Technical 58 GMC 100 engine swap

Hey guys,

My truck has the original Pontiac 336 with the 4spd Hydro-matic.

I've found a 1960 389 with a 4spd auto and after some searching on this forum, it looks like it would bolt right in. The motor mount is in the front, instead of side to side, just like the 336 and I think it would mate up with the hydro-matic. I'm hoping the motor just needs cleaned up and reassembled. If I can figure it out I'll add a few pics!

Before I pull the trigger on this motor / tranny I thought I would ping you guys for a little confirmation.

Also, the owner wants to trade straight across for a 66 GTO tri-power setup, worth about $2k.

So, deal or no deal lol.

Carl-

 

I was hoping to not have to rebuild this engine and I realize it's hard to tell from photos, but how does it look?

 

To upload a pic from your phone click the upload a file, then select photo library or take a pic

 

Thanks!

 

Hard to tell just from pics.
Remove the caps, look at bearings and journals. If they look good, check clearances with plasti-gauge.
Then measure and inspect bores.
Inspect the heads. Clean em and check for cracks, bad valves……I will remove springs and check guides.

 

That's the rub right there...you don't know if the engine is good or not until you get it all bolted together and installed.

Also, what condition is the tripower setup in? The value of that varies quite a bit from one that needs a complete rebuild to one that is concours ready.

 

Agreed, I didn't see a ridge in the cylinder walls but don't see any hone marks either. The owner tells me it was "gone through" 25 years ago haha. I was thinking I should get hardened seats in the heads, check the guides while it's apart.

 

It's in really good condition...carbs are supposed to have been rebuilt.



Unfortunately the engine is about 5 hours away, guess I'll have to be ready to walk away if it turns out to be a builder. I got all excited cuz I think it would be a direct replacement for the 336.

 

Not sure I gathered what you would be trading straight across for the tripower setup? Otherwise, seems like a cool direction to head for your pickup as long as the 389 is in good shape or you don’t mind going through it. What kind of shape is the engine in your truck? Not sure the 389 would gain you much unless you are just wanting something a little more displacement or your 336 is in need of rebuilding.

 

Well... you have a tri-power that the "carbs are supposed to have been rebuilt" and he has an engine that was "gone through" about 25 years ago. Both descriptions are "iffy"...IF the tri-power is really worth $2K, and IF the engine has 25 years on a "freshen-up", I'd say sell the tri-power and put the $$ into your existing engine. The 389 is a crapshoot until you install and run it, then it could turn into a money pit. Same with the Hydramatic.

 

I’d wonder why a good running engine has been taken apart?

Regardless, if the going rate for that engine trans combo in unknown condition is the same value as your intake, why not?
That said I’m not the type to spend 2k on a used engine and transmission in unknown condition.

Now the flip side (I have these little imps on opposing shoulders talking in my ears) I’ve made trades that I gave more than the worth/value that I was getting in return, usually because I had something taking up space I wanted.

But that Tri-Power would fit in my closet.

 

In my opinion the 389 is worth about 4 to 500 bucks, in the real world the tripower is worth 12-1500. The 389 is going to need gone through, but would be a nice upgrade. Good Luck

 

Ok, I see you might be trading the tripower (that you own) for the 389 and transmission? I would rather have the tripower or sell it for what it is worth to fund an engine that is in known condition. That 389 torn apart isn’t worth what the tripower is (if that is the trade in question here).

 

I bought a 283 that was built years ago and never started.
Assembled with white lithium. The lithium had the consistency of caulk.
So a complete tear down and inspection.
The heads had been worked as well. I’ll still remove the springs and check guides. Add new seals and work the valves.
Crank journals looked good and had good clearances. The cylinders don’t looked honed correctly so I’ll check and rehone them.

 

- do not ditch that original motor/ trans set up - very rare - even if needs rebuild - worth good $ to restoration crowd - most have been ditched over the years for Chevy motor / trans - by pass the 389, too many unknowns and too far to risk the gamble - guy with motor likely will just sell your carb set up and be money ahead - but, your truck/do what you want

 

If those silver valve spring retainers are aluminum, they need to go. It looks like one has already been replaced, maybe because it pulled through.

 

Price out the rebuilding cost of the 389, and then make your decision. It will be quite obvious, even assuming every little bolt is still present for the 389.

Also, check with some of the Pontiac dudes about front motor mounting on different YEAR Pontiac engines, you might get a surprise.

While Pontiac blocks with the exception of the front motor mounts GENERALLY interchange, other things don't. As an example, on a 1964 GTO, replacing a factory 4-barrel with a factory 1964 tripower required fabrication of a totally unavailable alternator bracket.

Personally, I would rather buy a pig in a poke, than a pig in many pokes; but maybe just me.

Jon.

 

I am going to be doing something similar at some point, will be replacing a 1957 347 (Pontiac Star Chief) with a 1960 389. In 1960 they changed from "reverse" to "conventional" flow cooling, which means the timing cover is a bit different and possibly some radiator hoses.

I am looking to convert my 389 to reverse flow, which I think means drilling a couple holes in the block decks and using the water distribution tubes from the earlier heads and the earlier timing cover. I need to compare the blocks to see the differences, but I heard it can be done.

Your heads appear to have been converted to adjustable rocker studs with poly-locks, and may also have been converted to pushrod oiling (as opposed to oiling through the rocker studs). You might want to look into that further. If oiling through pushrods the oil feed to the heads should probably be plugged off.

 

The 336 is pretty tired, burning oil and like to mark it's spot. I don't mind going through the 389 but didn't want to have to machine the block get over bore pistons etc...

The 336 is rated at 200HP, where the 389 is ~325. Also, the 4spd I have shifts REALLY hard between 2nd and 3rd and probably needs rebuilt. So the 389 and tranny can be prepped in the garage while I can still get Sunday morning breakfast in the truck ;>).

 

Interesting that there is no timing cover with the 1960 engine. My 336 is reverse cooling and the front motor mount is on the timing cover. My understanding is that 1960 was the last year of the front to back mounts with anything newer mounting side to side. I haven't been able to find a 1960 timing cover yet for comparison.

You may have guessed that I am not a mechanic and didn't notice the difference in the heads. There are actually 2 sets of heads included with the engine.

Picture of the reverse cooling on the 336

 

The 60 front cover has the provision for the front motor mount. The trans in the pickup is a 4 spd dual range unit, while the trans w the 389 is a 4 spd dual coupling unit...not the same. The earlier trans will bolt up to the 389 with some judicious grinding on the crank flange.

 

I would keep the tri-power and find a 389/400 that it fits, you can always work out the engine/trans mounts.

 

More on reverse flow differences (and other good info) here:
http://www.pontiacsafari.com/EngineCooling/index.htm

1960 was a transition year, last year for the timing cover chin mount and the earlier transmission bolt/starter setup.
The 1960 timing cover is a single year item. There is a possibility that I may have a spare cover, would need to dig through some parts.

On the rocker arms, pushrod oiling should have holes in the rockers where the pushrod seats. Its hard to find correct replacement rockers for these early heads but the SBC rocker looks pretty close (but might need custom pushrod lengths and adjustable valvetrain). Later Pontiac rockers are quite different, as they changed the valve angles.

 

Listen grasshopper!

Pat

 

Yea, I see the light! I going to back out of the trade and maybe offer to buy the engine outright.

Thanks for the insight everyone.

Carl-

 

If your concern with the hydramatic in your truck is related to a too hard 2-3 shift...I believe there are adjustments at the carb and the bell crank at the rear of the intake manifold to control and adjust that...at least that's the case with mid 50's era Olds hydramatics. Others might chime in.

And I too would not trade the tripower for a pile of unknown condition engine parts connected to a dirty hydro.

 

It's only money (and your money, not mine) so here's what I would do...
Pass on the trade... he's after your tri-power with a lopsided trade. Run, don't walk!
Keep feeding the 336 cheap oil and go on the hunt for a rebuildable 389 (one of my favorite engines), front OR side mount. You can make mounts that can be easily removed to return the truck to stock configuration (think maximum buyer base in the future), same with trans mount (if needed).
School yourself (through Pontiac and GTO sites) on the TRUE value of your tri-power. You might get a pleasant surprise.
DON'T be tempted to install a BBC, SBC, MoPar, F*@d or Cadillac! The 389 is the right choice!
Rebuild what you find (it CAN be done without selling a kidney if you aren't going racing).
Take a deep breathe, make a plan, and don't jump unless you know what you're jumping into!
In the end you'll have a cool rig that hasn't been 'bastardized' and will hold its value better than a questionable swap, and a 389 has a higher cool factor than anything else you could put in there.
Good luck!

 

^^^^what he says......

 

Agreed. Seems there are some pretty decent deals at times when someone decides they need to “upgrade” to a late model fuel injected motor and pulls a good running old V8. I have a buddy that recently bought a 57 Pontiac 347 motor and transmission including a tripower out of a very nice restored car with very low miles for $1500. He will be using it in his Model A coupe hot rod.

 

The 389 would be a nice upgrade but worth less than the TP. The '60 front cover is about a $200 piece as it's the only "regular" or non reverse cooling system piece with the "chin" mount. Allows newer motor in 55-58 cars. Very desirable. You would need to retain the driver''s side exhaust manifold, at least in a 55-58 Car application.
Great project!
Or bore your 336 to a 347-370 CID.