I am rebuilding a SBC for my '40 Chevy P/U. After taking the crankshaft to a reputable local machine shop to get checked out and cleaned up, I was told I need new .030 bearings. I am reading books teaching myself how to do this but after getting the bearings and crankshaft installed and the bolts torqued to specs (70 ft/lbs for a 350 V8), I cannot get all the pistons installed because the crankshaft will not turn. At all! It seems like the crankshaft should turn by hand just a little.
Before installing pistons, see how easy the crank turns. If hard to turn loosen one main cap at a time til it loosens up. The crank should be stamped rod undersize and main undersize. It is possible for the mains to be .030 and the rods another size. peace
Main caps for a small block are numbered & they have an arrow on each, make sure arrow points towards the front, I personally would never use a crank that was cut .030. Throw it away & buy a crank from Summit or other retailer
I do know that the arrows all point in the correct direction. I wish that a new one was in the cards but not right now.
main caps are numbered 12345 #1is front. arrows should all point to the front. Do you have the rods installed in the right position? If the machine shop installed the pistons on the rods are sure you are putting them in in the correct cylinder? Most machine shops install pistons in firing order but put in box in sequence. If this is the case you probably have some rods in backwards
Hi Maybe I can help you, if you can bring the block, caps, main bearings, and crank to my shop I will sort out the caps for you and set the crank and torque it - no charge I'm on San Fernando Rd. at Sheldon All Engine Machine 9358 San Fernando Rd. Sun Valley Ca. 91352 231-750-3429 Van
Take Vandy up on the offer!!!! It's one of the few sensible quotes here. SBC do not have the main caps marked with cast-in numbers. The crank should spin very freely with out any rods installed. If the caps are mixed up, any machinist worth their salt can figure it out. A little trick here and there. Rods don't give a shit which cylinders that they go in. Although yes there is a correct way to install the rod in relationship with the crankshaft. I hope you did not have rods in and torqued to 70. If you did, throw away the rod bolts and start over by having a shop resize the rods with new bolts. .030 under crank, with the correct radius in the fillet, no problem. Remember the old way to stroke the crankshaft, under cut with small journal rods???
I have NO problem whatsoever with a -.030 crank, I dont know where some guys get some of these screwy ideas.
Take the guy up on his offer for sure. Did you have assembly lube on the crank? The caps are almost assuredly mixed up. As a side note, don't torque the main caps on the crank until you have the rods installed. Yes, it should spin free with the rods out, but it is a lot easier to rotate the assembly without all the torque. As for the .030" crank, no worries, it is still useable. If the machine shop says it's cool, it's cool. Racers in the 60s and 70s used to turn their brand new Chevy cranks to .060 to reduce friction. I would have no issue with .030"
I've got a factory reman Ford 351 roller motor and it came with a 30 under crank. I asked my engine machinist if that was ok and he said they have even gone that far on really high hp motors with no problems. Don
I also agree that a crank properly ground .030 under is not an issue. I cant count the number cranks we ground from large journal to small journal... or 400 mains to 350 mains or all the cranks we stroked by grinding for a smaller dia bearing. Its not an issue as long as its ground correctly and has the proper radius
ive got a .030 crank in one of my sbc.and it sees some really high rpm.and i mean really high.and its still there.and its been there for awhile.
You need more than .001 on the mains. Second, plastigauge is not all that accurate, especially when youre down to a thou. Third, if you mixed the main caps up, and youre showing .001, the alignment may be a problem causing a bind. So, as someone said, take it to a good machine shop, line hone it and mic the clearances and get the correct bearings. While youre there, mic the rod journals and big end of the rods and buy the correct bearings. Good luck. The crank, when installed, should spin easily by hand.
Another thought, albeit a stretch. When they told you that the engine needed .030 over bearings, did they possibly say, or imply that the crank also needed to be turned .030 under? I'm assuming that the crank is already a .030 under crank, and if it is, there should be markings on the crank as pointed out earlier in this thread.
Get some Plasitgauge from the auto parts and check your clearances. Your machinist may run his stuff tight if so you will probably not turn the crank by hand when the mains are torqued. Anyway I never trust the machinist even if I am him. Check your clearances even if all you do is use plastigauge. Contrary to popular belief engines are not bolt together there are some things that need to be checked prior to assembly. BTW I run my engines pretty loose and I still use a *crank turner to assemble. * A little socket the slips over the crank snout.
Hats off to Vandy for offering to help! If the caps aren't numbered, you can match them up to the block by looking at the crosshatch on the inside of the caps and block. A little time consuming, but worth the effort. I think line honing the mains would be a last resort and expensive. A crank should turn very easily (1 finger easy) with the crank installed and torqued down. Don't go any further until you get it fixed. Larry T
If the bearings were torqued with the wrong cap, move the caps to their correct location but keep the bearings with the mated half they were forst torqued with. The shells crush some at the ends and can be loose with another half. Not enouth crush can allow them to spin or move around.
Years ago I got into the habit of turning the crank a full rotation or more after I torqued each main cap down and then again after I torqued each rod cap down. It's saved me a lot of headaches over the years. It might add five minutes or so to an engine assembly job but you know right when and where you run into a problem. I'd be loading it up and heading to Vandy's shop in a heartbeat. He can make sure that everything is right on it along with matching the caps.
Unless it is a forged crank, why bother using it if you can get a 10/10 crank polished & chamford for 129.00 from Summit
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