after fitting new alu heads , I did a mistake in lashing the valves.

set them cold at 0.012 in and 0.014 ex , instead than 0.022 and 0.024
it has been my mistake in reading the specs...I read the ZL1 specs...

My engione has L88 cam , solid lifters

I have fired up the engine and run it for about 10-15 minutes just to adjust the timing , filling the cooling system...not driven the car.

should I fear for such tight valve lash or can I do a short ride , heat the engine and then readjust the valve lash to exhact specs?

I would like to lash the valves with engine not running ( to don't have lot of oil all around in the engine bay ). Any advise to do a good job?

 

Fear it? You should fear spiders, okay, but lash on the tight side in this instance isn't a big deal.

Run the engine to operating temp. Turn it off and run the lash on one bank. Fire the engine again to op temp, and run the lash on the other bank.

Only the cam designer knows why the lash specs are what they are. It's not uncommon to run a tighter lash since it will increase your duration and is frequently done in dyno sessions to see if the engine would like more cam.

If it were me, I'd get the lash in or close to spec before putting any miles on it. A little tight is better than a little loose.

 

yup!

 

Aldo, with your combination, if you try and set the lash with it running, all you'll get is a feeler gauge with the end chewed off. (don't ask how I know!)

Like gerry said, a little tight is better than loose. Adds too much shock into the valve train. I'd set them to specs before I get too many miles and also keep a close eye on everything until you do get some miles on it. I'd expect the valve train to "loosen" up as things begin to wear in and seat.

 

i could never understand why some folks insist on setting lash with the mill running......

 

Elle88,

Heres how i was taught 20 years ago and love it... Get it close cold to your cam spec card... As others said not that critical if your a few thousandths off.... I like to run the mill till operating temp, then with a helper, pull both covers off and all 8 plugs... (You can do one side at a time if help is unavailable....) Add starter bump switch or known as remote switch..(race cars have a button to solonoid for this reason...)

Then rotate engine doesnt matter which one you start on but rotating by hand you can cover more of them.. I use a black marker to mark em when done... When EXHAUST starts to OPEN Adjust INTAKE!!!! When INTAKE starts to CLOSE Adjust EXHAUST!!!! That simple and your on the Base circle of the cam.. Never messed one up yet... I love solid lifters especially in a big block!!!!!

 

...yup..great post......that was the HARVY CRANE method in the early sixties when he first founded crane cams.....i have been using the method for over 30 years without a hiccup on solids,rollers and hydraulics..even cold on an engine stand..

 

Let us know how it performs on pump fuel!

 

Thanks everybody.

road test tomorrow, today is raining.

 

No time yet for adjusting valve lash ....but I made a short 3-4 miles ride around the shop to check something here and there ( I couldn't wait to drive the car...)

here are some issues.

- leak at exhausts gaskets. already re-tightened after and during the first warm up but still leaking. gaskets are these.
http://store.summitracing.com/partde...5&autoview=sku

-already retorqued the intake bolts after first warm up , but some vacuum issues
the power brakes , after one braking, loose vacuum and need more effort. headlights come up slow. I see no leaking-broken vacuum hose.
I measured the manifold vacuum at idle after A/F screw adjust and it reads 5.9" hg . before head replacement was about 6.2-6.7". too low? L88 cam and dual plane oem intake with just 1/2" communication between the 2 planes

my mech says that being possibly valve lash too tight , some valves are possibly not totally closing, causing a low vacuum condition. I think we'll adjust valve lash tomorrow

Aldo

p.s. I run now a L88 cam with 10:1 CR and about 100 oct ron gas. before heads replacement was 11.3 :1 CR , 102-103 oct .
the car behaves about like before in terms of cam "stall" at off idle-critical just as before. so the lower CR doesn't seem to cause a worsening of the already critical situation.

Timing : I have setted the timing at 16 deg@1000rpm , 29deg@2000rpm , 35deg@3000rpm
I think I'll add 2 more deg initial timing

 

I have basically the same setup I get 12-14" vacuum @ idle. Actually, I have a wee bit more cam than the L-88 has/had. Headlights are slow, and the vacuum assist on the brakes goes away pretty fast at idle, other than that it's great.

 

I set my lash cold. I set it 2 thousands tighter and when it warms up it gets looser and is at the spec I need.

 

or my vacuum gauge is wrong or there's something strange...
you have a zl1 cam if I remember and double my vacuum...my emgine's and yours vacuum should be closer one to the other
BTW brakes were properly working before heads replacement and vacuum now is just a bit less

 

Low cylinder pressure causes low vacuum. You look for the usual suspects: maladjusted carb, vacuum leak, late ignition timing, poor ignition performance, restriction in the exhaust, excessing valve overlap (might be in your lash), poor compression. That should give you enough to start with.

 

as long as the valves are set .010 too tight....idle vacuum will be lower than it would be at proper lash settings.....

 

If your L-88 has aluminum heads, the valve lash will open up 0.004-0.008" when hot compared to cold lash settings making you 0.006" too tight (acceptable range from stock lash.) Vacuum issues can be ignition timing and fuel mixture related too, if Air/Fuel ratio is off low vacuum and if ignition is retarded, low vacuum can result. Yiu may also want to check for gasket leaks around carb and cylinder heads with a can of spray carb cleaner (idle will increase if there is a gasket leak and carb cleaner is sprayed on it.)

 

my 074 ls6 heads grow .006 from cold to hot. I set the lash hot the first time and then let the heads sit overnight and check the same valve the next day and you will find exactly how much your will grow. Then you never have to run the valves hot and burn your fingers and restart the motor for the other side. The EOIC is the best and only way to set lash. This comes from the motor guy at rousch, they only set valves at room temperature

 

Set lash correctly and pull all the vacuum lines off the carb and plug the ports noting where they go. Start the motor and check vacuum. Then plug each thing back in one at a time. If you get a sudden drop your leak is in that vacuum system. Your vacuum shouldn't have dropped with only a head change.
with checking for a leak at the carb base. It would suck if it was an intake manifold gasket leak. Running too tight of lash can burn an exhaust valve or wipe a lobe and will cause a drop in vacuum. Set that first.