end, with rare exception will just expedite the demise of the old bottom end. (unless it was recently rebuilt with quality parts & machine work)


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## RMTZ67 (Mar 12, 2011)

I too intended on a top end only rebuild because it seemed to be running well. Then it started growing.$3500 Later I am putting it back together. Look up my thread "Cracked my 400 open for a new cam.look what i found".


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## BearGFR (Aug 25, 2008)

uscfan1976 said:


> The engine cranks first time every time, zero knocks or pings. It is a tight engine but the valves are worn


What's going on that makes you think the valves are worn?

Bear


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## uscfan1976 (Sep 4, 2018)

My guess is because I see some oil residue around the #8 cylinder and get some oily carbon deposits out of that side of the exhaust. Plus I want to be able to run pump gas if I need to. I plan of swapping out the intake and card at the same time.


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## My65goat (Jul 26, 2017)

uscfan1976 said:


> My guess is because I see some oil residue around the #8 cylinder and get some oily carbon deposits out of that side of the exhaust. Plus I want to be able to run pump gas if I need to. I plan of swapping out the intake and card at the same time.


If I were you I would do a leak down test before anything. A leak down test will show if there is any compression lost and where the compression is leaking ( rings, intake valve or exhaust valve). If the cylinders are holding good you can just change valve seals rite on car. 

I have done a few top end rebuilds in the past, and like some have mentioned i did have bottom end problems afterwards.


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## geeteeohguy (Feb 2, 2008)

My65goat said:


> If I were you I would do a leak down test before anything. A leak down test will show if there is any compression lost and where the compression is leaking ( rings, intake valve or exhaust valve). If the cylinders are holding good you can just change valve seals rite on car.
> 
> I have done a few top end rebuilds in the past, and like some have mentioned i did have bottom end problems afterwards.


THIS^^^. A leakdown test will tell you the condition of the engine...rings, valves, the whole thing. If you have less than 15% leakdown, replace the valve seals. You could also very easily remove the engine and perform a re-seal/re-gasket job, which would allow you to inspect the bearings and timing chain. I removed the 400 out of my '67 about 7 years ago because it was leaking oil everywhere, and while I was at it, I inspected the internals, and found them to be fine, with the 90,000 miles I had put on it since the '88 rebuild. I also replaced the core plugs and detailed the engine compartment at the same time. Cost was minimal.


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