Ramjet 502 re-assembly

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Three weeks later I still don't have a cam and things pretty much fell apart. David V. got sick after we talked and dropped the ball and never sent the order to Terry Walters so he could get it to Mike Jones. Then David was unavailable for a few days to answer some questions I had regarding rockers, etc. I e-mailed Terry a week later after I found out the cam wasn't ordered and told him to go ahead with the cam order, sent him the specs David and I agreed to, and he finally ordered the cam. Mike Jones got the order and we found out that he has no 105 LSA compatible cores available and his supplier is back-ordered and can't tell him when he'll receive them. Apparently David's customers have been sucking up those cores this year.

Mike Jones has a slight disagreement with David's theory on LSA and says I don't really need an LSA that tight for what I'm trying to do. So I cancelled my order with Terry/David and discussed cam specs with Mike instead. I'll use my payment to Terry to apply toward a set of roller rockers and a pair of .027" Cometic head gaskets.

Mike and I arrived at a cam spec that he believes will work fine with my stock springs, lifters, and new roller rockers I want to install. He went with a bit more conservative profile than the one David chose, because he said with the other profile I'd have problems with my springs and lifters. He says I might have to change pushrods due to the smaller base circle, but with the thinner head gasket he's not sure. I'll have to assemble it and check. Here's what he is recommending and what I ordered last week:

108 LSA
280/280 advertised duration (.006")
226/226 @ .050"
.335"/.335" lobe lift
.603"/.570" valve lift with 1.8/1.7 rockers (nominal)

David's testing has shown that the COMP 1620 1.7 rockers deliver an actual 1.759 ratio, and the COMP 1828 1.8 ratio rockers deliver an actual 1.813 ratio. This would give me .607" lift intake and .589" lift on the exhaust. I could go with the higher 1.8 ratio on the exhaust but David said my exhaust side flows well and doesn't really need the added lift.

Mike recommended I go with Scorpion aluminum rollers, since they have a set with eight 1.8 and eight 1.7 rockers for less than the COMP rockers cost and he thinks they're better quality. The issue I have with them is that David's testing says they deliver actual 1.932 and 1.79 ratios. That would give me .647" lift intake and .599" lift exhaust. I'm afraid the intake lift would be too much. My coil bind limit with .060" margin is .645" on at least one spring when shimmed to 150 pounds on the seat. Plus the open pressure will increase on the pushrods and lifters which might lead to lifter issues. Mike thinks my lifters will work fine with 1.8 rockers, but I'm not sure about 1.9.

I've read about this ratio issue and some posts say that once the real spring is installed (instead of a checking spring) the actual observed lift is less due to valvetrain deflection. Mike says that's true, especially with aluminum rockers. It's hard to believe you can get .040" less lift from deflection. The problem is you can't predict the actual lift without trying the rockers on the engine.

So I may stick with the COMP rockers even though Mike doesn't really like them. They do have a larger shaft and bearings than most other roller rockers.

Mike says the leadtime is 2 weeks and I'll be going to Montana for a week so it should be here when I return. This whole thing has been a bit frustrating, but I felt a custom cam was reasonable for this engine to perform like I want it to.

Since I know that my springs will work with the new cam, I went ahead and re-measured them and finalized the positions of each spring, retainer, and lock on the heads. I have ordered spring ID locators and some shims which I'll need to get to 150 pounds on the seat. At .600" lift I will have an average of 366 pounds over the nose on the intakes with the 8 highest rate springs. Mike Jones says that should be enough to get to 6000 RPM with my current parts.

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I received my valve spring locators and tried them on the heads. Unfortunately, the spring pocket are a little smaller than 1.550" and the locators are a little bigger than that. Since the locators I found were the best fit for my heads and springs, I sanded the OD down a little to make them fit the spring pockets. I also got some more shims so now I can re-assemble my heads as soon as I find the time.

On the rockers I decided to order one of each from Summit and measure the actual lift once I get my cam. Then I can decide which set to buy and just return the single ones with my composition head gaskets for a refund. I also got some pushrod length-checker tools.

I have been told that I should get better lifters with my new cam so I asked COMP about their OEM replacements and they told me my lifters are fine at my spring pressures and theirs are essentially the same as OEM. I did a little research today based on a recommendation in David Vizard's book.

In his book, Vizard has a picture of a pair of stock Gen VI 454/502 hydraulic roller lifters and says:

"These are stock lifters as per GM Gen VI 454 or 502. Avoid their use for anything other than a 5000 RPM stock rebuild. If you want to use factory lifters get the ones used in GM's performance division's 572."

So, I looked up the part number of the Ramjet/ZZ502 lifters in the GM parts list: 17120061 (Delco HL122)

Then I looked up the part number of the 572/620 lifters in the GM parts list: 17120060 (Delco HL121)

From everything I've been able to find these lifters are the same or at least fit the same applications. Summit sells them at different prices but the descriptions are the same, and interchange listings I've found include both of them along with aftermarket replacement part numbers.

I've also been told that my lifters will start giving me problems (noise) at much over about 150 pounds on the seat. I don't understand why that happens, since there's really no pressure on the lifter when it's on the cam's base circle. Apparently there's no issue with over the nose pressures. So I dug further into it.

My springs in stock form are 140 pounds on the seat at 1.94" installed height and are part #12462970. I looked up the 572/620 springs and they're part #19172596 with 230 pounds on the seat at 2.00" installed height. That's a huge difference in both seat pressure and over the nose pressure (.632" lift). The 572/720 has solid rollers.

So I'm curious how the lifters work with that much seat pressure in the ZZ572 application if the others start making noise in the 502 application at 150+ pounds. Since they're different part numbers, could there be that much difference in the way they work? They look identical and they interchange, but Vizard seems to think the 572 lifters are better for some reason.

What would make a hydraulic lifter noisy at higher seat pressures?

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I can't seem to find ANYTHING about lifter noise issues at high seat pressures, but some say a hydraulic lifter won't live with seat pressures close to 200 pounds. If they can stand 400+ pounds, why can't they stand 160?

And I can't find anything explaining the difference between the OEM 17120060 and 17120061 lifters, except for a couple of other guys asking about them. I sent Vizard an e-mail asking what the difference is, since he recommends the 060 over the 061.

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I got the valve springs all shimmed and the heads back together today with the exception of #1 cylinder. Half of the retainer lock is screwed up....I think it may be for a 5/16" valve stem instead of 11/32" since the radius is smaller. Weird that the factory did that, as it screwed up installed height and the retainer wasn't properly locked in place. I ordered a couple of new ones and will put it together when they arrive.

I set the seat pressure at 150 pounds on all valves and used the highest rate springs on the intake valves. That took .075" more shims on the driver's head intakes except for #5 and #7 which took .060" more, and .045" more shims on the driver's head exhausts. It took .060" more shim on the passenger head intakes, and .045" on the passenger head exhaust, except for #4 which took .060" more. I have no idea how the factory determined the shims needed, but I've measured everything twice with consistent results.

Even with these shims I have well over .840" between the retainer and seals, and can go to .645" lift with a .060" minimum margin before coil bind.

I think the springs were significantly under the specified 140 pounds seat pressure. My numbers say they were in the 125 pound range on the seat which would put them at about 345 at .600". I suspect that's why guys complain about valve float under 6000 RPM with these crate engines. Glad I "blueprinted" the springs .

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I got back from vacation last night and still don't have a cam . Got ahold of Mike today and he informed me that his supplier was out of "stepped nose" cores that are used in the Gen VI BBC, but they're now on the way and he should be able to turn the cam around in 2 days after he gets the cores. I also got a new pair of OEM valve locks so I can finish the heads.

I tried getting information on the GM 572/620 lifters from David Vizard, since he recommended them in his book. He told me he doesn't know the difference but since GM used a big aftermarket HR cam and stiff springs with those lifters they should be "better". Not a real convincing answer.

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Well this is getting pretty damn frustrating . I checked the valve locks and THEY DON'T FIT! The Ramjet 502 and the ZZ502 are the same base engine, and in fact mine was shipped as a ZZ502. I got the part number here, from the Chevrolet ZZ502 parts list:

https://www.chevrolet.com/content/da...ications-1.pdf

It shows GM P/N 3947880, QTY 16, for the locks. I assumed they would come 2 per pack (since 32 are required), but I went ahead and ordered 2 anyhow from a Chevy dealer using that part number. They look similar, but not the same. Here's 3947880 and I got 2 of them, not two pairs:


I had also looked up the part number on this Chevrolet Ramjet 502 parts list, and it says "N/A" so I used the ZZ502 number:

https://www.chevrolet.com/content/da...e-12499121.pdf

I just searched for another site and found this one that lists the lock for the RJ502 as GM P/N 12366992, QTY 32 required.

http://www.crateenginedepot.com/pdfs/BB_RJ502.pdf

I have no idea why they're different, but I found a pic for 12366992:



These look identical to the parts I have. Notice it looks like a -.050" lock, not a standard one. And it's sold as a PAIR under that part number, so why in the hell would you need 32 pairs of them as listed?

So now I have to try to find and order the right part...again. Goddam GM can't get their shit straight.

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Well I finally got the heads completely assembled. I got the right locks/keepers (12366992) off eBay and the heads are ready to go.

I ended up disassembling them, cleaning the ports, measuring all the springs and installed heights, shimming all valves to 150 pounds on the seat, installing internal spring locators, and replacing the seals. I really don't think I needed new seals, but I figured "might as well" .

I got all 5 trial rockers today and a message from Terry saying the Cometic head gaskets were shipped last week. My cam should be here this week, if Mike keeps his promised schedule.

I can't believe how damn long this stuff is taking.

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Still no cam today. Yesterday was 4 weeks since I ordered it and he quoted me 2 week turn-around. I called Mike Jones this morning and he got the core and has it rough ground. He said he still has to grind the inverse radii (all of his HR cams are IR) and finish it. He says it will ship on Monday so it will be 5 weeks by the time I get it (which is what Vizard told me). Sounds like he's swamped.

[Rick_L]

Here's an interesting article on the OEM Chevy lifters. Doesn't clear up any differences in the p/n's mentioned though.

http://hotrodenginetech.com/why-john...n-your-engine/

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Still no cam as of today. I'm starting to get pretty pissed off about this crap .

On June 22nd I ordered my cam, paid for it, and was quoted a 2-week turnaround. Three weeks later on July 12th I had heard nothing yet so I asked about the status and was told he didn't have any Gen VI BBC cores, but they were on the way and it would be a 2-day turn-around after they were received. IMO a core should have been ordered immediately after I placed my order. Another week later, last Friday July 21st, I called and was told the core was in, it was rough ground, and would be finished over the weekend to ship this past Monday, July 25th. Yesterday was 5 weeks from when I placed the order. I've received no notification of it being shipped, and I don't know HOW it's being shipped. If it doesn't show up by Monday, Mike is going to hear from me on and I'm not a happy camper.

I did finally get the Cometic head gaskets from Terry Walters yesterday after another delay. They were supposedly out of stock and Cometic had to make them.

While waiting for the parts I've worked on the valve covers and some more suspension parts. I still need to make sure the valve covers fit once I get the heads and rockers installed, but I went ahead and removed the powder coat by bead blasting...what a pain in the ass. Then I sanded the die casting parting lines down and smoothed them for painting. I'm probably going to leave the top raised features polished and paint the rest, so I sanded off the brushed aluminum finish scratches.

Any thoughts on how to do this the easiest way? I thought I'd just prime the entire cover, sand that off on top, apply basecoat and sand again, then clearcoat. Masking doesn't seem very practical.