Engine question. Complete rebuild vs top half only - Pontiac GTO Forum
User Tag List

 
LinkBack Thread Tools Display Modes
post #1 of 7 (permalink) Old 09-04-2018, 12:52 PM Thread Starter
 
uscfan1976's Avatar
 
Join Date: Sep 2018
Posts: 24
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Garage
Engine question. Complete rebuild vs top half only

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?
uscfan1976 is offline  
Sponsored Links
Advertisement
 
post #2 of 7 (permalink) Old 09-04-2018, 01:03 PM
 
11th Indian's Avatar
 
Join Date: Feb 2018
Location: Staten Island NY
Posts: 104
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 26 Post(s)
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)

Last edited by 11th Indian; 09-04-2018 at 01:14 PM.
11th Indian is offline  
post #3 of 7 (permalink) Old 09-04-2018, 07:43 PM
 
RMTZ67's Avatar
 
Join Date: Mar 2011
Location: Albuquerque N.M
Posts: 228
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 64 Post(s)
Garage
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".
Attached Thumbnails
Click image for larger version

Name:	20180609_121546.jpg
Views:	38
Size:	243.6 KB
ID:	115273   Click image for larger version

Name:	20180609_121539 8.51.50 PM.jpg
Views:	36
Size:	212.3 KB
ID:	115275  

Last edited by RMTZ67; 09-04-2018 at 07:46 PM. Reason: more info
RMTZ67 is offline  
 
post #4 of 7 (permalink) Old 09-04-2018, 09:11 PM
Super Moderator
 
BearGFR's Avatar
 
Join Date: Aug 2008
Location: Springtown, TX
Posts: 5,737
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 122 Post(s)
Garage
Quote:
Originally Posted by uscfan1976 View Post
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

BearGFR
Springtown, TEXAS
BearGFR is offline  
post #5 of 7 (permalink) Old 09-05-2018, 03:37 AM Thread Starter
 
uscfan1976's Avatar
 
Join Date: Sep 2018
Posts: 24
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Garage
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.
uscfan1976 is offline  
post #6 of 7 (permalink) Old 09-05-2018, 03:47 PM
 
My65goat's Avatar
 
Join Date: Jul 2017
Posts: 75
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Quote:
Originally Posted by uscfan1976 View Post
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.
My65goat is offline  
post #7 of 7 (permalink) Old 09-05-2018, 04:09 PM
64-67 Expert
 
geeteeohguy's Avatar
 
Join Date: Feb 2008
Location: Fresno, California
Posts: 8,478
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 99 Post(s)
Quote:
Originally Posted by My65goat View Post
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.
geeteeohguy is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Complete Engine Compartment Discussion

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
To rebuild or not to rebuild? dan woodland 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring 57 08-22-2016 07:51 PM
2004 Ls1 T56 Complete Part-Out or Complete Car olddohc 2004-2006 GTO Parts for Sale (Price & Pictures Required) 0 05-10-2014 03:06 AM
3.46 vs 4.11?? top speed vs 0-60???? QUIKSLVR04GOAT Drive train, suspension, alignment and brakes. 6 12-11-2008 06:38 PM
Magnacharger vs. Procharger vs. vs. STS Turbo vs.SLP Parts StocktonRaider 2004-2006 GTO General Discussion 0 05-27-2005 11:24 AM
Want to cut a full half second off your A4 GOAT at the track here it is: MaxHax Service, Maintenance and Technical Discussion 0 01-24-2005 02:09 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome