Master
SupporterGood afternoon all,
I am wondering if anybody can help me with the following issue please?
My 3.5L V8 (1984 110 - 60,000 km on motor) is making a sound like a rattle gun under load. It started doing it in 4th when under load going up a hill. Recently i did a hard trip down the highway (head wind, many hills, heavy trailer) and it rattled it's head off. It now has the same sound starting in 3rd, and it is worse in 4th. It doesn't rattle in 1st or 2nd, and the engine idles smoothly. The sound is definitely from the motor. It is worse when cold (doesn't need as much load), but is still bad when warm.
I have tried almost everything to find the source:
- I had the headers skimmed and put new gaskets in from engine to muffler.
- Made sure exhaust wasn't hitting anything.
- I thought it may be a pre-detonation sound, but i've tried retarding the timing, disconnecting vacuum advance and even swapped distributors.
- Checked that nothing was loose in the engine bay.
- I took the air cleaner and associated plumbing off in case any of that was rattling.
- Tried different height pedestals and shims.
- The oil pressure gauge reads well.
- My gut says head gasket, but the oil is clean and the compression test results are good (all around 180 psi). (Although, the sound only happens under load).
I am at a loss!
Many thanks,
Edward
Swaggie
SubscriberThe old girls used to have a problem with the exhaust valves sticking when under load.
You should however notice a loss in power at the same time.
Fix is to remove the heads and decarbonise the exhaust valves.
You may be able to have an approximate test by removing the rocker covers and tapping the exhaust valves with a hammer.
Boing is good clunk is bad
Regards PhilipA
Master
SupporterThank you Philip. That is interesting to hear, but not sure if that is my problem. They are reconditioned heads, about 5,000 km old.
I took a video if the noise. You can hear it really well in the film, but i cannot work out how to upload it. I'll keep trying.
Edward
Master
SupporterVideo attached - hopefully!
RoverLord
cracked exhaust gasket.
could also be a split in the exhaust joints or muffler.
Dave
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LordRover
SubscriberDoes it still have the air pump and lines in the heads or plugs ?, I had a similar sound in my 85 3.5 RRC so replaced the head gaskets. Noise still there and found that one of the crimped over pipes was loose.
Removed all and welded them up and problem solved.
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Master
SupporterHi Swaggie,
No air lines or pump.
That must have been annoying changing the head gaskets for nothing!
Edward
Master
SupporterYou might be on the money Blknight! I tried loosening a couple manifold bolts to see what noise that would make. Interestingly, the new noise produced had a similar sound at the same tempo. I then tightened all the manifold bolts some more. The noise is still there, but it has definitely decreased a bit!Originally Posted by Blknight.aus
Although my gaskets are new, I have been doing some research and some say (including Pacemaker headers) to use some high temp RTV sealant on the gaskets. I'll try this shortly and report back. Can composite gaskets be reused?
Edward
Master
SupporterAdding sealant to the exhaust gaskets didn't fix the noise. Took it for a drive without the bonnet, and the noise is definitely coming from the engine bay. So off come the heads this weekend!
Edward
Master
SupporterDoes it sound like pinging ?
What type of fuel are you using ? If in doubt fill the tank with 98 from BP. BP is normally the best quality you can buy.
If it is pinging badly you may have a distributor problem or you can get hotspots in a chamber that cause detonation.
Ian
Bittern
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