After a good deal of consideration, I'm thinking of changing out the std 8:1 pistons for a set of std bore 9.75:1 pistons and rings with a minimum of work, as in, not pulling the motor down, except the bare minimum to change the pistons and heads in situ.
I will of course check anything I can get to in the process and replace if necessary.
I have been working on a pair of small valve C heads to swap the J ones out.

The 4v 455 has done around 125K miles. It has good oil pressure, doesn't blow any smoke and a compression check revealed all 8 cylinders show reasonable std compression with minimal variance. I've had the rocker covers off and inside was clean with no sludge deposits. It has had an easy life, I'm guessing just loping along.

Is this a viable way to go on the cheap for a few more pony's, or am I heading for trouble with the 455?

I've done this before with other makes and not had any issues.

Waddaya rekan?
.

 

The Olds is no different from any other motor in this respect, but with 125K, the MIGHTASWELLS will really kick in. You'll need to hone the cylinders at a minimum. You MIGHTASWELL put in new rod and main bearings. You definitely need to change the timing chain if you haven't done it yet. You will almost certainly need valve seals. There will never be a better time to change the oil pump, either.

You get the idea.

 

Thanks Joe. A hone, timing chain and sprockets, Toro pan and rod bearings is what I had in mind as a minimum.
I'll check the big end bearings, but if every thing is within spec I'll leave it. The oil pump will be swapped out as I'm changing the pan.
The C head I've been playing with has new seals and valves lapped in.

 

Ok ready to do this.
I want to take the 455 back to pre smog spec and performance levels. I don't want to pull the whole thing down, or spend more coin than necessary. The car is not going to see the 1/4 mile.. I just want.

So, any recommendations on pistons and rings?
These seem to be what I'm after, according to the ad; (size will depend on what I find)

OLDSMOBILE 455 PISTONS+RINGS KIT
This listing is for a set of eight (8) standard bore Sealed Power cast aluminum pistons and moly piston ring set (Hastings/Perfect Circle/MAHLE) for 1968-76 Oldsmobile 455ci V-8 engines with 4-barrel carburetor. P/N (8) 369P+40141CP. Piston specs are as follows:

STANDARD BORE: 4.1250"
HEAD TYPE: Recessed head .120" deep x 2.940" diameter
RING LANDS: 5/64"-5/64"-3/16"
COMP. DISTANCE: 1.725"
PIN DIAMETER: .9806"
NOTES: 9.75:1 CR high compression w/4 Bbl. carb.

How do you buy gudgeon pins for these, measure the rod bearings and order them to suit? I'm guessing I'll have to replace those as well.

I'm replacing the J heads with a pair of rebuilt small valve C heads.
Is there going to be an issue with valve clearances when I put it together?

The cam part number in my '73 looks to be the same for the earlier 455's pre smog, so it stays.

I'll fit a new water pump, timing chain&sprockets, inspect the bores and hone, inspect and measure the big end journals & replace the bearings, same with the mains.

Cant get hold of a Toro sump so I'll leave it and just replace the oil pump.

I have dual exhaust running to the rear from the stock manifolds now. (blocked off the crossover hole in the pass side)

Stock 800cfm QJet and 4bbl intake stays for the time being. Is there any benefit in using say, an RPM Airgap inlet?
It has to all fit under the hood with original aircleaner (I have modified it a bit for improved airflow)

The whole thing needs to look original for the stupid laws here.

New gaskets on anything I take off. Any thoughts on head gaskets?

Am I missing anything? going to pull the top and bottom off next weekend.

 

Do not buy a stock oil pump with the pressed in tube for pickup.Buy a bolt on type pickup Mildon pump.There have been plenty guys who lost oil pressure and some who lost the engine to oil pressure failure.JMO

 

Keep in mind that those pistons are .010" shorter than the factory pistons and therefore will result in slightly lower compression than expected.

Are the C head chambers any smaller than the J head chambers? They come from the factory with the same size. Have the C heads been milled any?

Just guessing combustion chamber volume about 82cc, piston-to-deck clearance at .025", head gasket .040", and the dish volume in the new pistons 19.4cc, I calculate right at 9.0:1 compression ratio. And that is not factoring in the .010" shorter pistons.

 

Thanks Ken.
C combustion chambers are probably a bit smaller, heads have been milled about .008 thou.
Should I look for a set of pistons closer to the factory piston height? Not sure what TRW/ speed pro pistons measure, any others I should consider?

I could re machine the heads a bit or is that going to stuff up valve clearance?

 

How do you buy gudgeon pins for these, measure the rod bearings and order them to suit? I'm guessing I'll have to replace those as well.
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Wrist pins should come with the pistons, they have to be individually fitted to the 1/10,000 inch. Not a mix-n-match item that you buy anywhere.



I'm replacing the J heads with a pair of rebuilt small valve C heads.
Is there going to be an issue with valve clearances when I put it together?
===============
No but plan on carefully verifying your lifter plunger preload and adjusting accordingly, what with so many changes to the cam/valve positioning relationship- different [shaved?] heads, different gasket, valve job altered valve stem position, etc.



I'll fit a new water pump, timing chain & sprockets, inspect the bores and hone, inspect and measure the big end journals & replace the bearings, same with the mains.
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I would recommend a ridge reaming. Typically the Olds V8 does not develop a huge Chevesque ridge, but neither is it zero thousndths of an inch. You do not want the new pistons and rings hitting the old ridge. An hour or two well spent.



The whole thing needs to look original for the stupid laws here.
================
Huh, who gets to decide that? What do they do, look for "Edelbrock" on the intake? Grind it off. Make "OLDSMOBILE" letters and apply them. Voila' it's a factory part.



New gaskets on anything I take off. Any thoughts on head gaskets?
=================
I recommend 'em
Have used them on every engine assembled, with no complaints yet.
:-)
I will let others specify which ones are good to use at this time.

 

2.94x2.94x.120x12.87 is 13.34, not 19.4, sorry.
Couple that with a .027 gasket or so and you'll be much.closer to the original figure of 9.75:1.
And stock C's are better than J's because the intake throat doesn't neck down like the J's do.
And I agree, use the regular Performer, NOT the RPM.

 

You know what they say about free advise.

Since your not going to rebalance the rotating assembly,?? I would make certain to get the piston assembly weight as close to the stock assembly ( rings, pins, piston) as possible.

 

If I'm not mistaken, deck height on a 455 big block is 10.625 and rod length 6.735. Combine that with a comp distance of 1.725 the pistons will be .040 in the hole. Using the 13.34 cc head and .027 gasket info that Cutlassefi provided, my calculator comes up with 9.47 to 1 ratio.........

 

Hmmm, yeah. Same calculations but 13.34 cc dish volume = 9.3:1 compression ratio. Use thinner gaskets and it bumps up to 9.53:1. The actual combustion chamber volume will have an impact on the CR.

 

With the stock smog cam, he probably doesn't want much more than 9 to 1 anyways.