Hot Rods bought this vintage race olds 303 today

Any decent automotive machine shop can grab a piston ring catalog and match then up by bore size and a piston to measure ring grooves... not that hard to do

 

Jahns did sell some forged pistons but those are definitely sand cast. I know the HAMB is all about being traditional, but knurled pistons? Really?

 

If you are sure of the diameter of the pistons Jahns BITD used 1/16” top and second rings and the oil ring is 3/16”. Common stuff, sold everywhere.
Your 3.897 measurement plus .008 for piston to wall clearance suggests those pistons are for a .030 bored block.

 

I can work with that.

 

You have to remember, I live in L.A. There isn't a racer or machine shop anywhere near me. I'd have better luck trying too find and honest person here.

 

https://www.rossracingengines.com/

Tony knows Olds motors

 

Wow what a find! The heads have 10 cast over center ex ports. This means they are 1956 hds. Very sought after, bigger ports & valves.It might have a "hot cam" with solid lifters & maybe adjustable rocker arms. In my opinion piston clearance is extremely excessive .Years ago we ran the same cast Jahns in dirt track racers (50 wt oil) at .007" clearance. I think you will have a lot of compression blow by. You can try knurling them for a short life band aid fix if you are not going to make a street engine .I don't know all the answers,but I built my first "hot" Olds engine 1958 & Still running a hopped up Rocket in2020. A great find, have fun. Greg

 

I used to use EMS (Engine Machine Services) in Inglewood and Vellio’s in Lawndale when I lived in L.A. Both did a wide range of hot rod machine work. I would have the pistons and cylinders miked to get an accurate piston-to-cylinder wall number. Knurling will take the rattle out of the excess clearance but it won’t last more than 10-15k miles. That may be ok for a fairgrounds cruiser.


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Well, I was just told that no one has ever made replacement connecting rod bearings for 1949 olds, so I guess I will be moving up to 1950-1956 connecting rods.

Slowly getting it built, one concrete foot at a time.

 

That’s odd, Kanter, Egge, Speedway, no one?


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Those valve covers are cool, any more info on those?

 

nada

 

I bought that engine originally from the family of the original builder. It was listed here on the hamb by them, years ago. The valve covers are handmade and super light. Even when new they probably did about a 75% job in keeping the oil where its supposed to be. They probably weigh half as much as a stock tin cover...theyre super cool, early 60s period race stuff.

 

Very neat. Thanks for the info.

 

Instead of knurling, you might check into Line-2-Line coatings, they have a high build abradeable skirt coating that is also a graphite lubrication style sacrificial coating, that can do a pretty large clearance build-up. Much the same as what is coming on new production coated pistons.
Coat to reduce clearance more than needed, then the coating clearances itself in operation. A lot more stable than knurling, longer life too.

 

I second using this coating... we used it (or a similar product) for years with great results

 

Had to chuckle a bit looking at “terms” toward the bottom where it says COD (cash on delivery) have to have a few years behind you to know what that means in this day where most things are pre-paid or paid for with credit card.

 

Did you measure the pistons on the skirt or at the top next to the top sing groove? That could explain the excess clearance. Pistons are smaller above the top ring.

 

I'm going to drag my engine and pistons back to my machinist and have him properly measure my bore and piston, my tools suck!

I guess I need to find a set of 303 olds rods also since there are no aftermarket bearings for 1949!

 

This fellow has rods up in CO fwiw

https://denver.craigslist.org/pts/d/denver-oldsmobile-rocket-engine-parts/7226218522.html

 

Thank you