Mercruiser 350: clicking noise at high RPM

[thedillybar]

Had the engine apart to replace a head gasket. This is a 1987 Mercruiser (Chevy) 350 w/ Thunderbolt IV electronic ignition (yes it has electronic advance). Also replaced spark plugs with same plug number, but an updated (looked a bit different), AC Delco MR43T.

Put it back together as per SELOC manual
-> adjusted valve lash by tightening until play was gone in the pushrod (couldn't rotate the rod by hand), then tightened another 3/4 turn
-> set timing to 8* BTDC with engine idling (as per spec). Tach on the dash read around 500rpm, but difficult to read. I adjusted the idle as far down as it would go w/o the engine stalling, then set timing.

Took it out on the water, and it started making a clicking noise around 3000rpm. Retarded the timing (without a light) and it got better, but started clicking around 3500rpm. Continued to retard timing until clicking was gone completely. Haven't had a chance to check what it is with a timing light. My guess is it's now around 4* BTDC.

Runs around 4000-4100rpm...max power is 4600rpm.

I'm not too familiar with what spark-knocking or bad valve lash sounds like, but if I had to guess what bad valve lash sounds like this is it.

Maybe the valves only make noise at high power and retarding the timing is just stealing power but not really fixing the problem??

 

[Uraijit]

Re: Mercruiser 350: clicking noise at high RPM

When you adjusted the lash, did you turn the engine over until the lifters were all the way in the down position?

You have to adjust each valve when it's all the way in the down position, or you're going to have a noisy valve train. It will generally sound more like a "rattle" though.

If your timing is too advanced, it will sound more like a "ping".

A "click" is usually a sticky lifter. There's also the possibility that the "clicking" that you're hearing is the spark jumping out of where it should be. Are your wires in decent condition? Try firing it up at night (with a water supply of course), and see if you see any spark jumping around. If retarding the timing helped, you may have reduced the "load" on the ignition system, and lowered the resistance to the point that it stops jumping.

 

[thedillybar]

Re: Mercruiser 350: clicking noise at high RPM

Yep, lined up the timing mark w/ 0* and set the lash on some valves...then rotated the crank 360* and set the other valves. (as per the manual)

Also checked that the lifters appeared to be in the lowest position when setting the lash.


If the valve lash is incorrect, will they make noise if the engine is at high rpm but no load (e.g. in neutral)?

 

[Uraijit]

Re: Mercruiser 350: clicking noise at high RPM

I edited my post just before you replied. You might wanna go back and read it again. Sorry.

 

[thedillybar]

Re: Mercruiser 350: clicking noise at high RPM

The plug wires are new (<1 yr)...one of the caps doesn't seem to seat right on the plug and I haven't gotten around to replacing it yet.

The insulating cap on top of the high tension lead coming out of the ignition used to be painted on and isn't anymore...but it fits pretty tightly around the connection and I doubt a spark is finding its way out there.

Could try at night, but it only does it when under load. (engine cover up while driving it)

 

[QC]

Re: Mercruiser 350: clicking noise at high RPM

Took it out on the water, and it started making a clicking noise around 3000rpm. Retarded the timing (without a light) and it got better, but started clicking around 3500rpm. Continued to retard timing until clicking was gone completely. Haven't had a chance to check what it is with a timing light. My guess is it's now around 4* BTDC.

How would this make a sticky or noisey lifter better? Retarded timing and the noise went away . . . hmmmmmmmm

 

[Uraijit]

Re: Mercruiser 350: clicking noise at high RPM

Wait a min! Are you saying that the noise is COMPLETELY gone now that you retarded the timing enough?

I guess I didn't read the post closely enough... If the problem's gone, what are we talking about?

 

[MikDee]

Re: Mercruiser 350: clicking noise at high RPM

When you set the timing, did you disable the electronic advance first? I'm not sure how your Thunderbolt 4 system works, but usually you have a certain procedure to follow, before setting the initial timing on electronic spark advance units.

 

[QC]

Re: Mercruiser 350: clicking noise at high RPM

Wait a min! Are you saying that the noise is COMPLETELY gone now that you retarded the timing enough?

I guess I didn't read the post closely enough... If the problem's gone, what are we talking about?

And THAT was what I was wondering . . .

 

[bomar76]

Re: Mercruiser 350: clicking noise at high RPM

Yep, lined up the timing mark w/ 0* and set the lash on some valves...then rotated the crank 360* and set the other valves. (as per the manual)

Dunno what manual you are using, but that is NOT the way to get all the lifters on the cam base circle to adjust valve lash.

 

[45Auto]

Re: Mercruiser 350: clicking noise at high RPM

Dunno what manual you are using, but that is NOT the way to get all the lifters on the cam base circle to adjust valve lash.

Don't know what manual you're using, but what Dillybar did (#1 at TDC, set exhaust 1-3-4-8, intake 1-2-5-7, rotate crank 360 so #6 is at TDC, set exhaust 2-5-6-7, intake 3-4-6-8) is EXACTLY what the procedure is in the Mercruiser factory manuals.