engine rattle

[rosco]

Hi all,
since re-furbing my engine bay and having raised the red motor r/hs engine mount , on re-fitting, connecting and putting the car back on the road - the engine has developed a "rattle" from 2000 rpm and above at moderate looads (less than 15" vacuum). I have tested all fittings, and searched intensley for anything loose or in close proximity which may be causing this noise without success.
At the recent Tenterfield nationals, the symptoms persisted for the entire first day's running (from Vic) but disappeared during day two.
On the trip home, it came back again occasionally and "drove" me mad.
I removed the plugs on arriving home and found the rear two slightly pink in colour - premium unleaded with flashlube used for entire trip.
I am almost at the stage of taking the car and having it run on a dyno whilst I scour the engine bay for its location.
Does any member know if detonation causes pink deposits on plugs?
I am probably jumping at shadows but am currently of the opinion somehow that numbers 5 & 6 may be running lean.
I do no believe I have a vacuum leak in the manifold, booster connection or associated fittings.
The engine will not ping under full load at revs below 2K.

It does not use any oil, water (but unfortunately against my most dedicated attempts - still consumes fuel) and returned around 27/8 mpg for the entire trip up to Qld @ 60 & 70 mpg (179 motor, 3:08 diff, aussie box).

I have checked engine mounts, exhaust fittings, throttle connections, PCV valve, engine/trans/subframe attachments.

If and when ( I will find this!) the source is found I will post the membership.

Hoping some person may be able to offer suggestions outside my lines of thought.

frats,
Rosco

[petrolhead]

I've had a few odd rattles in the cars that I've owned and found them to be simple little problems.
1)baffle loose in the muffler
2)bellhousing dust cover touching flywheel
3)tailshaft vibration travelling up to the engine
4)hairline crack in the inlet manifold.
The last might be one for you to check as when cool will run R.S. untill it heats up and the expanding metal ends up sealing the crack.
It may not fix your problem but I hope it helps.
Regards
Petrolhead

[rosco]

Thanks p/h,
I did consider looking at the inlet manifold. It is the water heated alloy type.
I will shortly fit a pair of headers (186-S) and will stress the inlet manifold around a bit when I get it our. I know that pouring thin oil over the manifolds will probably give some indication if there is a leak but I don't have the heart (or fire extinguisher) to do it. My bay is quite clean and the thought of having to seek out any escaping oil over the engine is not an attractive proposition.
I had also considered the baffle in the muffler, the revs and load issues would certainly co-incide with the outcome.
I think the header issue will reveal that one as well.
This issue with pink deposits on the plugs has me miffed....... it would certainly explain the detonation if it is lean on the rear two.
I usually keep a keen eye on the plugs after a long trip - they have always been uniform white cored with a light grey around the outside.
This pink colour is new to me - we no longer use lead - at least that's my belief in optimax/ultimate?
Thanks for your input.. I will reveal to all when I find it - just hope it isn't in the workings of the engine.
frats,
Rosco

[Devilrod]

I know that pouring thin oil over the manifolds will probably give some indication if there is a leak but I don't have the heart (or fire extinguisher) to do it. My bay is quite clean and the thought of having to seek out any escaping oil over the engine is not an attractive proposition.

Hey Rosco,

Try spraying WD40 or RP7 on the inlet manifold and if there is a leak the revs go up (quite easy to notice!) and is a fairly safe option mess and fire hazard wise. I have used this method alot.

Another trick I have also learnt is the use of water to find a misfire or cylinder that is down. Spray the water onto the exhaust at each exit point form the head, the water should evaporate instantly if it doesn't you have found the dud cylinder! I know this doesn't help you but I thought I would share it anyway....

Good luck..

[rosco]

Thanks devilrod,
sounds good to me. Just have to let some retailer extract some of my hard earned coupons to procure a can.
Let you know when I run the test,
frats,
Rosco