Ohiomark

I've read that thses engines require more attention than the 300 or 350 HP engines regarding valve adjustment? What is the recommended schedule and how involved is this? I've adjusted VW 1200CC bug motors, but obviously this is a different animal...

MikeM

10-12 thousand miles. unless you run it extremely hard or the engine is worn.

It's very simple. Lot's of posts same question as yours. Do a search.

There's also posts about tightening up the lash from the factory specified clearance. Many, including myself do not recommend doing that.

ohiovet

I have a 340 HP 62 and I also check the valve lash around 5,000 miles ( every 2 or 3 years) and adjust if needed. if you don't race this interval has been fine for me.
Also listen for odd noises and you might want to adjust them if you hear anything strange..

Critter1

I agree with that MikeM character. He knows what he's talking about. Definitely go with the correct original factory setting of .030" for both intake and exhaust.

Pay no attention to the man behind the curtain that keeps telling folks to set the lash tighter than .030".

63Corvette

I set mine every race weekend...........sometimes every session

OldKarz

I have set mine 1-2 times in last 10 years....simple. Great engines!

pop23235

These engine require attention, but not necessarily on the valve adjustment! They want to run!

cv67

x2.theres a reason they spec that lash

Also use new polylocks you wont be adjusting as often. Its when they get worn out you will be adjusting them more often.

aaronz28

Duke and John's "tighter" than .030 setting is specifically referring to valve trains that use Factory Stamped Original Equipment rockers...

they were supposed to be 1.5 ratios - but in actuality, due to sloppy stampings - the real ratios were more like 1.2-1.3 - which means less effective duration and less lift - tightening the lash up helps achieve the factory specs of the cam.

NOW - for those of us who use any aftermarket rocker - be it a traditional stamped arm, or a roller tip - the tolerances are far more accurate - and chances are that 9-out of 10 rockers will actually measure 1.5 ratios. I use the comp 1.52 roller tip - and .030 is perfect - with poly-locks - my engine sees 6k on a regular basis - i've not had to tighten a lock since i put it together. I've checked it once or twice with a gauge to be sure - but never had to re-adjust one.

if you have the "O" stamped rocker arms still, and have not measured to see exactly what their ratio is - you can tighten them up and the motor will like it providing you are 100% certain you set them when the lifter is on the base circle - you can not use the TDC method as even at tdc, the 30-30 cam is on the ramp already - if you have true 1.5 ratio arms - it will not like the increased overlap, although you can tune it to run quite well - just it acts like a bigger cam - and we really don't need a bigger cam than the 30-30

having said that - tightening up the last with true 1.5 arms generally requires additional timing, carb tuning etc.

A

Frankie the Fink

Tighter lash specs aside....the solid lifter adjustment procedure is no trouble at all once you get your own system down. As stated...every couple of years works for my C1 and I have the task down to about 40 minutes including double checking the lash...

The question really seems to be, "Would you avoid the higher performance motors because of the extra maintenance?" The answer is, "No!"

SWCDuke

NO, THE OE PRECISION STAMPED ROCKERS ARE NOT "SLOPPY"!

The ratio varies throughout the cycle and this is true or ANY conventional rocker arm, both shaft mounted or ball and stud like Chevy and Pontiac engines, no matter what the vendor says. It's basic Euclidean geometry.

The actual lash point and max lift actual ratios are specified in the Hinckley-Williams valve adjustment paper if anyone is interested.

Duke

aaronz28

I misunderstood the article - this is the paragraph that states it -

"Set them cold at .026"/.026". The actual measured (stamped
rocker arm) ratio at the lash points is actually about 1.37:1 (not the
design 1.5:1, which is a max lift measurement), so the clearance
ramp, which is exactly .020" high on the lobe, is all taken up at .0274"
clearance; .030" clearance with the valve closed is too loose - the
ramp ends/begins before the .030"clearance is taken up, resulting in
the valve being lifted off and returned to the seat at greater than ramp
velocity. This will contribute to valve seat recession, and can cause
valve bounce at the seats at high revs - it will also be noisy."

So then why did GM spec .030 instead of .026? somewhere I also read that the FI engines were originally slated for .025 Lash with the 346 cam - but that was changed to .030 so that they could get enough cranking vacuum for the signal valve. Is this the case, or did I imagine that.

SWCDuke

For one thing you have an old, obsolete version of the paper. The latest is dated September 2008 and has updated lash specs and other information.

The lash spec on the 30-30 cam engineering drawing is .025", and this is based on the 1.5 "design ratio" times the .017" clearance ramp height. Apparently Chevrolet was not concerned about the slight rocker ratio variation throughout the cycle and simply ignored it.

It's never been determined why all the service literature specified .030", but it has been opined that it was to improve idle quality on FI engines, which were always more of an issue than on equivalent carbureted engines, and that's a reasonable opinion.

Also, the max ratio, which occurs at max valve lift is NOT the 1.5:1 design ratio. It's less. Read the paper!

Duke

ohiovet

Here is a explanation of the subject for you uneducated people who care.
Bruce B just joking...



Euclidean geometry - Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Euclidean_geometry
Wikipedia
Euclidean geometry is a mathematical system attributed to the Alexandrian Greek mathematician Euclid, which he described in his textbook on geometry: the Elements. Euclid's method consists in assuming a small set of intuitively appealing axioms, and deducing many other propositions (theorems) from these.

aaronz28

So my referece to the article was technically in-accurate - -

however, I can assure all without doubt - that the OE rockers are not 100% in tolerance... and certainly not now after 50years worth of mileage.

I have a whole box in my garage with about 60-70 "O" stamped rockers that I've removed from various SHP engines over the years.

When I first read this article - i assumed (incorrectly apparently) that the variance in the rocker stamping was the reason for the discrepancy -

so i grabbed a handful, and started measuring max lift of a 346 (30-30) cam at the lobe, and the valve and doing the math... Guess What???

out of about 10-12 rockers I measured, there weren't two that were within what I'd call acceptable tolerance. Now I suppose it could have been routine wear and/or grooving of the rocker from the ball that made the measurements all over place - but it confirmed how I originally, albeit an incorrect understanding of the article.

MikeM

Years ago, one of the major cam grinders that also sold roller rockers made the same statements about the stamped rockers. So, they claimed a much more accurate, consistent valve action with their roller rockers. They also claimed they had a true 1.5 ratio. For whatever that might be worth on a street engine.

I'd think it reasonable to assume the GM engineers knew what the working net ratio of their stamped steel rocker was when they designed the 30-30 cam whether it was 1.30 or 1.50 or something in between. I would also follow their recommended lash clearance of .030. Years ago, I tried that tight .025 spec on my '69 Z with a 4.11 gear and it flat killed the low end. The engine was a little quieter though. I went back to .030. Others have had similar experiences with the tight lash.

aaronz28

i remember reading this very thing.... and whether or not it was marketing hyperbole, i did go through the whole process of measuring some new vs old and found the statement to be accurate.

again - how much that consistency is worth on a daily driven street vehicle is debatable - but when i measured the original rockers - I was seeing +/- .025 valve lift -

on the comp roller tips - they were all spot on - maybe a variance of .002 and at that amount - who cares

MikeM

So, if you tightened the lash to .025 from .030 you still had the +/- .025 variation on the lift with factory rockers? But you did increase duration. Correct?

If I was building a NHRA legal stock engine, I'd be picking through a pile of rockers and get the best ones to optimize performance.

aaronz28

when i measured - i set the rocker for zero lash - similar to the way you'd degree a cam in.... although i did double the work - measuring the lobe lift with one dial - and then measuring the valve travel with a dial on the top spring retainer... it was a pain in the *** for sure.

the worst of the rockers i found yielded .448 before lash - that could have been a particularly worn rocker arm - but others were around .460 and out of all the ones i checked - i found one rocker that measured exactly .485 max lift - and interestingly enough, one that measured .493

so i just decided to shelf all of those rockers and thats when I decided to order up the Manley stamped versions... i measured 3 of them, and they measured (with the 30-30 cam of course) .483, .485, and .486 I thought that was consistent enough for my street engine.

aaronz28

also - i didn't have a degree wheel on I did this - i was basically interested to see just how/if the max lift would be different with a handful of different rocker arms.... It would stand to reason that less valve lift would also indicate less valve duration using that particular rocker...