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I have had this thought for a while and that is to bore and sleeve my 253 to 308.
The 253 in my HG is due for it’s 1st rebuild and is original to the car.
I have full CNC machine shop facilities and I can bore and make the sleeves myself.
My thoughts are boring to 4.250”, plus 001” to 002” interference fit with a shoulder/step at the top at 4.375” by .125” or .187” long. A liberal application of high heat resistant locktite, then press in, finish bore and hone to 4”inch.
I realise I would be boring into water gallery’s but the interference fit and locktite will give a good seal.
Before I get serious, is there anything that could burst this thought bubble?
Casting strength etc?
I want to keep the original block with the car but like the idea of a little extra grunt being it needs a rebuild anyway. She already has a quadrajet, factory dual exhaust.
Any thoughts? |
j.williams |
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Don't bother. You risk destroying your original block. Just keep it aside and find a 308/304/350 block. They are not hard to find. If you want to sleeve something buy one already 60 thou for next to nothing and sleeve it. You can use everything from the 253 other than the crank and those are cheap anyway. You'll buy a 60 thou red 308 short for a few hundred bucks.
What gearbox? |
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Trimatic.
If I was to go down that path, would I have to use a pre pollution date coded block to avoid any emissions hassles when changing engine number in nsw?
Back to my original thinking, I am confident enough in getting the machining right, it’s more about the if the 253 can physically have done what I am intending to do.
I can’t see anything that would make it unfeasible.
Maybe I am have missed something. |
j.williams |
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Just don’t use your original block, try on an old worthless 253 block. I’d have given you one but I threw them all away.
Just use a 308H, or QT or 11QT, no one would notice.
Biggest hassle will be finding a 4spd block, most around are TH pattern today. If you are going to deck it anyway during rebuild a 1983-7 308 or 304 block looks just like a 1973-77 block without its engine number. |
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Your probably right. Might be safer to use another 253H block. I would only lose a day of my time machining. If decking you don’t even have to restamp the engine number when using these modern cnc borers and mills. The original number can be interpolated with the exact same font which is a bit scary for the big high dollar collectables. Then again it’s only lazy machinist who machine the original number off in the 1st place. Definitely want to give it a go and see if it’s a workable idea. Edited by user Sunday, 31 May 2020 5:51:35 PM(UTC)
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j.williams |
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Don't use a 253H. Get a QR from a HJ-HZ or a HR from a Torana. They have the same block strengthening as HJ on 308, same as L34. Even a VR from a Commodore. |
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I didn’t know that, thanks for the advice. |
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I've got an old 253H block that's 60th plus a hone so she's only good for a museum piece. Block dates are HQ but was registered in my HT. I'm in n/e vic if you want a test block.
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The very late red blocks (from mid 1978) are actually XT5 (Blue) blocks. These have the longer valley bolt bosses, making them stronger again too. |
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Great idea. Looking forward to the results
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