Setting valve lash 428 cbj
 

How do you set the valve lash on an engine when you do not know the cam specs? I have a 1968 428 cobra jet with dove aluminum heads. My mechanic checked the valve lash and it varied from 0-.0024. Luckily the engine only had about 1500 miles on it since the last adjustment on the valves. When we took the valve covers off we did notice that one of the support posts for the rocker arm was backing out.

We had to remove the intake manifold to change the gasket and he said that the heads were more significantly ported than the Edelbrock Performer RPM manifold. I cannot recall the exact number rights now. The rocker arms are top notch, as well as the valve seals. My mechanic, who races, said that the original builder did not spare any expense in building this engine. I was told that it has a competition cam, but we do not have the cam specs. My mechanic was concerned about setting the lash too tight and causing long-term damage to the cam and lifters. He also said, an I have seen in other posts, that sometimes the intake and exhaust are set with a different lash. He set them all to .0014 cold, was thinking about going with .0012 but was concerned that it might be too tight. There was a little chatter early, but then as the engine warmed up it appears to have gone away. He said that we can always tighten them down more if the chatter continues.

So what lash should I use and how to you go about figuring out the cam specs without tearing the engine down?

Thanks.

Jim

Wow, that's a really great question. What I would do is pull the rockers off and put a gauge on the push rod and get an accurate measure of the cam lobes for intake and exhaust. Then I would compare those numbers to the most common "bigger name" cams for the years surrounding the build time. You might even call the builder, or post a message in the engine forums, asking what brand of cam that builder was partial to. That might help get you closer.

Patrick,

Thanks for your suggestions. I am going to run the engine for a little bit and then bring it back for more adjustments. My mechanic is not happy with the plastic oil pressure line and wants to replace it with a copper one. He says that he ahs seen the plastic ones melt and then the engine quickly pumps all of the oil out.

Unfortunately, from my understanding the original owner passed away and I have no idea who he had build the motor. I do not think that it was one of the major builder's, such as Keith Craft or Southern Automotive. If anyone out there did the engine build on ERA 717, please let me know. I called Peter at ERA and they have nothing on record of who did the build. It might even have been the original owner.

Maybe somebody knows a clever way of getting accurate lift/duration numbers without having to pull the rockers off and sticking your gauge on the push rod. There might even be a special tool for doing that.

whoa there turbo...i would re-read that post again patrick.....

you set the lash to what?

.0014? a thou and a half?
if this is really where he set them i would not drive it. if this had mechanical lifters i would be setting them at .024 hot.
then you will be at least safe while you figure out what cam is in it
.0014 is going to break stuff

He just has his decimal off. .0014 is the thickness of typical paper. I don't think my feeler gauges even go down that low.:LOL:

Wait a minute...
 

... we are talking solid lifters here, correct?:confused:

that is a possibility, but what if his decimal isn't off.
another take on it is ....if i set my cam to fourteen thou, things would break too.
the OP said he raced.......raced what? JR dragster? RC cars? turtles?

Well, alright... point taken.:cool: The OP should confirm his correct numbers, paying careful attention to that pesky decimal position, and confirm that he has solid lifters and not hydraulic ones.

Yep, .024-.025" would be a safe lash spot for a solid flat tappet cam until you figured out exactly what you have.

That's what mine turn out to be when they're HOT, and I set them COLD to .018" -- and I have an old style SFT cam.

Brent, do you know any clever way to figure out the lift/duration without removing the rockers?

thanks for substantiating my statement Brent.
in a lot of cases with aluminum heads the lash grows with it warming up.
in some cases it stays where you set it cold. for instance, when you mill the rocker bosses down and install T&D's, on my motor anyway, there is absolutely no change from cold to hot. i have checked this 5 times now on my heads.....once i got a one thou difference, but i chalk that up to error in the feel.
the biggest lash i have seen is on some off the shelfl Crowers, lash spec is .024 Int-Exh


could set an indicator on the VC rail and measure the valve retainer dipping

I've never had the lash not grow when hot on an aluminum head combo....you have an interesting scenario there. I can always count on my iron block/aluminum head combos growing about .006" when hot. All-aluminum FE's grow about .011". My all-iron stuff either does not grow or it grows a few thou.

Patrick, all lash specs are always given as hot. You can remove the lash, then check valve lift at the valve, then divide by the rocker arm ratio to get lobe lift. Measuring duration at the valve is going to be tricky, but it can be done with a degree wheel and some patience.

Lash specs are derived from taking the lash ramp and multiplying it by the rocker arm ratio. You really need to talk to the cam grinder to get a dead on spec, but unless it's a tight lash lobe, you're pretty safe in the .025-.030" range.

Assuming he's got solid lifters, then let's just set it at 24 HOT and knock off early for the day.:) Now watch, it will turn out he's got hydraulics....

Yeah, the part about chattering at first, then going away has me a little puzzled.

:3DSMILE:, and they're set to .0014. and we all look like blabbering idiots:3DSMILE:

Brent i too find my lash strange, its the reason i keep verifying they don't move. that was with the solid roller, i will now start running solid flat tappet.
so that may change the dynamics a little.

Well, let's just have him try and squish them down a bit and see what happens.

that i will agree on

Noooooooooooooo

But he can see if there is some hydraulic lifter bleed down which would indicate hydraulics----then if so-----------

OK, no squishing then. Just start it up cold, run it just long enough to pump them up, measure the lash, then wait a while and see if the lash grows. Of course, a true mechanic would bill out the time that you sit, wait and watch for that lash to grow. A great mechanic would do several cars at the same time and bill the watch and wait time to all of the owners, with no pro rata discount, of course.:cool: