I learned something new today.



I learned something new today.

Postby Loves302Chevy » April 13th, 2015, 7:54 pm

Today I finally installed the pistons in my reconditioned 334 SB Chevy (.030 over, stroked 305). While installing the pistons, the camshaft was already in the block with NO timing set attached. After the 5th piston, as I gently rotated the crank around, it came to a stop. It turned out be that the shoulder of a connecting rod was hitting a cam lobe. I did not think that this was possible, since these rods have capscrews and a stroker design and all these same parts were run in this same block in the past. I installed the timing set and everything was OK. So if my timing chain were to fail, not only would the pistons smack some valves, but the connecting rods would hit the cam and break it in pieces. I guess this is another surprise with stroker combos. Does anyone know if this happens with a stock 305 or 350? Thanks, Mike.
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Re: I learned something new today.

Postby philly » April 13th, 2015, 10:45 pm

the few engines ive done, ive never put the cam in before the rotating assembly... im genuinely curious now too... as ive slid camshafts in i always rotate them as they go and on atleast one motor i have felt contact so that may have been what i was feeling. very good question i hope grumpy or someone with more engines under their belt than me can shine some light on this.
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Re: I learned something new today.

Postby grumpyvette » April 14th, 2015, 9:55 am

yes the cam lobes can very easily contact the connecting rods when the cam index is out of its proper timing, on almost any chevy engine the cam lobe center lines will be spaced at between 103 and 116 degrees, with the piston at TDC theres SUPPOSED to be about .060 MINIMUM clearance between the connecting rod bolts and cam lobes, this is a mandatory clearance check point and a plastic cable tie can be used to gauge clearance, its best done on each individual connecting rod to cam lobe clearance point AFTER the cams been degreed into the block as each connecting rods being installed but Ive generally done it during the several trial assembly points where I check other clearances like block to connecting rod clearance.
if you think about it the cam lobes will pointing basically up in the 180 degrees of rotation and be lifting the valves when the pistons are on the way up the cylinders, and point down toward the crank mostly when the crank throws pulling the rods downward,away from the top of the engine
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LOOK AT THE TWO REAR CYLINDERS
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thats why on some stroker crank engines a SMALL BASE CIRCLE cam is used to MAXIMIZE CLEARANCE,between the two moving parts.
a cams lobe lift is the difference the lifter moves off the cams base circle between its base circle and its max lobe lift, thus a cam with a 1.1" diam base circle and a .400 lobe lift would have a , .400 lobe lift and if you had 1.5:1 ratio rockers a .600 valve lift, but if you wanted more clearance you could use a smaller base circle at .900, and a 400 lobe lift this would allow the connecting rod, to sweep by with an additional amount of cam lobe to connecting rod bolt clearance, the change in diameter generally requires a swap to a stronger cam billet core . vs cheaper cast core,to maintain cam strength

removing the rod caps during clearance checks while building your 383 ,does seem to allow you to see the clearance issues a bit easier

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the cam rotates while indexed by the timing chain at 1/2 crank shaft speed , there are connecting rods designed to provide additional clearance.
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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: I learned something new today.

Postby Loves302Chevy » April 15th, 2015, 12:59 am

I was going to post some pictures, but yours are much clearer. With the timing set installed, I used a piece of insulated solid copper wire for my gauge that measured .100". I slowly rotated the crank and it stopped when the wire became pinched between the connecting rod and cam lobe. Because the wire is soft, I continued to rotate the crank as the insulation and wire were compressed and then released. I then measured the pinched thickness --- .060".
I didn't bother to check the other cylinders because these exact parts have been run before - same block, crank, pistons, rods and camshaft. Mike.
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