SBC 350 Valve Lash Adustment

[Vetman]

When I retired a few years ago I treated myself to some tuning parts including alloy 64cc heads, air gap manifold, roller rockers, and some dress up parts. The car already had a mild performance camshaft upgrade. These new parts sat under my study desk for a couple of years until I summoned up the courage to pull down my perfectly running engine in order to fit them.

I invested in a Leakdown Tester to test cylinder leakage once the new heads were fitted. One cylinder leaked on the new head exhaust valve. I spoke to Edelbrock and was told that this would bed in and stop leaking.

I watched many YouTube videos including many on valve lash adjustment. I went through the process one cylinder at a time using the method of rotating the pushrod between finger and thumb while tightening the rocker nut until friction was felt. I then the applied a recommended amount of extra tightening. This advice varied between 1/4 and 3/4 of a turn. I used 1/2 turn. I completed all cylinders but decided to repeat the leakdown test. I found a number of the cylinders were now leaking on the valves. I concluded that my valve lash adjustment had lifted some of the valves off their seat.

I repeated the operation but this time I tightened the nuts while checking up and down pushrod slack. I then used a 1/4 turn extra tightening. I repeated the leakdown test and now all cylinders, apart from the existing exhaust valve leak, were sealed.

Later, after running the car for say 100 miles, I repeated the leakdown test on the dodgy cylinder and it no longer leaked on the exhaust valve.

My experience suggests that valve lash adjustment is a very sensitive operation.

 

[Roscobbc]

When I retired a few years ago I treated myself to some tuning parts including alloy 64cc heads, air gap manifold, roller rockers, and some dress up parts. The car already had a mild performance camshaft upgrade. These new parts sat under my study desk for a couple of years until I summoned up the courage to pull down my perfectly running engine in order to fit them.

I invested in a Leakdown Tester to test cylinder leakage once the new heads were fitted. One cylinder leaked on the new head exhaust valve. I spoke to Edelbrock and was told that this would bed in and stop leaking.

I watched many YouTube videos including many on valve lash adjustment. I went through the process one cylinder at a time using the method of rotating the pushrod between finger and thumb while tightening the rocker nut until friction was felt. I then the applied a recommended amount of extra tightening. This advice varied between 1/4 and 3/4 of a turn. I used 1/2 turn. I completed all cylinders but decided to repeat the leakdown test. I found a number of the cylinders were now leaking on the valves. I concluded that my valve lash adjustment had lifted some of the valves off their seat.

I repeated the operation but this time I tightened the nuts while checking up and down pushrod slack. I then used a 1/4 turn extra tightening. I repeated the leakdown test and now all cylinders, apart from the existing exhaust valve leak, were sealed.

Later, after running the car for say 100 miles, I repeated the leakdown test on the dodgy cylinder and it no longer leaked on the exhaust valve.

My experience suggests that valve lash adjustment is a very sensitive operation.

Made even more 'difficult' when you try to carry out the adjustments with the engine whilst still hot. By the time you've done the last one the engine has 'cooled off' and you'll possibly have a noisy lifter and run though the same procedure again as the lifters also bleed down......

 

[Vetman]

The first time I did this early in my ownership, I used a feeler gauge with the engine running, and set a gap like I did for other cars. The clickity noise was terrible so I tighten them until the noise stopped. A hot and oily way of doing it.

 

[Roscobbc]

The first time I did this early in my ownership, I used a feeler gauge with the engine running, and set a gap like I did for other cars. The clickity noise was terrible so I tighten them until the noise stopped. A hot and oily way of doing it.

As you've said - with hydraulic lifters you tighten-up the adjustment and at the same time rotate the respective pushrod untill it starts to bind - then tighten a further amount to 'preload' the lifter and remove any play. The amount one tightens varies depending on who suggests but 1/4 of a turn for a cooking engine up to 3/4 tirn for performance engines seem the norm.

 

[Vetman]

I think the problem with the rotating method is that with oiled connections you can apply preload during this first adjustment before you then apply extra preload. Anyway I guess practice makes perfect if you do it often. I thought about this today after watching a C3 video where the mechanic did the adjustment in a very robust way with large spanner pulls. I think if you are going for 3/4 turn then you should check that you haven’t pushed them off the seat before moving on.

 

[Forrest Gump]

I think the problem with the rotating method is that with oiled connections you can apply preload during this first adjustment before you then apply extra preload. Anyway I guess practice makes perfect if you do it often. I thought about this today after watching a C3 video where the mechanic did the adjustment in a very robust way with large spanner pulls. I think if you are going for 3/4 turn then you should check that you haven’t pushed them off the seat before moving on.

I don’t think you would have “overdone“ finding the initial contact point wether you are spinning the pushrod or just feeling when the slack goes. You can pretty much just turn the nut and feel the contact - a bit like when using a micrometer. The half turn of pre-load is just moving the hydraulic lifter down its bore slightly to ensure it always remains in contact with the pushrod. Maybe when the preload is first applied it could unseat the valve if the lifter is full of oil but it should bleed back until the valve is seated. I’m not sure how long that bleed-back would take on a static engine. When the engine is running, the lifters would quickly sort themselves out.

 

[Vetman]

I will have another go at this now that my new parts are bedded in.

 

[Forrest Gump]

What heads and roller rockers did you go for out of interest, much improved performance?
Ive got Scorpion double roller rockers. It was a shame to hide them under the valve covers!

 

[Vetman]

My engine is an L48 with TH400, standard other than Performer Plus cam, double roller steel timing set, 2101 inlet manifold, and Holley 600cfm. It ran well perhaps 0-60 in 7 seconds. I modified it this time with Edelbrock E- Street 64cc alloy heads, Performer Air Gap manifold, and Scorpion Racing roller rockers and hardened pushrods. I also added 1-5/8” long tube headers running to existing 2-1/2” pipes and Flowmaster silencers. When I removed the old smog heads I found the original pistons, with the original steel gasket on one bank and an aftermarket gasket on the other, suggesting one head had been removed in the past. The bores looked reasonable.

The state of engine modification now is equivalent to an Edelbrock top end kit with gross 315 bhp @ 5000rpm, and gross 381 lbs- ft torque @ 4000rpm. The car is very quick once underway but might benefit from a higher stall converter if tyre smoke was wanted. The bottom end and transmission are untouched.

Some photos.