Reading Tom Dewitte's thread: https://www.corvetteforum.com/forums...cam-shaft.html

I've been reading here on this forum and other places where it seems that flat tappet cams can not be reliably installed and run anymore. Yet for many decades car manufacturers built millions of flat tappet cammed engines, started them up at the factory cold, drove them off, and delivered them to customers that drove them tens of thousands of miles. I don't think that they replaced valve springs after a 20 minute high idle run in either.

Is there a coherent reason why this is so hard today? What changed, and what is the cause? If the problem can be defined, actions can be taken to prevent the problem.

Label me "afraid to buy a cam."

 

Kevin,
Here's a really good video with explanations...grab a cup of coffee, it's long.

 

I've done a couple engine rebuilds the last couple years (I'm not a professional.....), all using Comp Cams products. I followed their break in procedure to the letter (including using their break-in oil and removing the inner valve spring when applicable) and have had no issues.

There is another 427 I built last year that will get fired up soon. I'll use the same procedures and I don't expect any issues. Of course I just jinxed myself...............

Wiping cams is a real issue, but, in my limited experience over the years (maybe a dozen or so flat tappet builds), using the cam manufacturer recommended parts and procedures for break in I've not had any issues. Many have done just as I have and ended up with a wiped cam, maybe I've just been lucky......

Tom

 

My machinist tells me the current lifters lack the proper dome, and I've heard the metal isn't up to the task. Some blame it on cam cores also. I solved all that by taking a couple old cams and having them reground, and they grind lfters also. I run several flat tappets and chose a sft for my current project. I was lucky to have Howard's cam saver solid lifters on the shelf from a dozen years ago, so feel pretty good about all of it. Grinding is cheap, or at least this guy was, so I had him grind a second core to L78/LS6 specs to put on the shelf. I won't be buying new anymore.

 

Zinc additives are supposed to be the cure. But why not go to a roller cam; it's not going to change the outward appearance. Keep all of the original parts in case you want to sell the car.

 

My story is 15 years ago when I had my problems with cams going flat in my 396. The engine builder followed the book and wasn't his first time doing flat tappet cams we used all the correct break in oil and assembly lube yada.. well I had two go flat. Once on his engine stand after break in. He broke in the day before all was well. He knew I was coming to get it so a few hours before I was going to get there and before he took it off the stand he fired it up to make sure all was well. Then it went flat. So we rebuilt it again All was well on the stand. Put it back in my car I drove it for about 50 miles and went flat again. So the engine builder took the cams and had them Rockwell hardness tested and both were soft. Both were Crane cams. He told me he wasn't doing it a third time so we put in a GM roller cam.

 

I haven't used a flat tappet cam in any of my engines since 1996. For the cost of doing a cam swap twice because a cam went flat on you, will cost more than if you just went to hyd roller from the get go. The only reason flat tappets cams are still around are because people are cheap and don't want the hassle or even understand how to set the cam endplay. If you can afford a C2 you can afford to install a roller cam. Do it right once and be done with it.

 

This isn't voodoo, it's a product of cam/lifter material, profile, spring pressure, block condition, and lubrication. We all know folks that have had failures, and some have had personal failures, but to just move on to different technology and not understand why they fail doesn't complete your education. Don't misunderstand my line of reason here, there are advantages, and the biggest is exacting your valve events when flat tappets are subject to greater limitations. The rollers have their setbacks, noise, cost, and even failures, and when a lifter goes away, your engine can be done. I own 3 roller engines, all but my factory issued LS are noisy at idle, one hydro, one solid. Hate that. I'm not wringing out every last hp, so as long as they provide quality lubes, I'll still be using flat tappets. This isn't sticking my head in the sand, it's understanding the entire equation.

 

We covered this in this thread a few months ago
https://www.corvetteforum.com/forums...post1607415645

Summary
It's not due to soft materials or not enough zinc in the oil. It's due to incorrect geometry between the lobes and lifters which prevents the lifter from rotating as it should.

The reason the geometry is off varies.
1) equipment used to grind lifters are out of tolerance and the skilled individuals that used to operate them retired
2) demand for solid lifter and cams have been dropping which makes it hard to financially justify solving #1
3) attention to lifter bore tolerances and not testing lifter rotation during assembly

 

Just had a little talk about this with my machinist.....he claims current ft lifter domes can reach as little as 002 when they should be .005. I'll have to measure a couple here to varify.

 

I’m no expert on this topic neither but the more I read on this issue it seems like it all goes back to Rockwell hardness out of spec. On cam/lifters or cam lobe & lifter taper/crown is out of spec.. (putting aside all the normal break in procedures were followed)..

Cam lobe/lifters taper is a must for lifters to rotate in their perspective bores, something I kinda heard back in the day but NEVER checked for it.. just assume all the machine work was built into the part:-).. I guess those days are over with?

I’ve done a handful of sbc cam swaps back in the day & just would perform all the normal like many of us had done like prime the oil pump, add the lifter/cam lobe break in lube on all lobes/lifters etc. & get it on fast idle as soon as possible etc.etc.

** BUT 1 thing I never checked for after running the lash on all the cylinders was to verify lifter rotation before starting the engine… so I recommend to put a paint dap/marker on all the lifters & make sure they are turning in their perspective bores while rotating the engine over or you can use your method of visual inspection for rotation etc.. sooooo I’m planning Lord Willing on doing 1 more solid lifter cam change hopefully in my current engine & WILL be checking for lifter rotation:-)**

** If ALL lifters aren’t rotating in their perspective bores DO NOT even think about going further on assembling this engine until you find out why lifters are not rotating, if they aren’t rotating they are gonna fail**

Good Luck to all
Chalie

 

Wonderful! Just as I'm about to get back into my '64 project, with engine start-up among the major steps, this issue heats up. Bad enough I'm on a learning curve, now the goal posts seem to be moving.

Several years ago, in an attempt to stay stock to the 327/250 the car was born with, I went looking for a replacement cam close to original. Searches on here and other sources at the time kept saying Sealed Power CS-274 was what I wanted. It was a common cam, but apparently it was suddenly pulled from the shelves at FLAPS, nobody knew why. Finally found one and put it on the shelf, and after a few years it's in the car. Now I'm wondering if that was pulled from sale due to a high failure rate, although I have not found any indication that's the case.

And as we speak of lifters - a while ago I realized I screwed up and put the old lifters in on the new cam so I was about to place a Summit order. Reading how widespread this issue is becoming makes me wonder whether there IS a good answer. I'm not looking for *****-to-the-wall power, but I AM looking for reliability. A lot of y'all have forgotten more about this task than I'll even know, and even here the jury is split between "follow the procedure properly and you'll be fine" and those who feel inferior parts will possibly doom even an experienced builder to likely failure.

Strike one is my own inexperience at doing this, strike two is the stop-and-start with lengthy times in between my working on it. Now it sounds like crap products could cause strike 3.

 

In the last 30 years Federal Mogul has gone though bankruptcy, I think, twice. Several years ago Carl Icahn bought F-M, axed all the low volume, low profit product lines and then sold it to Tenneco. That's the reason all the OE equivalent parts for vintage Chevrolet engines from F-M disappeared. It has nothing to do with poor quality. If you bought lifters with the CS-274 the combination should be fine as long as you use OE equivalent valve springs,

Elgin and Howard's Cams offer virtually all equivalent OE cams. If you buy one from them for sure buy their lifters, Also ask who manufacturers the lifters and who does lifter face finish grinding. I am beginning to believe that one failure issue is improper grinding of the lifter crowns.

Also, don't use the gorilla valve springs they recommend. Use OE equivalent valve springs (GM 3911068, Sealed power VS-677, if you can find them) Both may be tough to find, but the GM Performance catalog now has valve springs that appear to have the exact same specs as the ...068 as follows.

​​​​​​

94666580

SINGLE WITH DAMPER

• Outside Diameter: 1.241˝
• Pressure at Installed Height: 80 lbs. @ 1.700˝
• Solid Height: 1.150˝
• Average Weight (lbs @ in): 267

• Retainer Part Number: 14003715
• Valve Seal Kit: 10132715
• Production spring for 350-/290-HP engines

Note that the 350/290 crate engine has the same part number cam as the L-46/82 from '69 to '79, 3996962. This cam is essentially the same as the L-79 cam, except for the IPOML being 4 degrees later than the L-79 cam at 114 degs. ATDC and better lobe dynamics. Use it for L-79 rebuilds, but install it with the Cloyes manufactured NAPA adjustable OE truck replacement roller chain that allows it to be installed 4 degrees advanced to bring the IPOML back to 110 degs. ATDC, same as the L-79 cam.

I don't know who manufactures these parts from GM, but I think it's reasonable that they enforce adequate quality standards, and if you buy from an aftermarket cam grinder do your due diligence. Ask if the cam is Parkerized (like old GM cams, aids breakin), lifter sources and machining and make sure you install it with moly assembly grease on the mating surfaces, install a pint of GM EOS or equivalent and do the 2000-2500 RPM break in for 20-25 minutes. Then change filter, but don't change the oil, just top off and drive about 500 miles before you change.

Duke

 

Thanks Duke. Some of those corporate raiders sure left a path of destruction behind them, and we are still feeling the fallout.

In my case I bought cam only back then, and was about to order lifters, pushrods and rockers from Summit. It looks like the two choices for OEM equivalent are Summit's own brand and Comp. Also Crower "CamSaver" lifters which claim to deliver more oil flow. Those Crowers do claim to have a "precision ground face and finish".

So doing homework it looks like Howard's lifters are about 5 times the price of Summit's house brand - ouch, but if they make the difference between run and fail.....problem is, it sounds like there are multiple factors involved. OP says he's "afraid to buy a cam" and I'm starting to be "afraid to buy valve train components" as well.

 

Lots of good information here, but you mention fear, and I'm not immune to being intimidated by things out of my control. I'll only add, that fear or instilling fear has been a known marketing tool for some time. There's a cam grinder/vendor over at team chevelle that is relentless at it.

 

So Duke do you see any problem with the GMPP 10212811 spring I bought? It's a single spring vs the 94666580 which is a double spring.

 

Agree - it can be unsettling knowing what could happen. All we can do is gather all the info possible, make a logical decision, be careful, and hope for the best. My logical side says "You will handle it fine". My other side says "Oh ****, I just know it's going to bite me".

I'll add that in many complicated efforts,, there are contrary schools of thought - each with their own highly respected and successful experts. One guru says "always do ____" Another guru says "Never do ____" No matter which you choose, you are discarding the advice of one (or more) of them

 

GM sells a lifter kit. I have no ideal who makes them, but the individual lifter part number, 523770 is the exact same replacement hydraulic lifter number as shown in my seventies vintage Corvette P & A catalogs!

12371044

Hydraulic Lifter Kit (Set of 16)

• Used on 1986-and-older Gen I and Gen II-style engines
• Kit includes 16 hydraulic flat tappet lifters of P/N 523720 and is designed for use with standard-length pushrod kit or 100” kit
• Use P/N 5232720 for single lifter pieces

Here's the home page:

https://www.chevrolet.com/performanc...ponents/engine

Duke

 

The ...580 is not a double spring. It's a single spring with damper just like the vintage OE 3911068. Note that the ...811 spring doesn't mention having the damper like the ...580 spring, which appears to be identical to the OE ...068 spring. The specs are so close that I don't understand why both would be offer, and I also notice that a different retainer is specified, and the ...811 doesn't specifiy a seal kit, and I don't know what type of seal is in the kit specified for the ...580 spring.

So I really can't answer your question since there's not enough infromation to know the difference

10212811

SINGLE SPRING

• Outside Diameter: 1.250˝
• Pressure at Installed Height: 80 lbs. @1.700˝
• Solid Height: 1.200˝
• Average Weight (lbs @ in): 256

• Retainer Part Number: 10241744
• Valve Seal Kit: N/A
• CT350/350, 350 HO engines

94666580

SINGLE WITH DAMPER

• Outside Diameter: 1.241˝
• Pressure at Installed Height: 80 lbs. @ 1.700˝
• Solid Height: 1.150˝
• Average Weight (lbs @ in): 267

• Retainer Part Number: 14003715
• Valve Seal Kit: 10132715
• Production spring for 350-/290-HP engines

As far as cams go:

3896962

Hydraulic flat tappet

• Duration @ .050" Lift (deg): I: 222 / E: 222
• Maximum Lift (in) w/1.5 rocker*: I: .450 / E: .460

• Lobe Centerline (deg): 114
• Used in 350-/290-HP crate engine

24502476

Hydraulic flat tappet

• Duration @ .050" Lift (deg): I: 212 / E: 222
• Maximum Lift (in) w/1.5 rocker*: I: .435 / E: .460

• Lobe Centerline (deg): 112.5
• Used in 350 HO and CT350 engines

GM could certainly do a better job on high level cam specs. I assume by "centerline" they mean the inlet point of maximum lift, or is it the exhaust? And remember that (IPOML + EPOML)/2 = LSA, so they should either specify the LSA or EPOML to completely characterize the camshaft.

In any event as I previously stated I prefer the ...962 cam for L-79 rebuilds, but install it with an adjustable timing set to bring the IPOML back to 110 deg. ATC.

The ...476 appears to be slightly milder - about the same inlet closing point as the ...962 retarded four degrees with a little less overlap for a slightly tamer idle and a bit more low end torque with about the same top end power.

Given all the "issues'" with today's flat tappet camshafts and all the information and misinformation on the Web that makes it difficult to cull out the truth, it may be a good idea to buy valve train parts from GM, even if they cost a bit more, but there are many sources for these parts, so shop around for the best price.

Duke

 

2002 Engine LM7 5.3L in running condition complete with ECU and accessories for near the cost of a flat tappet cam swap
The 2002 junk truck engine supports 800bhp for 200,000 miles, perfect for a swap low cost if you have iron engine already

I'm not saying everyone should replace their antique original engines with other antique engines (LM7 is antique already)
What I am saying is, if you are going to spend money on modification in pursuit of a performance application (which I do not believe most are looking to do for this gen corvette)
Then wouldn't it be best to start with the most reliable affordable platform available? Rather than running expensive circles at a failing inadequate unsuitable foundation

logic flow for solving performance problems in aging vehicles
Non-original engine looking to modify for performance -> Cost, reliability & performance analysis -> Lowest cost, highest reliability per performance outcome

Take minutes to put it down into a spreadsheet and determine the most logical solution to the performance 'problem'