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#1
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Help! Urgent rebuilding info needed
We are rebuilding a 400 for our circle track car and are very stumped about the bottom end assembly. we installed and torqued the crank and it spins nice and freely, then we installed the pistons and the whole assembly still rotated not easily mind you but still freely. however when we torque down the rod bolts the assembly gets progressivly harder to turn over until it is basically impossible. should it be this tight? i cant see it being easy with a fresh bore and new rings but i dont think the starter could even turn it over in its present state. any advice would be greatly appreciated as we are trying to have the motor ready to race by this weekend.
Thanks alot in advance P.S. for what its worth we are using the original crank and rod caps BUT we are using the pistons and rods from the original motor in the race car, but the macine shop bored the new block to suit these pistons |
#2
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you mixed different caps with different rods?? if so then that is probably the reason... are the bearings the right size? (.020 bearings on a .010 crank etc.....could happen, ya never know...) did you have the crank turned?
thats about all i can think of now...just sumthin to chew on...good luck! |
#3
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Are you checking clearances? Use plastigage! Also sounds like you have a bad rod or diff cap as pointed out before by 72roadrunner! But if your checking clearances this should be a problem!
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#4
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I did mix the caps from one engine with the rods of the other since they were both from standard sized 400's I didn't think that was a problem so I took the best crank and matched the rod caps with it. However as I mentioned the pistons and rods are from the other motor since they were 30 over. Should I switch back to the original caps for those rods or even switch back to the other crank? I will plastiguage it tonite too
thanks alot |
#5
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plastiguage is very useful as pointed out by 6 packin . have you had the rods reconditioned? you might wanna have a machinest do that. basically they make sure the cap+rod together are perfectly round. another thing to have done is to have the rods side-cut and clearanced by a machinest too.
just some more things to munch on!! |
#6
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Thanks for the suggestions so far, just a quick question though, how hard should it be to manually turn over the bottom end when all the pistons are in etc?
Thanks |
#7
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well, if it's built tight, but correctly, i don't think you should be able to do it by hand, but the starter shouldn't have any problems, and a breakover bar (1 1/2 foot long i think) should be very easy...just cause its so long...
mine was real tight after we put it together...i could turn it over with my break over bar, then when we put the heads on, it got even harder cause of the compression... as long as all of your clearences are fine, i don't think there should be a problem...but then again, i'm thinkin again... |
#8
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Your best bet is to get the rods recomditioned . you will probably never get all the caps back in the right places. even if you feel lucky enough to pull it off chances are you will spend the weekend after doing it again. good luck
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#9
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stop where you are!!!!!
The rod cap switch is FOR SURE the problem.
Rod caps can't even be turned 180, on the same rod. They must be installed in the exact postion they were removed. Rods are numbered to the hole, by stamping numbers on the side of the big end of the rod on opposite sides of the line between the cap and the rod itself. Stamped on one side(both pieces) only, so the cap will always be installed the same way. Dan's right, you'll never get them right again. Take the rods in to get them resized. The rod brgs may have to be replaced again as well, if you got them all torqued up. YOU MUST RESIZE. ALL OTHER CHECKS ARE IRRELAVENT ATTHIS TIME The rod size is VERY prescision machining. Measured in ten thousandths of an inch. As for turning over torque. A short block, with no heads, and new rings brgs ect, should have a rotating torque of about 5foot pounds per hole(40 pounds on a v8) easiy measured with a beam style wrench. |
#10
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Won't turn over?
Dave571 is straight on. Re-build rods or have trouble. You can NEVER mix and match rod caps without haveing them re-machined.
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#11
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Mind if I join the crowd??
Have the rods re-sized. |
#12
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rods
put the caps that belong to those rods back on, take it all the way apart and you can get the caps back on the correct rods by matching machining marks. as far as the amount of force necessary to turn it , a small block chevie with heads and valve train installed, but no spark plugs, takes no more than 45 ftlbs. to turn with a 1/2" drive torque wrench
as far as the rods you are dealing with, I would recommend re-sizing them. |
#13
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Thanks for all the great advice, I went home last night and found all the old caps in a box rematched them up with right rods and guess what, the engine turns over nicely with a breaker bar! Anyways I have another concern we installed the cam last night and I was wondering how much should it be able to slide around in there? I noticed that the service manual mentions a thrust plate on small blocks to control end play but there isn't one shown for a big block. We have it properly torqued in and it still slides around a bit is this o.k.? I never checked to see if the original cam had any slop in it before dissassembly
Thanks |
#14
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When you say you have the cam torqued in properly what are you saying? If I understand right you have the timing chain and gears all on and the cam gear torqued down??? As far as the thrust plate there is none for the BB. Yes when all is put together it will slide a little in and out but it wont come out because the chain is holding it back from slipping out all the way. There is a solid cam button that you could run if you are using a roller or a solid. It fits between the timing cover and cam gear.
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#15
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The Cam shaft on a big block is pushed towards the rear of the engine by the cut on the oil pump drive gear/ dist drive shaft. The back of the cam sprocket acts as a thrust plate.
Without the gear in, the cam will move quite a bit. After torquing down the rod bearings, with the wrong caps, I'd get new ones. |
#16
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If the timing gear stops the cam from rear movement, why would one of my cams pushed the cup out the back of the block?
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#17
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Don't know, but that's how it works.
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