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Old 10-27-2015, 10:55 AM
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Novice needs 402 BBC valve train help

Mostly novice builder here. At a stuck point.
402 BBC. Decided to replace old tired cam and clean up the stock heads. Doing all the work myself and enjoying it save for this dilemma. Got a Comp Magnum Roller cam (:578 lift) with roller lifters. Went with new push rods recommended for the cam. 3/8 7.725 intake/8.684 exhaust. Also replacing stock rockers with purchased Summit aluminum roller rockers 1.7 ratio. Bigger than stock rocker body means stock studs no long enough right? Keep reading.
Re-using stock screw in studs. Also guide plates. Hereís where Iím stuck.
Put lifters in, push rods and started to mount rockers. Not happening on intake valves. Rocker studs too short. Can get rocker on the exhaust, not the intake. In addition, when cam rotated to base circle intake push rod barely clears push rod guide plates. BTW: does anybody make a push rod guide plate thatís not raised?
I understand the base circle on roller cams is smaller. Yes? No?
Do I fix this with replacing the push rods (with 8.380 intake/9.350 exhaust) and longer rocker studs?
Thanks in advance.

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Old 10-27-2015, 01:48 PM
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If the stock heads don't require guide plates due to how the head aligns the pushrod, then DO NOT use guide plates as you are going to create a heck of an issue that will lead to alot of metal grindings in the oil which will be be extremely bad of course. 2nd, I have no idea how anyone can advise of a pushrod length without knowing if the block or head have been shaved and also without knowing the head gasket thickness.

https://www.youtube.com/watch?v=o5is...ature=youtu.be

Take a look see - this method works pretty well.

Do you have any part numbers or casting numbers you give us?
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Old 10-27-2015, 02:19 PM
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Stock heads came with guide plates. Was gonna re-use them. No head work or machining. gasket compressed at .039 in. Stock heads #3909802
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Old 10-27-2015, 02:52 PM
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Oops on the guide plate thing, I missed the BBC part.
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Old 10-27-2015, 05:43 PM
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A quite common problem with BBC's with non stock components. The pushrod seat in the roller lifters is not the same height as flat tappet lifters. Pushrod length will have to be measured and custom length pushrods purchased..

I just went thru this with a customer.. I told him the proper measured length.. But his buddies, all "experts" had him order different.. He ordered four different sets of pushrods. One set by overnight. Then ordered the proper length that I told him..

Bet the guy at Summit was real tired of talking to him on the phone and refunding the stuff.
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Old 10-27-2015, 06:04 PM
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Rememeber. Novice here. Would take a recomendation on the rod lengths. Intake and exhaust. I know proper way is to measure with adjustable. I'm limited on budget and time and tools. 1.7 too much also? Live in Ohio so I'm driving to Summit tomorrow to get the rods and studs. Will take a safe recomendation. Thanks.
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Old 10-27-2015, 06:49 PM
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1.7 is the BBC stock rocker ratio.

A pushrod checker can be made from old stock pushrod. Cut in two then shorten one of the halves about 5/8 inch. get a 1 3/4" no.10 fine machine screw, cut the head off. Thread two nuts down to center of the modified screw. Insert the ends into the two pushrod pieces and adjust length up and down with the two nuts.

I have several of these made up for engines that don't have popular lengths. I usually braze the nuts to the pushrod and double nut the shaft/screw. But not needed in a pinch.
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Old 11-03-2015, 07:11 PM
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Your pushrod length is incorrect. I just changed over to a roller cam in my 454 and this was the biggest concern. I also used the summit roller rockers and they are a quality piece for the money. Your also gonna need to get some tall valve covers when using roller rockers.
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Old 11-05-2015, 10:19 PM
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Quote:
Originally Posted by [email protected] View Post
1.7 is the BBC stock rocker ratio.

A pushrod checker can be made from old stock pushrod. Cut in two then shorten one of the halves about 5/8 inch. get a 1 3/4" no.10 fine machine screw, cut the head off. Thread two nuts down to center of the modified screw. Insert the ends into the two pushrod pieces and adjust length up and down with the two nuts.

I have several of these made up for engines that don't have popular lengths. I usually braze the nuts to the pushrod and double nut the shaft/screw. But not needed in a pinch.
The ONLY way to know what length push rod is to measure, just like Bob said here. Too many different components and a huge lift cam to guess. You also need to roll the cam thru a lift and observe where the rocker is contacting the valve stem to get it centered with the correct pushrod length. You need to get this geometry right or you're going to throw away a lot of money in damaged components. Do you know if the valves will clear the pistons with that much lift ??? A stock piston may not have enough dish or relief cut for that cam. Just throwing a high lift cam in without checking clearances doesn't work very well.
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