BROKEN VALVE SPRING ??? Help !
 

Engine- 1986 Mercury 420, stock.

Port engine popped through carb when I was getting on plane. I left off, it idled fine. I took off again and was running steady 3500 rpm and started popping again. I stopped. Engine still runs great, idles smooth, but now making a ticking sound on right bank, not a rocker or lifter, but deeper, like a wrist pin or valve. Just a tick, not a knock. I drove in on starboard engine and finally got a chance to look at today.
Constant ticking noise at idle. Gets louder / faster, consistant with rpms. Engine runs fine otherwise, no miss or rough idle. Revs up good.
I revved engine hard several times trying to listen / diagnose. As I was doing this, ticking noise went away, but now has popping through carburetor. It has a constant pop-pop-pop through carb at idle and gets worse as you rev it.
The engine seems to idle and run fine, but this popping is constant, like somebody is hitting underside of intake with a hammer.
Is this a broken valve spring ???

I need help. Give me your thoughts please.

Re: BROKEN VALVE SPRING ??? Help !
 

Possibly..

You can compression test that bank to isolate the cylinder.

I'd pull the VCs to get a closer look.

Popping through carb is a valvetrain problem (so long as firing order is in check).

Re: BROKEN VALVE SPRING ??? Help !
 

I`m planning on pulling the valve covers tomorrow. I gotta get the manifolds out of the way first.... :rolleyes:

I figure if it`s a valve spring, I`ll replace the whole set and probably do the other engine too.

Before removing parts, is there anything else I should look for ?

Re: BROKEN VALVE SPRING ??? Help !
 

you can check it with a vacoum gage

Re: BROKEN VALVE SPRING ??? Help !
 

I`ve got a vacuum gauge. What should I look for ? Bouncy reading ?

Re: BROKEN VALVE SPRING ??? Help !
 

You may have a bent or broken valve. Check the height of all the valve stems when the valves are closed. I believe the 420's have dual valve springs, one should close the valve at slow speeds. A compression test done and repeated with the rocker arm removed should indicate a problem requiring the head to be removed. It could be a valve seat problem.

A vacuum test should show a fluctuating reading. Let us know it you see this.
JB

Re: BROKEN VALVE SPRING ??? Help !
 

bouncy reading at idle

Re: BROKEN VALVE SPRING ??? Help !
 

Could also be a flat cam lobe.

Re: BROKEN VALVE SPRING ??? Help !
 

if you THINK it is a valve spring... if that even OCCURS to you... do not turn the enginge again for any reason... forget all this vacuum gage nonsense and just pull the vc and check....

think about it.... IF it is a spring and it IS broken... you have pieces floating around and the REAL possibility that the VERY next time you rotate it the you will lose the keepers and the valve will fall in ...WHY in gods name take the risk ? there was a post here a couple weeks ago by a guy who said he heard a suspicious noise in his motor so his diagnostic procedure was to pull MAX revs at MAX load ....

geeze... have some mechanical sympathy . you are DEAD right so far... you caught it early and have probably avoided major damage... don't screw up now. pull the vc's and look.

whats the downside ? if you are wrong and the springs are good ... thats great... youve wasted some time and a few gaskets... but if you are RIGHT then your conservative and intellegent approach has saved you a world of grief and a lot of money...

i don't remember reading ANYWHERE that if you suspect something bad mechanical is wrong, that you should continue running and turning the motor until it breaks for a confirmation that your intuitions were correct.

Re: BROKEN VALVE SPRING ??? Help !
 

Ah, the "Trial by Fire" method of tuning and diagnoses. http://www.turbomustangs.com/smf/Smi...ault/spend.gif This is about as effective as pouring fuel on a stack of $100 bills and igniting them.

Re: BROKEN VALVE SPRING ??? Help !
 

I agree 100%

I appreciate all of the replies, but I was thinking that a compression test and vacuum gauge check were really only going to pinpoint which cylinder had the problem. I am actually not that concerned about WHICH cylinder to look at. If I`ve got any valvetrain problems, I`ll find it when I pull the VC.
My main concern here, was in asking if I was on the right track, in thinking I had a broken spring. I think the concensus here is that I probably do, but need to yank the VC to investigate.
I TRULY appreciate all of the suggestions. This is an invaluable forum with some genuine intelligence out there.
I am going out to work on the boat right now. I hope to find some answers. God knows I would rather be on the water than turning wrenches today.
I will post my findings later today.

Thanks for all the help !

Re: BROKEN VALVE SPRING ??? Help !
 

Here's your cam card. It has the recommended spring # and specs if you end up needing springs.

Part Number: 132561 Grind Number: H-228/312-2S-14 T1.2
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1967 Up CHEVROLET 8 FAIR IDLE, STANDARD CAMSHAFT FOR MERCRUISER 400, 405, 420, 425 HP AND 525SC-454 CU. IN. ENGINES, APPLICABLE TO 350, 365, 370 HP MILDLY MODIFIED ENGINES WITH FREE-FLOWING ABOVE WATER EXHAUST SYSTEMS FOR PERFORMANCE APPLICATIONS, 9.5 TO 11.5 COMPRESSION RATIO ADVISED. BASIC RPM 2800-5800
Engine Size Configuration
396-454 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 312 @Valve 530 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 324 @Valve 551
Rocker Arm Ratio 1.7

Cam Timing: TAPPET @.005
Lift: Opens Closes ADV Duration
Intake 35 BTDC 83 ABDC 298 °
Exhaust 87 BBDC 39 ATDC 306 °

Spring Requirements: Triple Dual Outer Inner
Part Number 99893
Loads Closed 130 LBS @ 1.850 or 1 27/32
Open 330 LBS @ 1.320
Recommended RPM range with matching components
Minimum RPM 2800
Maximum RPM 6600
Valve Float 7200

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 5 BTDC 43 ABDC 109 228 °
Exhaust 57 BBDC (1) BTDC 119 236 °

Remarks:
CAMSHAFT IS GROUND WITH .0012" LOBE TAPER.

Re: BROKEN VALVE SPRING ??? Help !
 

Glad you listed the cam specs. Looks like I`ll be needing a cam. Yup, Exh lobe, cyl #8 --- flat.
Everything else looks good...
I have to pull the engine to swap the cam. . . :(

Re: BROKEN VALVE SPRING ??? Help !
 

don't foget... all the grindings from that lobe went somewhere.... clean clean clean EVERYTHING

Re: BROKEN VALVE SPRING ??? Help !
 

Glad you found the problem. A lot of poeple never let us know what they find, thanks. The hydraulic lifer is probably eaten up too. You must have almost no exhaust lift at all to pop thru the carb.