# Rattle sound in motor @ 1500 to2000 RPM



## wlbuckles (Apr 3, 2010)

I have a stock 65 389 tri -power gto w/ a rattle sound in the motor @ 1500-2000 rpm. I have replaced the cam, lifters, push rods, rocker arms and have adjusted the lifters according to specs. Still Have the Problem. I put the stethascope all over the motor and only detect the sound thru the intake and at different points of the headers. Could it be Valve Springs ? Need Help !! Am at whits end. Thanks.:confused


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## Instg8ter (Sep 28, 2010)

are you running stock heads (compression ratio)? if so what type of gas are you feeding it? Stock motor is over 10:1 comp and would have detonation on 89 octane, try a tank full of 93-97 if you can (afford) get it.


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## wlbuckles (Apr 3, 2010)

The heads are 76. Stock heads for the 65 389 4 barrel motor. In Mich. the best at the pump is 92 and I put in a bottle of Gummout Octane w/ half a tank of 92. What next ?


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## jetstang (Nov 5, 2008)

run better gas, like race gas. Also back off the timing til it stops, like 0 degrees timing. Sounds like its rattling under load due to compression. Is it noisy at idle, or when revving it out of gear? Guy I got my 66 from said to put moth balls in the gas to raise octane, he does it on his 428, I haven't tried it, but may work.


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## Instg8ter (Sep 28, 2010)

hey WL i am just south of Metro Airport, try Shell stations, they carry 93 and 110 race gas here you can run a mix to get you where you need to be...also what jet said, may need to sacrifice a bit of power to make it happy


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## Eric Animal (Oct 28, 2007)

The moth ball thing is an urban legend.....don't do it......IMHO Eric


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## jetstang (Nov 5, 2008)

Eric Animal said:


> The moth ball thing is an urban legend.....don't do it......IMHO Eric


I haven't tried it, but know some that do. If the car doesn't ping after using them, then it works. I just haven't had a car I was willing to try it on. Maybe I'll try it in my lawn mower, lol..:cheers


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## mikes06goat (Jan 13, 2009)

Flexplate bolts tight?


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## freethinker (Nov 14, 2009)

wlbuckles said:


> I have a stock 65 389 tri -power gto w/ a rattle sound in the motor @ 1500-2000 rpm. I have replaced the cam, lifters, push rods, rocker arms and have adjusted the lifters according to specs. Still Have the Problem. I put the stethascope all over the motor and only detect the sound thru the intake and at different points of the headers. Could it be Valve Springs ? Need Help !! Am at whits end. Thanks.:confused


probably not valve springs. probably not detonation. that will not show up unless under a load.
we need more information. is it constant? does it change with rpms? does it do it hot and cold?is it a solid noise or tinny?


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## geeteeohguy (Feb 2, 2008)

I'm with freethinker. The car won't ping unless you're driving it. If you have a rattle when you're standing at the fender and peering at the engine, it's not detonation. Noises have a way of "transfer" in and engine and driveline. It could even be a cracked harmonic balancer. Valvesprings typically will not make noise unless broken. Could be lifters. The #76 Head did not come on '65 GTO's. It is a "Big car" head that came on other 389's. All '65 GTO's had the #77 head, which was also used on Big Car 421 engines. The good news is that the 76 head is slightly lower in compression: 10.5 as opposed to the 10.75 that Pontiac rated the #77's at.


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## wlbuckles (Apr 3, 2010)

OK Guys, Here what I can tell you at this point. Once I get the engine warm enough to idle @ 900, I put the car in neutral, set the parking brake, adjust the idle to where it makes the rattle sound @ approx. 1500 -2000 rpm. It also makes the same tinny rattle in 2nd,3rd, & 4th gear rolling. I backed off the timing a few degrees as sugested and it seemed to help considerably. One guy told me if that was indeed the case then buy a ac delco recurve kit and install the heavier springs to cut back on the advance. Then put the timing back to norm. Any thoughts ????? Thanks much Guys.


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## jetstang (Nov 5, 2008)

True, if they put an advance curve kit in it, then that would fix it. If it is to hold the timing longer, then the problem will show up at a higher RPM as you haven't changed the total advance. If backing a little timing out, try some more, if it fixes it you have three choices: 1) Retarded timing, throw race gas in it sometimes to show the real potential of a Pontiac, best choice if you can get it to run decent retarded. 2) Run race gas all the time, or a suitable mix, 50/50 w/Premium 3) Rebuild the engine to lower the compression with dish pistons..


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## Instg8ter (Sep 28, 2010)

did you find any high octane gas? i am betting if you put a tank of 102 (half 93 half 110) it will go away, if so you should run the highest octane as you can get/afford as detonation will shorten your engines life and beat the crap out of your bearings, or think about a new set of heads to get your compression ratio down to around 9:1 to be able to run 91 safely. another option is thicker head gaskets probably .072 or so that will bring the compression down. there are formulas for computing comp. base on chamber volume, deck height, gasket thickness, etc. only way to tell for sure is to take the heads off and spec it all out.


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## Thumpin455 (Feb 17, 2010)

Well there is always my solution to running high compression engines on the street. And what do ya know, 4 pumps in town. Sometimes I wish I lived downstate, only having one E85 pump sucks.

This makes me want to do a tripower now. Time to find some of my 2 barrel carbs and get some base plates.


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## MITYGTO (Jun 10, 2011)

*Rattle Sound*



wlbuckles said:


> OK Guys, Here what I can tell you at this point. Once I get the engine warm enough to idle @ 900, I put the car in neutral, set the parking brake, adjust the idle to where it makes the rattle sound @ approx. 1500 -2000 rpm. It also makes the same tinny rattle in 2nd,3rd, & 4th gear rolling. I backed off the timing a few degrees as sugested and it seemed to help considerably. One guy told me if that was indeed the case then buy a ac delco recurve kit and install the heavier springs to cut back on the advance. Then put the timing back to norm. Any thoughts ????? Thanks much Guys.


The fact that retarding the timing helped would lead one to believe it is definately detonating.

A few questions if you don't mind.........

Did the engine do the same thing before you swapped out the cam? 

You also mentioned the need to warm it up to idle at 900 rpm. How big is the cam?

How long have you owned the car, is the compression ratio stock?

Is your fuel mixture correct?

Does it do this both cold and hot?


In theory ANY 64-70 high compression engine tuned to factory specs will detonate on pump gas as modern gas even 92 octane simply does not meet the octane requirement of the engine. Backing out the timing is a band aid at best. You end up losing throttle response and the coolant temp will increase. Detonantion can also be inaudible, you don't hear it as you pound the bearings to death.


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## freethinker (Nov 14, 2009)

there is no way you will hear detonation noise at 1500 rpm no load. its something else. how does the noise react when you accelerate and decelerate the engine no load?


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## MITYGTO (Jun 10, 2011)

*Rattle sound in motor*



freethinker said:


> there is no way you will hear detonation noise at 1500 rpm no load. its something else. how does the noise react when you accelerate and decelerate the engine no load?


You may be right, that is why I asked for more info, especially if this started after the cam swap. Can't think of very many "mechanical problems" that will improve with retarding the timing ?????


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## Thumpin455 (Feb 17, 2010)

Are you sure you got the right lifters with the high shoulder? There is a difference between chevy lifters and Pontiac lifters. They could be clattering due to loss of oil pressure right at the lifter. Its really hard to tell what it is without hearing it. If I was standing next to the car while it was running I could probably tell you where its coming from. Too bad videos dont work as well as real life.


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