Funny engine noise when engine is hot.

[poorboy]

Replaced the cam and lifters and heads on a 87 turbobuick because of a bad #3 lobe. Also replaced the coilpack, plugs and wires.

Finally got the car running smoothly and made some short trips to shake the car out.

BLMs 139 at idle, 115 at constant speed, 128 when coasting. Compression test on cylinders showed 165 to 170 in all cylinders. New oil, EOS, coolant and fresh gas.

The car seemed fine enough to return to the owner. Drove 125 miles at 65 mph and 2800 rpms for almost 2 hours. Water temp 170 F and oil pressure 40 psi for most of the trip. Never went over 10 psi of boost.

The last two blocks from the owner's house, the engine sounded like something inside was hitting another part, but this only occurs when the engine is heat soaked and above 2000 rpm. Car idles fine with no strange noise and also runs fine with no strange noise until heat soaked.

Checked #3 exhaust rocker, and it's moving up and down.

Don't think it's a lifter because it's not a ticking sound, and there is no sound at idle.

Unlikely to be a head gasket as there is no "fftt" sound.

Don't think it's a bearing as it's not really a knocking sound, and it doesn't happen at idle.

Hope it's not a burnt valve because the engine idles well and it doesn't sound like an exhaust leak.

Any ideas?

As well, the valley between #3 and #5 manifold starts to glow when under load for an extended period.

 

[Hotrodbuick]

You said rocker on number 3 is loose? Do you have a roller cam or hydraulic? If hydraulic cam you should be able to push the lifters down a little bit, if not lifter may be collapsed. Did you break the cam in before you went out an drove it or just started up an went?

 

[Hotrodbuick]

Also try posting a video with the noise.

 

[Chuck Leeper]

"As well, the valley between #3 and #5 manifold starts to glow when under load for an extended period"

The MOST popular point for cracks to evolve. Check to see. The tinny noise could well be a cracked header tube. Escaping, hi temp gas, may be causing the red glow, by heating the edges of the crack....

 

[poorboy]

Thanks for the replies.

Hello Hotrodbuick,

Rocker #3 is not loose, it's cycling normally. I used GM lifters with the hardened seat. Comp Cam cam lube and broke it in for 15 minutes at over 3000 rpm. I pulled the intake again afterwards and looked at the lifters, and they looked great. Will try and get a recording of the noise.

Dear Mr. Leeper,

Unfortunately the noise is not a tinny one. I've encountered the common #3 and #5 exhaust manifold crack before, and the mainfold on this car has been welded up. I'll check it again, but unfortunately, I don't think the noise is coming from this area. I think if memory serves me correctly, the exhaust noise from a hairline crack in the header is more apparent when either the engine is cold as the metal hasn't yet expanded, or under boost when the pressure increases.

They used a lot of material building up the valley between #3 and #5 filling in the crack on the manifold repair, and I wonder if the hot spot there is caused by the differential heating of the two different materials.

 

[Hotrodbuick]

Oh ok must have misread that my bad. Still trying to figure out what would make it glow between 3 an 5, has me stumped :/

 

[charlief1]

A glowing manifold is usually either a lean or rich condition. Have you pulled the plugs out to see what they look like?

 

[Hotrodbuick]

I was thinking the same thing. Or exhaust valves are not opening an closing like they should. X2 on pull the plugs out

 

[poorboy]

Will pull the plugs. Now that I think more about it, it almost sounds like knocking from detonation, which I believe happens when the engine is really warm.

I have a soundbite, but don't know how to load it up. I can forward it to anyone who is interested in hearing it if you would be willing to pm me your email address.

I'm going to pour a bottle of STP octane boost in to see if that makes the difference. When I put on the heads, I thought there was a fair amount of carbon on them. I'm hoping this is the problem as it is minor and I've replaced basically everything else. If it is, I'll pour in some seafoam to clean the tops of the pistons.

 

[charlief1]

Octain booster is a total waste of $. Do a little research about it and read the Q&A sections of the wesites. The last question is usually the one they don't wnat you to read. "Does it raise the octain for gas to ... level?" The answer is always no.

 

[poorboy]

Bummer. I was hoping it would raise it about 4 points just to see if it was detonation.

 

[charlief1]

It might raise it .1 but it will never raise it enough to be cost effective, sorry.

 

[poorboy]

I was only going to use the octane booster to determine if detonation was the problem. No access to scantool at the moment. If it solved the problem, I was going to use seafoam to clean the tops of the pistons.

 

[Black Six]

Will pull the plugs. Now that I think more about it, it almost sounds like knocking from detonation, which I believe happens when the engine is really warm.

I have a soundbite, but don't know how to load it up. I can forward it to anyone who is interested in hearing it if you would be willing to pm me your email address.

I'm going to pour a bottle of STP octane boost in to see if that makes the difference. When I put on the heads, I thought there was a fair amount of carbon on them. I'm hoping this is the problem as it is minor and I've replaced basically everything else. If it is, I'll pour in some seafoam to clean the tops of the pistons.

Did you ever find the problem? I am having the same issue.