coled18

Hello everyone,

Recently I rebuilt my engine but overheated it and scorched the cylinder walls and damaged the rings a bit. Now it takes forever to start and blows a little oil. It is also starting to make a ticking noise right after I replaced the cam, lifters and pushrods. I am looking at doing a complete overhaul this winter and overboring the old block to a 355. The block isn't damaged to my knowledge. Have you all ever over bored a SBO 350 and if so do you all have any information on how much this would cost? It seems like all the internet has is SBC kits...

oddball

Extremely common. Most 350 blocks can be bored either 0.030" or 0.060". Pistons and rings in both sizes are commonly available. Just search for Olds 350 parts and the oversize variants are usually listed next to the stock size. Don't search on the new displacement size - that nomenclature isn't really used by the industry.

As for cost, well, It Depends. Basic machine work (clean, bore, hone) is probably $300-$400. The shop needs to install the pistons (<$100). A stock-type set of pistons and rings should be <$200. The noise might be damage to main or rod bearings, which would mean grinding the crank and new bearings. (~$300-$400) New bearings are probably a good idea regardless (~$200). Are you doing the assembly yourself or paying the shop? Rates vary, but that can be another $200.

The first $1,000 goes really really fast. A basic rebuild should cost less than $2,000. Yes, things can be done cheaper, I just consider those realistic budgets to watch out for all the little gremlins that pop up.

olds 307 and 403

What year 350? What compression ratio and performance are you looking for? A couple of my cylinders would not clean up to the 4.065" hone only size available from CP and Mahle, so I went with the Mahle 4.100" piston.

OLDSter Ralph

Why did it overheat ?

Fun71

When buying pistons, take careful note of the piston dish and compression height. The readily available rebuilder cast pistons have HUGE 24cc dishes and are .030” or so short on compression height, which results in compression ratio in the 7.xx:1 range.

cutlassefi

^^^^^^^^

coled18

Great question! I was just stupid about rebuilding it. I didnt put enough coolant in the radiator. Perhaps the last possible thing I could've messed up on.

coled18

Thank you, this is the kind of info I was looking for in terms of tips and tricks. Much appreciated.

coled18

Its a 1972 block, looking for around 10:1 compression. Nothing too crazy but something decent. I have an Edelbrock 7111 intake, and a holley 600cfm. Aftermarket cam, but Ill upgrade the cam once the new pistons are in. I also need a decent pair of headers as well. Do you think stock heads and non adjustable rocker arms would work?

coled18

Tracking! In your experience do you think aftermarket heads would be a must buy if I overbored the old block? If I had the time, I would typically do everything myself but for the sake of contingency Ill plan on paying for labor as well.

oddball

Aftermarket heads are not a must.

Pros:
Can run higher compression since they're aluminum
They generally flow better than OE heads
No exhaust crossover!
Price can be a wash between setting up aftermarket heads and refurbishing OE heads, sometimes it's even cheaper to get aluminum heads ready to run than fixing up OE heads.

Cons:
All current aftermarket heads have the large big block chamber, so need to plan appropriately to get the compression ratio back down or cut a ton off the deck of the head
Can't use a mechanical pump on a small block

e.g., I kept my 7a heads on my 350, but switched to Edelbrock on my 403.

If your current heads are in good shape then I'd just leave them as-is, especially if you're just trying to do a refresh.

Do double check all the valves and valve guide clearances. I've had trouble with OE heads with the middle exhaust valves seizing because they were too tight, then sticking open, hitting the piston, etc etc etc. After that my preference was to keep OE guides a little loose and just accept burning some oil.

But if the option is trying to get a set of old/core OE heads freshened up vs going new, well it's a good discussion.

oddball

Generally no. Almost every aftermarket cam has a smaller base circle, throwing everything off.

But, the Comp adjustable roller tip set is extremely affordable. Throw away the pinch nuts - use poly locks - and throw away the pushrods - measure to get the right length, then buy a better quality pushrod. I've literally bent a dozen of those noodle pushrods they put in that kit. And for anything street that roller tip kit is perfectly acceptable.

I went to the Harland Sharp on my latest generation mostly just for giggles. And they're pretty.

olds 307 and 403

Good call on checking the valve to guide clearance, I believe. 0026" is the minimum on cast iron guides on the center exhaust ports, on unfilled heads. My fresh #6 measured .0028 to .0030". I would have never guessed to check that measurement, this site is very valuable. Basically you are looking at Speedpro forged pistons if you need 10+ to 1 without excessive milling and decking. Those pistons sit further below deck than modern pistons, so around a .025" milling for 0 deck. Unless your block can clean up with a hone, then CP has a 4.065" bore 1.5mm ring pack piston as well. The Speedpro are a very old design, thick rings and heavy but durable. You need an additional .0045" minimum of piston to wall clearance. The 10cc dish 4032 alloy 1mm ring pack Mahle forged pistons require .0025" minimum of clearance, .0035" on an all out race motor. Getting 9.6 to 1 with your 72 block and heads is easy with the Mahle pistons. The Mahle pistons sit .013" below deck, my deck needed cut .016" to straighten. With Felpro Blue .042" compressed head gaskets, it leaves a perfect. 039" quench. With 68cc heads, that gives 9.5 to 1. It will depend what your block will need. Hopefully the new small chamber Edelbrock heads come out by spring. Also seriously consider a 750 cfm carb.

BillK

Just want to say that you must have some awful inexpensive machine shops in your area

And I seriously doubt that you will find a set of decent cast pistons for less than $200... pistons only.

Just don't want the op to be shocked when he gets real prices.

olds 307 and 403

There is no good cast pistons for the Olds 350, unless 7 to 1 compression is the goal and 4000 rpm is all you plan on. Even the Speedpro forged pistons with rings are $500. The really good Mahle pistons are $650 for pistons, pins, locks and rings. The CP are even more money.

skyhigh

I think you guys missed that he has a 7111, so wouldn't that require alum heads and or port work? get that wallet out, nothing will be cheap.

cutlassefi

No, you can use the 7111 on irons or aluminum without touching it if you want to. I just did it on my mule.

Fun71

Same with my engine using factory iron heads.

skyhigh

How much HP is lost due to not having matching ports do you think?

olds 307 and 403

Dave it is more the lower flow through the iron small block heads, or lack thereof. There is enough material on the 7111 to match factory BB or the current aluminum heads. I believe the small block iron have about 10cc smaller runners than the 177cc Edelbrock. The new Edelbrock flow about 50 cfm more on the intake side and about 25 cfm on the exhaust side than early 350 heads with W31 valves installed. It will be interesting if they keep the SB sized opening on the final Edelbrock head.

cutlassefi

You’ll see when I post the Dyno sheets. Three different manifold combinations with the new SB head.

deadeyejedi

are they all aluminum intakes or did you use an iron intake for testing on the mule?

cutlassefi

All aluminum.