I've got a 425 block that i'm going to start building up. this block is already 0.030" over stock bore. Cylinder walls look like they are in reasonable shape, so maybe i can get away with cylinder align hone after crank mains are align honed and block is decked. o No: we'll see. however, what if the machinist has to go to 0.040" over bore to true everything up? I know pistons exist, but is this a reasonable thing to do with a 425? anything that might be tricky? (thinner walls getting hot, etc.) Thx!
Sonic test 1st!!!!! Even .030" over is a ????? In the factory manual they only recommend .010". Any 401/425 that I build I usually use an epoxy to the bottom of the big freeze plugs to add stability. DO NOT align hone or bore. Will have a forever lose timing chain. Spend the extra to have the bores checked before. Most machinists want to do things the easiest way. It's actually harder to accurately measure the bores than it is to align hone or bore & the reality of actually making things worse is a REAL reality. Most times you will see that it's a waste of $$$$. If you are having custom pistons made anyway have them lower the pin height to bring the piston closer to the deck rather than decking. This is just the beginning.
Thank you very much for the advice! What are you looking for in the cylinder wall thickness for a sonic test, >0.10"??? I can see how to manage compression using the pin height suggestion. What if the production block deck height is not square?
I think a friend of mine did his .60 over. Did he sleeve it? I can't remember His is a dual quad engine.
You would be surprised at how accurate the original machining was. On the last block I did which was a '63/401 the deck height was within .001 & the block square was within .002". The crank was within 1/4*. Close enough for anything but an all out racer.
My 425 is .030 over. The machinist said that was about as far as he wanted to take it. It works fine. I would however, take Tom's advice. He knows of what he speaks. Mine went the .030 out of necessity - three years sitting in a field on the ground is not a good way to store an engine!
My 401 had to go to .040 over, so far no problems. The only reason I went this way is because blocks are next to impossible to find up here in Canada, and importing one from the US costs around $1000 in shipping costs. I know because I tried. My engine is dead stock, and will probably never be raced. (Who the hell races Electras anyway?) It will get used, but never really abused. So hopefully it'll hold out for as long as I'm going to own it. However, if you want to do it right, take Tom's advice, he's about the third person I've read saying that Nails should never be taken over .010.
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I will join Tom is saying, dont hone the main saddles....it will do more harm than good....and in a border line case, I would lightly hone and reuse the same size bore before i would bore it too thin.... a block is good for just so many rebores....or if you have mega bucks you can sleeve all 8 cyls.... or find another block....
I guess I stand corrected; - there are people who successfully race Electras. I loved that clip of that 66 4 door hardtop dusting that Monte. I wouldn't have thought it possible. Thanks for making my day!:beers2:
Block is in for sonic test - we'll see... What are the specs for crank saddle alignment? +/-0.001"? If the crank saddle alignment in the block is out by a few 0.001", will align honing this amount of material adversely impact the timing chain? What is the limit before timing chain slack will become a problem? ).005"? 0.010"? Thx!
The 425 block is through hot tank, magnaflux and sonic test for cylinder walls. Machinist definitely thinks the cylinder walls will require another 0.010" to clean-up scouring in the bottom of 3 cylinders. Lowest wall thickness was 0.112" in the bottom of a cylinder, non-load side. Most of the walls are at 0.130". 0.040" overbore will maintain thicknesses of all cylinder walls above 0.100". Any problem with wall thickness close to 0.100" on a 425 NH??? Thx!
Because of the weight of the reciprocating assemblies in our "Nails" no wall should be thinner than .150". Anything thinner & the bottom of the cylinders start flexing. As you can see even the original bore was kinda iffy. i would still use the epoxy to the bottom of the big freeze plugs. All this will do is give more longevity to the engine since less movement is being made the rings will last longer, hense the longevity part.
Those wall thickness numbers are a little scary. I would fill the lower water jacket areas for sure to help support the cylinders. All the heat is in the area of ring travel in the cylinders. (I have a Supercharged Flathead Ford Dragster & I filled the entire Waterjackets will "Hard Block" filler to support my thin 3/8ths over cylinder walls / I only run 1/4 mile at a time so engine does not get too hot) I use Sonic checking equipment at my work (I'm a QA Inspector) The Accuracy while checking wall thickness is very touchy. If you hold the Probe incorrectly when checking a round surface you will get alot of variations in your readings. The special Checking fluid can also cause inaccurate readings if too much or too little is used. The potential for some human error is always a factor. Lets hope the readings on your block are a little off, but towards the safe side. I find it hard to believe the factory blocks are that thin.(.150 Maybe) They didn't have the modern "Thin Wall" Casting technics in the early 60's. Core Shift in a spot IS possible. Unless the water jackets are really corroded, like from a previous life in a SALT WATER Boat I bet your at least safe for a street engine. My 2 cents, Kevin K.
Buick started with the thin wall casting process in 1957. On the old LT block we had been running & having major leak-down problems with. After re-ringing would be OK for about 25-35 runs then the bad leak-down would be back. Finally Sonic tested & had some cylinder walls nearer the bottom of the Cyl. Valley side, that were only .090" thick. This was with only a .030" overbore. Especially in the later years of the "Nails", around '61 or so core shift was a MAJOR problem. Nothing was done about it as the new series of engines was going to be coming out shortly, '67, but this was started around 1959.
There was a guy on the Yahoo group (Paul) that had his 401 sonic tested. Wall thickness on the standard bore ranged from 0.180 to 0.300. Average was around 0.230". and Steve had his 64 425 sonic tested (4/3/2007) and it was even thinner...
Ok, turns out there was a communication problem on the actual sonic test measurements. Lowest reading for a loaded cylinder surface was 0.112" near the bottom of cylinder #2. Lowest reading was 0.098" on a non-load surface in cylinder #4. So, 0.040 over std will yield 0.107" wall thickness in a load region (bottom of cyl2), and 0.093" for non-load surface. Machinist insists that the block will not work in current condition due to high degree of scoring in 3 cylinders. Also says the scoring in the lower region of some cylinders is significant so bore to 0.040" may not be enough to clean the cylinders for ring travel. Current testing is at $300 (hot-tank, magnaflux, sonic test). Not sure if it is worth continuing with this block given the condition and all the warnings regarding over bore. Disappointing, feels like throwing money down the toilet. Expensive lesson. ou: The machinist suggested honing the worst cylinders 0.040" over std. to see if they will clean-up enough for ring travel. Lowest ring depth will depend upon eventual CR and piston design - can anyone offer a typical number for ring surface depth in one of these engines? Thx,
Blocks are fairly scarce; there's a number of them around here but who knows what condition they're in. I'd be asking how much the guy wants to sleeve the three worst cylinders and then bore as needed to suit the fourth-worst.
i would find out how much it would cost to sleeve all the cylinders. then you would know the block is ok. as stated before those blocks are hard to fine in good condition. jim
Your not reading replies. Fill the bottom of the block with an epoxy to stabilize the walls & add some strength. It will be less than an inch & will NOT affect cooling. Problem is internal coolant areas in block need to be spotless. I use muriatic acid. Does aGREAT job.
