Bad knock under load

blue beasty · Feb 6, 2018

I'm thinking the worst

Doesn't do it when starting up, ticking over or if revs are slowly increased but as soon as the engine is put under load a noise that sounds very metallic to me come from the rear top as far as I can tell.

Tappets are all set and everything looks normal under the cover.

Just changed the manifold gasket after a suggestion it may be that and it was split on no4 exhaust but a new gasket hasn't made any difference... I was dubious anyway.

It has just had a head gasket change (nasty BP copper job) but no obvious sign of it being gone and has been running fine.

Noise appeared under light load on a short journey, hasn't been worked hard or overheated and the noise gets worse as the engine warms up.

Thoughts?

Bobsticle · Feb 6, 2018

Have you had the air filter off whilst driving.

If so have a look in front of the butterfly. Sounds like a woodpecker has been sucked in.

blue beasty · Feb 6, 2018

Bobsticle said:
Have you had the air filter off whilst driving.

If so have a look in front of the butterfly. Sounds like a woodpecker has been sucked in.

Yeah....unlikely unless it had an oil bath on the way

Thor1950 · Feb 6, 2018

Pikey isn't stuck under there trying to get out is he?

Bobsticle · Feb 6, 2018

Hope its not as bad as it sounds. Could it be a little end?

blue beasty · Feb 6, 2018

Bobsticle said:
Hope its not as bad as it sounds. Could it be a little end?

That's my main suspicion, not sure why though.

It appeared out of nowhere, i know blowing the head gasket isn't great but wasn't driven as soon as symptoms appeared and there was no real oil contamination. Oil was flushed and replaced with a new filter anyway.

It'll have to wait until I have time to strip and investigate which isn't going to be for a while

Land Raver · Feb 6, 2018

It sounds from the vid clip almost like an induction related noise. It doesn't appear steadily progressive with load like a mechanical issue. I wonder if it could be electrical related?

Mulcaster1 · Feb 6, 2018

Could sound a little mad but could the rocker shaft be broken? The reason why I say this is due to a similar issue I had a few years ago with a ford ohv engine

blue beasty · Feb 6, 2018

Mulcaster1 said:
Could sound a little mad but could the rocker shaft be broken? The reason why I say this is due to a similar issue I had a few years ago with a ford ohv engine

It's possible but no obvious sign. Rough plan is to strip off rocker shaft, remove head and then drop the sump unless the problem becomes apparent on the way.

Bobsticle · Feb 6, 2018

could be a sticky valve or anything. Hope its an easy fix.

blue beasty · Feb 6, 2018

Bobsticle said:
could be a sticky valve or anything. Hope its an easy fix.

Makes sense to do a compression test before pulling it to bits I guess.

Tall Ratbag · Feb 6, 2018

It's interesting how the noise depends on the engine load. It might be possible to isolate the cylinder responsibe by repeating the engine rev test with each plug lead removed in turn. A compression test [snap! you said this while I was typing!] before you begin dismantling might also be helpful.

As well as the obvious bearing failures which you're considering, there are more unusual possibilities - detachment of the piston crown, for example. So, if you've got the head off, and the sump off, but can't see a problem, it can still be worth taking the pistons and rods out.

cornish rattler · Feb 7, 2018

A relative of mine back in the late 70's had this on a new to him rover SD1 V8 he was a trained rover mechanic and after doing the obvious check's he stripped the engine down rebuilt it and still had the same problem, anyway by chance my dad went round just for a visit ( self trained mechanic ) and worked out the Rotor arm was duff and replaced it with a new one and problem was solved, mite be worth a check

blue beasty · Feb 7, 2018

cornish rattler said:
A relative of mine back in the late 70's had this on a new to him rover SD1 V8 he was a trained rover mechanic and after doing the obvious check's he stripped the engine down rebuilt it and still had the same problem, anyway by chance my dad went round just for a visit ( self trained mechanic ) and worked out the Rotor arm was duff and replaced it with a new one and problem was solved, mite be worth a check

She was missing a little on tick over, I don't think it's related to the noise but I went through the plugs leads etc. and she's running smooth. Cap and arm look fine.

Kinda out of ideas other than compression test and pulling her to bits

Thor1950 · Feb 7, 2018

blue beasty said:
She was missing a little on tick over, I don't think it's related to the noise but I went through the plugs leads etc. and she's running smooth. Cap and arm look fine.

Kinda out of ideas other than compression test and pulling her to bits

there isn't a push rod that is plugged up and not getting oil to a rocker arm is there?

blue beasty · Feb 7, 2018

Thor1950 said:
there isn't a push rod that is plugged up and not getting oil to a rocker arm is there?

All looks well lubed with fresh oil. Rocker shaft is retained by headbolts but I took it off and replaced complete when I did the head gasket.

I'll strip it when I get to it this time but I'd expect anything like that to be more continuous and worse on start up rather than only under load.

sausage · Feb 7, 2018

I had the same symptoms on a Datsun a series engine ,after a head gasket replacement similar noise ,I replaced the head gasket, retourqed and set clearances and never found any problems ,the noise was gone after the second go at it ,weird

JimS · Feb 7, 2018

It's odd it's only under load, could it be detonation, has the timing slipped somehow

Hicap phill · Feb 7, 2018

@blue beasty if you need hand PM me. I'm up for some winter spannering.
Pressure test & ignition test.

ER1C · Feb 7, 2018

blue beasty said:
Thoughts?

You have beautiful hands

Bad knock under load

Leaks an prone to bits dropping off

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Leaks an prone to bits dropping off

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Leaks an prone to bits dropping off

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