valve adjustment

[Stingray74CC]

hi all,

I've been reading through the valve adjustment threads that have been posted here in the past. Good info, but I had a question that wasn't answered.

Lets just say the specs say that there's a .030 gap for the rockers. Will reducing this gap give any more performance due to higher lift or should I leave that alone.

 

[WhalePirot]

Follow the specs

Too tight (small) of a gap does not allow for adequate thermal expansion and incomplete valve closure, which could burn the valve(s).

 

[rpounds]

Amen to that brother!!! Burning the valves is not a lot of fun! Besides, if . . . and that's a BIG IF, there is any performance improvement, you would never be able to feel or see it . . .

Stick to the correct clearances and you'll be nothing but happy, happy, happy . . .

 

[Stingray74CC]

Thanks for the advice. I'll let ya'll know how it goes after this weekend. I'm doing it Saturday afternoon.

 

[rwd]

Reducing the gap is not advisable, but if the gap has increased significantly over spec due to wear or whatever (including previously being set incorrectly), and it very likely has, setting it correctly can definitely increase performance.

Had that issue on a bb, and the difference that setting the lash made was night and day. It even changed the sound of the engine. Since most specs require the engine to be warm and running, and some of the engines squirt oil all over the place, they used to make clips that fit over the rocker holes so that running the engine with the covers off while setting the valves doesn't make a mess. It might be worth getting a set, just in case. If you don't need them, you can leave the package sealed and take them back. FWIW.

 

[1DOWN6TOGO]

i definitely recommend getting clips to keep ur oil in the engine.
i adjusted mine a few weeks ago. i didn't know (or consider) that hot engine oil was going to be spraying out at me. well, my high volume oil pump made quite a mess, burnt the hell outta me, and forced me to go buy a few more quarts.

we learn from our mistakes. one day i'll be a genius. if i survive that long.

 

[Stingray74CC]

adjustment done

Well, I started the day and the job thinking that my 427 would have mechanical lifters. I began adjusting the gaps and something didn't seem right. I went inside to ask "the experience" (I like to keep a retired mechanic around when I'm trying to tear something up.). He came out took a look and after pressing on the rockers told me that I had hydraulic lifters. NEWS TO ME!!! Is the right for that engine or has someone switched something up during the rebuild? I looked through some books but didn't come up with anything.

 

[Tom Bryant]

Anthony,

In '69 the 390 and 400 hp engines had hyd. lifters. The 435, L88 and ZL1 had solids.

Back in the day of the "097 Duntov" cam ('57-'63) the lash specs were .012 intake, .018 exhaust. It was a common racer trick to run the intakes at .008 and pick up a little performance. In any case I wouldn't vary very far from specs and then only on a cam with wide lash specs.

Modern cams are probably speced at optimum from the start.

Tom

 

[Stingray74CC]

Thanks for the info Tom. I'm gonna have to do a little more researching on my engine to see what exactly is under my hood. We did adjust the valves as "the experience" thought necessary. He told me to put the book away. hahaha I think I may have picked up a little bit from it.

I actually went under the valve covers in an attempt to stop a tapping noise that I thought was a noisy rocker arm. The noise didn't stop. It also sounded like it could've been a exhaust leak. I'm going back to that theory now. I've already replaced the manifold gasket and that didn't stop the noise. Now I'm thinking that I have a crack in the manifold. Those darn things are $350 each. whew....maybe a good time to go with some headers.

 

[WhalePirot]

A mechanic's stethoscope, a long screwdriver or similar tool can be used to probe for those mechanical noises. It takes a bit of practice to weed out the various noises, but the 'ticker' can be isolated.

If you go to headers, I strongly suggest that they be coated, preferably ceramic. The underhood temperature increases from the thinner walled exhaust pipes is high. The thermal efficiency and flow of the coated ones is improved, as I have felt with my seat-of-the-pants meter. The added bonus is corrosion protection 'back east'. The wrap works well, but interfered with my bolt access and could absorb moisture (corrosion). The hot coating, inside reduce boundary layer drag on the gas flow. Check visually, for obstructions from the manufacturing process.

Consider the downstream flow capacity, too. The headers will improve exhaust flow, but, 1) will be optimized with adequate pipes and mufflers, downstream, and 2) may required a mixture enrichment due to better exhaust gas scavenging from the cylinders.

Buy it right; buy it once.

 

[Stingray74CC]

one step ahead of ya

We actually used a mechanics stethoscope. Didn't come up with anything. Can a cracked exhaust manifold be repaired even if I do find the crack?

How about this. Take a spray bottle of soapy water and spray it around the manifold and look for bubbles. This may only work when the manifold is cold or would it work at all? Anybody else have any techniques for finding a crack in the exhaust manifold?

I would like to keep the manifolds on the car. Plus I don't have the money to run out and buy new ceramic coated headers or a new manifold for that matter. ($350) That's why I've been so persistent in locating this racket and not just replacing the exhaust manifold.

Thanks for the tips. Ya'll have fun in Bowling Green. I wish I could be there.

 

[vmrod]

I would like to get some valve covers with removable tops. So, it will contain oil during valve adjustments.

When I put a new engine in my vette, I was adjusting the valves. (in my garage) Oil which leaked onto the manifold ignited. Fortunately, a fire extinguisher was handy! Since then, I always insure that I have something to put out a fire!