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Old 01-25-2005, 01:48 PM
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What is involved in Changing Camshafts?

Hey Guys, I have been puttering around on engines for 30 years, but have never rebuilt one or done an intake change, or Cam swap.
what is involved in changing a cam, what all has to come off IE rad,water pump, damper etc..
I will be changing the Intake (Performer RPM) and Putting a Comp 260H, lifters, and Timing Set . and Topping it with a 575 Speed Demon.
when I do it , it will have to be done in just 1 or 2 days and it has to be right.
BTW its a 305 77 Impalla

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Old 01-25-2005, 03:01 PM
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Well you need the intake off, water pump off, timing cover off, and about 2.5-3 feet of clear space in front of the timing cover to take the old cam out and insert the new one.

Its pretty straight forward. This is how I usually do it. First I set the engine at TDC on the #1 stroke.

Take the intake off. Valve covers off. Loosen the rocker arms. Pull the pushrods and lifters.

Take off the waterpump and timing cover. Then the cam gear and chain. Slide out the camshaft. Coat the lobes and bearings of the new cam with plenty of moly lube. Then basically go in reverse order. You can install the gears with the alignment dots at 6 oclock(cam) and 12 (crank) but you'll have to turn the crank 1 revolution for it to be at TDC on the compression stroke. Not a biggie. Some people install the gears at 12 and 12, which is TDC of the compression stroke. The crank really doesn't know what stroke its on . . . it just depends on where you set the cam.

Some cam manufacturues recommend advancing the cam a few degrees. If this is the case they'll have their own specs and you'll need a degree wheel to do this.

To get the timing cover back on you'll have to drop the oil pan a bit in the front.

I usually soke my lifters in oil for about 12 hours before putting them in so plan ahead. Once the lifters and pushrods are in go through your rocker adjustment process.

After that is done, drop the intake on using the correct gaskets and torque procedure and let it cure for 24 hours before firing it up.

Id recommend getting a haynes manual for your engine as it will have all of these procedures pretty clearly written.

I know I forgot something but hopefully this is a (vague) start.

Oh. Forgot breaking it all in.

I usually run the new cam for about 20 mins at 2100 RPM. I then pull the oil and oil filter and inspect it for anything out of the ordinary. A little fine metal powder is normal. I then change the oil and drive it. After about a week I change the oil again just because I am paranoid.
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Old 01-25-2005, 03:58 PM
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Don't forget, you will have to lower the front of the oil pan to get the timing cover off. Then get it to seal again... The radiator will probably need to come out too.
It's a lot of work, for questionable gains.

Have you thought about getting another engine to rebuild to the specs you are looking for? Then just swap them, probably just as easy, I've done both a few times.

Good luck.
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Old 01-25-2005, 04:03 PM
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I think quite the opposite. Its actually not a whole lot of work for potentially the greatest gains an engine can experience. Along with the heads, the camshaft is the a main determining factor in an engines potential to make power.

It can be done in 1 or 2 days easily. Always helps to have friends help. Just make sure you have ALL the supplies and tools handy. You'll need a harmonic balancer puller and installer. Thats about it as far as specialty tools are concerned (a degree wheel perhaps if the cam needs degreeing).
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Old 01-25-2005, 04:09 PM
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Yes I have thought of that as well, and do plan on getting an engine and a 200-4r

the Master plan is too Hybridize a Datsun 260Z.

But the Chevy is the work car and the Carb that is on it, has a severe problem with the choke.
If I have to replace it , again I want to replace it with something worth while.
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Old 01-25-2005, 04:12 PM
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Well I don't know, maybe. I've done a lot of work in 30 years and I wouldn't want to do it.
The factory spends a ton of money dyno testing cams carbs etc for all around driveability. I think it's hard to pick a cam and carb out of the air and expect better performance. You might pick up some power but you will lose someplace else. Engines are so cheap these days I think it would be better to build one up from scratch with a specific goal in mind, more fun too.
But that's just me...

J
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Old 01-25-2005, 05:34 PM
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Inspect the journals on the cam that you remove,inspect for wear. Just in case the bearings need replaced,so you do not eat a new cam on old wore out bearings.It would not be a bad idea to prime the engine with oil before start up even though it is a cam swap and not a complete overhaul,moly lube is thick and getting oil to the cam upon sartup is crucial.Use a good bead of RTV gasket maker on the front and rear of the intake instead of the rubber gaskets that are supplied.
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Old 01-25-2005, 06:02 PM
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If it's your work car why not just pick up a stock four barrel manifold and a 600 cfm Edelbrock? Or if it already has a Q-jet on it, just get a new one. Isn't Edlebrock making them now?
I don't know what a "Speed Demon" carb is but if it's 575 cfm it should be fine for that motor.
Keep your hard earned money and save it towards the rod you really want.
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Old 01-25-2005, 07:04 PM
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Given the typical HP figures of the stock 305's there is a lot to be gained. It just depends on if you are going for more power, more economy, etc. Technology has changed since the 70's especially in camshaft profiling. I imagine your 305 puts out anywhere from 200-220hp, not a lot, even for a 305.

To give you an idea of a cam swap, a friend and I did one on a TPI (fuel injection) 85 Corvette in two days. This included removing the hood (and putting it back on) installing the cam (which required all cooling and AC components be removed) and breaking it in. With two people its not a hard project at all. Like I said, get a book, it will help a lot.
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Old 01-27-2005, 06:06 AM
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I will definitely get the Small Block chevy book, and I am seriously looking into a 383. I think an Edelbrock Performer RPM Air Gap intake, Vortec Heads, Comp 268H cam, and possibly a 625 Speed Demon, running through a Bowtie Overdrive 200-4r should make the ole 260 scoot quite well.
I think I have remedied the choke problem on the Chevy, so I wont have to replace it right at this time.

one more question (well at least 1 more)
Assuming a 2600lb car, 200-4r, going through a 3.59/1 rear end, on 17 inch wheels 45 ratio.
what will be the largest cam I can run with Full street-ability?
Could I use a 270M or would the lower gear ratio make it an unhappy Camper?

And can the Vortec heads handle the .470 lift without modification or would I need the modded vortecs?
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Old 01-27-2005, 05:12 PM
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replacing cam

id suggest a complete rebuild if u plan on switching the cam. i mean at this point the heads will be off and so will the intake as well as water pump , harmonic balancer, and timing cover. i mean yes it takes a little work to rebuild the engine however i seen your looking to increase horsepower and two things to remember when adding horsepower is what condition the pistons are in and wether there up for the test generally upon pulling the heads and all else if u were to pull the pistons ud find scratches and crankshaft wear which potentially there again could be bad if u are looking for horsepower, and honestly u may consider a new oil pump after finding shavings in the oil as thius could get in your engine as this is never good, and to whoever said that metal shaving should appear in the oil after putting in a new cam is wrong if there getting shaving there is a problem with your bearing as well and this is also dangerous.
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Old 01-27-2005, 05:41 PM
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You do not have to pull the heads to swap a cam.
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Old 01-27-2005, 08:56 PM
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Do you need to go through the same cam break-in with a roller cam?

Dave
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