[mn65bis]

I have a 70 chevelle with a stock 402/350hp engine. Auto trans, 331 gears fact intake, carb and converter. 92k miles.
It needs a valve job so I decided to freshen it up. It runs strong as is and seems like a high 14 sec car. This car is a cruiser and easy driving is the most important factor. Is there a limit to the amount of lift stock rockers can handle? Any suggestions on a cam grind?
Thanks

 

[64SS427]

Any 40 year old cam design is outdated. Call a couple cam companies and see what they suggest for your combo/ situation. Everybody is going to have a different opinion so do expect to see some differences.

If it were mine I would be looking for something with about 268 advertised duration, with as much as I could get @.050 for that, probably around 230, on a 108 LSA with as much lift as I could get.

Devin

 

[Tom Mobley]

if you're just pulling the heads for a valve job leave the cam and lifters alone, IMO. It's a much larger job to pull the cam and there's problems with new non-roller cams.

my advice: be real careful here. very easy to fall into the "As long as I'm in this far....." syndrome. Unless you've got lots of time and money you don't want to go there. If someone tries to tell you the fresh valve job will blow out the rings or similar blow them off, politely if possible.

Why exactly do you think it needs a valve job? does it have a burnt valve?

 

[magicrat56]

just my 2cents,but I think I would leave it alone, had 2 69's always has impressed me how hassle-free they ran. remember its a cruiser,have fun tuning instead of heavy wrenching. I ran one 402 with a L-78 solid without rocker problems so I guess around .520 lift? the older cam profiles like from CRANE,COMP,ISKY.....were slower designed ramps which kept the valvetrain quiet.

 

[mn65bis]

It has a shake to it at idle in drive. It has sat for 35 years but doesn't smoke and still runs strong. It has new wires tried 2 sets, 2 caps, points, plugs and rebuilt carb. I will do a compression test next as I suspect a problem. I was thinking after all those years a ball hone, bearings and rings wouldn't hurt but maybe I should just leave it all alone and get a valve job if it is the problem. I have to admit I've lost my share of camshafts and maybe the risk isn't worth the hp gain.

 

[sschevellefan]

A friend of mine has a similar engine in his 66. He`s running a comp 280 magnum. Runs strong and makes alot of power for a "stock engine" with just a cam swap. Remember to read the oil stickys and break it in correctly.

 

[Tom Mobley]

may have a vacuum leak, affects idle quality without really affecting the way it runs on the road. get some road miles on it, then run a compression check before anything else.

You start tearing into that thing, there's nowhere to stop. have the fat wallet handy.

 

[VinceS427bb]

stock lift limit on rocker arms is in the .520 to .550 range depending on your heads.
if mine i would go for a mild aftermarket cam or even swap over to a factory roller cam with some after market roller-lifters.
there are several takeout factory type roller cams that are cheap-$$$
here is a link about these;
http://www.chevelles.com/forums/showthread.php?t=264788

 

[mr]

I have a 70 chevelle with a stock 402/350hp engine. It runs strong as is and seems like a high 14 sec car.

... if you're just pulling the heads for a valve job, leave the cam and lifters alone, IMO.

... it may have a vacuum leak, that affects idle quality without really affecting the way it runs on the road.

I think I would leave it alone, remember its a cruiser, have fun tuning instead of heavy wrenching.

I ran one 402 with a L-78 solid cam without rocker problems, so I guess around .520 lift ...

... stock lift limit on rocker arms is in the .520 -to- .550 range, depending on your heads.

x2, ... unless it impossible to live with, I'd leave it alone until a major malfunction happens, then deal with it.

 

[mn65bis]

I think the thing to do is just confirm the need for a valve job then pull the heads and get it done and see how it runs. I'll check it out this week and let you guys know how the comp test went.

 

[Tom Mobley]

compression test: all 8 plugs out, ignition disabled, battery fully charged, carb blocked open

 

[mn65bis]

Pulled all 8 plugs, they looked nice and clean, All cylinders were at 175 give or take a few pounds except for #2 that read 50 lbs. Pulled the head and it still had the steel shim gasket, cylinder walls looked real nice and I could still see some cross hatch marks? Valves look kinda crusty and the exhaust valve lost it's seal due to the crust. Lots of bent pushrods but it looks like an easy fix if the head isn't cracked.

[/url] 027 by mn71w30, on Flickr[/IMG]

[/url] 028 by mn71w30, on Flickr[/IMG]

 

[mn65bis]

[/url] 022 by mn71w30, on Flickr[/IMG]

 

[SWHEATON]

You lots of bent pushrods = over reving the poor L34!/LOL!!!

Could be slightly bent non sealing valve on the cyl with low comp.(only 50psi?)

While the heads & intake are off remove the lifters (MUST keep location integrity of lifters ) so you can inspect cam to eunsure its not an issue with a cam lobe-s or lifter-s going bad causing low compression on 1 cyl.

And while we are on that subject since this is a FT cam'd motor what mfgs oil and grade are you running in it? (Hope its oil properly formulated with additonal ZDDP required for old school FT cam'd motors)

Could be a bad valve spring casing low comp on 1 cyl too that should be caught durring valve job @ machine shop.

Lastly,with stock 10.25.1 comp along with the very small short duration cam the L34 396 came with creating higher cyl pressure it may detonate at times on todays lower octane 93 non leaded ethenol'd fuel it was never designed to run on in the 1st place.

That 40+ yr old motor motor was designed to run on LEADED FUEL WITH A MIN OF 98 0CTANE AND NO ETHENOL ADDED and on hot summer days at times you had to step up from 98 0ct leaded fuel to Sunoco's 260/advertised as 102 octane fuel in those motors to avoid detonation if you hammered it on a hot day.

So dont expect much from todays lower octane 93 non leaded ethenol'd pump fuel in your motor that was never designed to run it in the 1st place esp if running a proper timing curve which could end up in detonation city.

You can back off base timing to stop detonation but that results in power/perf loss and higher idle in traffi ctemp too.

I run the real deal " real lead 130 booster) in my 69 396 so mi can run a full proper steet perf ign timing curve for max power.

I mix the real lead booster with 93 octane pump fuel to get approx 97-98 octane which the motor repsonds very well to with it approx 9.8 or so comp.

It runs pretty dang spunky for being just a mild built .030 over 396 now 402 bbc with approx 9.8 comp,mild HYD FT perf cam ,tweaked q-jet for better perf on stock intake along with mild pocket port on heads and extrude honed ex manifolds along with flowmasters & stock size 26" tall tires , m20, &1 2 bolt w- 3:31's .

But it would detonate on 93 fuel by itself without the lead booster esp on a warmer day when accell under load and or when at WOT pulling some gears.

If you find cam to be toast and you decide to go easy repl route staying with hyd Ft cam PM for a nice cam rec that will significantly inc perf without hurting driveability at all with auto trans.

It would be a mild HYD FT perf cam with mild lobe design that should not be a candidate for failure like some of the more agressive ft designs out there today with more radical lobe design. That can be an issue esp if you dont use proper quality assmebly lube that stays put untill ya fire it up breakin or dont use proper oil/oil additive for breaking in a mild HYD FT perf cam along with proper oil for a mild hyd perf cam post breakin too!

Good luck.

Scott

 

[nashville beth]

I was agreeing with Tom to leave the cam alone, but since you've gone this far.....

Just kidding. BUT I do think the cam I'm running would be ideal:

Howards hyd roller : 219/227 duration

http://www.summitracing.com/parts/hrs-123515-10/overview/make/chevrolet

Stock long-slot rocker arms that came on L88's:

http://www.crateenginedepot.com/Rocker-Arm-Kit-12368085-P9495C578.aspx

And Howards pushrods :

http://www.summitracing.com/parts/hrs-95220

This is the biggest cam I would run in a small 402.

The next step down is 213/221, which would be a great choice too, especially with a stock converter.

http://www.summitracing.com/parts/hrs-120235-12/overview/make/chevrolet

 

[mn65bis]

Thanks for the help guys and listing the cams so I can go back and find them in the future. I decided to just get the one cylinder touched up and re install the head. I am surprised that a stock cam would be bouncing off the pistons like that to bend all those pushrods. I will confirm the lift of the today and get the head fixed.

 

[kettbo]

ok, gonna fix the one valve seat...

check EVERY lifter bottom while you are in there for wear
myself, I'd go for new valve springs...figured out why you have a lot of bent pushrods?
My guess, too many revs on too mild/tired of a spring.

Yes, the 396/350s were good runners back in the day. Thing is, the days for good fuel have passed. You need good octane for that cam or go with a somewhat larger new grind to better run with the stuff they call gas now

 

[mn65bis]

I've driven the car a couple hundred miles already and if it pings it isn't noticeable. I filled it with 93 oxy fuel and the timing is up on 36. I'll check the lifters but I'll need a little more persuasion on the spring change. Wouldn't a higher spring pressure add to the risk of cam lobe failure? The springs are a double spring and it does seem to rev fairly high. How about a rev limiter?

 

[kettbo]

I did not see signs of detonation on your picture of the #2 cyl. Good.
When I said HIGHER, more precisely was thinking you had an engine with a lots of use, maybe weak springs. Probably would have been better if I had stated SPEC on the spring pressure. Still curious on the bent pushrods. I'd be taking a good look as you are inside the engine already.

Correct, springs with a LOT of seat pressure can lead to cam/lifter failure
Good oils, plenty of threads here on this, can prevent this failure
You do need a certain spring pressure to get the job done. You say double spring, perhaps you do have enough pressure.

I saw no valve hits on your piston
Your engine may rev higher than the power band. The lobe profile will cause the valve to float at a certain rpm, this is not good. I'd guess in the 5000-5500rpm range. But the POWER range is lower...IIRC, great torque but done dealing around 4800rpms. Need some help from the guys just a tad older than me on this. All my BBCs when I was young had big cams already.