Pushrod length after cam change
March 14th, 2018, 02:50 PM
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Pushrod length after cam change
Hello folks, I have a stock 1968 Toronado 455, I changed the camshaft to a Comp Cam 260H grind number camshaft (part number #42-228-4). I am using new Comp Cam OEM style replacement lifters, OEM replacement rocker arms and brackets. I have an adjustable push rod to measure for the ideal length. I have measured for push rods before on small block Chevys but never on a big block Olds. Since the 455 I have is equipped with non-adjustable rockers the measuring method is different that what I have done in the past. Does anyone have a detailed list of steps on how to measure for push rods on a 455 Oldsmobile. Or if someone has used the same setup as what I am using and knows what length of push rods I need to use. Thanks for any help in advance. I attached the cam specs for both stock and aftermarket cams.
March 14th, 2018, 03:20 PM
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March 14th, 2018, 10:40 PM
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February 6th, 2019, 01:55 PM
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February 24th, 2019, 02:14 PM
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Olds with non-adjustable rockers is not a SBC with adjustable rockers.
With non-adjustable rockers, pushrod length does NOTHING except set lifter preload. If you've got "some" preload, but not "excessive" preload...you're pretty much done. Some lifters have more than 1/4" of plunger travel, most have not quite that much, and certain "high performance" hydraulic lifters have only a few thousandths. Typically, the plunger would be depressed 0.050--0.100. Anywhere in that range is fine--so long as the lifter has at least that much plunger travel.
With non-adjustable rockers, pushrod length does NOTHING except set lifter preload. If you've got "some" preload, but not "excessive" preload...you're pretty much done. Some lifters have more than 1/4" of plunger travel, most have not quite that much, and certain "high performance" hydraulic lifters have only a few thousandths. Typically, the plunger would be depressed 0.050--0.100. Anywhere in that range is fine--so long as the lifter has at least that much plunger travel.
February 25th, 2019, 05:58 AM
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Because Oldsmobile rockers are non-adjustable, the cam manufacturers typically adhere to the factory specifications for the camshaft base circle dimensions unless you are running an extreme effort solid roller or something with very high lift (not hydraulic cam ranges), or huge stroker crank that requires a reduced base circle cam.
The only variations you are likely to see here is if the heads were shaved or different thickness head gaskets were used. Even then, you should be in the range of hydraulic lifter tolerance.
The best way to measure to is (with intake off) measure the gap between the lifter snap ring & the plunger. A .040 depression is about ideal. If it is far off, you can buy shims that go under the rocker stands to lessen the preload.
I've read that .020-.070 is an acceptable range.
The only variations you are likely to see here is if the heads were shaved or different thickness head gaskets were used. Even then, you should be in the range of hydraulic lifter tolerance.
The best way to measure to is (with intake off) measure the gap between the lifter snap ring & the plunger. A .040 depression is about ideal. If it is far off, you can buy shims that go under the rocker stands to lessen the preload.
I've read that .020-.070 is an acceptable range.
February 25th, 2019, 06:58 AM
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Because Oldsmobile rockers are non-adjustable, the cam manufacturers typically adhere to the factory specifications for the camshaft base circle dimensions unless you are running an extreme effort solid roller or something with very high lift (not hydraulic cam ranges), or huge stroker crank that requires a reduced base circle cam.
February 25th, 2019, 09:40 AM
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April 10th, 2020, 04:29 PM
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BUT, if you,or in this case" I" am dealing with a cam with a "smaller Base circle" than stock ( Smaller by .150" diameter). Olds 350 Non adj valve train. So wouldn't it require .075" Longer pushrods to make up the difference because the lifter is .075" farther down in the lifter bore ??? thank you
April 10th, 2020, 05:38 PM
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You need whatever pushrod length gives you appropriate lifter preload. Pushrods are the LAST thing you buy to complete a long-block, because so many things influence the required pushrod length--base circle, decking the block, decking the heads, head gasket thickness, etc. It's a little easier with non-adjustable pushrods, because rocker-to-valve-tip geometry is "built into" the rocker and pedestal system. 'Course, you still need to have valve tip heights correct.
April 11th, 2020, 12:26 AM
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Hello folks, I have a stock 1968 Toronado 455, I changed the camshaft to a Comp Cam 260H grind number camshaft (part number #42-228-4). I am using new Comp Cam OEM style replacement lifters, OEM replacement rocker arms and brackets. I have an adjustable push rod to measure for the ideal length. I have measured for push rods before on small block Chevys but never on a big block Olds. Since the 455 I have is equipped with non-adjustable rockers the measuring method is different that what I have done in the past. Does anyone have a detailed list of steps on how to measure for push rods on a 455 Oldsmobile. Or if someone has used the same setup as what I am using and knows what length of push rods I need to use. Thanks for any help in advance. I attached the cam specs for both stock and aftermarket cams.
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