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Big Block question

chiefheaphy

chiefheaphy

1/2 ton status
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Mar 13, 2007
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Location
East MASS
Motor was rebuilt, ran for 3000 miles then sat for eight years. Changed the fuel pump and it started up, sounded good. Changed the oil a few days later, started it up and it was ticking constantly and knocking randomly if at all.

I have since swapped an edelebrock performer 750 for the q-jet. REadjusted the valve train. Added some seafoam. Changed oil. Adjusted timing. Checked flexplate and fuel pump, as far as I can tell they are both fine. I feel like a physician with the hose to ear trick, but cant seem to pinpoint much.

Besides this goddam tick(which sounds louder on the side of the truck than in the engine bay) and the sporadic three second knock that accompanies it, the thing screams. I am going to replace all lifters and rods as well as retorque heads and manifolds.

My questions:

TRuck has an RV cam/hydro lifters, Is this adjusted any way other than the common stock way?

Can I use new hydro lifters on the old cam?


Thanks guys.
Brian
 
no you cannot just put new lifters in. somtimes you can get away with it if you break it in like you would after a cam swap, but that doesnt always work. if anyhting take the old lifters apart and clean them, they probably have some buildup and are sticking. try to remeber which lobe they came from but thats not critical if you get em mixed up. also you adjust the same as stock.
 
Yes you can install new lifters on the cam. You never want to install old lifters on a new cam though. Also, after sitting for that long i'll bet the rings are froozen in the pistons, that would account for the knock you're hearing since the rings are what support the piston and keep it running true in the cylinder. Running the engine may loosen and free the rings up but if not then you're looking at tearing the engine apart and trying to get the rings out without damaging the pistons.

If you decide to try and clean the old lifters and re-use them THEY MUST be installed on the same lobe they came off of.
 
How long have you ran it how hot has it got, well warm. Are all the push rods flowing oil, sounds like you may have a lifter that doesn't want to pump up right.
 
Big block chevys are notorius for wiping camshaft lobes. I have seen it numerous times..and yes they may even seem to run well. The engine is large enough to carry a dead cylinder pretty well. Check to be sure one or more of the cam lobes is not round.
 
what is the best way to check without taking out the cam. Once I have the intake off I can visual inspect that all the lifters have up and down travel when the engine is cranked?
 
odin said:
Big block chevys are notorius for wiping camshaft lobes. I have seen it numerous times..and yes they may even seem to run well. The engine is large enough to carry a dead cylinder pretty well. Check to be sure one or more of the cam lobes is not round.
Click to expand...
All because of a poor designed oil path to the back number 7 and 8 cylinder areas.

I've seen a tube with a fitting that you drill and tap in the lifter galley which improves oil flow to lifters as the tube has tiny holes in it to which is supplies oil directly to each lifter. Heard it saves the camshafts, too. BC Engineering makes them.
 
chiefheaphy said:
what is the best way to check without taking out the cam. Once I have the intake off I can visual inspect that all the lifters have up and down travel when the engine is cranked?
Click to expand...


A dial indicator to measure rocker arm or pushrod movement.
Sometimes its obvious enough to see with the intake off.
 
Before you tear into it too far, it maynot hurt to check your fuel pump. I once somehow put a small block fuel pump on my 427. It sounded like I lost a cam. They look simular, but are not the same. Good Luck.
 
So I pulled the intake and am kinda relieved that I finally found a problem. The number 8 exhaust lifter is concave and shorter than all the rest. The corresponding cam lobe is round. This would cause things like bad idle, bad fuel efficiency, low vacuum...ticking?

001-10.jpg


I am going to grab a comp cams low end torque camshaft and some 3/8 pushrods. Can I lose the quide plates or should I get larger ones? Any tricks to replacing cam with the motor still in the truck? I'm assuming it is close to impossible to do without taking off the rad support.

Thanks
 
Certainly would cause lots of problems! Basically that cylinder cant get rid of the pressure it builds so when the intake valve opens it is firing pressure back up through the manifold and carb.

I like the Comp 4x4 cam that i have in my 454, pulls really strong. 3/8 pushrods are a size up I think and I dont believe that they are neccesary for your application. You wont be spinning the motor all that fast anyway, and the valve springs that match those cams aren't incredibly stiff.

Changing out a cam with the motor installed isnt that hard. Just pull everything off that is in front of the engine and have at it. Some guys have cut the radiator support but then on some trucks it is bent by design, like GM knew people were gonna change out cams. Keep everything clean, especially all sealing surfaces, and then follow the book step by step!
 
If you change to larger pushrods you will need guideplates to match. Because of the canted valves on BBCs the guide plates are mandatory.
 
cant get the cam out. It moved about 3/4" inch then stopped. I dont want to force it. Any suggestions? What could it be caught up on?
 
Distributor needs to be removed, along with all lifters, and fuel pump so that the fuel pump pushrod is down and out of the way.
 
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