Riddle me this: 155K 'Survivor' 400/335 in '67 GTO - does it really need a rebuild?
 

The shop where the car sits now has done some preliminary testing, oil sampling, etc on my original 400/335 (TH400) engine.

Verdict - 190-210 lbs across the board in all the cylinders. Oil testing shows typical traces of iron, copper (not at fatal levels, but on par for the age.) Starts and runs fine, needs a splash of gas if it has sat for a while (> week to 10 days.) No smoke, either, not hearing clatter or rod knock.

Still, it feels soft... and oil is everywhere like an episode of Landman.

So to the question: yank it, re-gasket, clean up the heads, stab in a cam, or go the whole nine yards and do a full rebuild?

It won't be seeing the strip, but an all-day R/T to Norwalk or points west not out of the question.

Leaning rebuild, but these are tough old birds and that can sometimes create more issues (to say nothing of the cost) than it solves.

Let it fly...

It’s only original once ! If it runs good leave it alone

As
For needing a cup of gas that sounds like the well plugs in the carb leaking

155K, she's ready for her rebuild. R&R the trans and rear too. Then add another 100K.

I'm about to hit 140K on my 67 400/335. Original pistons. It had a valve job in the 70's I'd guess. I'm not sure if it was re-ringed/re-shelled (bearings) in the far past (I've had this thing for 38 years), but 15 years ago I performed a re-seal and took out the crank for inspection of bearings. Everything measured in spec. I scraped the tops of the pistons and the chambers of the heads, but replaced nothing except the timing chain, gaskets and a Best Gasket PTFE rope seal. I came so close to putting in a 068 cam, but did not because the original 067 cam and lifters (or whatever it is) are noiseless.
The pistons are a little noisy in their bores when cold, but it's as quiet as a church mouse when warmed up and perfect oil pressure. Yes it's on the creampuff/grandpa end of the spectrum, but what a great engine. Your description of your engine seems just like this one...it had good caretakers in the past and might just continue to run well with some minor TLC. I vote just clean up and re-seal unless you realy want more power.

Also, I've had great experience with my late model Quadrajet ('79 Olds). I rebuilt it to a Ruggles recipe, and the car can sit overwinter for 5 months and start up perfectly on two pumps of the gas pedal in less than 10 seconds. (basically enjoying the late model carb reliability with no evaporation or bowl leakage problems)
Good luck in your decision!
dave

If the rear main is leaking then pull it down to fix that.

Leave the pistons in and replace bearings if need.

That 4 bbl motor was built with Moraine 400 series bearings which are great bearings , so if they only show normal ware I would not hesitate to reuse them.

If it’s feeling weak even with your cylinder pressure readings then you need a new timing chain and gears also.

With that 155K on it I would also replace the O ring seals on all 16 valves and while your at it stuff a .030” shim under each valve spring.

If your running ethanol cut gas then it’s normal for it evaporate , if your motor is hard to restart when fully warmed up ( cranks ok) then your carb might have a fuel leak of some sort.

If it runs good, has great compression, with no noise, I dont see any reason to rebuild it unless you just want to.

Steel timing gear? Dished lifters? Wiped cam lobes? Worn valveguides, carbon-caked intake valves.

That's suspiciously high for an "original" engine. Are you SURE the gauge is accurate?

Easy. You pull the heads off to re-gasket...LOOK at the bores. Either you still see hone-marks at the top of the cylinder, and no ridge...or you pull it down. You yank the pan, pull a main cap and a rod cap, and the bearings are in great condition...or you pull it down.

For that matter, a borescope might tell the tale of hone-marks, depending on the resolution of the camera and screen.

It's a 60 year old Pontiac V-8 with 150K on the clock. It is worn. Worn out is in the eye of the beholder. It comes down to your personal goals. If you want a leak free, dependable driver to cruise around in on the weekends, I would remove the engine, clean it up and reseal the entire thing with a gasket set. The end result would be a reliable cruiser making 275-maybe 300 HP tops but would run just fine. Could probably accomplish this for $300-400. To do a proper rebuild, replacing all the parts to blueprint it properly back to like new condition would run 5-7 K to have it done by someone who knows what they are doing. The result would be the same engine making 340-375 HP using all stock castings and modern pistons and rings.
If you live in the Dayton, OH area and I think you do, shoot me a PM for an intriguing option where you can build it yourself for free, (labor), and have a great engine fresh off the dyno when finished. (assuming your over 55 years old).

Hard to imagine it not having blow bye. Also hard to believe it’s always had the proper fuel

If it’s still in the car at the shop have them perform a leak down test even if you have to foot the bill for a tester for them to use on it.

You will find it handy to have once you get it.

If that engine is out of the frame, then hone and rering, valve job, cam, lifters, bearing inserts, gaskets, and seals. Done. Many more miles of enjoyment.