Just put rebuilt heads on the motor and fired it up... what's that sound?

[boatinjoe]

so the title says it all. i just did the top end on this old lady and fired her back up and this is what i heard.

i was thinking exhaust leak, but plugs are tight and i felt no blow-by around the manifold gasket. also, the issue is isolated to a single cylinder. disconnecting the plug wire from the #7 cylinder stops the sound completely. the sound returns as soon as the wire is reconnected.

all help or ideas are appreciated. thanks

 

[Reinell-BRXL-191]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

Have you traced back all the plug wires and made sure that they are in the correct firing order.. sounds like a cylinder is firing on the wrong portion of the stroke.. (detonation) This will be more obvious as the rpms climb, as the engine will not be able to get over the mis-fire and will cause stumbles.. have your tried reving it a little?

Also the engine sounds out of time when you are trying to start it..

 

[boatinjoe]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

Have you traced back all the plug wires and made sure that they are in the correct firing order.. sounds like a cylinder is firing on the wrong portion of the stroke.. (detonation) This will be more obvious as the rpms climb, as the engine will not be able to get over the mis-fire and will cause stumbles.. have your tried reving it a little?

Also the engine sounds out of time when you are trying to start it..

the timing does sound off... and i can't figure out why, i double/triple checked everything and i don't know what i could have missed.

as far as the firing order goes, i double checked at installation, then again today.

here is a shot of it running at 2000 rpm no-load.

 

[81 Checkmate]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

How did ya do the valve adjutment?

 

[boatinjoe]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

How did ya do the valve adjutment?

rotated the engine through the cycle, tightening the rockers to no-lash for each cylinder at TDC

 

[Lyle29464]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

With the engine running I would back off the rockers one at a time till I heard it it clacking then tighten till it's quiet. add 1/2 turn. ( slowly)

 

[81 Checkmate]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

No expert here...But i would say you have some of them to tight..

The way i do it is set them like you did and back nut off 1/4 turn....then start the motor with valve covers off and redo the adjustment
untill they are not clattering.

Then reset your timming.

Good luck!

 

[boatinjoe]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

No expert here...But i would say you have some of them to tight..

The way i do it is set them like you did and back nut off 1/4 turn....then start the motor with valve covers off and redo the adjustment
untill they are not clattering.

Then reset your timming.

Good luck!

will double check valve adjustment tomorrow. thanks

 

[koolhandluke]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

No expert either, but I have successfully made the same repair on my GM V6. Was the distributor lined up to TDC on #1 or to its original position before removal? Looks like you were thorough,; just tossing it out there. Howard Sterndrive details a procedure adjusting the valves with a compression gage that is worth checking into. I would guess you could find it in a search of related posts.;

 

[Nivekt]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

Sorry I cant help, but I just wanted to say that you did a great job on the rebuild of that old motor. She is puuuurdy!

 

[Silvertip]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

The proper "engine running" valve setting is loosen the rocker nut until the lifter clatters, slowly turn the nut down until the clatter just stops. The 3/4 turn DOWN -- again slowly. I agree that the timing or firing order is wrong in the first video. A weak battery might also account for the labored cranking.

 

[southkogs]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

Just did mine recently - I'm no expert, but similar vintage - I really had to fight my valve lash. Yours sounds like mine did when I did the valve lash by the manuals "cold, not running" method. I went back and did the "hot, engine running" method, and had to back off about a 1/4 from where the manual said they should be set.

 

[boatinjoe]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

Sorry I cant help, but I just wanted to say that you did a great job on the rebuild of that old motor. She is puuuurdy!

thanks. and truthfully that's what burns the most about the funky running... i was very meticulous about getting everything done nice and clean. i spent god knows how many hours pulling parts, cleaning and painting.. got the thing together and this is how she repays me.

 

[hayward6]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

I hate mentioning things like this, but even the most seasoned mechanic can sometimes get the simple things wrong , so don't take this the wrong way... Is there any chance you have the firing order backwards? that's just about how a motor would sound if you got 50% of the cylinders firing. I've done it myself, so just offering up some experience Also a compression check of each cylinder will help you find a valve adjustment problem in a specific cylinder. The way that motor turns over sounds like the compression variance between the cylinders may be high. Good luck, and I agree! Nice clean work there!

 

[boatinjoe]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

I hate mentioning things like this, but even the most seasoned mechanic can sometimes get the simple things wrong , so don't take this the wrong way... Is there any chance you have the firing order backwards? that's just about how a motor would sound if you got 50% of the cylinders firing. I've done it myself, so just offering up some experience Also a compression check of each cylinder will help you find a valve adjustment problem in a specific cylinder. The way that motor turns over sounds like the compression variance between the cylinders may be high. Good luck, and I agree! Nice clean work there!

no offense taken. believe me i'm certain i made a mistake somewhere. as far as plug wiring, i've now quadruple checked (checked it again tonight as i was pulling plugs for a compression test) unless my distributor is rotating in a direction other than clockwise (also visually verified) or the firing order is somehow different from what is listed on the intake manifold (1-8-4-3-6-5-7-2), those wires are going to the right holes.

i took the boat out and put it in the water yesterday to put a few hours on it and see how it performed. not very well...
tonight i pulled the plugs to do a compression test.

the plugs all looked clean,light brown patch on one side of the insulator, like good combustion, no excess oil or any sign of water.
the compression test shows that the odd cylinders are severely disadvantaged. 90-60-90-75 on that side. about 120 psi on the even cylinders.

so im thinking that my head gasket never seated/sealed properly. I'm wondering if that could cause that popping sound?

 

[southkogs]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

...so im thinking that my head gasket never seated/sealed properly. I'm wondering if that could cause that popping sound?

... yeeeouch, I hate to even say this because of how bad I feel about it ... but "yes, the head gasket could cause a popping sound." I know that because it's what triggered me to change mine. I didn't hear the same noise in your video that I heard on mine, but it sounded like a little kid not quite firing a pop-gun right. Just a light, but consistent "pop" while the engine was running ... and no power.

I was getting zero compression on #2 & #3 on mine, and the gasket was completely gone between the two cylinders.

 

[boatinjoe]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

... yeeeouch, I hate to even say this because of how bad I feel about it ... but "yes, the head gasket could cause a popping sound." I know that because it's what triggered me to change mine. I didn't hear the same noise in your video that I heard on mine, but it sounded like a little kid not quite firing a pop-gun right. Just a light, but consistent "pop" while the engine was running ... and no power.

I was getting zero compression on #2 & #3 on mine, and the gasket was completely gone between the two cylinders.

looks like the intake and one of the heads are coming back off.

going to run a wet compression check tomorrow just for the heck of it too.

 

[southkogs]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

looks like the intake and one of the heads are coming back off.

going to run a wet compression check tomorrow just for the heck of it too.

What a drag! Sorry Joe. Engine looks fabulous though - mine doesn't look half that pretty.

 

[81 Checkmate]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

Joe did ya adjust the valves before the boat splash?

I realy think that is were your problem lies!

 

[81 Checkmate]

Re: Just put rebuilt heads on the motor and fired it up... what's that sound?

Just like your compresion test showed.....If you have some valves to tight they are not seating correct...therfor lossing compression.

Good luck!