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Old 07-07-2009, 11:21 AM
GMR GMR is offline
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sbc pushrod length using stock rockers

I've read lots of info on checking pushrod length when using roller or roller tip rockers. I've built 2 sbc's using those procedures and they seem to be doing all right. Now I'm building another, only this time using stock stamped steel self aligning (RHS vortec heads) shoe type rocker arms.

I can't find any writeups on a procedure for determining pushrod length when using stock type rockers. I understand that during normal operation the hydraulic lifter will self-adjust to compensate somewhat.

I've tried using the roller rocker type method (i.e. witness marks on the valve tip), but wondering if this is valid.

I have a 350 decked to 9.00", RHS vortec heads, screw in studs, Comp 268H cam, ROL head gasket (bolts torqued to 5 lbs, measured gasket thickness uncompressed as .050), GM stamped steel self-aligning 1.5 rockers, Comp solid lifter for checking purposes, adjustable pushrod checker, LT1 springs.

Using a dial caliper to measure the checking pushrod, it seemed that 7.950 and 8.000 length pushrods yielded a centered, but very wide, witness mark on the valve tip. These two pushrods also yielded the most lift at .441 and .445 respectively (cam is advertised as .460 lift).

I can get more lift with a longer pushrod but the witness mark seemed too far towards the exhaust. A shorter pushrod yielded less lift and the mark was more towards the valley.

I'm thinking a shorter than stock pushrod would be expected since the block is decked and the heads are closer to the cam centerline. So I'm not sure about my testing conclusions.

Does this sound reasonable or am I out in left field? Am I making too much of this, should I just put in stock length pushrods and let the lifter compensate.

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Old 07-07-2009, 05:21 PM
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I can't find any writeups on a procedure for determining pushrod length when using stock type rockers. I understand that during normal operation the hydraulic lifter will self-adjust to compensate somewhat.

...........I fail to see how the lifter would care what type rocker is being used. You're using a solid lifter for checking. The distance from the pushrod cup to the face of the lifter body should be the same as an operating hydraulic lifter for the same motor application.

I've tried using the roller rocker type method (i.e. witness marks on the valve tip), but wondering if this is valid.

..........Again, I fail to see how it could differ from roller rockers to stamped steel rockers. A rocker is a rocker is a rocker.....

Using a dial caliper to measure the checking pushrod, it seemed that 7.950 and 8.000 length pushrods yielded a centered, but very wide, witness mark on the valve tip. These two pushrods also yielded the most lift at .441 and .445 respectively (cam is advertised as .460 lift).

.............I seem to remember reading something by Racer Brown years ago that said the radius of the rocker tip on a stamped/production-type rocker is 5/8ths of an inch (0.625"). If this were a roller tip, the diameter, therefore, would be an inch and a quarter (1.250"). It makes sense to me that a roller with a 1.250" diameter is going to make a wider mark on the valve stem tip than a smaller roller-rocker-arm roller.

I can get more lift with a longer pushrod but the witness mark seemed too far towards the exhaust. A shorter pushrod yielded less lift and the mark was more towards the valley.

...........Center the witness mark and move on.

I'm thinking a shorter than stock pushrod would be expected since the block is decked and the heads are closer to the cam centerline. So I'm not sure about my testing conclusions.

...............Your thinking may be correct if you were using the same cylinder head on the motor in both instances, but you're not. Without extensive measuring, you do not know for sure if the dimension from the valve stem tip to block deck on these heads is the same as the production heads that came off the motor. Variables could include valve seat to head deck measurement and valve length.

Does this sound reasonable or am I out in left field? Am I making too much of this, should I just put in stock length pushrods and let the lifter compensate.

...........Again, I don't understand your pre-occupation with the lifter. A hydraulic lifter, during operation, will have very close to the same dimension from lifter face to pushrod cup as the solid lifter you're using for checking. Yes, I think you're making too much of this. I'm sure someone sharper than I am will chime in if I'm overlooking the obvious.
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Old 07-07-2009, 06:12 PM
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GMR, by your description, if I was putting it together, I would use stock length push rods. I see no reason to worry about the deck height. After the lifters pump up, you should be closer to the advertised .460 lift.
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Old 07-07-2009, 09:17 PM
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You know, I struggled a bit in trying to word my questions correctly - I knew I had questions, just wasn't sure how to express them. Anyway, thanks to both of you for wading through. Your responses are very helpful.
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