Valve adjustment, spitting back,

[The73vetteman]

I had the heads on my L48 rebuilt last winter and then i put the motor back together myself (reusing the rocker arm stud nuts - this may be significant - read on). It ran but I had a little trouble with it spitting back thru the carb. I checked the valve lash (by turning the push rods) and found play in most of them. I tightened them up and it ran ok.

Now, maybe 200 miles later, I'm getting the same symptons again - spitting back once or twice coupled with distinct 'tap tap' sounds from the engine when cold. I'm thinking that the lash has opened up again and I think I remember reading that the nuts securing the rocker arms can work loose.

Does it sound like this is my problem, and if so, any tips for how to secure the nuts in place? If I just need to buy new, any suggestions for a source?

Thankin' you in advance,
'73

 

[curtis]

It sounds like maybe you have some valves not closing all the way . It could be from inproper adjustment.

are you running hydraulic or solid lifters? there is a major difference in adjusting valve lash with the two. one very quick way to set hydraulic lifters is to start engine with valve cover off. oil will splatter all over h___, so put some rags around the head. work on one valve at a time, loosen one rocker nut till you here a clicking sound, then slowly tighten it 1/2 turn past where clicking stops. do this for every rocker on one side then do other side. solid lifters must be done with engine off and in a ver y specific order.

 

[Tweek]

If they came loose once, I would check, and replace them! Though I have had the stock setup of rockers and nuts on and off many times without this happening, pulling the valve cover to see will tell you for sure. How many miles are on the lifters and camshaft? I replaced my rockers with Power Plus roller tipped PT# PFM-66906 at 1.52 ratio for 99.95 from Bowtie Performance. I'm not sure if it made the HP gains they claim on the roller tip, and 1.52 ratio, but it didn't hurt! Good luck and keep us posted
Ron

 

[wishuwerehere82]

Vetteman,

I believe the valve studs on a stock head are pressed into the casting. I have heard of cases when using high rate springs, the studs can start pulling out. A ticking sound indicates that your valve to lifter clearance is increasing for whatever reason.
Possible reasons:
Lifter faces are wearing
Pushrod ends are wearing
Nuts are coming unadjusted
Valve faces are burning and building up slag
Valves guides are sticking

Since you are getting popping and ticking, I would check out everything, including the valves. Doing a compression test will weed out the burnt valves. Visual inspection of the cam lobes, lifters, pushrods, and studs will reveal any other problems. it 's only an intake manifold teardown, but probably worth the time.

 

[The73vetteman]

Thanks for the suggestions everyone.

To answer your questions, I have hydraulic lifters (standard on the L48 I believe) and the engine has done 116,000 miles. Although the valves, guides and springs were all new last year I believe the lifters etc are original.

My guess is that I need new nuts. Any idea where the best place would be to buy them?

'73

 

[Tweek]

Vetteman, I wouldn't just take it for granted that it's just the nuts coming loose, though, that would be great if that's all it is. What concerns me is the new springs on the heads, the added pressure could be pulling the studs or trashing your old cam lobes. New parts on old engines sometimes make funny combo's! I rebuilt my heads on a old 350 with 80,000 miles, it wasn't long when it started to burn more oil, the added pressure of the good valve job started to push oil past the rings and I was back to where I started, burning oil and more smoke! I would guess that any Napa or good auto parts store would have those nuts, never hurts to try, Good luck
Ron

 

[cscarlson]

one word "kool nuts"

 

[curtis]

check your spark plug wires and distributor cap. may be you have leaking wires from one to the other especially between #5 and #7 cylinder. or a carbon track or cracked cap. maybe its something simple like this.


on the dirty side if you cam is disintegrating you can use a dial indicator on each rocker at the pushrod end to check lift. all exhaust should be very close to same measurements and all intakes should be close to each other. if you check on the valve side or rocker this checks the lifters and cam together. and could indicate a collapsed or stuck lifter if the pushrod side is OK.

 

[The73vetteman]

Curtis, Tweek, everyone,

Thanks for all your suggestions. I'm going to start by trying new nuts. At 72c each from CarQuest it seems like an easy thing to try. I think I'll also check the lift as Curtis suggested.

I'll let you know if this solves the immediate problem. I have a feel tho' that Tweek is right about rebuilt cyl heads creating problems in the older areas. Think it'll last out until winter when I can get the engine out?

'73