1987 Merc 350 noise at high RPM, timing related

[dan t.]

Re: 1987 Merc 350 noise at high RPM, timing related

just shot inthe dark, check the casting #s on the heads. you may have 305 heads.this would give you higher compression. 150 to 180 is quite a spread, you generaly want all cylnders within 10% of each other.good luck

 

[thedillybar]

Re: 1987 Merc 350 noise at high RPM, timing related

Call me offsides yet I've never had out of adjustment rockers-hydraulic lifters give this symptom either - but obviously some of the resident experts have so that very well could be it.

I don't believe it was brought up but did you check the max timing at say 3000-4000 rpm?? I know nothing about your specific distributor workings or timing within the "Thunderbolt IV", but could you have a centrifugal-mechanical (or possibly vacuum, ie from wrong vacuum source) advance issue that is throwing in too much advance at higher RPM's etc.?

This was one of my first thoughts too. The Thunderbolt IV is electronic and generally thought to be bulletproof (not that it is). Above 4400rpm the Thunderbolt IV advance is 22*. See page 14 here.

Just a quick question, and not to be insulting. When you set the valves at zero plus 3/4 did you make sure each one of them was on the flat side of the cam lobe? Hope you find the answer.

Yes, I set the lash on some valves when #1 was at TDC, then rotated crank and adjusted valves, etc...as per the manual.

They sound tight to me too.
Did you perform the valve adjustment with the engine running at operating temperature?

Engine was cold (air temp was probably 75* F).

If the valves were to tight it wouldn't cause detonation. If the valves are to tight, the valve timing essentially changes, and your going to lose some compression. On top of that if the valves are to tight they are going to float at a lower RPM.
I would double check the lash first, then be looking for a lean condition as Bondo said. The other question is how big a boat are we pushing with this engine?

20' Baja, approx 2500 lb. One of the smallest boats from the factory with a Mercruiser 350.

just shot inthe dark, check the casting #s on the heads. you may have 305 heads.this would give you higher compression. 150 to 180 is quite a spread, you generaly want all cylnders within 10% of each other.good luck

Hope I would've checked the numbers before installing, but worth a check.

Thanks for all the help, probably won't be able to work on her till this weekend. Will clean carb & replace filters again, back off rocker nuts 1/2 turn, and check part numbers on heads & Thunderbolt IV.

 

[Bondo]

Re: 1987 Merc 350 noise at high RPM, timing related

back off rocker nuts 1/2 turn,

Ayuh,...

If you can get the valve covers off, without pulling the manifolds,...

I'd bring along an extra roll of Bounty's,+ run the valves while the motor is Warmed,+ Idling...
Then there's No Question about their Adjustment...

 

[n2ostroker]

Re: 1987 Merc 350 noise at high RPM, timing related

Take it from someone that chased this same problem for a month back in the summer.
Your valves are too tight....

As for the 305 heads on the 350.. Even if they were it wouldn't detonate like that. I run 305 HO heads on my 350 and I run flat top pistons (~10.4:1 compression) and after getting the valve adjustment right it'll pull to 4800rpm with 8* initial and 93 octane in a 20' Thompson Cuddy. With the dished factory Mercruiser pistons you'd be fine.

I'd adjust them with the motor running. It's easy and they'll be right when done. I'd guess you'll have to back them off a good bit, probably a 1/2 turn or more. Start the motor and back each nut off one at a time till it clacks then slowly tighten it till the noise quits and turn a 1/4 turn further.

 

[JustJason]

Re: 1987 Merc 350 noise at high RPM, timing related

any chance you have a differenct compression gauge???...... 180psi seems kinda high on a carb'd motor. If the motor was brand new you'd probably see 150-160ish. To much compression would most certainly cause a hi rpm knock... especially with lower octane fuel.

 

[thedillybar]

Re: 1987 Merc 350 noise at high RPM, timing related

Take it from someone that chased this same problem for a month back in the summer.
Your valves are too tight....

Appreciate the advice. I assume you had the noise at high rpm. Did you try adjusting the timing to make it go away?

any chance you have a differenct compression gauge???...... 180psi seems kinda high on a carb'd motor. If the motor was brand new you'd probably see 150-160ish. To much compression would most certainly cause a hi rpm knock... especially with lower octane fuel.

The compression gauge is without a doubt a cheap one. All of the cylinders were 165-180, except for #5 which was 150. The #5 cylinder also saw water from the blown head gasket.

I am not overly familiar with the reman process...if they resurface the heads do they typically add material so you'll see the same compression ratio with the same head gasket thickness?

 

[captmello]

Re: 1987 Merc 350 noise at high RPM, timing related

All of the cylinders were 165-180, except for #5 which was 150.

I Had my heads rebuilt this summer (350 ci.)

I did pay for resurfacing as well. After running the motor a couple hours or so, i did the compression test. 6 cylinders were at 155, one at 160, one at 150.

Your high compression could be the problem.

When I installed the heads, I did the valves with the engine running. I hadn't adjusted hydrolic lifters before and was very easy, and a bit mess as Bondo mentioned. I went 1/2 turn after they stopped slapping.

Motor runs strong at all RPM.

Good Luck!!

 

[n2ostroker]

Re: 1987 Merc 350 noise at high RPM, timing related

Appreciate the advice. I assume you had the noise at high rpm. Did you try adjusting the timing to make it go away?

My 305 was busted when I bought the boat so I built a 355 to take its place. I used all the parts from the 305 including the heads to build the 355. I had to clean the water/oil slurry from all the lifters. Put it all together adjusted the valves to 0 lash and went a 1/2 turn past.

Motor ran great. Had a little stutter when I first put it in the water. Then it seemed to take off like it should only it wouldn't go past 4000-4100 rpms. Backing the timing off seemed to help. Later as things went on the timing did nothing and eventually wouldn't pull past 2000rpms and if it did it would pop and spit while running. Backfired out of carb and all.
Rebuilt the carb and rejetted it. Changed plugs twice. Ran a bunch of Lucas octane booster. Moved timing everywhere. Nothing seemed to make any real difference.
Pulled the valve covers and started backing off the valves and found 2 pushrods bent. Wound up having to back each nut off about 3/4 of a turn. Some a little more.
The lifters bleed off as they sit or in my case I washed all the oil out of them which throws all you pre-running valve adjustments off.

Afterwards it ran like it should. Jumps on plane and pulls to 4800rpm(55mph) like nothing could stop it. Lesson learned on small block Chevrolets.....

 

[thedillybar]

Re: 1987 Merc 350 noise at high RPM, timing related

Motor ran great. Had a little stutter when I first put it in the water. Then it seemed to take off like it should only it wouldn't go past 4000-4100 rpms. Backing the timing off seemed to help. Later as things went on the timing did nothing and eventually wouldn't pull past 2000rpms and if it did it would pop and spit while running. Backfired out of carb and all.
Rebuilt the carb and rejetted it. Changed plugs twice. Ran a bunch of Lucas octane booster. Moved timing everywhere. Nothing seemed to make any real difference.
Pulled the valve covers and started backing off the valves and found 2 pushrods bent. Wound up having to back each nut off about 3/4 of a turn. Some a little more.

Sounds a bit different than my problem...I don't seem to lose power at all, it just starts clicking. However, point well taken that apparently it's very easy to overtighten the valve lash on these engines.

 

[thedillybar]

Re: 1987 Merc 350 noise at high RPM, timing related

After some research, it sounds like a bad cam chain tensioner can make this kind of noise. Maybe when the valve lash is overtightened, it puts additional load on the cam chain and makes the clicking noise.

 

[n2ostroker]

Re: 1987 Merc 350 noise at high RPM, timing related

There is no cam chain tensioner on a small block Chevy. Maybe a bad timing chain or gear but doubtful.

I'd quit guessing and try the valves then report back. Before you know it you'll have a hundred ideas in your head and create 5 more problems chasing one that might be simple.

 

[n2ostroker]

Re: 1987 Merc 350 noise at high RPM, timing related

I know you've probably checked but have you double checked to make sure the plug wires are in the correct order 1-8-4-3-6-5-7-2? It's easy to get one or 2 off a position.

Also if you can't get the revs up you have a loss of power.

 

[KJSmitty]

Re: 1987 Merc 350 noise at high RPM, timing related

After some research, it sounds like a bad cam chain tensioner can make this kind of noise. Maybe when the valve lash is overtightened, it puts additional load on the cam chain and makes the clicking noise.

So are you now stating that it's a mechanical "tick" vise a "ping" from detonation etc.? (If so, strange that it goes away with a timing adjustment).

Is the fuel pump a mechanical type - on the engine (as in driven off the cam)? I ask because they too can cause a lifter like ticking noise when worn out. - As mentioned above, Chevy V8's (of your vintage), don't have a timing chain tensioner.

Keep at it.

 

[Maclin]

Re: 1987 Merc 350 noise at high RPM, timing related

The last point from KJSmitty jogged my thoughts some. Pinging and knocking comes from more than one cylinder and is not quite as regular as a tick from a lifter or the fuel pump actuation rod or lever. It also varies with load. If the noise you hear is always in synch with the rpm then it may not be detonation as you thought. Even a breached spark plug wire can make a ticking noise and would also change in tone somewhat as timing is adjusted. Hopefully it is not a piston pin or rod issue. This type of thing is hard to diagnose remotely, good thoughts here so far.

Oh, I do think you have more than one issue, and valve lash is definitely high on the list and is separate from the detonation or pinging issue (if that is what the noise is).

 

[thedillybar]

Re: 1987 Merc 350 noise at high RPM, timing related

So are you now stating that it's a mechanical "tick" vise a "ping" from detonation etc.? (If so, strange that it goes away with a timing adjustment).

Is the fuel pump a mechanical type - on the engine (as in driven off the cam)? I ask because they too can cause a lifter like ticking noise when worn out. - As mentioned above, Chevy V8's (of your vintage), don't have a timing chain tensioner.

Sounds like a mechanical tick to me, not a spark knock. It's only there at high rpm (under load). In neutral, no noise. Retard the timing 12*, no noise. I'm having a really hard time convincing myself it's not a knock...yet having a hard time believing I'd have to retard it 12* if it is indeed a knock.

Like many people said, I need to get off the computer and actually try some of the ideas. Hopefully Friday. Thanks all...keep the ideas coming.

 

[Bondo]

Re: 1987 Merc 350 noise at high RPM, timing related

I need to get off the computer and actually try some of the ideas. Hopefully Friday. Thanks all...keep the ideas coming.

Nope,....

No more Ideas until We get some Answers......

See ya Friday night......

 

[thedillybar]

Re: 1987 Merc 350 noise at high RPM, timing related

Re-did the valve lash today with the engine running (oil spray wasn't too bad).

Started the engine and let it warm up for about 10 minutes, then started adjusting. Had to back most of the rocker nuts off about 1 1/4 turns before the clicking started. Tightened until the noise went away, then an additional 1/4 turn. So most are a FULL TURN out from where they were before.

Thanks for all the help, I imagine this is it. Will let you know for sure when I get it out to the lake. Hopefully didn't do any extra damage.

 

[Bondo]

Re: 1987 Merc 350 noise at high RPM, timing related

Ayuh,....

I usually run'em at 1/2 to 3/4 turn,...
That's about the middle of it's hyd. travel...

 

[chiefalen]

Re: 1987 Merc 350 noise at high RPM, timing related

A full turn huh?

Let us know after you take it on the water, did you by chance look at the pushrods, where they bent? Maybe just a little?

 

[n2ostroker]

Re: 1987 Merc 350 noise at high RPM, timing related

A full turn huh?

Let us know after you take it on the water, did you by chance look at the pushrods, where they bent? Maybe just a little?

X2

You should definitely check them. I had a couple and mine were that tight on a few valves.
It should definitely run better now. That miss/tick/ping, whatever you heard was a valve or many valves being slightly open during the combustion and/or compression cycle.

It should run a little better now....