Crankshaft and Block Work - 1954 Pontiac
I picked up a 400 sbc at the wreckers for $100. The 400 block was in poor condition with one cylinder quite worn from a damaged piston. The crank had spun 2 rod bearings which will need to be ground down.
Top rod bearing is spun pretty bad and 2nd from top was spun but is okay.
The block needed to be bored out 0.040" for the one bad cylinder. This gives a displacement of 409 cid. The crank rods were ground 0.020" and the mains had to be taken down to 350 size of 2.450" from the std 2.650". I'm using spacer bearings which allows a 350 crank in a 400 block. Usually used to make a 377 cid. I also painted the block black (2 coats) so that it would show off the cheesy accessories better. New cam bearings and brass water plugs were installed.
The block is painted black and very clean main bearings installed
The crank was installed, main caps torqued to spec with plastigauge.
I plasti-gauged the main bearings to verify clearances and found that bearing #1 (closest to the front) had a bad taper of 0.001" clearance at the rear of the bearing and 0.003" at the front. I measured it twice just to make sure that I didn't squeeze the plasti-gauge removing the cap. This means that the block needs to be align honed.
I cleaned up the plasti-gauge and oiled all the journals. Reinstalled and checked to see if the crank by chance would spin easily. Spinning easily are not the words I would use! It definitely needed to be align honed. So off to the machine shop it went.
Tip of the week: When mounting the engine block to the engine stand, don't try to manouver the block on a hoist when bolting to the engine stand. Remove the engine stand's engine mount from the base and bolt it to the block. You can easily align the stand's engine mount's 4 mounting bolts without fighting the weight of the block. Grease the pivot with Permalube or white grease so that it will rotate much easier. Then you just have to slide the stand's pivot back into the stand's base. It's a lot easier to position the pivot back into the engine stand then try to line up 4 bolts to a block hanging in mid air!
Align Honing
At the machine shop, the caps had 0.003" taken off and the block/cap assembly aligned honed. The block was washed and needs to be painted again :-( The shop Precise Engine Rebuilders had told me that I would need a "special" rear main seal that cost $33 because the block was aligned honed. I thought that this sounded pretty fishy as only 0.003" had be taken off which is only 0.0015" play per seal face. So I went looking for 2nd opinions about this.
Unique Main Rear Oil Seal
After 3 days of discussing this with about a dozen machinists, mechanics and partsmen and on the Internet newsgroups and getting mixed answers from "it was a crock of sh**" to "yes it's needed", I finally found out that it was indeed true and was unique with 400 blocks only. The 400 block has 2.65" main journals while the 350 has 2.45" - no new info here. But the 400 block uses the smaller 350 oil seal. The rail that the seal fits over is at the 350 size (2.45"). When they go to align hone the block, they have to open up the seal rail to 2.65" dia so that the align hone arbor will fit into the block. The problem that the special seal fixes is not the 0.003" align honing material that is removed but the loss of metal in the seal rail (close to 0.200" in overall diameter) that's needed to hold the seal in place. It is a problem unique to the 400 sbc block hence the high price and need for the special seal. The seal that I used is a Fel-Pro #2909 for bore sizes 2.8406"-2.8415".
When I got the block back, I plasti-gauged it again and every bearing was identical at 0.002" clearance and absolutely no taper. Cleaned up the bearings and lightly oiled them then retorqued the caps back on. The crank spun very easily, I'm one happy camper! I checked the rear oil seal using the stock seal and something looked definitely wrong like it didn't quite fit properly as it should since the seal rails are now 0.200" larger than stock due to the align honing.
My nephew Ben and my late good friend Mark who educated us on the right way to rebuild an engine
Cleaning the block
It's very important to thoroughly clean the block before assembling the engine. Up to this point I had test fitted the crank and once I felt that everything measured right, it was time to start some serious cleaning. The block has to be cleaned with soapy water (dish soap works fine) and the cylinders brushed clean. The cylinder boring and honing leaves a very fine grit (around 1000 grit) that will very quickly grind your bearings down. The block should be cleaned until a white lint free cloth has no residue on it. You have to dry the block quickly preferably with an air hose to stop surface rusting. The oil passages and lifter bores should be cleaned with a brass wire brush (steel brushes are a no-no as they will score the surfaces).
Nice clean cylinders and block ready for assembly