Push Rod Problems

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Oct 29, 2007 | 01:30 PM

BBADPERFORMANCE

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Push Rod Problems

I'm new to the 300 six but not new to the combuston engine,
I have taken on a basket case of a sort.

The only history I have Goes as follows.
The motor is in a flip front end mud truck.
The motor had head trouble.
Put on new head.
Put in new Lunati cam 498 lift?
The old Push rods are 1/2 in. short. Why?
I asked if the new head had been ran with the old cam they said yes less
than 50 miles. So I'm not sure why the cams could change so much
pushrod length.
I think the studs are not pressed in all the way because you run out of
threads way before you get close.
Any help would be greatful.

I want to machine the head for screw in studs and put on roller rockers is this a solution?

Oct 29, 2007 | 02:12 PM

Silver Streak

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From: Broken Arrow, OK

It sounds like it might have previously had a roller cam in it. Rollers for the 300 are rare, but they are out there. If that's the case and you just installed a flat tappet the pushrods will be about 1/2" too short. Other than that I can't think of any reason for them to be that short. The 300 has the longest pushrods of any engine I can think of, so if there was a mistake made and they put the wrong ones with the engine they would almost certainly be shorter. 460 and 3.8 V6 rockers bolt on, but the pushrods are too short for them to work out of the box. I don't think it would be 1/2 an inch if it were a rocker problem.

Oct 29, 2007 | 05:58 PM

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I don't think it had a roller cam in it as he surely would have kept it.

what about the screw in stud and roller rockers?

Oct 29, 2007 | 10:00 PM

Silver Streak

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From: Broken Arrow, OK

Screw in studs and guideplates are always a good idea with a cam that tall, but I don't think they will solve your problem. It would be extremely odd if all 12 studs pulled out the same amount.

Oct 31, 2007 | 08:45 AM

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The rockers studs look very tall to me I think maybe they where not pressed all the way in or they are the wrong length, I no i said it had been ran with new head on it but I'm not sure if that is true because I can't understand how you can take out the stock cam and put in the new cam of alittle more lift and the same push rods end up 1/2 in. short.

Do you know where I can find some specs like rocker stud install height or lifter length.
Thanks,

Oct 31, 2007 | 04:43 PM

Silver Streak

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From: Broken Arrow, OK

I don't know where you'd find specs like those. The lifters are the same ones that the small block uses, so that tidbit might make it easier to find the number. Is your new cam ground on a smaller base circle? That would be really strange for a street cam, and even stranger that it would be that much smaller, but you never know.

Nov 7, 2007 | 07:21 PM

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I didn't see it come out but they pulled out the comp cam and put in a new lunati and i went over today to do some measuring and i put in a lifter and the pushrod and ran the nut all the way down and it was perfect. Go figure I don't know if it was a small base circle cam maybe a bad day for a cam grinder at comp. Thanks for all the help, I'll finish it tomorrow and post to say how it runs.