425 Engine Wear - What is Normal

J

JZRIV

Member
I am trying to confirm mileage on a 425 nailhead in 66 Riviera GS. The seller stated 27k when I bought the car and I assumed 127k. Much to my disbelief, I started to notice some signs it could actually be 27k despite its neglected condition on the surface and I figured tearing the engine down could shed light on the true mileage based on wear. I have some experience with 430s and 455s but none with the nailheads. Can a 100k mile swing in mileage be accurately determined by documenting internal wear?

The factory diameter spec on the bore is 4.3125. I measured 4.313 at the very top 1/4" where the piston ring does not touch. I took measurements in 5 locations in each the cylinder. The highest measurement at any point was 4.316 in 4 of the cylinders with the average being 4.315. This equates to average of .001 to .0015 on the cylinder wall itself. I have not miked them yet but there was no visible ring groove land wear on the pistons.

The rod bearing clearances were dead on factory spec of .002-.0023. Is that possible with 127k assuming good maintenance.

Appreciate any assessment from those who have experience on these engines. Thanks

Jason Z
ROA 775 BCA 29701
 
if you've got the car, check the condition of the foot pedal pads. <30k, they should look almost brand new. >100k, they'll be worn almost flat. this would also apply somewhat to the seat upholstery and carpet although those can take sun or water damage that make them look more 'used' than they actually are.
 
Also since it is a 425 it came in a car that has "brake reaction rod" bushings. These will be worn, or just replaced if the car has over 100,000 miles.
 
It's a rod that runs from the lower "A" frame to the front of the frame.
I have torn down many 401s and 425s, and by the time that they reach 100,000 miles to 120,000 miles they are worn out even though they sound OK when running.
 
The brake pad has some wear but not enough either way to say for sure. If it was mostly 127k highway miles I'd guess the pad wouldn't be worn much but if it was all city driving at 27k there could be some wear.

I did check the brake reaction rod bushing as well as the upper control arms and they both look good. The upper control arm bushings are dried out but not worn to one side like I would expect if over 100k.
Normally its not hard to tell 27k vs 127k mile cars but this one has seen so much neglect on the interior and exterior surfaces its making it difficult.

I also inspected the wide aluminum rocker moldings and while there is a couple larger dent type damages I'm not seeing the 1000s of small hits from little stones that I would expect to see...... but I am more used to seeing cars from the east. This car was from the Sacramento area so maybe the roads are cleaner.

It has 4 original working T3 headlights. One of the mufflers is the original date stamped 2-66. The driver seat bottom upholstery and foam does not appear to be flattened or worn smooth. There is some wear on the driver seat piping. The door pulls appear to be lightly used but again if the miles were all highway, that does not mean a lot. Thats why I was hoping to determine something from engine wear.

Normally I would still lean towards 127k but I am finding it very unlikely for there to only be .002 max of wear on the cylinders. All facts I have accumulated so far indicate it should at the very minimum be double that and most likely quadrupled.

The block is going to the shop today and I'll see what they have to say.

Thanks for the replies.
 
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