Valves rattling loud when I accelerate

[barrman]

I have an 89 16' searay with a merc 3.0L and have just replaced the distributor cap, rotor, ignition points, condenser, spark plugs, switched out my prop to 23" and rebuilt my carb. Now I notice when I start accelerating (about half throttle) there is a loud rattling coming from engine and one other curious thing is the RPM gauge occasionally starts jumping around. I'm assuming the distributor needs some work or it's a timing problem. Any other suggestions ? Could the prop change have an impact on this ?

 

[FreeBeeTony]

Re: Valves rattling loud when I accelerate

Sounds like you are way too far advanced.........

 

[Don S]

Re: Valves rattling loud when I accelerate

First set the dwell,don't just use a feeler gauge to set the points, the set the timing with a timing light and make sure the advance is working properly.

 

[barrman]

Re: Valves rattling loud when I accelerate

Wow, U guys are fast. Thanx for your help I look at buying a cheap timing gun this weekend and check it out.

 

[Silvertip]

Re: Valves rattling loud when I accelerate

Buy a dwell meter too. Dwell should be rock steady through the RPM range. If its varies, you have a worn distributor. That's impossible to diagnose without a dwell meter.

 

[Bondo]

Re: Valves rattling loud when I accelerate

Sounds like Detonation.......<br /><br />The 23" Prop is Over-Loading the Motor........<br />And,..<br />You Might have a Timing Issue..... How did you "Tune it Up", without a Timing Light ????<br />Make Sure the Carb isn't Too Lean,... That'll do it Too......<br /><br />What's binary ???......................

 

[hondon]

Re: Valves rattling loud when I accelerate

A 23 pitch prop with a 3.0 in most situations ,certainly do'es sound a little tall.It sounds like the bye ear tune up thing has not worked well for you either.And,how much oil do you have in that oilpan?An overfull pan will give you these symptoms.

 

[deputydawg]

Re: Valves rattling loud when I accelerate

If the dwell, timing, carb mixture are all good and you still have the problem, check your gas. Octane in the gas is what controls detonation. Sounds like you probably have pre-detonation problem (firing the mixture too early). If everything else checks out fine see what gas you have. Mix some octane boost in the gas and see if that helps. You can get this stuff at wal mart pretty cheap.<br />Just wondering, if you get the engine good and warm, shut it off and wait about 2 minutes, then try to start it. If it turns slow or seems to "catch" while it is turning over, this is also a problem with timing. Considering your recent work around the distributor this will be your problem.

 

[ziggy]

Re: Valves rattling loud when I accelerate

deputydawg, wondering why you think octane booster will fix his wagon? i would think that if he gets his engine in tune. useing a tach/dwell, and timing light and a service manual to get it adjusted properly, per manufature specs. the rattly valves (detonation) will go away as it should. i don't know where ya can get substandard fuel at. not that you can't, cause i have. and it was devistating to my fuel system too . but it doesn't seem likely to me. especialy since he was just working with the ign. system w/o the proper tools or info it seems. and if that don't cure it, i'd go to the rebuilt carb next. double checkin that. <br />just my opionin, but i don't believe to much in additives. if a engine is in it's stock form. why don't the mfg. suggest useing additives.

 

[DJ]

Re: Valves rattling loud when I accelerate

As long as all the engine adjustments are correct, I believe the 23" prop is adding to the situation.<br /><br />That's putting a serious lug, on that little engine. Not unlike driving around in overdrive all the time. Sure its going to rattle.

 

[flashback]

Re: Valves rattling loud when I accelerate

What is your rpm at WOT? you need to know that..

 

[QC]

Re: Valves rattling loud when I accelerate

I actually respectfully disagree with DJ. Factors that contribute to knock (detonation) are timing, octane, intake air temp, engine temp and load, but if all others are within acceptable range, load should not matter. He is right about the lug, but it's the other way around. If the others are wrong; load adds to the situation.

 

[Bondo]

Re: Valves rattling loud when I accelerate

Quietcat,....<br />You're Welcome to Your opinion,.........<br /><br />But,..<br />Even If All other Factors Are Correct,.....<br /><br />Excess Load Will Induce Detonation Instantly........<br />All By Itself..........<br /><br />And,... You Also Forgot Fuel Ratio......... A Lean Mix can also be a Contributing Factor....

 

[waterone1@aol.com]

Re: Valves rattling loud when I accelerate

I'd throw my two cents in Bondo's camp. If you have ever owned an older manual shift car or truck, you learn real quick to down shift when going up a steep hill, or the engine will knock. From the original post, there are several variables (timing, dwell, mixture and prop)any one of which or a combination can cause this problem, although the timing and dwell are the most obvious.

 

[trog100]

Re: Valves rattling loud when I accelerate

too low an octane fuel.. timing slightly advanced.. mixture slightly lean.. engine in need of decarb.. too hot a running plugs.. engine over heating..<br /><br />i think i have em all.. all the above could make an engine knock.. the knock will be always be worse at low heavy load engine rpm.. <br /><br />too big a prop will make the situation worse and if every thing else is on the edge actually cause the knock as u load the engine.. gentle acceleration should lessen the knock..<br /><br />slightly retarding the ignition will also lesson the knock factor till the real cause of the problem is discovered..<br /><br />trog100

 

[QC]

Re: Valves rattling loud when I accelerate

Bondo etc., fun debate . . . <br /><br />Think about this way. Every reasonably modern engine should be able to run the full RPM range on the lug curve (full load) on a dyno. Yes, controlled conditions, but that was the point, if all else is right, lug should not cause knock. If it does, something else is wrong.<br /><br />Basically what trog said . . .

 

[Bondo]

Re: Valves rattling loud when I accelerate

Quietcat, fun debate . . .<br /><br />Agreed,.........<br /><br />But,... A 23" Prop on a 3.0l is Over-Load.......<br /><br />"Excess Load Will Induce Detonation Instantly........"<br /><br />True..??..

 

[trog100]

Re: Valves rattling loud when I accelerate

cast iron heads is the weak spot with these old boat engines.. with a 9 to 1 compression ratio they are on the edge with todays leadless fuel.. he he<br /><br />the manufacturers timing settings wont be based on maximum power.. they will be based on minimum knock.. higher compression ratios without diesel knock was why moderm engines all moved over to alloy heads..<br /><br />trog100<br /><br />ps.. its a good idea not to give your engine full (or too much) throttle till the revs build up to about 3500 rpm..

 

[flashback]

Re: Valves rattling loud when I accelerate

Hey QC Can you squat with 150#, probably. but try 350# and you will get a definite knock.. . anyway, I figure ya won't change my mind, I drove a 3 speed on the column when I learned to drive..

 

[LubeDude]

Re: Valves rattling loud when I accelerate

Originally posted by Bondo:<br /> Quietcat, fun debate . . .<br /><br />Agreed,.........<br /><br />But,... A 23" Prop on a 3.0l is Over-Load.......<br /><br />"Excess Load Will Induce Detonation Instantly........"<br /><br />True..??..

VERY VERY TRUE BONDO <br /><br />You are absolutly correct! Its likely the prop.