Nop

After removing my DS inner fender I was finally able to take a complete inventory.

I have a '70 Oldsmobile Cutlass Supreme with a 4bbl 350, originally high comression/~310BHP

My numbers so far:

VIN:

342570Zxxxxxx: a 1970 Fremont car.

Engine:

3955582: "Heavy casting" 350
30Zxxxxxx: '70 Olds, Fremont, VIN matches

TH350:

70 JL172 D, apparently the right "JL" for my car.

Oil filler tube:

0223247, also apparently from '70

Intake manifold:

404520 casted at the rear

So far so good. Now the more suspect things

Carb:

Quadrajet 17054938, a post-70 (74?) Cadillac (#3) carb for an automatic trans?!?!?

Heads:

#8 heads. Nooooo! The 73-76 79cc heads with 8:1 compression ratio.

Didn't drive a lot of miles so far, the Cutlass is torn apart at the moment, but I'd say it doesn't pull like a >250HP V8, be it SAE horse power or not...

I replaced my worn, crudded and misfiring points with a Pertronix, starts way better already. I'll check my ignition timing as soon as the car drives again, but timing looks good for now.

What am I going to do next? I definitely don't want to tear the engine apart right now and to be honenst I don't even want to pull my heads - too many MAWs piled up already.

I know, "no pain no gain", but what smaller tasks can I perform while working on the car 1-2 hours a day?

* See if I can get a glimpse of my pistons to see what top shape they have. What do I look for exactly?
* Hope that only the original (#5?) heads were replaced with #8 ones? Why would someone do that?
* Get a pair of correct (#5?) heads?
* Any ideas on all the #'s? Something else looking suspicious?

Thanks, guys and gals

nsnarsk65cutlass

What #s on the block that will tell you if the heads have been transplanted.Someone on here will know as i don't.

Nop

Sorry, I don't understand what you mean by that?

The heads are not the ones that the '70 4bbl 350 came with originally, so they're transplanted.

nsnarsk65cutlass

I missed 3955582 on your first post then i'd say yes someone replaced the heads with later ones.Also carb 1705 #s are 1976-79 not sure on the rest 4938.

MDchanic

Photographs might help us to assess your entire set-up.

You can also look inside the spark plug holes with a scope to see the pistons - the should have a V-shaped notch on their front edges if they are high compression.

I don't want to think about how much it would cost to ship a pair of heads to Europe.

- Eric

Nop

So I'm looking for the low-dish pistons with a small V-shaped notch, 1st row middle picture?



What other pictures would you like to see?

Ah, peanuts!

What original heads would I look for? #5?

MDchanic

Correct. It's not hard to see with a bore scope or similar device.

- Eric

tru-blue 442

# 6's would be the correct
heads for 1970.

MDchanic

True, but from a functional perspective, 5s, 6s, 7s, or 7As should all work as well, if you are able to find any "over there."

- Eric

tru-blue 442

Agreed.

Nop

OK, my USB bore scope will arrive tomorrow.

Nop

Additional info: The intake manifold is a iron #10, casting 404520 - didn't find any info about it besides it is a standard '70 manifold.

Here we go:

Took a random shot at cylinder #4 with my new amateur gynecologist USB gadget, bingo:

piston4_01.jpg

piston4_02.jpg

Looking at the printed chart I posted this looks like a shallow dish to me. Plus one V-shaped notch. Do you agree?

Last question: Why would someone put the high-cc heads on? Afraid of horsepower?

MDchanic

Yes, those look like shallow-dish pistons to me, with the correct V-notch, but, boy are those pictures hard to see.

As for why change the heads?
Three reasons I can think of off the top of my head:
1.) Original heads were no good - loose guides, leaking, burned - and these were the cheapest / easiest replacements to find
2.) In the early 1980s, when there was no high octane fuel available, they were changed to prevent detonation
3.) Somebody wanted the #6 heads, and took them before selling the car.
Odds are you'll never know.

If you replace them with correct heads and correct steel 0.016" (0.4mm) head gaskets, you will probably need 100 octane gasoline (using the current European octane rating scale), but if you use a regular FelPro 0.043" gasket, you may get away with using 98 octane.

- Eric

Nop

Tilt your screen or stand up for better contrast... I'll try to get some better pics outta that awesome $12 device.

Nop

Good morning.

Does anybody have a nice pic of a clean HC piston crown? Yes, that scope is crap basically, but with an image for comparison it'll be easier.

Used 102 ROZ/88 MOZ (Euro) plus lead additive for the first two fills, as I assumed high compression. I'll stick with that.

So apparently there's no common cause I didn't know besides the obvious reasons, OK.

I'll have a look for 5/6/7/7_A heads then.

nsnarsk65cutlass

Hard to see but to me looks like a lot of pitting ?or detonation wear on the piston?

Nop

From the cam's live video that looks a bit clearer than the stills I rather think it's a thick flaky coal crud.



Circled a supposed chipped off flake of coal.

What seems strange to me is the gap between cylinder wall and piston crown - it looks rather large in relation to the bore radius?

Engine is running very very smooth though without rattling or any other strange sounds like .25 piston clearance

MDchanic

Yeah, as nsnarsk65cutlass said, it's really hard to say anything about the surface because of the photo quality. If everything is working well, I wouldn't worry about it now, and if you're going to replace the heads, you'll see them directly soon enough anyway.

- Eric