I have a 14 degree Dart Olds headed aluminum 632. It has Babbitt 55mm cam bearings and an aggressive profile. The spec’s are: 117 lobe separation, duration @50 284 I 310 Ex., lobe lift is .524 I .485 Ex. and using 1.75 rocker ratios. Gross lift is .917 I and .849 Ex. The problem I am having is, the engine is very hard to turn over, even with the spark plugs out.
Without the rockers on the torque at the crankshaft is 20-25 lbs. With the exhaust rockers bolted on it’s 90 lbs and with intake and exhaust rockers on it’s a bit over 150lbs. The engine made ok power at 1136 on the dyno but I would like to get some of you experienced engine builders to chime in with where to look to find the problem. To me it seems as if there is a spring bind thing going on but I am using the PSI 1248 springs and the installed height is 2.100.
Some people tell me this isn’t so unusual, and some say it is terrible. I tend to agree with the terrible part. That said, I haven’t checked the torque until this weekend and find it to be awfully tight. What concerns me the most is that it could put too much tension on the timing belt. Any help would be appreciated.
The 1248 is good for .900 lift. Have you looked very close at the intake springs at max lift?
Abbott Racing Heads
Yes, I have looked but will be looking closer this weekend with checker springs.
Theoretical lift and actual lift can be two different things so you need to check it. Also as stated those springs are rated for .900 lift @ an installed height of 2.100" so you need to check that also. When checking for coil spring bind, check each coil separately.
If this is not your issue, then check the cranking voltage at the starter, needs to be at least 9v cranking.
I will check it with a dial indicator this weekend along with installed height and spring mic. I have already done that but I am missing something.
That 1248 spring has a coil bind number of 1.130 and the gross lift on the exhaust is .849. That shouldn't even be close enough to coil bind set up. I will need to check and be sure what actual installed height is and gross lift numbers.
given your intake lobe lift, minus .025 lash and .015 deflection, .877 with an accurate 2.1 installed height you should end up with about .093 or so of space.
Triple springs with 375/ 1050 will surely be hard to turn over.
|DRR Top Comp
You can't turn the engine over by the crankshaft, The camshaft in this sbc is bigger, this engine won't turn over with more than one intake and exhaust rocker by the crankshaft. We made a tool for turning the engine over which bolts on the flywheel.
That's normal, don't ring the crankshaft bolt off in the crank, trying to turn it over front whatever you do.
High spring load/babbit bearing... Nature of the beast.
I'm going to check the installed height on every spring, check the actual lift at the valve, and after that if all is good I will sell it. I just didn't want to sell it if there was something wrong with it.
BBC Big Block Chevy Crankshaft Crank Key Turning Socket Tool 396 427 454 7.4L
Illegitimi non carborundum
I need to get one of these, thanks!
I would like to see a picture of the tool, if possible.
|DRR Top Comp
Good way to break the key way off - no torque
|DRR Top Comp
Think flywheel tool, make it as bad azz as you like. Pulling from the outside of the flexplate makes for plenty force.
Imagine the starter turning a gear keyed crankshaft snout.
If the engine has bushing style lifters they increase the turning torque greatly.
It does actually. I would have thought it wouldn't be as much torque to turn it.
|DRR Top Comp
The camshaft requires 1100, 1200, maybe 1300 open spring pressure.
Our sbc is 1400 plus.
A regular flexplate tool will turn it fairly easy.
Keep your teeth out of way.
Holy crap, It is a friggin everyday 632 with a .500 lobe stick.
1000 is plenty, and depending on rpm usage, which looks to be 74-7600 it does not need a 1400 pound spring.
Posting pictures of a SPECIALIZED non bracket race SBC does nothing to help the guy, much less help him.
Obviously he is not even close to being experienced as people are posting pictures of a crank socket, to which he has never seen.
Do not send him off into oblivion with stupid posts.
For your information, I've seen one and have something that works better. I don't have a 1300 lb spring pressure over the nose. I am not new to this, just to GM stuff. I can't believe they design a race head, an ex Pro stock for that matter, with a 2.100 installed height. All my Mopar stuff was more than that. I'm just not an everyday engine builder and never had something that was this hard to turn over so was asking for help deciding whether or not something was bound up. I appreciate people's opinions, even yours but no one is sending me into oblivion.
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