L78 tune up
 

It's time to tune up my L78. What are the valve lash specs?

Re: L78 tune up
 

Back in'66 I think GM was calling for .020 intake and .024 exhaust. By '70 they were calling for .024 and .028. Looser gives more bottom end torque. I run .022 intake and .024 exhaust with the stock cam. Our 427 ran almost 200K miles that way and our L78 about 30K since we bought it. Seems to work for us.

Re: L78 tune up
 

What cam was put in it when it was rebuilt? The cam card will tell what lash the manufacturer intended...our Crane/GM cam calls for 24/28, but someone told me the cam card on the same cam *now* calls for like 24/26?

Re: L78 tune up
 

As far as I know the engine is still stock.

Re: L78 tune up
 

Still stock, as in rebuilt to stock specs, or as in it's an untouched short block from back in the day with original guts? If so, 24/28 is where you'll wanna be...a little tighter is "ok", but *do not* go any looser...

Re: L78 tune up
 

Yes, rebuilt from what I know. Thanks.

Re: L78 tune up
 

What's "a little bit tighter", .001, .002, etc. Just curious.

Re: L78 tune up
 

Thereabouts...if you get too tight, the thing won't wanna rev and you're putting too much stress on the valvetrain...but conversely, too loose and you'll hammer your lifters to pieces. From .022-.028 is probably the safe zone assuming it's an older stock cam...I've seen a newer replacement cam with 16/16 figure, and then of course some of the newer tight lash cams take that a step further.

Re: L78 tune up
 

[ QUOTE ]
From .022-.028 is probably the safe zone assuming it's an older stock cam...

[/ QUOTE ]

Is that setting them hot or cold?

Re: L78 tune up
 

Hot, always hot...

Re: L78 tune up
 

What about an L89 ??....................

Ken

Re: L78 tune up
 

Can't remember off hand, it's posted somewhere around...but I'll grab my tune up manual or my Sun sheets and check!

Re: L78 tune up
 

L89 is the same procedures... https://www.yenko.net/ubbthreads/imag...mlins/wink.gif https://www.yenko.net/ubbthreads/imag...ns/naughty.gif

Re: L78 tune up
 

Buizilla's right. A HOT aluminum head motor with the same camshaft would use the same valve lash as a HOT cast iron headed motor. A COLD lash setting would be different between an alum. head motor and a cast iron head motor. I too, frown upon the cold lash.

Re: L78 tune up
 

Interesting, my old Chevrolet service manual calls for 22/24 lash on an L88...