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I acquired our second C3 about 3 weeks ago, a 1976. The seller was a nurse who told me the engine was built about 4 years ago and about 2000 miles put on since. I’m a small engine mechanic, in business now for 15 years Briggs, Kohler, Kawasaki, Echo etc, and have a question about reworking the top of this 350. The mods I can confirm are, .030 over, flat top pistons, cam lift measures .316 both in and ext, valve springs are not stock, heads are. The springs on the aluminum heads I have are 130 seat and 330 open. So, should I change the lifters for these new heads or change the springs to break in the new parts?
From: At my Bar drinking and wrenching in Lafayette Colorado
At 2,000 miles, the break-in period is done. On the dyno, we consider break-in complete within the first 2 mild dyno pulls, which is within 15 minutes of the engine achieving stable oil temp. Why in the world would you feel a need to change the lifters, which are broken in to the cam..? Your spring pressure at 130 on those new heads is very high. Might want to re-consider that, unless this is a roller cam with some very aggressive ramps..
The engines that I work on every day mostly have solid lifters, and the primary wear to the lifters is the point that the lifter hits the push rod. We change lifters more than push rods. I bought these heads a few years ago because I thought I wanted a roller. I didn’t know if the new springs would affect the lifters and I need to treat it like a new cam or if it was better to use the current set-up. This is not my area of expertise. Do you think the spring pressure is much to high for gross lift well under .500 and it is necessary to change springs?
Agreed, much wiser to replace springs with correct springs for the cam. No need to change lifters whatsoever. And do measure and get correct length pushrods for your setup.
Those springs you have are stiffer than your needs. Not a lot of lift on your cam so I doubt you need much spring. I would swap out those springs and go with a set of "Z/28" springs. Cheap and reliable. They were not originally used on Z/28's but that is how they are sold in the marketplace.
On small block Chevy engines the pushrods are not a high wearing item. The lifters and flat tappet cam interfaces are more common wear items. Stiff springs contribute to that.
So, just so I understand.....you bought hydraulic roller heads and put a flat tappet cam in?
What size (O.D.) are the springs? 1.47?
The above mentioned Z/28 spring, lock, retainer kit from Elgin is a bargain and work great with flat tappets up to .500 lift or so.......
You are lucky it didn't wipe the lobes...but I would get them out of there for the sake of longitivity......
So, just so I understand.....you bought hydraulic roller heads and put a flat tappet cam in?
What size (O.D.) are the springs? 1.47?
The above mentioned Z/28 spring, lock, retainer kit from Elgin is a bargain and work great with flat tappets up to .500 lift or so.......
You are lucky it didn't wipe the lobes...but I would get them out of there for the sake of longitivity......
Jebby
He bought a car with a recently rebuilt engine that already had the flat tappet, he wants to put heads he had previously purchased set up for a roller on this engine... At least thats my understanding of it. He asked if he should change the springs or lifters with the new heads once they are installed.
I agree with comments above.The springs are not hard to change. Ive done it twice not with cam changes and prior to building the engine in my car pretty much all of the engine experience I had was small engine... I did some work to an air cooled VW I owned but that could arguably fall into the small engine category since it was more like a motorcycle engine than anything. Theres plenty of youtube content on it.. You will want to buy a spring shim kit and a spring height checker which are cheap. Otherwise consider swapping the cam to a retro roller like I did the second time around.
x2 on swapping your springs out. 130 is for a roller...or a real nasty big solid flat tappet.
You will destroy the cam with those bigger springs in no time flat. Metal shavings will take your bearings and crank out...sure you know that.
Wow! That's a lot of spring pressure! Thanks Y'all for all the advice after 15 years of lawnmowers and chainsaws I've forgotten how different these machines can be. I'll change the springs, should be much easier putting the new springs on that taking these off, pushed the limits of my spring compressor. I would like to install a roller cam, but after just buying the car I don't think the wife is going to go for a $1000 cam. Again, thank Y'all for the replies.
Wow! That's a lot of spring pressure! Thanks Y'all for all the advice after 15 years of lawnmowers and chainsaws I've forgotten how different these machines can be. I'll change the springs, should be much easier putting the new springs on that taking these off, pushed the limits of my spring compressor. I would like to install a roller cam, but after just buying the car I don't think the wife is going to go for a $1000 cam. Again, thank Y'all for the replies.
since you have to replace the pushrods and such anyway... a roller cam can be done for more like $500 at this point so I would consider it (especially since you already have the springs installed) .... I used these https://www.rockauto.com/en/parts/en...ve+lifter,5548 (comes to about $200) and there are a lot of retro roller cams for just under $300 like https://www.ebay.com/itm/19484039054...oAAOSwOK9iDSBYall you need is a cam button and brass tipped fuel push rod ($20-30)... most retro cams work with stock or replacement distributor gears.
I went with a flat tappet 262/268 cam first and then regretted not going roller for like 8 years so I finally upgraded last year and it was worth it IMO. I went with the comp 270HR cam... I have a 355 with flat tops and 64cc chamber heads. no more worry and oil additives for me. plus the advantage of the roller is the valves can stay open longer on each stroke so a bit more efficiency and power.
Last edited by augiedoggy; Feb 26, 2022 at 04:12 PM.
Spring pressure and lifters
